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Sample records for young eruptive star

  1. NEW CANDIDATE ERUPTIVE YOUNG STARS IN LYNDS 1340

    SciTech Connect

    Kun, M.; Moór, A.; Szegedi-Elek, E.; Apai, D.; O'Linger-Luscusk, J.; Stecklum, B.; Wolf-Chase, G.

    2014-11-10

    We report on the discovery of three candidate eruptive young stars, found during our comprehensive multi-wavelength study of the young stellar population of the dark cloud L1340. These stars are as follows. (1) IRAS 02224+7227 (2MASS 02270555+7241167, HH 487S) exhibited FUor-like spectrum in our low-resolution optical spectra. The available photometric data restrict its luminosity to 23 L {sub ☉} < L {sub bol} < 59 L {sub ☉}. (2) 2MASS 02263797+7304575, identified as a classical T Tauri star during our Hα survey, exhibited an EXor-type brightening in 2005 November at the time of the Sloan Digital Sky Survey observations of the region. (3) 2MASS 02325605+7246055, a low-mass embedded young star, associated with a fan-shaped infrared nebula, underwent an outburst between the DSS 1 and DSS 2 surveys, leading to the appearance of a faint optical nebula. Our [S II] and Hα images, as well as the Spitzer Infrared Array Camera 4.5 μm images, revealed Herbig-Haro objects associated with this star. Our results suggest that amplitudes and timescales of outbursts do not necessarily correlate with the evolutionary stage of the stars.

  2. Search for rapid inner disk re-arrangements in a young eruptive star

    NASA Astrophysics Data System (ADS)

    Kóspál, Á .; Á Brahám, P.; Kun, M.; Henning, Th.

    2012-03-01

    Young eruptive stars form a spectacular class of Sun-like pre-main sequence objects. They are characterized by strong optical outbursts due to enhanced accretion from the circumstellar disk onto the star. Recently, some unusual eruptive stars were identified where the brightening was due partly to enhanced accretion and partly to a dust-clearing event which reduced the extinction along the line of sight. In 2010, the outburst of a so-far unknown young star, V2492 Cyg, provided an opportunity to study the dust clearing phenomenon. Here we report on the first results of our coordinated Herschel, Spitzer, and ground-based monitoring of V2492 Cyg. Comparing the amplitude of observed variability at different wavelengths from optical to far-infrared, we investigate the physical cause of the extinction changes towards the star. We consider two scenarios: (1) a transient appearance/disappearance of a large amount of dust in the system either due to dust condensation/evaporation driven by the changing accretion heating, or being released from the disk surface by turbulence; (2) a pre-existing, long-lived dust structure that moves in/out of the line of sight, similarly to the orbiting warp in the inner disk of the low-mass young star LRLL 31. The Herschel/PACS 70 and 160 μm light curves trace the effect of rapid inner disk re-arrangements on the outer cold disk and help to decide between the two scenarios.

  3. Radial velocity variations in the young eruptive star EX Lupi

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Mohler-Fischer, M.; Sicilia-Aguilar, A.; Ábrahám, P.; Curé, M.; Henning, Th.; Kiss, Cs.; Launhardt, R.; Moór, A.; Müller, A.

    2014-01-01

    Context. EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by optical and near-infrared outbursts attributed to highly enhanced accretion from the circumstellar disk onto the star. Aims: The trigger mechanism of EXor outbursts is still debated. One type of theory requires a close (sub)stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of the EXor class, and test whether they can be related to a close companion. Methods: We conducted a five-year RV survey, collecting 54 observations with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector, the equivalent width of the Ca 8662 Å line, the asymmetry of the Ca II K line, the activity indicator SFEROS, the asymmetry of the cross-correlation function, the line depth ratio of the VI/FeI lines, and the TiO, CaH 2, CaH 3, CaOH, and Hα indices. We complemented the RV measurements with a 14-day optical/infrared photometric monitoring to look for signatures of activity or varying accretion. Results: We found that the RV of EX Lup is periodic (P = 7.417 d), with stable period, semi-amplitude (2.2 km s-1), and phase over at least four years of observations. This period is not present in any of the above-mentioned activity indicators. However, the RVs of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M⊙ central star with msini = (14.7 ± 0.7) MJup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold or hot stellar spot as well. We found that in our simple model, the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely. Conclusions: We qualitatively discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion; the second scenario is more consistent with the observed properties of EX Lup. In this scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation of 0.06 au would make EX Lup a unique binary system. The companion also has interesting implications on the physical mechanisms responsible for triggering the outburst. This work is based in part on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 079.A-9017, 081.A-9005, 081.A-9023, 081.C-0779, 082.C-0390, 082.C-0427, 083.A-9011, 083.A-9017, 084.A-9011, 085.A-9027, 086.A-9006, 086.A-9012, 087.A-9013, 087.A-9029, and 089.A-9007.Tables 2 and 3 are available in electronic form at http://www.aanda.org

  4. The Progenitor of the FUor-Type Young Eruptive Star 2MASS J06593158-0405277

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Ábrahám, P.; Moór, A.; Haas, M.; Chini, R.; Hackstein, M.

    2015-03-01

    Only a dozen confirmed FU Orionis-type young outbursting stars (FUors) are known today; this explains the interest in the recent FUor eruption of 2MASS J06593158-0405277. Its outburst and expected decline will be subject to numerous studies in the future. Almost equally important for the understanding of the eruption mechanism, however, is the physical characterization of the FUor’s precursor. Here we analyze unpublished archival data and summarize—and partly revise—all relevant photometry from optical to submillimeter wavelengths. Our analysis implies that the FUor is possibly associated with eight T Tauri star candidates and a strong Class 0 source. Adopting a distance of 450 pc for the FUor, we derive a quiescent bolometric luminosity and temperature of {{L}bol} = 4.8 L ⊙ and {{T}bol} = 1190 K, typical for young Class II sources. The central star has a temperature of {{T}eff} = 4000 K, a mass of 0.75 M ⊙ , and an age of about 6 × 105 yr. The SED implies a circumstellar mass of 0.01-0.06 M ⊙ , and the system is surrounded by a faint infrared nebulosity. Our results provide an almost complete picture of a FUor progenitor, supporting the interpretation of future post-outburst studies. Based on observations made with the Herschel Space Observatory. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  5. Exploring the circumstellar environment of the young eruptive star V2492 Cygni

    NASA Astrophysics Data System (ADS)

    Kspl, .; brahm, P.; Acosta-Pulido, J. A.; Arvalo Morales, M. J.; Balog, Z.; Carnerero, M. I.; Szegedi-Elek, E.; Farkas, A.; Henning, Th.; Kelemen, J.; Kovcs, T.; Kun, M.; Marton, G.; Mszros, Sz.; Mor, A.; Pl, A.; Srneczky, K.; Szakts, R.; Szalai, N.; Szing, A.; Tth, I.; Turner, N. J.; Vida, K.

    2013-03-01

    Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims: In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 ?m and 2.2 ?m from the ground and between 3.6 ?m and 160 ?m from space. Methods: We analyze the light curves and study the color-color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results: We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions: The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation. This work is based on observations made with the Herschel Space Observatory and with the Spitzer Space Telescope. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.Tables 1 and 2 are available in electronic form at http://www.aanda.org

  6. Cold CO Gas in the Disk of the Young Eruptive Star EX Lup

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Ábrahám, P.; Csengeri, T.; Gorti, U.; Henning, Th.; Moór, A.; Semenov, D. A.; Szűcs, L.; Güsten, R.

    2016-04-01

    EX Lupi-type objects (EXors) form a sub-class of T Tauri stars, defined by sudden sporadic flare-ups of 1–5 mag at optical wavelengths. These eruptions are attributed to enhanced mass accretion from the circumstellar disk to the star, and may constitute important events in shaping the structure of the inner disk and the forming planetary system. Although disk properties must play a fundamental role in driving the outbursts, they are surprisingly poorly known. In order to characterize the dust and gas components of EXor disks, here we report on observations of the 12CO J = 3‑2 and 4–3 lines, and the 13CO 3–2 line in EX Lup, the prototype of the EXor class. We reproduce the observed line fluxes and profiles with a line radiative transfer model and compare the obtained parameters with corresponding ones of other T Tauri disks.

  7. Dynamics during outburst. VLTI observations of the young eruptive star V1647 Orionis during its 2003-2006 outburst

    NASA Astrophysics Data System (ADS)

    Mosoni, L.; Sipos, N.; Ábrahám, P.; Moór, A.; Kóspál, Á.; Henning, Th.; Juhász, A.; Kun, M.; Leinert, Ch.; Quanz, S. P.; Ratzka, Th.; Schegerer, A. A.; van Boekel, R.; Wolf, S.

    2013-04-01

    Context. It is hypothesized that low-mass young stellar objects undergo eruptive phases during their early evolution. These eruptions are thought to be caused by highly increased mass accretion from the disk onto the star, and therefore play an important role in the early evolution of Sun-like stars, of their circumstellar disks (structure, dust composition), and in the formation of their planetary systems. The outburst of V1647 Ori between 2003 and 2006 offered a rare opportunity to investigate such an accretion event. Aims: By means of our interferometry observing campaign during this outburst, supplemented by other observations, we investigate the temporal evolution of the inner circumstellar structure of V1647 Ori, the region where Earth-like planets could be born. We also study the role of the changing extinction in the brightening of the object and separate it from the accretional brightening. Methods: We observed V1647 Ori with MIDI on the VLTI at two epochs in this outburst. First, during the slowly fading plateau phase (2005 March) and second, just before the rapid fading of the object (2005 September), which ended the outburst. We used the radiative transfer code MC3D to fit the interferometry data and the spectral energy distributions from five different epochs at different stages of the outburst. The comparison of these models allowed us to trace structural changes in the system on AU-scales. We also considered qualitative alternatives for the interpretation of our data. Results: We found that the disk and the envelope are similar to those of non-eruptive young stars and that the accretion rate varied during the outburst. We also found evidence for the increase of the inner radii of the circumstellar disk and envelope at the beginning of the outburst. Furthermore, the change of the interferometric visibilities indicates structural changes in the circumstellar material. We test a few scenarios to interpret these data. We also speculate that the changes are caused by the fading of the central source, which is not immediately followed by the fading of the outer regions. Conclusions: We found that most of our results fit in the canonical picture of young eruptive stars. Our study provided dynamical information from the regions of the innermost few AU of the system: changes of the inner radii of the disk and envelope. However, if the delay in the fading of the disk is responsible for the changes seen in the MIDI data, the effect should be confirmed by dynamical modeling. Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 274.C-5026 and 076.C-0736. In addition, this work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

  8. The past photometric history of the FU Ori-type young eruptive star 2MASS J06593158-0405277 = V960 Mon

    NASA Astrophysics Data System (ADS)

    Jurdana-Šepić, Rajka; Munari, Ulisse

    2016-02-01

    The known FU Ori-type young eruptive stars are exceedingly rare (a dozen or so confirmed objects) and 2MASS J06593158-0405277, with its 2014 outburst, is likely the latest addition to the family. All members have displayed just one such eruption in their recorded history, an event lasting for decades. To test the FU Ori nature of 2MASS J06593158-0405277, we have reconstructed its photometric history by measuring its brightness on Harvard photographic plates spanning the time interval 1899-1989. No previous large amplitude eruption similar to that initiated in 2014 has been found, as in bona fide FU Ori-type objects. The median value of the brightness in quiescence of 2MASS J06593158-0405277 is B = 15.5, with the time interval 1935-1950 characterized by a large variability (˜ 1 mag amplitude) that contrasts with the remarkable photometric stability displayed at later epochs. The variability during 1935-1950 can either be ascribed to some T Tau like activity of 2MASS J06593158-0405277 itself or to the also young and fainter star 2MASS J06593168-0405224 that lies 5 arcsec to the North and forms an unresolved pair at the astrometric scale of Harvard photographic plates.

  9. Recovery From Giant Eruptions in Massive Stars

    NASA Astrophysics Data System (ADS)

    Kashi, A.; Davidson, K.; Humphreys, R. M.

    2015-12-01

    We perform radiation hydrodynamic simulations to study how very massive stars recover from giant eruptions. The post eruption star experience strong mass loss due to strong winds, driven by radial pulsations in the star*s interior, that operate by the κ-mechanism. The mass loss history obtained in our simulations resembles η Car*s history.

  10. Dwarf Star Erupts in Giant Flare

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This movie taken by NASA'S Galaxy Evolution Explorer shows one of the largest flares, or star eruptions, ever recorded at ultraviolet wavelengths. The star, called GJ 3685A, just happened to be in the Galaxy Evolution Explorer's field of view while the telescope was busy observing galaxies. As the movie demonstrates, the seemingly serene star suddenly exploded once, then even more intensely a second time, pouring out in total about one million times more energy than a typical flare from our Sun. The second blast of light constituted an increase in brightness by a factor of at least 10,000.

    Flares are huge explosions of energy stemming from a single location on a star's surface. They are caused by the brief destruction of a star's magnetic fields. Many types of stars experience them, though old, small, rapidly rotating 'red dwarfs' like GJ 3685A tend to flare more frequently and dramatically. These stars, called flare stars, can experience powerful eruptions as often as every few hours. Younger stars, in general, also erupt more often. One of the reasons astronomers study flare stars is to gain a better picture and history of flare events taking place on the Sun.

    A preliminary analysis of the GJ 3685A flare shows that the mechanisms underlying stellar eruptions may be more complex than previously believed. Evidence for the two most popular flare theories was found.

    Though this movie has been sped up (the actual flare lasted about 20 minutes), time-resolved data exist for each one-hundredth of a second. These observations were taken at 2 p.m. Pacific time, April 24, 2004. In the still image, the time sequence starts in the upper left panel, continues in the upper right, then moves to the lower left and ends in the lower right.

    The circular and linear features that appear below and to the right of GJ 3685A during the flare event are detector artifacts caused by the extreme brightness of the flare.

  11. Identifying Young, Nearby Stars

    NASA Technical Reports Server (NTRS)

    Webb, Rich; Song, Inseok; Zuckerman, Ben; Bessell, Mike

    2001-01-01

    Young stars have certain characteristics, e.g., high atmospheric abundance of lithium and chromospheric activity, fast rotation, distinctive space motion and strong X-ray flux compared to that of older main sequence stars. We have selected a list of candidate young (<100Myr) and nearby (<60pc) stars based on their space motion and/or strong X-ray flux. To determine space motion of a star, one needs to know its coordinates (RA, DEC), proper motion, distance, and radial velocity. The Hipparcos and Tycho catalogues provide all this information except radial velocities. We anticipate eventually searching approx. 1000 nearby stars for signs of extreme youth. Future studies of the young stars so identified will help clarify the formation of planetary systems for times between 10 and 100 million years. Certainly, the final output of this study will be a very useful resource, especially for adaptive optics and space based searches for Jupiter-mass planets and dusty proto-planetary disks. We have begun spectroscopic observations in January, 2001 with the 2.3 m telescope at Siding Spring Observatory (SSO) in New South Wales, Australia. These spectra will be used to determine radial velocities and other youth indicators such as Li 6708A absorption strength and Hydrogen Balmer line intensity. Additional observations of southern hemisphere stars from SSO are scheduled in April and northern hemisphere observations will take place in May and July at the Lick Observatory of the University of California. AT SSO, to date, we have observed about 100 stars with a high resolution spectrometer (echelle) and about 50 stars with a medium spectral resolution spectrometer (the "DBS"). About 20% of these stars turn out to be young stars. Among these, two especially noteworthy stars appear to be the closest T-Tauri stars ever identified. Interestingly, these stars share the same space motions as that of a very famous star with a dusty circumstellar disk--beta Pictoris. This new finding better constrains the age of beta Pictoris to be approx. 10 Myr.

  12. Instability considerations for massive star eruptions

    SciTech Connect

    Guzik, J. A.

    2004-01-01

    We propose a mechanism to explain the observed properties of the giant eruptions of 'supernova imposters' such as {eta} Car and P Cyg. This mechanism must be episodic, generate a large amount of energy, and be very deep-seated, in order to lift about 10 solar masses out of the deep gravitational potential well of these massive evolved stars. We suggest that nonradial gravity mode oscillations capable of existing in the core grow slowly to sufficient amplitude to cause an episode of mixing. This mixing generates a burst of nuclear energy deep in the star that is responsible for the observed large mass ejection and bolometric magnitude increase.

  13. Eruptive star V1180 Cas now in outburst

    NASA Astrophysics Data System (ADS)

    Antoniucci, S.; Arkharov, A. A.; Efimova, N.; Kopatskaya, E. N.; Larionov, V. M.; Di Paola, A.; Giannini, T.; Li Causi, G.; Lorenzetti, D.; Vitali, F.

    2013-09-01

    In the framework of our optical/near-IR EXor monitoring program dubbed EXORCISM (EXOR optiCal Infrared Systematic Monitoring - Antoniucci et al. PPVI), we have been observing since two months the variable star V1180 Cas, associated with the dark cloud Lynds 1340. This source has been originally recognized as a young eruptive object by Kun et al. (2011, ApJ 733, L8), who observed a powerful outburst (5-6 mag in the Ic band) in the period 2005-2008.

  14. Young Stars in IC 2118

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Sepulveda, Babs; Maranto, Tony; Weehler, Cynthia; Roelofsen, Theresa; Rebull, Luisa

    2006-02-01

    IC 2118, the Witch Head Nebula (~210 parsecs), is a region of star formation located near the supergiant star Rigel in the constellation Orion. Last year, we observed the head of the nebula and approximately QUADRUPLED the number of young stars known here. We propose using IRAC and MIPS to continue our investigation by observing the densest part of the rest of the cloud. Our team proposes to use IRAC and MIPS observations to (1) investigate star formation, (2) look for likely cluster member stars with infrared excesses, and characterize this young star population by obtaining their colors and therefore estimates of masses and ages, (3) study the distribution of stars, their relationship to the ISM, and the possibilities of triggered star formation, (4) compare the young star population, distribution, and age to other similar sites of star formation, e.g., IC 1396 and (5) produce a dramatic image of the interstellar medium in the region surrounding IC 2118. Since this region is in the Orion constellation near the bright star Rigel, it provides additional appeal to students and the general public.

  15. Young Stars in IC 2118

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Rebull, Luisa; Daou, Doris; Maranto, Tony; Roelofsen, Theresa; Sepulveda, Babs; Weehler, Cynthia

    2005-02-01

    IC 2118, the Witch Head Nebula (~210 parsecs), is region forming stars located near the supergiant star Rigel in the constellation Orion. Kun et al. (2004, A&A, 418, 89) have determined that IC 2118 is on the near side of the Orion-Eridanus Super Bubble and that stellar winds from the Orion OB1 association may be triggering new star formation in the nebula. We propose using IRAC and MIPS to reexamine a small dense region of this nebula where Kun et al. have spectroscopically identified three 2MASS sources as T Tauri stars embedded in the cloud. Previous all-sky surveys, including both IRAS and 2MASS, have included this region, but not to the resolution that Spitzer can provide, and there are few studies of this particular region in the literature. Our team proposes to use IRAC and MIPS observations to (1) investigate star formation, (2) look for likely cluster member stars with infrared excesses, and characterize this young star population by obtaining their colors and therefore estimates of masses and ages, (3) study the distribution of stars, their relationship to the ISM, and the possibilities of triggered star formation, (4) compare the young star population, distribution, and age to other similar sites of star formation, e.g., IC 1396 and (5) produce a dramatic image of the interstellar medium in the region surrounding IC 2118. Since this region is in the Orion constellation near the bright star Rigel, it provides additional appeal to students and the general public.

  16. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    We first review the evidence pertaining to the lifetimes of planet-forming disks of gas and dust around young stars and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation caused by the heating of the disk surface by ultraviolet radiation. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks, and this talk focuses on the evaporation caused by the presence of a nearby, luminous star rather than the central star itself. We also focus on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We find a possible explanation for the differences between Neptune and Jupiter, and make a prediction concerning recent searches for giant planets in large clusters. We discuss recent models of the infrared spectra from gaseous disks around young stars.

  17. Studying Young Stars with Large Spectroscopic Surveys

    NASA Astrophysics Data System (ADS)

    Martell, Sarah L.

    2016-01-01

    Galactic archaeology is the study of the history of star formation and chemical evolution in the Milky Way, based on present-day stellar populations. Studies of young stars are a key anchor point for Galactic archaeology, since quantities like the initial mass function and the star formation rate can be studied directly in young clusters and star forming regions. Conversely, massive spectroscopic Galactic archaeology surveys can be used as a data source for young star studies.

  18. Eruptions at Lone Star Geyser, Yellowstone National Park, USA, part 1: energetics and eruption dynamics

    USGS Publications Warehouse

    Karlstrom, Leif; Hurwitz, Shaul; Sohn, Robert; Vandemeulebrouck, Jean; Murphy, Fred; Rudolph, Maxwell L.; Johnston, Malcolm J.S.; Manga, Michael; McCleskey, R. Blaine

    2013-01-01

    Geysers provide a natural laboratory to study multiphase eruptive processes. We present results from a four–day experiment at Lone Star Geyser in Yellowstone National Park, USA. We simultaneously measured water discharge, acoustic emissions, infraredintensity, and visible and infrared video to quantify the energetics and dynamics of eruptions, occurring approximately every three hours. We define four phases in the eruption cycle: 1) a 28 ± 3 minute phase with liquid and steam fountaining, with maximum jet velocities of 16–28 m s− 1, steam mass fraction of less than ∼ 0.01. Intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction; 2) a 26 ± 8 minute post–eruption relaxation phase with no discharge from the vent, infrared (IR) and acoustic power oscillations gliding between 30 and 40 s; 3) a 59 ± 13 minute recharge period during which the geyser is quiescent and progressively refills, and 4) a 69 ± 14 minute pre–play period characterized by a series of 5–10 minute–long pulses of steam, small volumes of liquid water discharge and 50–70 s flow oscillations. The erupted waters ascend froma 160 − 170° C reservoir and the volume discharged during the entire eruptive cycle is 20.8 ± 4.1 m3. Assuming isentropic expansion, we calculate a heat output from the geyser of 1.4–1.5 MW, which is < 0.1% of the total heat output from Yellowstone Caldera.

  19. Recovery from Giant Eruptions in Very Massive Stars

    NASA Astrophysics Data System (ADS)

    Kashi, Amit; Davidson, Kris; Humphreys, Roberta M.

    2016-01-01

    We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption—i.e., following a supernova impostor event. Beginning with reasonable models for evolved VMSs with masses of 80 M⊙ and 120 M⊙, we simulate the change of state caused by a giant eruption via two methods that explicitly conserve total energy. (1) Synthetically removing outer layers of mass of a few M⊙ while reducing the energy of the inner layers. (2) Synthetically transferring energy from the core to the outer layers, an operation that automatically causes mass ejection. Our focus is on the aftermath, not the poorly understood eruption itself. Then, using a radiation-hydrodynamic code in 1D with realistic opacities and convection, the interior disequilibrium state is followed for about 200 years. Typically the star develops a ˜400 km s-1 wind with a mass loss rate that begins around 0.1 M⊙ yr-1 and gradually decreases. This outflow is driven by κ-mechanism radial pulsations. The 1D models have regular pulsations but 3D models will probably be more chaotic. In some cases a plateau in the mass-loss rate may persist about 200 years, while other cases are more like η Car which lost >10 M⊙ and then had an abnormal mass loss rate for more than a century after its eruption. In our model, the post-eruption outflow carried more mass than the initial eruption. These simulations constitute a useful preliminary reconnaissance for 3D models which will be far more difficult.

  20. Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics

    NASA Astrophysics Data System (ADS)

    Karlstrom, Leif; Hurwitz, Shaul; Sohn, Robert; Vandemeulebrouck, Jean; Murphy, Fred; Rudolph, Maxwell L.; Johnston, Malcolm J. S.; Manga, Michael; McCleskey, R. Blaine

    2013-08-01

    Geysers provide a natural laboratory to study multiphase eruptive processes. We present results from a 4 day experiment at Lone Star Geyser in Yellowstone National Park, USA. We simultaneously measured water discharge, acoustic emissions, infrared intensity, and visible and infrared video to quantify the energetics and dynamics of eruptions, occurring approximately every 3 h. We define four phases in the eruption cycle (1) a 28±3 min phase with liquid and steam fountaining, with maximum jet velocities of 16-28 m s-1, steam mass fraction of less than ˜0.01. Intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction; (2) a 26±8 min posteruption relaxation phase with no discharge from the vent, infrared (IR), and acoustic power oscillations gliding between 30 and 40 s; (3) a 59±13 min recharge period during which the geyser is quiescent and progressively refills, and (4) a 69±14 min preplay period characterized by a series of 5-10 min long pulses of steam, small volumes of liquid water discharge, and 50-70 s flow oscillations. The erupted waters ascend from a 160-170°C reservoir, and the volume discharged during the entire eruptive cycle is 20.8±4.1 m3. Assuming isentropic expansion, we calculate a heat output from the geyser of 1.4-1.5 MW, which is <0.1% of the total heat output from Yellowstone Caldera.

  1. Young and Waltzing Binary Stars

    NASA Astrophysics Data System (ADS)

    2001-10-01

    ADONIS Observes Low-mass Eclipsing System in Orion Summary A series of very detailed images of a binary system of two young stars have been combined into a movie . In merely 3 days, the stars swing around each other. As seen from the earth, they pass in front of each other twice during a full revolution, producing eclipses during which their combined brightness diminishes . A careful analysis of the orbital motions has now made it possible to deduce the masses of the two dancing stars . Both turn out to be about as heavy as our Sun. But while the Sun is about 4500 million years old, these two stars are still in their infancy. They are located some 1500 light-years away in the Orion star-forming region and they probably formed just 10 million years ago . This is the first time such an accurate determination of the stellar masses could be achieved for a young binary system of low-mass stars . The new result provides an important piece of information for our current understanding of how young stars evolve. The observations were obtained by a team of astronomers from Italy and ESO [1] using the ADaptive Optics Near Infrared System (ADONIS) on the 3.6-m telescope at the ESO La Silla Observatory. PR Photo 29a/01 : The RXJ 0529.4+0041 system before primary eclipse PR Photo 29b/01 : The RXJ 0529.4+0041 system at mid-primary eclipse PR Photo 29c/01 : The RXJ 0529.4+0041 system after primary eclipse PR Photo 29d/01 : The RXJ 0529.4+0041 system before secondary eclipse PR Photo 29e/01 : The RXJ 0529.4+0041 system at mid-secondary eclipse PR Photo 29f/01 : The RXJ 0529.4+0041 system after secondary eclipse PR Video Clip 06/01 : Video of the RXJ 0529.4+0041 system Binary stars and stellar masses Since some time, astronomers have noted that most stars seem to form in binary or multiple systems. This is quite fortunate, as the study of binary stars is the only way in which it is possible to measure directly one of the most fundamental quantities of a star, its mass. The mass of a star determines its fate . Massive stars (with masses more than 50 times that of the Sun) lead a glorious, but short life. They are hot and very luminous and exhaust their energy supply in just a few million years. At the other end of the scale, low-mass stars like the Sun are more economical with their resources. Being cooler and dimmer, they are able to shine for billions of years [2]. But although the mass determines the fate of a star, it is not a trivial matter to measure this crucial parameter. In fact, it can only be determined directly if the star happens to be gravitationally bound to another star in a binary stellar system. Observations of the orbital motions of the two stars as they circle each other allows to "weigh" them, and also provide other important information, e.g. about their sizes and temperatures. Orbital motions The understanding of orbital motions has a long history in astronomy. The basic laws of Johannes Kepler (1571-1630) are still used to calculate the masses of orbiting objects, in the solar system as well as in binary stellar systems. However, while the observations of the motion of the nine planets and moons have allowed us to measure quite accurately the masses of objects in our vicinity, the information needed to "weigh" the binary stellar systems is not that easy to obtain. As a result, the mass estimates of the stars in binary systems are often rather uncertain. A main problem is that the individual stars in many binary systems can not be visually separated, even in the best telescopes. The information about the orbit may then come from the motions of the stars, if these are revealed by spectroscopic observations of the combined light (such systems are referred to as "spectroscopic binaries"). If absorption lines from both components are present in the spectrum, the measured wavelength of these double lines will shift periodically back and forth. This is the well-known Doppler effect and it directly reflects the changing velocities of the stars, as they move along their orbits and periodically approach and recede from the observer. Such spectroscopic observations therefore allow to measure the orbital velocities of the stars. It is exactly the same technique that is used to study and weigh extra-solar planets orbiting other stars [3]. However, this method has an important limitation. From the spectroscopical observations alone, it is only possible to deduce limits on the masses, as the inclination of orbits to the line-of-sight is usually unknown. The masses derived in this way (for stars as well as for exoplanets) are therefore only lower limits on the actual masses. Eclipsing Binaries However, fortunate observational circumstances sometimes allow to obtain all information about the stellar orbits. If a binary system is viewed (almost exactly) edge-on, the stars may pass in front of each other from time to time. Astronomers refer to this phenomenon as an "eclipse" and speak about an "eclipsing binary". The effect is similar to a "solar" eclipse as seen on the Earth, whenever the Moon passes in front of the Sun. Like the Moon blocks the sunlight, less light is received from the eclipsed star and thus the combined light from the binary system decreases during the eclipse. The way this happens (astronomers speak about the system's "lightcurve") then provides the additional information about the inclination of the orbit that is needed to determine exactly the stellar masses in a "spectroscopic" binary system. Very accurate values for the stellar diameters and the surface temperatures of the two stars can also be deduced. In short, when a full set of observations is available, it is possible to give a comprehensive description of an eclipsing binary system and its components. Eclipsing, spectroscopic binaries thus represent true cornerstones for the determination of stellar masses , and as such they are fundamental for our understanding of stellar evolution . Rather few such systems are known, but they can also be used to check ("calibrate") other, indirect methods to derive stellar parameters. It is on this background that the first discovery of an eclipsing binary system with two young, solar-like stars is of great interest. The Orion Binary Young stars are not so easy to find. One way is to look for their high-energy emission from a hot corona, created by their enhanced magnetic activity. The object RXJ 0529.4+0041 was first discovered in this way by the X-ray satellite ROSAT. Subsequent optical spectroscopy showed this object to be a young, low-mass spectroscopic binary system. And when a team of astronomers [1] used a 91-cm telescope at the Serra La Nave observing station on the slope of the Etna volcano (Sicily) to monitor the light curve, they also discovered that this system undergoes eclipses. All data confirm that RXJ 0529.4+0041 is located in the Orion Nebula at a distance of about 1500 light-years. This is one of the nearest star-forming regions and almost all stars in this area are quite young. Spectroscopic observations soon confirmed that the binary system was no exception. In particular, fairly strong absorption lines of the fragile element Lithium [4] were detected in both of the binary stars. As Lithium is known to be rapidly destroyed in stars, the finding of a relatively high content of this element implies that the stars must indeed be young. They were probably formed no more than 10 million years ago, i.e., in astronomical terms, they are "infant" stars . High-resolution spectroscopic observations, mostly with the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory , were used to determine the radial velocities of the stars. From these, a first determination of the orbital and stellar parameters was possible. The orbital period turned out to be short. The two stars swing around each other in just 3 days. This also means they must be very close to each other (but still entirely detached from each other) - the detailed analysis showed that the distance between the two components is only 12 solar radii, or a little more than 8 million kilometres. If you would image yourself standing on the surface of the smaller star, the disk of the companion star would extend some 15° in the sky. This is 30 times larger than our view of the Sun! ADONIS observations The short orbital period and the even shorter duration of the eclipses, only 6 hours, posed a real challenge for the observers. They decided to obtain further high-angular resolution observations with the ADaptive Optics Near Infrared System (ADONIS) on the 3.6-m telescope at the ESO La Silla Observatory. Most fortunately, early ADONIS images demonstrated that this binary stellar system has a third companion, sufficiently far away from the two others to be seen as a separate star by ADONIS. This unexpected bonus made it possible to monitor the light changes of the binary system in great detail, by using the third companion as a convenient "reference" star. In December 2000 and January 2001, detailed ADONIS images of the RXJ 0529.4+0041 system were obtained in three near-infrared filters (the J-, H- and K-bands). ADONIS is equipped with the SHARP II camera and eliminates the adverse image-smearing effects of the atmospheric turbulence in real-time by means of a computer-controlled flexible mirror. As expected, the new, extremely sharp images of RXJ 0529.4+0041 greatly improved the achievable photometric precision. In particular, as the image of the third component was perfectly separated from the others, it did not "contaminate" the derived light curve of the eclipsing binary. The movie Primary eclipse Secondary eclipse ESO PR Photo 29a/01 ESO PR Photo 29a/01 [Preview - JPEG: 375 x 400 pix - 87k] [Normal - JPEG: 750 x 800 pix - 240k] ESO PR Photo 29d/01 ESO PR Photo 29d/01 [Preview - JPEG: 375 x 400 pix - 112k] [Normal - JPEG: 750 x 800 pix - 272k] ESO PR Photo 29b/01 ESO PR Photo 29b/01 [Preview - JPEG: 375 x 400 pix - 90k] [Normal - JPEG: 750 x 800 pix - 240k] ESO PR Photo 29e/01 ESO PR Photo 29e/01 [Preview - JPEG: 375 x 400 pix - 112k] [Normal - JPEG: 750 x 800 pix - 280k] ESO PR Photo 29c/01 ESO PR Photo 29c/01 [Preview - JPEG: 375 x 400 pix - 94k] [Normal - JPEG: 750 x 800 pix - 256k] ESO PR Photo 29f/01 ESO PR Photo 29f/01 [Preview - JPEG: 375 x 400 pix - 112k] [Normal - JPEG: 750 x 800 pix - 280k] Caption : Six individual frames from the ADONIS movie of the RXJ 0529.4+0041 eclipsing, binary stellar system, corresponding to the time around the "primary" and "secondary" eclipses, respectively. For a detailed explanation, read the text. ESO PR Video Clip 06/01 [512 x 448 pix MPEG] ESO PR Video Clip 06/01 (150 frames/00:06 min) [MPEG Video; 512 x 448 pix; 871 k] ESO Video Clip 06/01 shows the ADONIS images of the RXJ 0529.4+0041 eclipsing, binary stellar system, as recorded in three near-infrared filters (J, H, and K; to the left), with the observed light-curves (top) and a graphical representation of the system during a full orbit, as it would look like to a nearby observer. More details in the text The ADONIS images have been combined into an instructive movie ( PR Video Clip 06/01 ). The left-hand panel shows the eclipsing binary system (it is the upper right and brighter of the two objects; the light from the two stars merge into a single point of light) and the well visible third component (lower left), as they were recorded by ADONIS in the three different filter bands. As the two stars in the binary system move around each other in their orbits, eclipses occur and the brightness of the binary system clearly changes - it may help to play the movie several times to see this more clearly. For reference, the Universal Time (UT) and the orbital phase (increasing from 0 to 1 during a full revolution) are continuously displayed in the movie. The right-hand panel shows a build-up of the observed light curves for the binary system. It represents the brightness difference between binary system and the third object that shines with constant light. Both the primary, deeper and the secondary, less deep eclipses are well visible. The primary eclipse was observed on December 8, 2000 and is here displayed at phase zero. During this minimum, the brightness of the binary system decreases by about 45% (0.4 magnitudes). The primary eclipse takes place when the smaller component blocks the light from the brighter and hotter star. The orbital motions of the two stars are illustrated by a computer-generated, animated sequence. The secondary eclipse (at phase 0.5) dims the light from the system less; it occurs when the larger and brighter star almost completely (about 90%) hides its smaller companion. The second minimum was recorded on January 12, 2001. None of the eclipses is therefore "total". The stellar parameters A detailed analysis of these high-precision light curves allowed the astronomers to determine the orbits and hence, to perform an extremely accurate measurement of the fundamental stellar parameters for the two young stars of RXJ 0529.4+0041 . The star that is eclipsed during the primary eclipse (the "primary") is the more massive and also the hotter and brighter of the two stars. Its mass is 1.3 times that of our Sun, i.e., about 2.6 10 30 kg [2]. Its diameter is nearly 1.6 times larger than that of our Sun (i.e., about 2.2 million km) and the surface temperature is found to be a little more than 5000 °C, or a few hundred degrees cooler than the Sun. The "secondary" star is slightly lighter than our Sun. Its weight is about 90% of that of the Sun (1.8 10 30 kg) and the diameter is 20% larger (about 1.7 million km), while the surface temperature is 4000 degrees. In fact, these two stars are still so young that most of their energy comes from the contraction process - the first phase during which they are formed from an interstellar cloud by this process is not yet over and they are still getting smaller. It is by this process that collapsing stars heat up enough to start nuclear burning. When infant stars in RXJ 0529.4+0041 eventually reach middle-age, their sizes will most likely also be quite similar to that of the Sun. The significance of RXJ 0529.4+0041 Few systems are known for which such precise determinations of the stellar parameters have ever been possible - and this binary system represents the first case where both the components are such young stars . A detailed comparison of the derived stellar parameters with current models for the evolution of young stars shows fairly good agreement for the primary component. However, there are certain discrepancies in the case of the secondary component, showing that the current models for the early stages of lower-mass stars must still be refined. More information Part of the results described in this press release are described in more detail in a scientific article ( "RXJ 0529.4+0041: a low-mass pre-main sequence eclipsing-spectroscopic binary" by E. Covino et al.) that has been published in the European research journal Astronomy & Astrophysics (Vol. 361, p. 49). Notes [1] The team consists of Elvira Covino (Principal Investigator), Juan M. Alcalá , Rosita Paladino (all Osservatorio Astronomico di Capodimonte, Napoli, Italy), Antonio Frasca , Santo Catalano , Ettore Marilli (all Osservatorio Astrofisico di Catania, Italy) and Michael Sterzik (ESO-Chile). [2] One solar mass corresponds to 1.99 10 30 kg, or about 330,000 times the mass of the Earth. The Sun is about 4500 million years old and its total lifetime is of the order of 12-13,000 million years. It is an interesting thought that if the Sun would have been somewhat heavier, its total lifetime might have been too short for living organisms to develop on the Earth. In fact, the biological evolution that ultimately lead to the emergence of human beings apparently lasted about 4 billion years; this corresponds to the total lifetime of a star that is only about 20 % heavier than the Sun. Note also the current ESO-ESA CERN educational programme on "Life in the Universe". [3] In the case of exoplanets, the planet itself is not visible, but the spectral lines from the star are seen to wobble due to the gravitational influence of the planet, cf. ESO PR 07/01. [4] Several ESO Press Releases concern observations of the element Lithium in stars, e.g., PR 03/99 (in a giant star), PR 08/00 (in a metal-poor star) and PR 10/01 (from a "swallowed" exoplanet).

  2. Candidates for Young Super Star Clusters in the Milky Way

    NASA Astrophysics Data System (ADS)

    Rahman, Mubdi; Matzner, C. D.; Moon, D.

    2011-01-01

    Massive Star Clusters (M > 104 M⊙) have been known to exist throughout the local Universe, but few such objects have been found within our own Galaxy. These clusters the majority of the galactic OB star formation, and thus dramatically alter their surroundings through winds, ionizing flux and radiation pressure, and supernovae, eventually destroying their natal clouds and inflating superbubbles which will erupt from the Galactic plane. We search for the young stellar clusters within the star forming complexes identified by Rahman & Murray (2010) using the WMAP free-free and Spitzer GLIMPSE 8 micron observations. Located far across the Galactic plane, these clusters are highly extinguished and crowded by field stars. Using the 2MASS catalogue, we have developed a method of identifying overdensities of sources with colours consistent with the extinguished upper main sequence coincident with the star forming complexes. The difficulty in this method comes from the large number of overlapping foreground sources in comparison to the expected number of cluster sources in any given candidate cluster. We identify a candidate for the most massive young cluster in the Galaxy (M 105 M⊙), which we have dubbed the Dragonfish Cluster. The candidate cluster is at a distance of 9.7 kpc and has a total ionizing luminosity of 7×1051 photons s-1. We identify nearly 400 OB star candidates associated with the cluster, to be confirmed with near-infrared spectroscopy.

  3. THE GALEX NEARBY YOUNG-STAR SURVEY

    SciTech Connect

    Rodriguez, David R.; Faherty, Jacqueline K.; Zuckerman, B.; Kastner, Joel H.; Bessell, M. S.; Murphy, Simon J.

    2013-09-10

    We describe a method that exploits data from the Galaxy Evolution Explorer (GALEX) ultraviolet and Wide-field Infrared Survey Explorer and Two Micron All Sky Survey infrared source catalogs, combined with proper motions and empirical pre-main sequence isochrones, to identify candidate nearby, young, low-mass stars. Applying our method across the full GALEX-covered sky, we identify 2031 mostly M-type stars that, for an assumed age of 10 (100) Myr, all lie within {approx}150 ({approx}90) pc of Earth. The distribution of M spectral subclasses among these {approx}2000 candidate young stars peaks sharply in the range M3-M4; these subtypes constitute 50% of the sample, consistent with studies of the M star population in the immediate solar neighborhood. We focus on a subset of 58 of these candidate young M stars in the vicinity of the Tucana-Horologium association. Only 20 of these 58 candidates were detected in the ROSAT All-Sky X-ray Survey-reflecting the greater sensitivity of GALEX for the purposes of identifying active nearby, young stars, particularly for stars of type M4 and later. Based on statistical analysis of the kinematics and/or spectroscopic followup of these 58 M stars, we find that 50% (29 stars) indeed have properties consistent with Tuc-Hor membership, while 12 are potential new members of the Columba association, and 2 may be AB Dor moving group members. Hence, {approx}75% of our initial subsample of 58 candidates are likely members of young (age {approx} 10-40 Myr) stellar moving groups within 100 pc, verifying that the stellar color- and kinematics-based selection algorithms described here can be used to efficiently isolate nearby, young, low-mass objects from among the field star population. Future studies will focus on characterizing additional subsamples selected from among this list of candidate nearby, young M stars.

  4. The inner disks of EXor-type eruptive stars

    NASA Astrophysics Data System (ADS)

    Sipos, Nikoletta; Kóspál, Ágnes

    2014-01-01

    EX Lupi-type young stars (EXors) show sporadic brightenings of several magnitudes, caused by the episodic increase in the accretion rate of the circumstellar matter onto the young star. As the inner disk plays a crucial role during the onset of the outburst, we examined the quiescent properties of the circumstellar environment of EXors, focusing on the inner regions. We found that in case of three EXors (VY Tau, V1143 Ori and EX Lup) the spectral energy distributions show no or weak excess above the stellar photosphere at NIR-MIR wavelengths, indicative of inner disk clearing. A detailed radiative transfer modeling of the sources revealed that the inner regions of these disks had to go through significant evolution, either the inner radius of the dusty disk is beyond the sublimation radius and/or the inner disks are flattened.

  5. Searching for Young Stars in Northern Orion

    NASA Astrophysics Data System (ADS)

    Urban, Laurie; Kraus, A.

    2011-01-01

    The Orion Molecular Cloud contains many known star-forming regions mostly located in the southern parts of the constellation. However, northern Orion is largely unsurveyed outside of a few well-established clusters meaning there could be more sites of ongoing star formation. We have conducted a search for young stars in northern Orion to find new star-forming regions. Using the MG1 Variable Star Survey we identified 2118 variable stars spanning a region of 30 deg2 from R.A.=4h 00m to 6h 30m and Dec=2.9 to 3.7 degrees. These stars’ variability could result from accretion or spots, which are common characteristics of young stars. We use several methods to detect candidate young stars from these data: selection cuts with color-magnitude diagrams (CMDs), measurement of proper motions and visual inspection of the source images. We make cuts to only include stars that have CMD positions consistent with the Orion sequence, have proper motions within 3 sigma of known Orion members, and are not contaminated by other nearby sources. These cuts identify an area between 5h 20m and 5h 52m in R.A. with a significant overdensity of 74 young star candidates. We will discuss in detail our selection cuts and the implication of these discoveries. This work was conducted by a Research Experience for Undergraduates (REU) position at the University of Hawai'i's Institute for Astronomy and funded by the NSF.

  6. Young stars in the Galactic center

    NASA Astrophysics Data System (ADS)

    Lu, Jessica R.; Ghez, Andrea M.; Morris, Mark R.; Clarkson, Will; Stolte, Andrea; Do, Tuan; Yelda, Sylvana; Anderson, Jay

    2014-05-01

    The central parsec of our Galaxy hosts not only a supermassive black hole, but also a large population of young stars (age <6 Myr) whose presence is puzzling given how inhospitable the region is for star formation. The strong tidal forces require gas densities many orders of magnitude higher than is found in typical molecular clouds. Kinematic observations of this young nuclear cluster show complex structures, including a well-defined inner disk, but also a substantial off-disk population. Spectroscopic and photometric measurements indicate the initial mass function (IMF) differs significantly from the canonical IMF found in the solar neighborhood. These observations have led to a number of proposed star formation scenarios, such as an infalling massive star cluster, a single infalling molecular cloud, or cloud-cloud collisions. I will review recent works on the young stars in the central parsec and discuss connections with young nuclear star clusters in other galaxies, such as M31, and with star formation in the larger central molecular zone.

  7. Kinematic History of Nearby Young Stars

    NASA Astrophysics Data System (ADS)

    Makarov, V. V.

    2004-12-01

    In the Solar neighborhood, devoid of giant molecular clouds and star-forming regions, stars younger than the Pleiades are found in considerable numbers, including several T Tauri stars. Some of the nearby young stars seem to be isolated field objects, others are members of loose swarms (mini-associations) of about 20 stars each, e.g., the TWA, Tucana and Horologium swarms. By tracking positions and motions of some 30 nearby young stars and 40 OB associations, clusters and kinematic groups backward in time, we find that most of the former were not dislodged from open clusters, associations or active SFR. The two best studied swarms, the β Pic and TWA are rapidly expanding. However, even in the most compact form, their size was quite large ( 20 pc), and the initial relative velocities too fast to interpret them as disintegrating non-hierarchical multiple systems. Both swarms had a fairly close passage of the Lower Centaurus Crux OB association 10-12 Myr ago, but were not parts of the Sco-Cen complex. The origin of several young stars appear to be associated with the giant complex of clouds and SFR in the Ophiuchus.

  8. K2 observations of young star clusters

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie

    2016-01-01

    In operation since 2014, the K2 mission is now acquiring high cadence, high precision, long time baseline on thousands of stars in the ecliptic plane. Unlike its predecessor the Kepler mission, K2 is observing a number of young to intermediate age star clusters. This provides the chance to not only look for relatively young planets, but to also study starspot evolution, accretion, and inner circumstellar disk dynamics on several month timescales. I will provide an overview of our K2 cluster photometry pipeline and highlight the variable processes evident in the first few campaigns.

  9. Bimodal Distribution of Geyser Preplay Eruptions: Lone Star Geyser, Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Namiki, A.; Hurwitz, S.; Murphy, F.; Manga, M.

    2014-12-01

    Geyser eruption intervals are determined by rates of water and heat discharge into shallow subsurface reservoirs and the conduit. In some geysers, small amounts of water discharge prior to a main eruption ('Preplay') can affect eruption intervals. Water discharge during preplay reduces the hydrostatic pressure, which in turn, induces boiling of water that is at, or near the critical temperature. Ascending steam slugs from depth can also lead to shorter eruption intervals (Namiki et al., 2014). In April 2014, we carried a five day experiment at Lone Star Geyser, Yellowstone National Park. Eruptions and their preplays were recorded with an infrared sensor that measured temperature variations immediately above the geyser cone (3.4~m high), temperature loggers that measured water temperature at the base of the cone and in the outflow channels, and visual observations. At Lone Star Geyser, during the preplay phase of the eruption, mainly liquid water is erupted, whereas the main phase of the eruption begins with the liquid-water dominated eruption and turns into the steam discharge. The temperature rise in an outflow channel indicates the occurrence of preplays and initiation of the main eruption. The acquired data suggests that the preplay patterns of Lone Star Geyser are vigorous and complex, consistent with previous observations (Karlstrom et al., 2013). Our new observations reveal two typical styles: 1) vigorous preplays with few events (<5) and long intervals (>20~minutes) that last approximately 40~minutes, and 2) less vigorous preplays that include several events (>5) with short intervals (few minutes), and continue approximately for one hour. Probability distributions of preplay durations show two peaks indicating the bimodal activity. The bimodality of Lone Star preplays may be a result of subtle change of temperature distribution in a convecting reservoir which has been observed in laboratory experiments (Toramaru and Maeda, 2013).

  10. Finding Young Stars in IC417

    NASA Astrophysics Data System (ADS)

    Odden, Caroline; Rebull, Luisa M.; Sanchez, Richard; Hall, Garrison; Dear, AnnaMaria; Hengel, Cassie; LaRocca, Mia; Lin, Samantha; Nix, Sabine; Sweckard, Teaghan; Wilhelm, Katie

    2016-01-01

    IC 417 is a young cluster in the constellation Auriga, towards the Galactic anti-center in the Perseus arm, at a distance of ~2.3 kpc. Previous studies suggested that there are young stars in this region; Camargo et al. (2012) identified several few-Myr-old clusters in this region from 2MASS clustering, and Jose et al. (2008) identified H-alpha excess sources. Since stars form from clouds of interstellar dust and gas, a signature of star formation is excess infrared (IR) emission, which is interpreted as evidence for circumstellar dust around young stars. We identified new candidate young stellar objects (YSOs) in IC 417 by incorporating near- and mid-infrared observations from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All-Sky Survey (2MASS). Infrared excess sources were identified by using a series of color cuts in various 2MASS/WISE color-magnitude and color-color diagrams following Koenig & Leisawitz (2014). We also assembled a list of OB and H-alpha stars from the literature, including those from Jose et al. (2008), and H-alpha bright stars from the IPHAS survey (Witham et al. 2008). Starting with this compiled list of approximately 200 interesting objects in the region, we then set about checking their reliability in three ways. We inspected the POSS, 2MASS, and WISE images of the sources. We assembled and inspected spectral energy distributions (SEDs) from archival data ranging from wavelengths of 0.7 to 22 um. Finally, we created and inspected color-color and color-magnitude diagrams. We find enough new YSO candidates to more than double the number yet identified in the IC 417 region. This research was made possible through the NASA/IPAC Teacher Archive Research Program (NITARP) and was funded by NASA Astrophysics Data Program.

  11. Radio and infrared properties of young stars

    NASA Technical Reports Server (NTRS)

    Panagia, Nino

    1987-01-01

    Observing young stars, or more appropriately, pre-main-sequence (PMS) stars, in the infrared and at radio frequencies has the advantage over optical observation in that the heavy extinction associated with a star forming region is only a minor problem, so that the whole region can be studied thoroughly. Therefore, it means being able to: (1) search for stars and do statistical studies on the rate of star formation; (2) determine their luminosity, hence, to study luminosity functions and initial mass functions down to low masses; and (3) to study their spectra and, thus, to determine the prevailing conditions at and near the surface of a newly born star and its relations with the surrounding environment. The third point is of principal interest. The report limits itself to a consideration of the observations concerning the processes of outflows from, and accretion onto, PMS stars and the theory necessary to interpret them. Section 2 discusses the radiative processes relevant in stellar outflows. The main observational results are presented in Section 3. A discussion of the statistical properties of stellar winds from PMS stars are given in Section 4.

  12. Probing Young Star Physics with Aperiodic Variability

    NASA Astrophysics Data System (ADS)

    Findeisen, Krzysztof

    2014-01-01

    Ongoing time domain surveys such as PTF, CRTS, and Pan-STARRS1, as well as upcoming surveys such as LSST, promise to revolutionize optical astronomy by providing a comprehensive picture of the variability properties of everything from local flare stars to distant quasars. Time domain surveys have already proven a boon for studies of young stars, whose variability is frequently aperiodic and may have time scales of days to decades, depending on the physics underlying the variability. I present an overview of the PTF-NAN (North America Nebula) survey, which allows us, for the first time, to simultaneously resolve day-scale variability and to monitor changes in photometric behavior in young stars over several years, without large data gaps and without any assumptions about periodicity. I describe preliminary results of the survey, including a search for episodic stellar behavior, a study of the most robust methods for identifying the characteristic time scale(s) of an aperiodic signal, and a characterization of the full range of amplitudes and time scales represented in optical variability of young stars.

  13. Young Star Probably Ejected From Triple System

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Astronomers analyzing nearly 20 years of data from the National Science Foundation's Very Large Array radio telescope have discovered that a small star in a multiple-star system in the constellation Taurus probably has been ejected from the system after a close encounter with one of the system's more-massive components, presumed to be a compact double star. This is the first time any such event has been observed. Path of Small Star, 1983-2001 "Our analysis shows a drastic change in the orbit of this young star after it made a close approach to another object in the system," said Luis Rodriguez of the Institute of Astronomy of the National Autonomous University of Mexico (UNAM). "The young star was accelerated to a large velocity by the close approach, and certainly now is in a very different, more remote orbit, and may even completely escape its companions," said Laurent Loinard, leader of the research team that also included Monica Rodriguez in addition to Luis Rodriguez. The UNAM astronomers presented their findings at the American Astronomical Society's meeting in Seattle, WA. The discovery of this chaotic event will be important for advancing our understanding of classical dynamic astronomy and of how stars evolve, including possibly providing an explanation for the production of the mysterious "brown dwarfs," the astronomers said. The scientists analyzed VLA observations of T Tauri, a multiple system of young stars some 450 light-years from Earth. The observations were made from 1983 to 2001. The T Tauri system includes a "Northern" star, the famous star that gives its name to the class of young visible stars, and a "Southern" system of stars, all orbiting each other. The VLA data were used to track the orbit of the smaller Southern star around the larger Southern object, presumed to be a pair of stars orbiting each other closely. The astronomers' plot of the smaller star's orbit shows that it followed an apparently elliptical orbit around its twin companions, moving at about 6 miles per second. Then, between 1995 and 1998, it came within about 200 million miles (about two times the distance between the Sun and the Earth) of its companions. Following that encounter, it changed its path, moving away from its companion at about 12 miles per second, double its previous speed. "We clearly see that this star's orbit has changed dramatically after the encounter with its larger companions," said Luis Rodriguez. "By watching over the next five years or so, we should be able to tell if it will escape completely," he added. "We are very lucky to have been able to observe this event," said Loinard. Though studies with computer simulations long have shown that such close approaches and stellar ejections are likely, the time scales for these events in the real Universe are long -- thousands of years. The chance to study an actual ejection of a star from a multiple system can provide a critical test for the dynamical theories. If a young star is ejected from the system in which it was born, it would be cut off from the supply of gas and dust it needs to gain more mass, and thus its development would be abruptly halted. This process, the astronomers explain, could provide an explanation for the very-low-mass "failed stars" called brown dwarfs. "A brown dwarf could have had its growth stopped by being ejected from its parent system," Loinard said. The VLA observations were made at radio frequencies of 8 and 15 GHz. T Tauri, the "Northern" star in this system, is a famous variable star, discovered in October of 1852 by J.R. Hind, a London astronomer using a 7-inch diameter telescope. At its brightest, it is some 40 times brighter than when at its faintest. It has been studied extensively as a nearby example of a young stellar system. While readily accessible with a small telescope, it is not visible to the naked eye. The observed orbital changes took place in the southern components of the system, displaced from the visible star by about one hundred times the distance between the Sun and the Earth. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

  14. An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula.

    PubMed

    Kastner, J H; Richmond, M; Grosso, N; Weintraub, D A; Simon, T; Frank, A; Hamaguchi, K; Ozawa, H; Henden, A

    2004-07-22

    Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor approximately 50 increase in the X-ray flux from a young star that is at present undergoing a spectacular optical/infrared outburst (this star illuminates McNeil's nebula). The outburst seems to be due to the sudden onset of a phase of rapid accretion. The coincidence of a surge in X-ray brightness with the optical/infrared eruption demonstrates that strongly enhanced high-energy emission from young stars can occur as a consequence of high accretion rates. We suggest that such accretion-enhanced X-ray emission from erupting young stars may be short-lived, because intense star-disk magnetospheric interactions are quenched rapidly by the subsequent flood of new material onto the star. PMID:15269761

  15. Eruptions at Lone Star geyser, Yellowstone National Park, USA: 2. Constraints on subsurface dynamics

    NASA Astrophysics Data System (ADS)

    Vandemeulebrouck, Jean; Sohn, Robert A.; Rudolph, Maxwell L.; Hurwitz, Shaul; Manga, Michael; Johnston, Malcolm J. S.; Soule, S. Adam; McPhee, Darcy; Glen, Jonathan M. G.; Karlstrom, Leif; Murphy, Fred

    2014-12-01

    We use seismic, tilt, lidar, thermal, and gravity data from 32 consecutive eruption cycles of Lone Star geyser in Yellowstone National Park to identify key subsurface processes throughout the geyser's eruption cycle. Previously, we described measurements and analyses associated with the geyser's erupting jet dynamics. Here we show that seismicity is dominated by hydrothermal tremor (~5-40 Hz) attributed to the nucleation and/or collapse of vapor bubbles. Water discharge during eruption preplay triggers high-amplitude tremor pulses from a back azimuth aligned with the geyser cone, but during the rest of the eruption cycle it is shifted to the east-northeast. Moreover, ~4 min period ground surface displacements recur every 26 ± 8 min and are uncorrelated with the eruption cycle. Based on these observations, we conclude that (1) the dynamical behavior of the geyser is controlled by the thermo-mechanical coupling between the geyser conduit and a laterally offset reservoir periodically filled with a highly compressible two-phase mixture, (2) liquid and steam slugs periodically ascend into the shallow crust near the geyser system inducing detectable deformation, (3) eruptions occur when the pressure decrease associated with overflow from geyser conduit during preplay triggers an unstable feedback between vapor generation (cavitation) and mass discharge, and (4) flow choking at a constriction in the conduit arrests the runaway process and increases the saturated vapor pressure in the reservoir by a factor of ~10 during eruptions.

  16. Dispersal of Disk Around Young Stars

    NASA Technical Reports Server (NTRS)

    DeVincenzi, Donald L.; Hollenbach, David

    2000-01-01

    Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km per second) ionized outflow, which persists for greater than or equal to 10(exp 5) years for disk masses Md approx. 0.3M*, may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free Spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star.

  17. Limited climate impact of the Young Toba Tuff eruption

    NASA Astrophysics Data System (ADS)

    Timmreck, C.; Zanchettin, D.; Graf, H.; Lorenz, S.; Niemeier, U.; Matei, D.; Jungclaus, J. H.; Crowley, T. J.

    2010-12-01

    Super eruptions have been linked to global climate change, biotic turnover, and, for the Younger Toba Tuff (YTT) eruption 74,000 years ago, near-extinction of modern humans. Very large volcanic eruptions produce extremely strong radiative forcing, which can affect the Earth system for longer times than the pure atmospheric residence time of the volcanic aerosol. This leads to large negative temperature anomalies at the surface and significant warming of the aerosol containing layers altering substantial atmospheric and ocean circulation and composition. Here we present and discuss Earth system model simulations of the YTT eruption taking into account also the temporal evolution of the volcanic aerosol size distribution, one of the largest uncertainties in prior calculations. We demonstrate that there is a large negative feedback that has heretofore not been considered and which greatly reduces the climate impact of the aerosol cloud. The temperature response of the YTT is shorter and weaker as previously estimated. The smaller response, plus its geographic patchiness, suggests that most biota have escaped threshold extinction pressures from the eruption.

  18. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; DeVincenzi, D. (Technical Monitor)

    2002-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source; 2) close stellar encounters; 3) stellar winds; and 4) photoevaporation by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r approx. or less than 10 AU), while photoevaporation is the principal process of disk dispersal outside of r approx. or greater than 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed he solar nebula is called into question. Finally, we model the small bright objects ('proplyds') observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV (ultraviolet) photons from the nearby massive star Theta(1)C.

  19. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2001-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r < or approx. equals 10 AU), while photoevaporation is the principal process of disk dispersal outside of r > or approx. equals 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed the solar nebula is called into question. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1)C.

  20. Many faces of young neutron stars

    NASA Astrophysics Data System (ADS)

    Vasisht, Gautam

    The hardware aspect of this thesis consists in the design, fabrication and assembly of twin analog Flexible Filter Banks at Caltech. These are user-friendly, workhorse, radio-pulsar search and timing instruments. Novel features include the flexibility in configuring channel center-frequencies and widths, the rapid sampling down to 25 ?s and a total instrument bandwidth ranging from a narrow 0.2 MHz to a mammoth 100 MHz. Frequency synthesis is used to downconvert, detect and sample the telescope receiver bandpass as 32 separate time-series in each polarization. The collected data are later subjected to standard pulsar search and timing algorithms in software.The vital scientific issue addressed here is the nature of young neutron stars. In the standard picture, young neutron stars are rapidly spinning radio-luminous pulsars, which may also display pulsed emission at high X-ray and ?-ray energies. However there is no evidence that all neutron stars are born according to this standard picture. We present radio or X-ray investigations of steady nebular emission produced by three clearly non-standard and ill-understood objects. In all likelihood, these are young neutron stars, a notion upheld by their association with young Galactic supernova remnants.Based on its display of high energy transients, the soft ?-ray repeater SGR 1806-20 is posited to be a seismically active "magnetar", i.e., a neutron star with a super-strong magnetic field (10[superscript 15] G) nearly three orders of magnitude greater than pulsar dipolar fields. Our VLA observations of fleeting small-scale structure around SGR 1806-20 provide intriguing, although preliminary, support for the magnetar model. In time, similar observations could unravel the riddle of soft ?-ray repeaters and possibly establish the reality of magnetars.X-ray observations of the remnant of the historical supernova of 386 A.D., SNR G 11.2-0.3 are presented. The nature of an embedded underlumnious plerion discovered in these observations argues for a central neutron star very different from the prototypical Crab pulsar. The urgency to undertake a large scale study of young and hollow Galactic shells in broadband X-rays with fine spatial resolution is elucidated.X-ray spectroscopy of the object 1E 1207.4-5209 at the core of the large remnant PKS 1209-51/52 has revealed a non-thermal source with a very steep spectrum. After considering various scenarios for lE 1207.4-5209, we conclude that its spectral signature, its lack of optical emission and its position at the center of a supernova remnant make it a source similar to the mysterious anomalous X-ray pulsars.A large and sensitive search for radio pulsar companions of massive stars was undertaken. Primary motivation stems from the recent discovery of binary radio pulsar B 1259-63 as the first member of such a population and a "missing link" in the current models of evolution. Prevalent expectations, based on binary evolution scenarios, suggested that many more such systems should exist and would be uncovered in sensitive targeted searches. Together with other smaller searches, this survey uncovered no pulsars orbiting early-type stars. We conclude that such binary systems must be rare.

  1. X-ray emission of young solar type stars

    NASA Astrophysics Data System (ADS)

    Casanova, Sophie

    1994-12-01

    T Tauri Stars (TTS) are young (<= 107 yrs) low mass (<= 2 Modot) stars. They have been originally characterized by strong emission lines (CTTS), and by IR excesses interpreted in terms of circumstellar disks. Ten years ago, the ``Einstein" satellite discovered the extraordinary X-ray activity of young low-mass stars. This activity, presumably magnetic in origin, is interpreted in terms of solar type flares, but up to 105 times more powerful than on the Sun. It also allowed to discover a new class of T Tauri stars called ``Weak line T Tauri Stars", without emission lines or IR excess and presumably without disk, which are 3 to 10 times more numerous than the CTTS. The ROSAT satellite, launched in 1990, has a much better resolution and sensitivity than ``Einstein". This work is based on the first ROSAT observations of molecular clouds, which are the stellar nurseries. 1) ROSAT X-ray study of the Chamaeleon cloud (see also Feigelson et al. 1993, ApJ, 416, 623). Using an important sample of young stars (60) in the Chamaeleon I star forming region, we have studied the influence of various stellar parameters on the X-ray emission. We find unexpected correlations of the X-ray luminosity with the stellar mass, radius and luminosity, but we could not detect any effect of rotation or age. These results are still unexplained by the standard dynamo theory of generation of a magnetic field. We show that the X-ray luminosity fonctions are the same for CTTS and WTTS which indicates that the X-ray emission mecanism is independent of the circumstellar disk, and that the X-rays can be used as a homogeneous tracer of all TTS. 2) ROSAT X-ray study of the ρ Oph Cloud (see also Casanova et al., 1995, ApJ, 439, 752). We show that the X-rays do also detect sources deeeply embedded in molecular clouds which are certainly very young. In fact it seems that even protostars (age ~105 yrs) are detected. For the embedded sources we estimate the bolometric luminosity from the dereddened J (1.25 microns) magnitude, and we findthe same correlation with the X-ray luminosity than for the visible stars of the Chamaeleon Cloud. Thanks to the near equality of the absorption in the keV X-ray and J bands we derive a relation between the X-ray counts and J magnitude which may be used as a selection criterion for the young stars. We also discuss the influence of the X-rays on the interstellar gas and dust. 3) Young stars far from dense cores. We then present the preliminary results of an on-going program of optical spectroscopy carried out at La Palma and ESO to caracterize the counterparts of new ROSAT sources far from the ρ Oph dense core. Thanks to the detection of the lithium absorption line and of the Hα emission line we classiify most of them as CTTS or WTTS. We show that great differences in the density of sources, in the WTTS/CTTS ratio and in the equivalent width of the lithium line exist between regions relatively close to one another in the sky. One possibility could be that these stars outside the dense core may be older, possibly ``Post T Tauri" Stars, on their way to the main sequence. 4) Variability of the Xray emission of T Tauri stars. The last part of the thesis deals with the study of time variability of the X-ray emission of TTS. These sources show evidence of variabilility both in the form of rare strong events (eruptions) and of more subtle variations of the presumed ``quiescent" emission. In some cases, we have access to the heating and cooling timescales which constrain some parameters of the plasma confined in flare loops. It is important to note that the X-ray emission of all strong sources is variable, which indicates that probably only the lack of statistics may prevent the detection of flares for the faint sources. Besides, a circumstellar disk has no influence on the variability of the star. In conclusion, X-ray are necessary to have access to the total population of young solar-type stars. They should allow to understand better the process of stellar formation and the evolution from the protostar down to the main sequence.

  2. New Young Star Candidates in BRC 27

    NASA Astrophysics Data System (ADS)

    Novatne, Lauren J.; Mattrocce, G.; Milan, T.; Quinonez, A.; Rebull, L. M.; Barge, J.; Amayo, R.; Bieber, H.; Block, L.; Cheung, E.; Cruz, A.; Elkin, D.; Figueroa, A.; Jakus, M.; Kelo, A.; Larson, O.; Lemma, B.; Li, Y.; Loe, C.; Maciag, V.; Moreno, N.; Nevels, M.; Pezanoski-Cohen, G.; Short, M.; Skatchke, K.; Tur-Kaspa, A.; Zegeye, D.; Armstrong, J.; Bonadurer, R.; French, D.; Free, B.; Miller, C.; Scherich, H.; Willis, T.; Koenig, X.; Laher, R.; Padgett, D.; Piper, M.; Pavlak, A.; Piper, M.; Venezio, E.; Ali, B.

    2013-01-01

    All stars originate from clouds of interstellar gas that collapse either under their own gravity or with external help. In triggered star formation, the collapse of a cloud is initiated by pressure, e.g., from nearby star(s). When the external source is bright stars, it can illuminate the rims of the cloud, creating bright-rimmed clouds (BRCs) to be visible at optical and infrared (IR) wavelengths. We searched for new candidate young stellar objects (YSOs) primarily using the March 2012 all-sky release of Wide-field Infrared Survey Explorer (WISE) data in BRC 27, which is part of CMa R1, a region of known star formation. Spitzer data of a 5’x5’ region centered on BRC 27 were presented by Johnson et al. 2012 and Rebull et al. 2012. We investigated WISE data within a 20 arcminute radius of BRC 27 0.35 sq. deg), combining it with Spitzer data serendipitously obtained in this region, 2MASS data, and optical data. We started from nearly 4000 WISE sources and identified about 200 candidate YSOs via a series of color cuts (Koenig et al. 2012) to identify objects with WISE colors consistent with other YSOs, e.g., having an apparent IR excess. There are about 100 objects in this region already identified in the literature as possible YSOs, about 40 of which we recovered with the color cuts. We investigated these literature YSOs and YSO candidates in all available images, and created spectral energy distributions (SEDs) and color-magnitude diagrams for further analysis of each object. We will present an analysis of our selected sub-sample of YSO candidates. This research was made possible through the NASA/IPAC Teacher Archive Research Project (NITARP) and was funded by NASA Astrophysics Data Program and Archive Outreach funds. Our education results are described in a companion education poster, Bonadurer et al.

  3. Young Stars Emerge from Orion's Head

    NASA Technical Reports Server (NTRS)

    2007-01-01

    This image from NASA's Spitzer Space Telescope shows infant stars 'hatching' in the head of the hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly three million years ago, may have initiated this newfound birth

    The region featured in this Spitzer image is called Barnard 30. It is located approximately 1,300 light-years away and sits on the right side of Orion's 'head,' just north of the massive star Lambda Orionis.

    Wisps of green in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked.

    Tints of orange-red in the cloud are dust particles warmed by the newly forming stars. The reddish-pink dots at the top of the cloud are very young stars embedded in a cocoon of cosmic gas and dust. Blue spots throughout the image are background Milky Way along this line of sight.

    This composite includes data from Spitzer's infrared array camera instrument, and multiband imaging photometer instrument. Light at 4.5 microns is shown as blue, 8.0 microns is green, and 24 microns is red.

  4. Shock Waves in Outflows from Young Stars

    NASA Astrophysics Data System (ADS)

    Hartigan, Patrick

    This review focuses on physics of the cooling zones behind radiative shocks and the emission line diagnostics that can be used to infer physical conditions and mass loss rates in jets from young stars. Spatial separations of the cooling zones from the shock fronts, now resolvable with HST, and recent evidence for C-shocks have greatly increased our understanding of how shocks in outflows interact with the surrounding medium and with other material within the flow. By combining multiple epoch HST images, one can create `movies' of flows like those produced from numerical codes, and learn what kinds of instabilities develop within these systems.

  5. Circumstellar material around young stars in Orion

    NASA Technical Reports Server (NTRS)

    Odell, C. R.

    1994-01-01

    The star cluster associated with the Orion nebula is one of the richest known. Lying at the nearside of the Orion Molecular cloud and at a distance of about 500 pc from us, it contains many premain-sequence stars with ages of about 300,000 yr. The nebula itself is a blister type, representing a wall of material ionized by the hottest star in the Trapezium group (member C). Although this is not the closest star formation region, it is probably the easiest place to detect circumstellar, possibly proto-planetary, material around these solar mass stars. This is because the same process of photoionization that creates the nebula also photoionizes these circumstellar clouds, thus rendering them easily visible. Moreover, their dust component is made visible by extinction of light from the background nebula. Young stars with circumstellar material were found in Orion on the second set of HST images and were called proplyds, indicating their special nature as circumstellar clouds caused to be luminous by being in or near a gaseous nebula. The brightest objects in the field had previously been seen in the optical and radio, and although their true nature had been hypothesized it was the HST images that made it clear what they are. The forms vary from cometlike when near the Trapezium to elliptical when further away, with the largest being 1000 AU and the bright portions of the smallest, which are found closest to the Trapezium, being about 100 AU in diameter. We now have a second set of HST observations made immediately after the refurbishment mission that provides even greater detail and reveals even more of these objects. About half of all the low-luminosity stars are proplyds. The poster paper describes quantitative tests about their fundamental structure and addresses the question of whether the circumstellar material is a disk or shell. One object (HST 16) is seen only in silhouette against the nebula and is easily resolved into an elliptical form of optical depth monotonically increasing toward the central star.

  6. A-Train Observations of Young Volcanic Eruption Clouds

    NASA Astrophysics Data System (ADS)

    Carn, S. A.; Prata, F.; Yang, K.; Rose, W. I.

    2011-12-01

    NASA's A-Train satellite constellation (including Aqua, CloudSat, CALIPSO, and Aura) has been flying in formation since 2006, providing unprecedented synergistic observations of numerous volcanic eruption clouds in various stages of development. Measurements made by A-Train sensors include total column SO2 by the Ozone Monitoring Instrument (OMI) on Aura, upper tropospheric and stratospheric (UTLS) SO2 column by the Atmospheric Infrared Sounder (AIRS) on Aqua and Microwave Limb Sounder (MLS) on Aura, ash mass loading from AIRS and the Moderate resolution Imaging Spectroradiometer (MODIS) on Aqua, UTLS HCl columns and ice water content (IWC) from MLS, aerosol vertical profiles from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument aboard CALIPSO, and hydrometeor profiles from the Cloud Profiling Radar (CPR) on CloudSat. The active vertical profiling capability of CALIPSO, CloudSat and MLS sychronized with synoptic passive sensing of trace gases and aerosols by OMI, AIRS and MODIS provides a unique perspective on the structure and composition of volcanic clouds. A-Train observations during the first hours of atmospheric residence are particularly valuable, as the fallout, segregation and stratification of material in this period determines the concentration and altitude of constituents that remain to be advected downwind. This represents the eruption 'source term' essential for dispersion modeling, and hence for aviation hazard mitigation. In this presentation we show examples of A-Train data collected during recent eruptions including Chaitén (May 2008), Kasatochi (August 2008), Redoubt (March 2009), Eyjafjallajökull (April 2010) and Cordón Caulle (June 2011). We interpret the observations using the canonical three-stage view of volcanic cloud development [e.g., Rose et al., 2000] from initial rapid ash fallout to far-field dispersion of fine ash, gas and aerosol, and results from numerical modeling of volcanic plumes [e.g., Textor et al., 2003] and discuss the degree to which the observations validate existing theory and models. We also describe plans for advanced SO2 and ash retrieval algorithms that will exploit the synergy between UV and IR sensors in the A-Train for improved quantification of ash and SO2 loading by volcanic eruptions.

  7. A BOW SHOCK NEAR A YOUNG STAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's Hubble Space Telescope continues to reveal various stunning and intricate treasures that reside within the nearby, intense star-forming region known as the Great Nebula in Orion. One such jewel is the bow shock around the very young star, LL Ori, featured in this Hubble Heritage image. Named for the crescent-shaped wave made by a ship as it moves through water, a bow shock can be created in space when two streams of gas collide. LL Ori emits a vigorous solar wind, a stream of charged particles moving rapidly outward from the star. Our own Sun has a less energetic version of this wind that is responsible for auroral displays on the Earth. The material in the fast wind from LL Ori collides with slow-moving gas evaporating away from the center of the Orion Nebula, which is located to the lower right in this Heritage image. The surface where the two winds collide is the crescent-shaped bow shock seen in the image. Unlike a water wave made by a ship, this interstellar bow shock is a three-dimensional structure. The filamentary emission has a very distinct boundary on the side facing away from LL Ori, but is diffuse on the side closest to the star, a characteristic common to many bow shocks. A second, fainter bow shock can be seen around a star near the upper right-hand corner of the Heritage image. Astronomers have identified numerous shock fronts in this complex star-forming region and are using this data to understand the many complex phenomena associated with the birth of stars. This image was taken in February 1995 as part of the Hubble Orion Nebula mosaic. A close visitor in our Milky Way galaxy, the nebula is only 1,500 light-years from Earth. The filters used in this color composite represent oxygen, nitrogen, and hydrogen emissions. Image Credit: NASA and the Hubble Heritage Team (STScI/AURA) Acknowledgment: C. R. O'Dell (Vanderbilt University)

  8. Chromospheric Activity in Young Galactic Cluster Stars

    NASA Astrophysics Data System (ADS)

    Soto, K.; Pilachowski, C. A.

    2003-12-01

    Spectra of the Ca II H and K line region of 80 late-type stars in seven young clusters were examined to obtain estimates of chromospheric activity, projected rotation velocity, radial velocity and spectral type. The spectra were obtained using the Hydra multi-fiber spectrographs on the Blanco 4-m and WIYN 3.5-m telescopes at the Cerro Tololo Interamerican Observatory and at Kitt Peak. The clusters ranged in age from the youngest, NGC 2264, at an age of about 3 million years, to the oldest, IC 4664, at an age of about 100 million years. The stars included in the study were selected to have dereddened B-V colors between 0.4 and 0.9. Chromospheric activity was estimated using indices measuring the emission in the cores of the Ca II lines compared to nearby continuum. Radial velocities were determined by cross-correlation with the solar spectrum. Projected rotation velocities were estimated by comparison with an artificially spun-up solar spectrum. No correlation was found between projected rotation speed and the degree of chromospheric activity, and stars the oldest cluster of our sample, IC 4665, showed the greatest degree of chromospheric activity. This research was carried out through the Research Experience for Undergraduates program at Indiana University Bloomington. Support from the National Science Foundation through AST-0139617 is gratefully acknowledged.

  9. The magnetic fields of young stars

    NASA Astrophysics Data System (ADS)

    Yang, Hao

    2009-06-01

    The T Tauri stars (TTSs) are young, solar-type stars which display many spectral pecularities. Understanding the magnetic properties of TTSs is a key to make sense of their curious behaviors. First, high resolution optical and infrared (IR) echelle spectra are analyzed to measure the surface magnetic field of the classical T Tauri star (CTTS) TW Hydrae. Key stellar parameters are determined from detailed spectrum synthesis of atomic and molecular absorption features in the optical, and then modeling the line profiles of the four magnetically sensitive Ti I lires in the K band yields the average magnetic field on TW Hydrae. Extensive Monté Carlo tests are performed to quantify systematic errors in the analysis technique, finding that reasonable errors in the effective temperature or surface gravity produce around 10% uncertainty in the magnetic field measurements. Then a similar analysis technique is applied to detect strong magnetic fields on 5 additional stars in the TW Hydrae Association (TWA) as well as 14 TTSs in the Orion Nebula Cluster (ONC). We combine these measurements with previous measurements of 14 stars in Taurus to study the potential evolution of magnetic field properties during the first 10 million years of stellar evolution. In addition, to probe the magnetic geometry on the surface of TW Hydrae, high resolution circular spectropolarimetry of this star is analyzed to measure the net longitudinal magnetic field. Significant polarization is detected on the final night of six consecutive nights of observing, but no net polarization is seen on other nights. This longitudinal field detection is still much lower than that which would be consistent with a dipole geometry on the stellar suface. On the other hand, strong circular polarization is detected in the He I l5876 and Ca II l8498 emission lines, indicating a strong field in the line forming regions of these features. Overall, strong magnetic fields of kG level are commonly found among TTSs and the magnetic configuration is probably not a simple dipole as current magnetospheric accretion theories assume. With magnetic pressure likely dominating over gas pressure in the stellar photospheres, the entire stellar surfaces could be covered with magnetic fields, and this might be responsible for the underproduction of the X-ray emission of TTSs. It is also suggested that these large-scale magnetic fields could be of a primordial origin.

  10. THE ASTROPHYSICAL IMPLICATIONS OF DUST FORMATION DURING THE ERUPTIONS OF HOT, MASSIVE STARS

    SciTech Connect

    Kochanek, C. S.

    2011-12-10

    Dust formation in the winds of hot stars is inextricably linked to the classic eruptive state of luminous blue variables because it requires very high mass-loss rates, M-dot {approx}>10{sup -2.5} M{sub sun} year{sup -1}, for grains to grow and for the non-dust optical depth of the wind to shield the dust formation region from the true stellar photosphere. Thus, dusty shells around hot stars trace the history of 'great' eruptions, and the statistics of such shells in the Galaxy indicate that these eruptions are likely the dominant mass-loss mechanism for evolved, M{sub ZAMS} {approx}> 40 M{sub Sun} stars. Dust formation at such high M-dot also explains why very large grains (a{sub max} {approx}> 1 {mu}m) are frequently found in these shells, since a{sub max}{proportional_to} M-dot . The statistics of these shells (numbers, ages, masses, and grain properties such as a{sub max}) provide an archaeological record of this mass-loss process. In particular, the velocities v{sub shell}, transient durations (where known), and ejected masses M{sub shell} of the Galactic shells and the supernova (SN) 'impostors' proposed as their extragalactic counterparts are very different. While much of the difference is a selection effect created by shell lifetimes {proportional_to}(v{sub shell}{radical}(M{sub shell})){sup -1}, more complete Galactic and extragalactic surveys are needed to demonstrate that the two phenomena share a common origin given that their observed properties are essentially disjoint. If even small fractions (1%) of SNe show interactions with such dense shells of ejecta, as is currently believed, then the driving mechanism of the eruptions must be associated with the very final phases of stellar evolution, suggestive of some underlying nuclear burning instability.

  11. Angular Momentum Evolution of Young Solar-type Stars

    NASA Astrophysics Data System (ADS)

    Amard, Louis; Palacios, Ana; Charbonnel, Corinne

    2016-01-01

    We present stellar evolution models of young solar-type stars including self consistent treatment of rotational mixing and extraction of angular momentum (AM) by magnetized wind including the most up-to-date physic of AM transport.

  12. Magnetic Stars in Young Clusters and Associations

    NASA Astrophysics Data System (ADS)

    Romanyuk, I. I.; Semenko, E. A.; Yakunin, I. A.

    2015-04-01

    We present a review of the current state of the problem. The spatial distribution of magnetic CP stars in the Galaxy corresponds to the distribution of normal A and B stars of the same temperature. Most magnetic Bp stars observed (61%) are the cluster stars, while most of Ap stars (75%) are the field stars. Evolution of magnetic fields of CP stars is preferably to be studied with the use of Bp stars in clusters of different age. A total of 85 CP stars of various types are identified among 814 members of the Ori OB1 association. The fraction of CP stars decreases with age for different cluster subgroups: from 21.4% in the youngest subgroup (d) to 7.7% in the oldest one (a). The association contains 33 magnetic stars, 11 of them were found as magnetic using the 6-m telescope. A strong field (the longitudinal component Be>3 kG) more often occurs in the hot Bp stars-members of the Ori OB1 association and among the members of the Scorpio-Centaurus cluster. What is not a general law—two cool magnetic Ap stars (HD 154708 and HD 178892) with a 7-8 kG longitudinal field Be have been found. The Babcock's (1960) star HD 215441 is the record dipolar surface field (Bs =34 kG) star yet. The chemical composition of weak- and strong-field stars does not differ, but strong-field CP stars have essentially larger continuum depressions.

  13. An Ultraviolet-Selected Sample of Young Stars

    NASA Astrophysics Data System (ADS)

    Findeisen, Krzysztof; Hillenbrand, L.; Carpenter, J.

    2009-01-01

    While we know of large populations of young stars having ages younger than 3 Myr and older than 100 Myr, traditional search methods are relatively insensitive to stars of intermediate age. This bias impairs studies of key stages of stellar evolution and of the star formation history of individual regions. We have used GALEX ultraviolet imaging of the nearby (140 pc) Taurus and Upper Scorpius star forming regions to search for 3-100 Myr old stars. Our method selects ultraviolet emission in excess of that expected from a main-sequence photosphere. We identify objects with such excesses by combining the GALEX photometry with 2MASS infrared photometry. We present these data as well as follow-up optical spectroscopy of a representative sample of objects that confirms or rejects their identification as young stars. Several other types of UV bright objects are serendipitously discovered via our methods.

  14. Variable stars in young open star cluster NGC 7380

    NASA Astrophysics Data System (ADS)

    Lata, Sneh; Pandey, A. K.; Panwar, Neelam; Chen, W. P.; Samal, M. R.; Pandey, J. C.

    2016-03-01

    We present time series photometry of 57 variable stars in the cluster region NGC 7380. The association of these variable stars with the cluster NGC 7380 has been established on the basis of two colour diagrams and colour-magnitude diagrams. 17 stars are found to be main-sequence variables, which are mainly B-type stars and are classified as slowly pulsating B stars, β Cep or δ Scuti stars. Some of them may belong to new class variables as discussed by Mowlavi et al. and Lata et al. Present sample also contains 14 pre-main-sequence stars, whose ages and masses are found to be mostly ≲5 Myr and range 0.60 ≲ M/M⊙ ≲ 2.30 and hence should be T-Tauri stars. About half of the weak-line T-Tauri stars are found to be fast rotators with a period of ≲2 d as compared to the classical T-Tauri stars. Some of the variables belong to the field star population.

  15. 8-13 Micron Spectroscopy of Young Stars

    NASA Technical Reports Server (NTRS)

    Hanner, M. S.; Brooke, T. Y.; Tokunaga, A. T.

    1997-01-01

    We presen 8-13 meu spectra of 23 young stars acquired with the UKIRT CGS3 spectromere, including T Tauri, Herbig Ae/Be, and FU Ori stars. Silicate emission and absorption features can generally be matched with the Trapezium emissivity, by employing simple models to account for optical depth effects.

  16. Inferring Rotation Periods of Young Stars from Synoptic Observations

    NASA Astrophysics Data System (ADS)

    Hartigan, Patrick; Johns-Krull, Christopher M.; Scowen, Paul

    2012-04-01

    Using known distributions for the periods, amplitudes and light-curve shapes of young stars, we examine how well one could measure periods of these objects in the upcoming era of large synoptic surveys. Surveys like the LSST should be able to recover accurate rotation periods for over 90% of targets of interest in regions near to massive-star formation. That information will usher in a new era in our understanding of how the angular momentum of a young star/disk system evolves with time.

  17. Brown Dwarfs and Giant Planets Around Young Stars

    NASA Astrophysics Data System (ADS)

    Mahmud, Naved; Crockett, C.; Johns-Krull, C.; Prato, L.; Hartigan, P.; Jaffe, D.; Beichman, C.

    2011-01-01

    How dry is the brown dwarf (BD) desert at young ages? Previous radial velocity (RV) surveys have revealed that the frequency of BDs as close companions to solar-age stars in the field is extraordinarily low compared to the frequency of close planetary and stellar companions. Is this a formation or an evolutionary effect? Do close-in BDs form at lower rates, or are they destroyed by migration via interactions with a massive circumstellar disk, followed by assimilation into the parent star? To answer these questions, we are conducting an RV survey of 130 T Tauri stars in Taurus-Auriga (a few Myr old) and a dozen stars in the Pleiades (100 Myr old) to search for stellar reflex motions resulting from close substellar companions. Our goal is to measure the frequency of BDs at young ages. Detecting a higher frequency of BDs in young systems relative to the field will provide evidence for the migration theory as well as set limits on the migration timescale. Two additional goals are (1) to investigate the effect of star spots in young stars on RV observations, and (2) to detect the youngest-known giant exoplanet. We present results from the first few years of this survey. Strikingly, after completing observations of a third of our sample, we have yet to detect a single BD. Thus we can set limits on the dryness of the BD desert at young ages and shed light on the mysterious early lives of these objects.

  18. Asteroseismology. Echography of young stars reveals their evolution.

    PubMed

    Zwintz, K; Fossati, L; Ryabchikova, T; Guenther, D; Aerts, C; Barnes, T G; Themeßl, N; Lorenz, D; Cameron, C; Kuschnig, R; Pollack-Drs, S; Moravveji, E; Baglin, A; Matthews, J M; Moffat, A F J; Poretti, E; Rainer, M; Rucinski, S M; Sasselov, D; Weiss, W W

    2014-08-01

    We demonstrate that a seismic analysis of stars in their earliest evolutionary phases is a powerful method with which to identify young stars and distinguish their evolutionary states. The early star that is born from the gravitational collapse of a molecular cloud reaches at some point sufficient temperature, mass, and luminosity to be detected. Accretion stops, and the pre-main sequence star that emerges is nearly fully convective and chemically homogeneous. It will continue to contract gravitationally until the density and temperature in the core are high enough to start nuclear burning of hydrogen. We show that there is a relationship for a sample of young stars between detected pulsation properties and their evolutionary status, illustrating the potential of asteroseismology for the early evolutionary phases. PMID:24993346

  19. Young low mass stars in the vicinity of Sigma Scorpii

    NASA Technical Reports Server (NTRS)

    Meyer, Michael R.; Wilking, Bruce A.; Zinnecker, Hans

    1993-01-01

    The region near Sigma Scorpii, a member of the Sco-Cen OB association, is examined for signs of recent star formation. Thirteen candidate young stellar objects are identified over an 80 x 80 arcmin region centered on Sigma Sco using the Point source Catalog and a recent survey for H-alpha emission-line stars. Near-infrared photometry, improved IRAS fluxes, and optical spectra are used to determine the nature of these objects. Four definite young stars are revealed, as well as one additional such object that fell just outside of the present target region. These stars, all of spectral type K or M, are argued to have formed in the vicinity of the B1 giant star Sigma Scorpii and to represent a subsample of the low-mass members of the association.

  20. Direct Detections of Young Stars in Nearby Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Ford, H. Alyson; Bregman, Joel N.

    2013-06-01

    Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-infrared dust emission. Such star formation has previously been difficult to directly detect, but using ultraviolet Hubble Space Telescope Wide Field Camera 3 imaging, we have identified individual young stars and star clusters in four nearby ellipticals. Ongoing star formation is detected in all galaxies, including three ellipticals that have previously exhibited potential signposts of star-forming conditions (NGC 4636, NGC 4697, and NGC 4374), as well as the typical "red and dead" NGC 3379. The current star formation in our closest targets, where we are most complete, is between 2.0 and 9.8 × 10-5 M ⊙ yr-1. The star formation history was roughly constant from 0.5 to 1.5 Gyr (at (3-5) × 10-4 M ⊙ yr-1), but decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a mass between 102 and 104 M ⊙. The specific star formation rates of ~10-16 yr-1 (at the present day) or ~10-14 yr-1 (when averaging over the past Gyr) imply that a fraction 10-8 of the stellar mass is younger than 100 Myr and 10-5 is younger than 1 Gyr, quantifying the level of frosting of recent star formation over the otherwise passive stellar population. There is no obvious correlation between either the presence or spatial distribution of postulated star formation indicators and the star formation we detect. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 11583.

  1. DIRECT DETECTIONS OF YOUNG STARS IN NEARBY ELLIPTICAL GALAXIES

    SciTech Connect

    Ford, H. Alyson; Bregman, Joel N.

    2013-06-20

    Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-infrared dust emission. Such star formation has previously been difficult to directly detect, but using ultraviolet Hubble Space Telescope Wide Field Camera 3 imaging, we have identified individual young stars and star clusters in four nearby ellipticals. Ongoing star formation is detected in all galaxies, including three ellipticals that have previously exhibited potential signposts of star-forming conditions (NGC 4636, NGC 4697, and NGC 4374), as well as the typical ''red and dead'' NGC 3379. The current star formation in our closest targets, where we are most complete, is between 2.0 and 9.8 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}. The star formation history was roughly constant from 0.5 to 1.5 Gyr (at (3-5) Multiplication-Sign 10{sup -4} M{sub Sun} yr{sup -1}), but decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a mass between 10{sup 2} and 10{sup 4} M{sub Sun }. The specific star formation rates of {approx}10{sup -16} yr{sup -1} (at the present day) or {approx}10{sup -14} yr{sup -1} (when averaging over the past Gyr) imply that a fraction 10{sup -8} of the stellar mass is younger than 100 Myr and 10{sup -5} is younger than 1 Gyr, quantifying the level of frosting of recent star formation over the otherwise passive stellar population. There is no obvious correlation between either the presence or spatial distribution of postulated star formation indicators and the star formation we detect.

  2. Explosions triggered by violent binary-star collisions: application to Eta Carinae and other eruptive transients

    NASA Astrophysics Data System (ADS)

    Smith, Nathan

    2011-08-01

    This paper discusses a scenario where a violent periastron collision of stars in an eccentric binary system induces an eruption or explosion seen as a brief transient source, attributed to luminous blue variables (LBVs), supernova (SN) impostors or other transients. The key ingredient is that an evolved primary increases its photospheric radius on relatively short (year to decade) time-scales, to a point where the radius is comparable to or larger than the periastron separation in an eccentric binary. In such a configuration, a violent and sudden collision would ensue, possibly leading to substantial mass ejection instead of a merger. Sudden energy deposition during the encounter could drive expansion of the optically thick envelope, causing a luminous transient source. Repeated periastral grazings in an eccentric system could quickly escalate to a catastrophic encounter. Outbursts triggered by tidal disturbances or powered by secondary accretion of the primary star's wind have been suggested previously. Instead, this paper proposes a much more violent encounter where the companion star plunges deep inside the photosphere of a bloated primary during periastron, as a result of the primary star increasing its own radius. This is motivated by the case of Eta Carinae, where such a collision must have occurred if conventional estimates of the present-day orbit are correct and where peaks in the light curve coincide with times of periastron. Stellar collisions may explain brief recurring LBV outbursts, such as SN 2000ch and SN 2009ip, and perhaps outbursts from intermediate-mass progenitor stars (i.e. collisions are not necessarily the exclusive domain of very luminous stars), but they cannot explain all non-SN transients. Finally, mass ejections induced repeatedly at periastron cause orbital evolution; this may explain the origin of eccentric Wolf-Rayet binaries such as WR 140.

  3. Young stars and protostellar cores near NGC 2023

    NASA Astrophysics Data System (ADS)

    Mookerjea, B.; Sandell, G.; Jarrett, T. H.; McMullin, J. P.

    2009-12-01

    Context: We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the h ii region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM 1. Aims: We study the distribution of gas, dust and young stars in this region to see where stars are forming, whether the expansion of the h ii region has triggered star formation, and whether dense cold cores have already formed stars. Methods: We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'×26' field along the boundary between IC 434 and L 1630. For some stars, which have sufficient optical, IR, and/or sub-millimeter data we have also used the online SED fitting tool for a large 2D archive of axisymmetric radiative transfer models to perform more detailed modeling of the observed SEDs. We identify 5 sub-millimeter cores in our 850 and 450 μm SCUBA images, two of which have embedded class 0 or I protostars. Observations with BIMA are used to refine the position and characteristics of the Class 0 source NGC 2023 MM 1. These observations show that it is embedded in a very cold cloud core, which is strongly enhanced in NH2D. Results: We find that HD 37903 is the most massive member of a cluster with 20-30 PMS stars. We also find smaller groups of PMS stars formed from the Horsehead nebula and another elephant trunk structure to the north of the Horsehead. Star formation is also occurring in the dark lane seen in IRAC images and in the sub-millimeter continuum. We refine the spectral classification of HD 37903 to B2 Ve. We find that the star has a clear IR excess, and therefore it is a young Herbig Be star. Conclusions: Our study shows that the expansion of the IC 434 h ii region has triggered star formation in some of the dense elephant trunk structures and compressed gas inside the L 1630 molecular cloud. This pre-shock region is seen as a sub-millimeter ridge in which stars have already formed. The cluster associated with NGC 2023 is very young, and has a large fraction of Class I sources. Table 2 is only available in electronic form at http://www.aanda.org

  4. Young Star Clusters and the Star Formation Ring Structure in M31

    NASA Astrophysics Data System (ADS)

    Kang, Yong Beom; Rey, S.; Lee, K.; Kim, Y.; Bianchi, L.

    2010-01-01

    Most recently, in addition to the unusual well-known 10 kpc ring seen in previous observations of M31, the presence of a second, inner dust ring was discovered in the disk of M31 (Block et al. 2006). The two off-center circular rings suggest that M31 has been distorted by very recent passage of its satellite galaxy through the disk. In this case, such a recent violent event may enhance the efficiency of star formation in the disk of M31. On the other hand, the existence of young star clusters in the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the disk of M31. Most of the young star clusters in M31 have similar characteristics to the blue star clusters in LMC. Star cluster system can be a tracer of galaxy formation and assembly, in the sense that significant star cluster formation is typically produced by major star-forming episode in a galaxy. Therefore, assuming that merging/accretion event may trigger high-level star formation in the disk of M31 than in quiescent galactic disks, it is intriguing to examine the properties of star clusters related with those of M31 disk. By studying the kinematics, age, mass, and spatial distribution of young star clusters in M31, we confirm the existence of plentiful young massive clusters associated with the disk of M31, and suggest that these young clusters may be outgrowth of a suggested recent merger occurred at the center of M31 disk.

  5. Binary Stars in Young Clusters -- a Theoretical Perspective

    NASA Astrophysics Data System (ADS)

    Kroupa, Pavel

    The preponderance of binary systems in all known stellar populations makes them exciting dynamical agents for research on topics as varied as star formation, star-cluster dynamics and the interiors of young and old stars. Today we know that the Galactic-field binary population is probably a dynamically evolved version of the Taurus--Auriga pre-main sequence population, and that the initial distributions of binary-star orbital elements are probably universal. Furthermore, N-body calculations tentatively suggest that OB stars form in energetic binaries near cluster cores, and that binaries with 'forbidden' orbital elements that are produced in stellar encounters, may turn out to be very useful windows into stellar interiors, potentially allowing tests of pre-main sequence evolution theory as well as of models of main-sequence stars.

  6. RCW 108: Massive Young Stars Trigger Stellar Birth

    NASA Technical Reports Server (NTRS)

    2008-01-01

    RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

    This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

    The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

    Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas clouds in RCW 108 to be compressed, leading to gravitational collapse and the formation of new stars.

  7. Young ?-enriched giant stars in the solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva; Hekker, Saskia; Mosser, Benoit; Elsworth, Yvonne; Bovy, Jo; Stello, Dennis; Anders, Friedrich; Garca, Rafael A.; Tayar, Jamie; Rodrigues, Thase S.; Basu, Sarbani; Carrera, Ricardo; Ceillier, Tugdual; Chaplin, William J.; Chiappini, Cristina; Frinchaboy, Peter M.; Garca-Hernndez, D. A.; Hearty, Fred R.; Holtzman, Jon; Johnson, Jennifer A.; Majewski, Steven R.; Mathur, Savita; Mszros, Szabolcs; Miglio, Andrea; Nidever, David; Pan, Kaike; Pinsonneault, Marc; Schiavon, Ricardo P.; Schneider, Donald P.; Serenelli, Aldo; Shetrone, Matthew; Zamora, Olga

    2015-08-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [?/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investigate the relation between age and chemical abundances for these stars, using a simple and robust approach to obtain ages. We first derive stellar masses using standard seismic scaling relations, then determine the maximum possible age for each star as function of its mass and metallicity, independently of its evolutionary stage. While the overall trend between maximum age and chemical abundances is a declining fraction of young stars with increasing [?/Fe], at least 14 out of 241 stars with [?/Fe] >0.13 are younger than 6 Gyr. Five stars with [?/Fe] ?0.2 have ages below 4 Gyr. We examine the effect of modifications in the standard seismic scaling relations, as well as the effect of very low helium fractions, but these changes are not enough to make these stars as old as usually expected for ?-rich stars (i.e. ages greater than 8-9 Gyr). Such unusual ?-rich young stars have also been detected by other surveys, but defy simple explanations in a galaxy evolution context.

  8. Young Star Cluster Aglow With Mysterious X-Ray Cloud

    NASA Technical Reports Server (NTRS)

    2002-01-01

    At a distance of 6,000 light years from Earth, the star cluster RCW 38 is a relatively close star-forming region. This area is about 5 light years across, and contains thousands of hot, very young stars formed less than a million years ago, 190 of which exposed x-rays to Chandra. Enveloping the star cluster, the diffused cloud of x-rays shows an excess of high energy x-rays, which indicates that the x-rays come from trillion-volt electrons moving in a magnetic field. Such particles are typically produced by exploding stars, or in the strong magnetic fields around neutron stars or black holes, none of which are evident in RCW 38. One possible origin for the particles, could be an undetected supernova that occurred in the cluster, possibly thousands of years ago, producing a shock wave that is interacting with the young stars. Regardless of the origin of these energetic electrons, their presence could change the chemistry of the disks that will eventually form planets around the stars in the cluster.

  9. Circumstellar disks of the most vigorously accreting young stars.

    PubMed

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

  10. Circumstellar disks of the most vigorously accreting young stars

    PubMed Central

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I.; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M.; Karr, Jennifer L.; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-01-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

  11. A young massive planet in a star-disk system.

    PubMed

    Setiawan, J; Henning, Th; Launhardt, R; Müller, A; Weise, P; Kürster, M

    2008-01-01

    There is a general consensus that planets form within disks of dust and gas around newly born stars. Details of their formation process, however, are still a matter of ongoing debate. The timescale of planet formation remains unclear, so the detection of planets around young stars with protoplanetary disks is potentially of great interest. Hitherto, no such planet has been found. Here we report the detection of a planet of mass (9.8+/-3.3)M(Jupiter) around TW Hydrae (TW Hya), a nearby young star with an age of only 8-10 Myr that is surrounded by a well-studied circumstellar disk. It orbits the star with a period of 3.56 days at 0.04 au, inside the inner rim of the disk. This demonstrates that planets can form within 10 Myr, before the disk has been dissipated by stellar winds and radiation. PMID:18172492

  12. A debris disk around an isolated young neutron star.

    PubMed

    Wang, Zhongxiang; Chakrabarty, Deepto; Kaplan, David L

    2006-04-01

    Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars. PMID:16598251

  13. Identification and Characterization of Young, Nearby, Solar-type Stars

    NASA Astrophysics Data System (ADS)

    Mamajek, Eric E.

    2004-08-01

    Post-T Tauri stars (PTTSs) are low-mass, pre-MS stars which have ceased accreting, and are not necessarily near star-forming molecular clouds. Historically, they have been difficult to identify due to their benign spectroscopic signatures. With recent all-sky X-ray surveys and proper motion catalogs, it is now possible to find PTTSs in large numbers. The nearest PTTSs will be important targets for future imaging surveys characterizing dust disks and planetary systems around young solar analogs. The goal of this work is to systematically identify samples of PTTSs, investigate the evolution of circumstellar disks, to infer the fossil star-formation history of molecular clouds, and to estimate kinematic distances to young stars lacking trigonometric parallaxes. We present the results of a spectroscopic survey which identified 110 PTTS members of the nearest OB association (Sco-Cen). We find that 2/3rds of the low-mass star-formation in each OB subgroup occurred in <5 Myr, and that only ~1% of solar-type stars with mean age ~13 Myr shows signs of accretion from a circumstellar disk. In order to assess how long circumstellar material is detectable around PTTSs, we conducted a 10 micron imaging survey of post-T Tauri members of the ~30-Myr-old Tuc-Hor association. The goal was to find evidence of either remnant accretion disks or dusty debris disks with orbital radii of <10 AU. Combined with data from other surveys, we conclude that mid-IR emission from warm dust grains in the terrestrial planet zones around young stars become undetectable compared to the stellar photosphere for nearly all stars by age ~20 Myr. Lastly, we present a technique for calculating distances isolated young field stars that currently lack trigonometric parallax measurements. The technique is a generalization of the classical cluster parallax method, but can handle anisotropic velocity dispersions and non-zero Oort parameters. Distances and isochronal ages are estimated for a subsample of PTTSs included in the Formation and Evolution of Planetary Systems (FEPS) Spitzer Space Telescope (SST) Legacy Science program. The techniques developed in this thesis will be useful for identifying the nearest, young star candidates from current databases.

  14. Bipolar outflows and Jets From Young Stars

    NASA Astrophysics Data System (ADS)

    Bally, J.

    2000-05-01

    Stars produce powerful jets and winds during their birth. These primary outflows power shock waves (Herbig-Haro objects) and entrain surrounding gas to produce molecular outflows. Many outflows reach parsec-scale dimensions whose dynamical ages can become comparable to the accretion age of the source star. Thus, these giant outflows provide fossil records of the mass loss histories of their parent stars. Jet symmetries provide tantalizing clues about the violent history of stellar accretion and dynamical interactions with nearby companions. These flows inject sufficient energy and momentum into the surrounding medium to alter the physical and chemical state of the gas, generate turbulence, disrupt the parent cloud, and self-regulate the rate of star formation. Recent observations have revealed a new class of externally irradiated jets which are rendered visible by the light of nearby massive stars. Some of these jets appear to be millions of years old, indicating that outflow activity can persist for much longer than previously thought. Stellar jets provide ideal laboratories for the investigation of accretion powered outflows and associated shocks since their time-dependent behavior can be observed with a rich variety of spectral line diagnostics.

  15. The evolutionary tracks of young massive star clusters

    SciTech Connect

    Pfalzner, S.; Steinhausen, M.; Vincke, K.; Menten, K.; Parmentier, G.

    2014-10-20

    Stars mostly form in groups consisting of a few dozen to several ten thousand members. For 30 years, theoretical models have provided a basic concept of how such star clusters form and develop: they originate from the gas and dust of collapsing molecular clouds. The conversion from gas to stars being incomplete, the leftover gas is expelled, leading to cluster expansion and stars becoming unbound. Observationally, a direct confirmation of this process has proved elusive, which is attributed to the diversity of the properties of forming clusters. Here we take into account that the true cluster masses and sizes are masked, initially by the surface density of the background and later by the still present unbound stars. Based on the recent observational finding that in a given star-forming region the star formation efficiency depends on the local density of the gas, we use an analytical approach combined with N-body simulations to reveal evolutionary tracks for young massive clusters covering the first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for the evolution of stars, these tracks provide equivalent information for clusters. Like stars, massive clusters form and develop faster than their lower-mass counterparts, explaining why so few massive cluster progenitors are found.

  16. Astronomers Discover Rotating Disk Around Young, Massive Star

    NASA Astrophysics Data System (ADS)

    1999-01-01

    Astronomers using radio telescopes in New Mexico and California have discovered a giant, rotating disk of material around a young, massive star, indicating that very massive stars as well as those closer to the size of the Sun may be circled by disks from which planets are thought to form. This is the most massive young star for which such a disk has yet been found. Debra Shepherd of the California Institute of Technology (Caltech) and Stan Kurtz of the National Autonomous University of Mexico, used the National Science Foundation's Very Large Array (VLA) radio telescope and telescopes of Caltech's Owens Valley Radio Observatory (OVRO) to make a detailed study of an object called G192.16-3.82, in the constellation Orion. They announced their findings at the American Astronomical Society's meeting in Austin, TX, today. What astronomers call Young Stellar Objects (YSOs) -- stars still in the process of formation -- are enigmatic objects, both drawing in material from their surroundings and expelling material outward at the same time. "The details of the interaction between these two processes are poorly understood," Shepherd said. "In addition, most theories are based on observing low-mass stars, and we don't know if things work the same way with higher-mass stars." "We now have the first unambiguous evidence for a rotating disk around a high-mass star that also is powering an outflow," Shepherd said. "We need to make more observations to confirm the finding, but this information will help test theories of how such young stellar objects operate." It has been difficult to study massive star formation, because massive stars are rarer than smaller ones, they tend to form in clusters, making observations more difficult, and there are few of them forming relatively nearby. The object that Shepherd and Kurtz chose is reasonably isolated. "We think it provides us with a good laboratory for studying the process," Kurtz said. The young star at the core of G192.16-3.82 is about six to 10 times more massive than the sun. The rotating disk and an "envelope" of material surrounding the star contain about 20 times the mass of the sun. VLA observations revealed the speed of material in the disk, indicating that the disk is rotating around the central star according to Kepler's laws of planetary motion, just as the planets of our Solar System do. The disk extends outward from the star more than 500 times the Earth-Sun distance. "This is comparable in size to the largest disks seen around smaller stars, but this one is at least four times more massive than those disks," Shepherd said. During star formation, the material in such disks is thought to be drawn into the new star by its gravitational pull, while other processes power an outflow of material into the surrounding space. The outflow in the region of G192.16-3.82 is one of the largest such outflows in our Milky Way Galaxy. The velocity measurements were possible because the disk contains water molecules that amplify microwave radio emissions in a manner similar to that in which a laser amplifies light. The water molecules that act as amplifiers -- masers -- both appear as bright spots on radio telescope images and are emitted at a specific, known radio frequency. The molecules' motion causes that frequency to be changed by the Doppler effect. The amount of change allows scientists to calculate the velocity. The VLA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

  17. Anomalous Spectral Types and Intrinsic Colors of Young Stars

    NASA Astrophysics Data System (ADS)

    Pecaut, Mark J.

    2016-01-01

    We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions and thus bias the inferred ages.

  18. Evolution of massive stars in very young clusters and associations

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1985-01-01

    Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

  19. X-Ray Outburst from Young Star in McNeil's Nebula

    NASA Astrophysics Data System (ADS)

    2004-07-01

    Observations with NASA's Chandra X-ray Observatory captured an X-ray outburst from a young star, revealing a probable scenario for the intermittent brightening of the recently discovered McNeil's Nebula. It appears the interaction between the young star's magnetic field and an orbiting disk of gas can cause dramatic, episodic increases in the light from the star and disk, illuminating the surrounding gas. "The story of McNeil's Nebula is a wonderful example of the importance of serendipity in science," said Joel Kastner of the Rochester Institute of Technology in Rochester, New York, lead author of a paper in the July 22 issue of Nature describing the X-ray results. "Visible-light images were made of this region several months before Jay McNeil made his discovery, so it could be determined approximately when and by how much the star flared up to produce McNeil's Nebula." The small nebula, which lies in the constellation Orion about 1300 light years from Earth, was discovered with a 3-inch telescope by McNeil, an amateur astronomer from Paducah, Kentucky, in January 2004. In November 2002, a team led by Ted Simon of the Institute for Astronomy in Hawaii had observed the star-rich region with Chandra in search of young, X-ray emitting stars, and had detected several objects. Optical and infrared astronomers had, as part of independent surveys, also observed the region about a year later, in 2003. After the announcement of McNeil's discovery, optical, infrared and X-ray astronomers rushed to observe the region again. They found that a young star buried in the nebula had flared up, and was illuminating the nebula. This star was coincident with one of the X-ray sources discovered earlier by Simon. Chandra observations obtained by Kastner's group just after the optical outburst showed that the source had brightened fifty-fold in X-rays when compared to Simon's earlier observation. The visible-light eruption provides evidence that the cause of the X-ray outburst is the sudden infall of matter onto the surface of the star from an orbiting disk of gas. In general, the coupling of the magnetic field of the star and the magnetic field of its circumstellar disk regulates the inflow of gas from the disk onto the star. This slow, steady inflow suddenly can become much more rapid if a large amount of gas accumulates in the disk, and the disk and the star are rotating at different rates. The differing rotation rates would twist and shear the magnetic field, storing up energy. This energy is eventually released in an energetic, X-ray producing outburst as the magnetic field violently rearranges back to a more stable state. During this period, a large amount of gas can fall onto the star, producing the observed optical and infrared outburst. A new buildup of gas in the disk could lead to a new outburst in the future. Such a scenario may explain why the brightness of McNeil's Nebula appears to vary with time. It is faintly present in surveys of this region of Orion in images taken in the 1960s, but absent from images taken in the 1950s and 1990s. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

  20. A multiwavelength study of young stars in the Elephant Trunk

    NASA Astrophysics Data System (ADS)

    López Martí, B.; Bayo, A.; Morales Calderón, M.; Barrado, D.

    2013-05-01

    We present the results of a multiwavelength study of young stars in IC 1396A, ``the Elephant Trunk Nebula''. Our targets are selected combining optical, near-infrared and mid-infrared photometry. Near-infrared and optical spectroscopy are used to confirm their youth and to derive spectral types for these objects, showing that they are early to mid-M stars, and that our sample includes some of the lowest-mass objects reported so far in the region. The photometric and spectroscopic information is used to construct the spectral energy distributions and to study the properties of the stars (mass, age, accretion, disks, spatial location). The implications for the triggered star formation picture are discussed.

  1. Magnetic propeller effect in the spectra of young stars

    NASA Astrophysics Data System (ADS)

    Grinin, V. P.; Potravnov, I. S.; Ilyin, I. V.; Shulman, S. G.

    2015-08-01

    The origin of the blueshifted narrow absorption components in the resonance sodium doublet lines observed in the spectra of some young stars is discussed. Such components are assumed to be formed by the interaction of the circumstellar gas with the stellar magnetosphere in the magnetic propeller regime. The results of observations for the post UX Ori star RZ Psc are discussed in detail. This star shows distinctive signatures of mass outflow in the absence of any clear accretion signatures. Such a picture is quite possible in the magnetic propeller regime. Estimates show that for this regime to be realized, the star must have a surface magnetic field of ~1 kG at an accretion rate that does not exceed 10-10 M . yr-1.

  2. Angular Momentum Evolution in Young Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Pinzón, G.; de La Reza, R.

    2006-06-01

    During the last decades, the study of rotation in young low mass stars has been one of the more active areas in the field of stellar evolution. Many theoretical efforts have been made to understand the angular momentum evolution and our picture now, reveals the main role of the stellar magnetic field in all pre-main sequence stage (Ghosh & Lamb 1979, ApJ, 234, 296; Cameron & Campbell 1993, A&A, 274, 309; Cameron & Campbell 1995, A&A, 298, 133; Kúker, Henning, & Rúdiger 2003, ApJ, 589, 397; Matt & Pudritz 2005, MNRAS, 356, 167). The mean rotation of most of the cool low mass stars remains roughly constant during the T Tauri stage. This can be explained by the disc locking scenario. This paradigm suggest that star start out as CTTS with periods of 4-14 days, perhaps locked to their disc, and that this disc is eventually lost mainly by accretion. At the current time, it is not clear that this is true for all low mass stars. Some authors have questioned its validity for stars less massive than 0.5 solar masses. Although the reality may eventually turn out to be considerably more complex, a simple consideration of the effects of and limits on disc locking of young low mass stars seems necessary.We have investigated the exchange of angular momentum between a low mass star and an accretion disc during the Hayashi Track (Pinzón, Kúker, & de la Reza 2005, in preparation) and also along the first 100Myr of stellar evolution. The model incorporates changes in the star's moment of inertia, magnetic field strength (Elstner & Rúdiger 2000, A&A, 358, 612), angular momentum loss by a magnetic wind and an exponential decrease of the accretion rate. The lifetime of the accretion disc is a free parameter in our model. The resulting rotation rates are in agreement with observed vsin and photometric periods for young stars belonging to co-moving groups and open young clusters.

  3. Young Stars Emerge from Orion's Head

    NASA Technical Reports Server (NTRS)

    2007-01-01

    This image from NASA's Spitzer Space Telescope shows infant stars 'hatching' in the head of the hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly three million years ago, may have initiated this newfound birth

    The region featured in this Spitzer image is called Barnard 30. It is located approximately 1,300 light-years away and sits on the right side of Orion's 'head,' just north of the massive star Lambda Orionis.

    Wisps of red in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked.

    This image shows infrared light captured by Spitzer's infrared array camera. Light with wavelengths of 8 and 5.8 microns (red and orange) comes mainly from dust that has been heated by starlight. Light of 4.5 microns (green) shows hot gas and dust; and light of 3.6 microns (blue) is from starlight.

  4. eROSITA - Nearby Young Stars in X-rays

    NASA Astrophysics Data System (ADS)

    Robrade, J.

    2016-01-01

    X-ray surveys are well suited to detect, identify and study young stars based on their high levels of magnetic activity and thus X-ray brightness. The eROSITA instrument onboard the Spectrum-Roentgen-Gamma (SRG) satellite will perform an X-ray all-sky survey that surpasses existing data by a sensitivity increase of more than an order of magnitude. The 4 yr survey is expected to detect more than half a million stars and stellar systems in X-rays.

  5. Young stars and outflows : case studies of three different regions

    NASA Astrophysics Data System (ADS)

    Gålfalk, Magnus

    Mass is clearly the most important parameter of a star as it determines the phases it will go through, its physical parameters, the elements produced and its life span. Two important processes that occur simultaneously in young stars are directly related to the final mass a star ends up with; the accretion of material onto the star from a circumstellar disk and the bipolar outflow of material from the star. These processes are related since the infalling material drives the outflow. The life span of circumstellar disks is also important for the possibility of life, as this limits the time available for planet formation. This may depend on the stellar mass and its environment. Three detailed observational case-studies are presented, a globule (B335) that is forming only one or two stars, a medium-sized star formation region (L1551) and a large cluster of young stars (YSOs) in a part of our nearest giant molecular cloud (L1641N). The first part of this thesis concerns finding YSOs by looking for mid-IR excess, indicative of circumstellar disks, using the ISO and Spitzer satellites in combination with ground-based observations. Other signs of youth are also used; H-alpha in emission (accretion), Li 6707 in absorption (Li is destroyed with age) and cloud membership based on extinction. The detection of 15 new YSO candidates in L1551 (Paper I) and 89 YSOs in L1641N (Paper II) is presented. In L1641N, distributions are presented of stellar age and mass. An empirical extinction law is found and the star formation history is presented. There seems to be an accelerated star formation with time. This can however also be explained, at least partly, by migration of older stars from the cluster - a migration that may very well be mass dependent. The second part concerns bipolar outflows. The discovery of six Herbig-Haro objects and at least 15 H2 objects in B335 is presented (Paper III) as well as proper motions for previously known objects. A planar shock model is used to calculate shock velocities. In L1641N (Paper IV) we discover a new outflow source and connect this to a number of H2 objects that are found to be part of this flow from proper motion measurements.

  6. HOT WHITE DWARF SHINES IN YOUNG STAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A dazzling 'jewel-box' collection of over 20,000 stars can be seen in crystal clarity in this NASA Hubble Space Telescope image, taken with the Wide Field and Planetary Camera 2. The young (40 million year old) cluster, called NGC 1818, is 164,000 light-years away in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. The LMC, a site of vigorous current star formation, is an ideal nearby laboratory for studying stellar evolution. In the cluster, astronomers have found a young white dwarf star, which has only very recently formed following the burnout of a red giant. Based on this observation astronomers conclude that the red giant progenitor star was 7.6 times the mass of our Sun. Previously, astronomers have estimated that stars anywhere from 6 to 10 solar masses would not just quietly fade away as white dwarfs but abruptly self-destruct in torrential explosions. Hubble can easily resolve the star in the crowded cluster, and detect its intense blue-white glow from a sizzling surface temperature of 50,000 degrees Fahrenheit. IMAGE DATA Date taken: December 1995 Wavelength: natural color reconstruction from three filters (I,B,U) Field of view: 100 light-years, 2.2 arc minutes TARGET DATA Name: NGC 1818 Distance: 164,000 light-years Constellation: Dorado Age: 40 million years Class: Rich star cluster Apparent magnitude: 9.7 Apparent diameter: 7 arc minutes Credit: Rebecca Elson and Richard Sword, Cambridge UK, and NASA (Original WFPC2 image courtesy J. Westphal, Caltech) Image files are available electronically via the World Wide Web at: http://oposite.stsci.edu/pubinfo/1998/16 and via links in http://oposite.stsci.edu/pubinfo/latest.html or http://oposite.stsci.edu/pubinfo/pictures.html. GIF and JPEG images are available via anonymous ftp to oposite.stsci.edu in /pubinfo/GIF/9816.GIF and /pubinfo/JPEG/9816.jpg.

  7. Young segment-scale eruption discovered on the eastern Galapagos rift during the GALREX 2011 Expedition

    NASA Astrophysics Data System (ADS)

    Embley, R. W.; White, S. M.; Hammond, S. R.; McClinton, J. T.; Rex, C.

    2011-12-01

    New high resolution mapping with an EM302 multibeam system and seafloor observations made with the Little Hercules remotely operated vehicle (ROV) during the July 2011 GALREX expedition have discovered a very recent eruption along Segment III (Christie et al., 2005) centered at 88 deg 19.5'W on the eastern Galapagos spreading center (GSC). The site was chosen for detailed study after a water column survey using a towed CTD package identified intense particle plumes rising up to 250m above seafloor along the entire segment (see abstracts by Baker et al. and Holden et al., this meeting). The segment is characterized by ridge-and-valley terrain with the most recent neovolcanic ridge extending, respectively, 25 km west and 20 km east of a central low-relief area that is quasi-circular, ~2 km radius, less than 30 m high. The neovolcanic ridge, revealed by the EM302 bathymetry to be a generally hummocky edifice less than 1 km wide and under ~40 m high, is cut by a very small axial graben barely resolved in the EM302 bathymetry. Two areas were surveyed during five ROV dives, four on the central area near 88 deg 18.5'W and one dive at 14 km east at 88 deg 10.8'W. A third high intensity plume target near the western extremity of the segment at 88 deg 27.2'W was not investigated using the ROV. The recent lobate and pillow lava flows were emplaced in narrow grabens along and adjacent to the neovolcanic ridge. In several places, the flow was observed to fill the axial graben. It is likely that the flow thickness ranges from meters to 10's of meters, depending upon the pre-eruption graben size and local effusion variations. However, no long, channel-fed lava flows were found. Flow boundaries based on preliminary ROV navigation average less than 100 meters across-axis. The lobate lavas all had a very similar glassy appearance and negligible sediment cover, making them easy to recognize amid the surrounding, older flows. The age of these lavas appeared visually younger than the youngest lavas observed near Rosebud vent field, which were erupted between 1990 and 2002. Diffuse venting characterized by high microbial productivity and mobile vent fauna on the young lavas were found at both sites and indicate a youthful hydrothermal system associated with a diking event similar to those characterized on the East Pacific Rise and Juan de Fuca Ridge during the past two decades (also see abstract by Shank et al., this meeting). Thus, the known extent of this eruption is at least 14 km along axis. If the third site to the west is also shown to be characterized by young lavas the diking event would be ~30 km in total length making it the longest submarine diking event documented to date and showing that single diking events can relieve stress over entire an segment on the GSC. This latest serendipitous discovery of a probable major seafloor spreading event emphasizes the need for a better monitoring system along eastern Pacific spreading centers to "catch" these events in real-time and provide context for follow-up in situ studies.

  8. An Intermediate Luminosity Transient in NGC 300: The Eruption of a Dust-Enshrouded Massive Star

    NASA Astrophysics Data System (ADS)

    Berger, E.; Soderberg, A. M.; Chevalier, R. A.; Fransson, C.; Foley, R. J.; Leonard, D. C.; Debes, J. H.; Diamond-Stanic, A. M.; Dupree, A. K.; Ivans, I. I.; Simmerer, J.; Thompson, I. B.; Tremonti, C. A.

    2009-07-01

    We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

  9. Uncovering the Properties of Young Neutron Stars and Their Surroundings

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald (Technical Monitor); Slane, Patrick

    2005-01-01

    The subject grant provides funding through the NASA LTSA program. This five-year grant involves the study of young neutron stars, particularly those in supernova remnants. In the fifth year of this program, the following studies have been undertaken in support of this effort and are discussed in this report. 1) 3C 58; 2) Chandra Survey for Compact Objects in Supernova Remnants; 3) G327.1-1.1; 4) Infrared Emission from Pulsar Wind Nebulae; and Cas A.

  10. Characterizing Variable Young Stars in NGC 2264

    NASA Astrophysics Data System (ADS)

    Morales-Calderon, Maria; Cody, Ann Marie; Stauffer, John R.

    2012-08-01

    In December 2011 we carried out an unprecedented 30 days of continuous photometric monitoring on the ~3 Myr cluster NGC 2264 using the Corot and Spitzer space telescopes, along with additional data from Chandra, MOST, and several ground-based observatories. The resulting high-precision, high-cadence lightcurves display a stunning array of variability in young stellar objects (``YSOs'') at wavelengths from X-ray through the mid-infrared. These data are a vital contribution to the understanding of YSO variability behavior and its connection to physical phenomena, including dynamics of the inner disk; they constitute a legacy dataset that will be valuable for years to come. What is needed now is a dedicated spectroscopic follow-up campaign to characterize the global properties of our sample and thereby correlate the observed variability with parameters such as temperature and extinction. We propose here to complement our extensive multiwavelength photometric monitoring dataset with a large set of low- resolution spectra from the WIYN/Hydra multi-object spectrograph.

  11. The Formation and Dynamical Evolution of Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Fujii, M. S.; Portegies Zwart, S.

    2016-01-01

    Recent observations have revealed a variety of young star clusters, including embedded systems, young massive clusters, and associations. We study the formation and dynamical evolution of these clusters using a combination of simulations and theoretical models. Our simulations start with a turbulent molecular cloud that collapses under its own gravity. The stars are assumed to form in the densest regions in the collapsing cloud after an initial free-fall time of the molecular cloud. The dynamical evolution of these stellar distributions is continued by means of direct N-body simulations. The molecular clouds typical of the Milky Way Galaxy tend to form embedded clusters that evolve to resemble open clusters. The associations were initially considerably more clumpy, but they lost their irregularity in about a dynamical timescale, due to the relaxation process. The densest molecular clouds, which are absent in the Milky Way but are typical in starburst galaxies, form massive, young star clusters. They indeed are rare in the Milky Way. Our models indicate a distinct evolutionary path from molecular clouds to open clusters and associations or to massive star clusters. The mass-radius relation for both types of evolutionary tracks excellently matches the observations. According to our calculations, the time evolution of the half-mass-radius relation for open clusters and associations follows {r}{{h}}/{{pc}}=2.7{({t}{{age}}/{{pc}})}2/3, whereas for massive star clusters {r}{{h}}/{{pc}}=0.34{({t}{{age}}/{{Myr}})}2/3. Both trends are consistent with the observed age-mass-radius relation for clusters in the Milky Way.

  12. The occurrence and properties of disks around young stars

    NASA Technical Reports Server (NTRS)

    Beckwith, Steven V. W.; Sargent, Anneila I.

    1993-01-01

    The paper discusses the occurrence and properties of disks around young stars, emphasizing in particular how these may relate to planet formation and the evolution of the solar system. The global properties of such disks often resemble those attributed to the primitive solar nebula, suggesting that conditions appropriate for planet formation commonly accompany the birth of low-mass stars. Disk masses, between 0.001 and 1 solar mass, are generally lower than those of the stars, and may represent only a fraction (less than about 10 percent) of the total system mass. From the paucity of near-IR radiation from some disks it is inferred that the inner regions there are gaps where the opacity from small particles becomes vanishingly small. Evidence is presented to the effect that gaps in the inner disks develop preferentially in the oldest objects, suggesting that, with time, matter is lost or accumulates into large particles such as planetesimals, which cannot yet be detected.

  13. New Insights from Aperiodic Variability of Young Stars

    NASA Astrophysics Data System (ADS)

    Findeisen, Krzysztof

    Nearly all young stars are variable, with the variability traditionally divided into two classes: periodic variables and aperiodic or "irregular" variables. Periodic variables have been studied extensively, typically using periodograms, while aperiodic variables have received much less attention due to a lack of standard statistical tools. However, aperiodic variability can serve as a powerful probe of young star accretion physics and inner circumstellar disk structure. For my dissertation, I analyzed data from a large-scale, long-term survey of the nearby North America Nebula complex, using Palomar Transient Factory photometric time series collected on a nightly or every few night cadence over several years. This survey is the most thorough exploration of variability in a sample of thousands of young stars over time baselines of days to years, revealing a rich array of lightcurve shapes, amplitudes, and timescales. I have constrained the timescale distribution of all young variables, periodic and aperiodic, on timescales from less than a day to ~100 days. I have shown that the distribution of timescales for aperiodic variables peaks at a few days, with relatively few (15%) sources dominated by variability on tens of days or longer. My constraints on aperiodic timescale distributions are based on two new tools, magnitude- vs. time-difference (Delta m-Deltat) plots and peak-finding plots, for describing aperiodic lightcurves; this thesis provides simulations of their performance and presents recommendations on how to apply them to aperiodic signals in other time series data sets. In addition, I have measured the error introduced into colors or SEDs from combining photometry of variable sources taken at different epochs. These are the first quantitative results to be presented on the distributions in amplitude and time scale for young aperiodic variables, particularly those varying on timescales of weeks to months.

  14. Young stars and protostellar cores near NGC 2023

    NASA Astrophysics Data System (ADS)

    Mookerjea, B.; Sandell, G.; Jarrett, T. H.; McMullin, J.

    We present the results of our investigation of the young (proto)stellar population in NGC~2023 and the L~1630 molecular cloud bordering the H II region IC 434, using Spitzer IRAC and MIPS archive data and JCMT SCUBA imaging. We have performed photometry of all IRAC and MIPS images, and used colour-colour diagrams to identify and classify all young stars seen within a 22 arcmin × 26 arcmin field along the boundary between IC 434 and L 1630. We identify a total of 95 mid-infrared sources and 5 sub-millimeter cores in our 850 and 450 μm SCUBA images, two (MM 1 and MM 3) of which have embedded class 0 or I protostars. We find that HD 37903 is the most massive member of a cluster with 20 -- 30 PMS stars. We also find smaller groups of PMS stars formed in the Horsehead nebula and another elephant trunk structure to the north of the Horsehead. Our study shows that the expansion of the IC 434 H II region has triggered star formation in some of the dense elephant trunk structures and compressed gas inside the L 1630 molecular cloud.

  15. IRAS22150+6190: A Poorly Studied Young Star

    NASA Astrophysics Data System (ADS)

    Kuratov, K. S.; Zakhozhay, O. V.; Miroshnichenko, A. S.; Zakhozhay, V. A.

    Many young stellar objects have been discovered in the course of the InfraRed Astronomical Satellite (IRAS) mission, which observed almost the entire sky in four photometric bands between 12 and 100 microns in 1989. These discoveries led to constraining the evolution of stars of various masses and the material that was left from the proto-stellar clouds. Investigation of young stars are important because they allow us to learn more about star and planet formation modes as well as better understand processes of the proto-stellar debris dispersal. Nevertheless, not all optical counterparts of such objects have been revealed or studied in detail. We report our multicolor optical photometric observations of IRAS 22150+6109 obtained at the Tien-Shan Astronomical Observatory near Almaty, Kazakhstan, as well as preliminary results of our analysis of the spectral energy distribution. Fundamental parameters of the star are estimated under an assumption that it has a zero-age main-sequence luminosity and a spectral type of B3. Our plans on further observations and modeling of the object are outlined.

  16. Misaligned protoplanetary disks in a young binary star system.

    PubMed

    Jensen, Eric L N; Akeson, Rachel

    2014-07-31

    Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star's equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process. PMID:25079553

  17. Young Stars Poised for Production of Rocky Planets

    NASA Astrophysics Data System (ADS)

    2004-11-01

    VLT Interferometer Studies the Inner Region of Circumstellar Discs [1] Summary One of the currently hottest astrophysical topics - the hunt for Earth-like planets around other stars - has just received an important impetus from new spectral observations with the MIDI instrument at the ESO VLT Interferometer (VLTI). An international team of astronomers [2] has obtained unique infrared spectra of the dust in the innermost regions of the proto-planetary discs around three young stars - now in a state possibly very similar to that of our solar system in the making, some 4,500 million years ago. Reporting in this week's issue of the science journal Nature, and thanks to the unequalled, sharp and penetrating view of interferometry, they show that in all three, the right ingredients are present in the right place to start formation of rocky planets at these stars. PR Photo 32a/04: Mid-IR spectrum of the inner disc around the star HD 142527, compared to those of common types of dust. PR Photo 32b/04: Mid-IR spectra of the inner and outer disc regions of three young stars. PR Photo 32c/04: Comparison of mid-IR spectra of various astronomical objects with those of the inner and outer disc regions of three young stars. "Sand" in the inner regions of stellar discs ESO PR Photo 32a/04 ESO PR Photo 32a/04 Mid-IR spectrum of the inner disc around the star HD 142527, compared to those of common types of dust [Preview - JPEG: 400 x 541 pix - 120k] [Normal - JPEG: 800 x 1032 pix - 280k] Caption: ESO PR Photo 32a/04 presents a mid-IR spectrum of the inner region of the protoplanetary disc around the young star HD 142527, as observed with the MIDI instrument at the VLT Interferometer (upper). Below it are shown laboratory spectra of two crystalline minerals as well as of an Interplanetary Dust Particle (IDP; captured in the Earth's upper atmosphere) with hydrated silicates and, at the bottom, a typical telescopic spectrum of dust grains in the interstellar space. The spectral "signatures" of crystalline pyroxene and olivine, i.e. peaks at wavelength 9.2 and 11.3 µm, respectively, are clearly visible in the spectrum of the inner stellar disc, demonstrating the presence of these species in that region of the disc. The Sun was born about 4,500 million years ago from a cold and massive cloud of interstellar gas and dust that collapsed under its own gravitational pull. A dusty disc was present around the young star, in which the Earth and other planets, as well as comets and asteroids were later formed. This epoch is long gone, but we may still witness that same process by observing the infrared emission from very young stars and the dusty protoplanetary discs around them. So far, however, the available instrumentation did not allow a study of the distribution of the different components of the dust in such discs; even the closest known are too far away for the best single telescopes to resolve them. But now, as Francesco Paresce, Project Scientist for the VLT Interferometer and a member of the team from ESO explains, "With the VLTI we can combine the light from two well-separated large telescopes to obtain unprecedented angular resolution. This has allowed us, for the first time, to peer directly into the innermost region of the discs around some nearby young stars, right in the place where we expect planets like our Earth are forming or will soon form". Specifically, new interferometric observations of three young stars by an international team [2], using the combined power of two 8.2-m VLT telescopes a hundred metres apart, has achieved sufficient image sharpness (about 0.02 arcsec) to measure the infrared emission from the inner region of the discs around three stars (corresponding approximately to the size of the Earth's orbit around the Sun) and the emission from the outer part of those discs. The corresponding infrared spectra have provided crucial information about the chemical composition of the dust in the discs and also about the average grain size. These trailblazing observations show that the inner part of the discs is very rich in crystalline silicate grains ("sand") with an average diameter of about 0.001 mm. They are formed by coagulation of much smaller, amorphous dust grains that were omnipresent in the interstellar cloud that gave birth to the stars and their discs. Model calculations show that crystalline grains should be abundantly present in the inner part of the disc at the time of formation of the Earth. In fact, the meteorites in our own solar system are mainly composed of this kind of silicate. Dutch astronomer Rens Waters, a member of the team from the Astronomical Institute of University of Amsterdam, is enthusiastic: "With all the ingredients in place and the formation of larger grains from dust already started, the formation of bigger and bigger chunks of stone and, finally, Earth-like planets from these discs is almost unavoidable!" Transforming the grains It has been known for some time that most of the dust in discs around newborn stars is made up of silicates. In the natal cloud this dust is amorphous, i.e. the atoms and molecules that make up a dust grain are put together in a chaotic way, and the grains are fluffy and very small, typically about 0.0001 mm in size. However, near the young star where the temperature and density are highest, the dust particles in the circumstellar disc tend to stick together so that the grains become larger. Moreover, the dust is heated by stellar radiation and this causes the molecules in the grains to re-arrange themselves in geometric (crystalline) patterns. Accordingly, the dust in the disc regions that are closest to the star is soon transformed from "pristine" (small and amorphous) to "processed" (larger and crystalline) grains. VLTI observations ESO PR Photo 32b/04 ESO PR Photo 32b/04 Mid-IR spectra of the inner and outer disc regions of three young stars [Preview - JPEG: 400 x 563 pix - 136k] [Normal - JPEG: 800 x 1126 pix - 282k] Caption: ESO PR Photo 32b/04 shows a schematic view of a circumstellar disc and the MIDI-spectra observed of the inner and outer regions of the discs around three young stars, HD 163296, HD 144432 and HD 142527 (black lines). In all of them, there are clear spectral differences between the inner and outer regions, indicating a difference in mineralogy. The general broadening of the spectral "mountain" in the inner discs is a sign of larger grains and the spectral peak at wavelength 11.3 µm indicates the presence of crystalline silicates, cf. PR Photo 32a/04. Also shown are best-fit model spectra (red lines), based on mixtures of the mentioned mineral species. Spectral observations of silicate grains in the mid-infrared wavelength region (around 10 µm) will tell whether they are "pristine" or "processed". Earlier observations of discs around young stars have shown a mixture of pristine and processed material to be present, but it was so far impossible to tell where the different grains resided in the disc. Thanks to a hundred-fold increase in angular resolution with the VLTI and the highly sensitive MIDI instrument, detailed infrared spectra of the various regions of the protoplanetary discs around three newborn stars, only a few million years old, now show that the dust close to the star is much more processed than the dust in the outer disc regions. In two stars (HD 144432 and HD 163296) the dust in the inner disc is fairly processed whereas the dust in the outer disc is nearly pristine. In the third star (HD 142527) the dust is processed in the entire disc. In the central region of this disc, it is extremely processed, consistent with completely crystalline dust. An important conclusion from the VLTI observations is therefore that the building blocks for Earth-like planets are present in circumstellar discs from the very start. This is of great importance as it indicates that planets of the terrestrial (rocky) type like the Earth are most probably quite common in planetary systems, also outside the solar system. The pristine comets ESO PR Photo 32c/04 ESO PR Photo 32c/04 Comparison of mid-IR spectra of various astronomical objects with those of the inner and outer disc regions of three young stars [Preview - JPEG: 400 x 471 pix - 128k] [Normal - JPEG: 800 x 942 pix - 272k] Caption: ESO PR Photo 32c/04 provides a comparison of the mid-IR spectra of interstellar dust grains (upper left), three solar system comets (left) and the outer and inner disc regions of the three young stars observed with MIDI and the VLTI. The similarities of the spectra in the same row are striking. The relative amount of crystalline content increases from the top towards the bottom. The present observations also have implications for the study of comets. Some - perhaps all - comets in the solar system do contain both pristine (amorphous) and processed (crystalline) dust. Comets were definitely formed at large distances from the Sun, in the outer regions of the solar system where it has always been very cold. It is therefore not clear how processed dust grains may end up in comets. In one theory, processed dust is transported outwards from the young Sun by turbulence in the rather dense circumsolar disc. Other theories claim that the processed dust in comets was produced locally in the cold regions over a much longer time, perhaps by shock waves or lightning bolts in the disc, or by frequent collisions between bigger fragments. The present team of astronomers now conclude that the first theory is the most likely explanation for the presence of processed dust in comets. This also implies that the long-period comets that sometimes visit us from the outer reaches of our solar system are truly pristine bodies, dating back to an era when the Earth and the other planets had not yet been formed. Studies of such comets, especially when performed in-situ, will therefore provide direct access to the original material from which the solar system was formed.

  18. Absolute parameters of young stars - II. V831 Centauri

    NASA Astrophysics Data System (ADS)

    Budding, E.; Erdem, A.; Inlek, G.; Demircan, O.

    2010-04-01

    Literature photometry and new high-resolution spectroscopy of V831 Cen are presented and analysed. Light and radial velocity curve fittings confirm the central pair of this young multiple system to be close to contact. Absolute parameters are found as follows: M1 = 4.08 +/- 0.07Msolar, M2 = 3.35 +/- 0.06Msolar, R1 = 2.38 +/- 0.03Rsolar, R2 = 2.25 +/- 0.03Rsolar, T1 = 13000 +/- 300K, T2 = 11800 +/- 300K distance of 110 +/- 10pc and age of ~20 +/- 5Myr. Detailed examination of the spectrograms indicates the third component (V831 Cen B) to be an Ap star. The orbit of the third star about the close binary is analysed using historic astrometric measurements. This allows an estimate of the third star's mass to be about 2.5Msolar, but this is sensitive to the adopted distance and inclination values. It is, however, confirmed by the measured radial velocity of the third star. To some extent, such analysis can also be applied to the fourth star (V831 Cen C). The derived properties can be checked against the system's membership of the Scorpius-Centaurus OB2 association.

  19. Discovery of solar system-size halos around young stars

    NASA Technical Reports Server (NTRS)

    Beckwith, S.; Skrutskie, M. F.; Zuckerman, B.; Dyck, H. M.

    1984-01-01

    Near-infrared speckle interferometric observations of five pre-main-sequence stars reveal a core-halo structure around two of these stars: HL Tau and R Mon. The halo light distribution is shown to arise from scattered light from small circumstellar particles. Halo sizes of 320 x 200 AU (alpha x delta FWHM) and 1300 x 1300 AU are deduced for HL Tau and R Mon, respectively, and the halo light is substantially bluer than the stellar light. The minimum mass of small particles in the scattering regions is comparable to the earth's mass in HL Tau and ten times greater in R Mon. Mass loss from the stars is almost certainly insufficient to produce the halo matter. The halos probably consist of relatively slowly moving matter bound gravitationally to the stars. From the size and mass of the circumstellar matter, it appears likely that these halos are in the early stage in the formation of planet-forming disks around the young stars.

  20. HUNTING FOR YOUNG DISPERSING STAR CLUSTERS IN IC 2574

    SciTech Connect

    Pellerin, Anne; Meyer, Martin M.; Calzetti, Daniella; Harris, Jason E-mail: martin.meyer@uwa.edu.au E-mail: jharris@30doradus.org

    2012-12-01

    Dissolving stellar groups are very difficult to detect using traditional surface photometry techniques. We have developed a method to find and characterize non-compact stellar systems in galaxies where the young stellar population can be spatially resolved. By carrying out photometry on individual stars, we are able to separate the luminous blue stellar population from the star field background. The locations of these stars are used to identify groups by applying the HOP algorithm, which are then characterized using color-magnitude and stellar density radial profiles to estimate age, size, density, and shape. We test the method on Hubble Space Telescope Advanced Camera for Surveys archival images of IC 2574 and find 75 dispersed stellar groups. Of these, 20 highly dispersed groups are good candidates for dissolving systems. We find few compact systems with evidence of dissolution, potentially indicating that star formation in this galaxy occurs mostly in unbound clusters or groups. These systems indicate that the dispersion rate of groups and clusters in IC 2574 is at most 0.45 pc Myr{sup -1}. The location of the groups found with HOP correlate well with H I contour map features. However, they do not coincide with H I holes, suggesting that those holes were not created by star-forming regions.

  1. The Search for Young Planetary Systems And the Evolution of Young Stars

    NASA Technical Reports Server (NTRS)

    Beichman, Charles A.; Boden, Andrew; Ghez, Andrea; Hartman, Lee W.; Hillenbrand, Lynn; Lunine, Jonathan I.; Simon, Michael J.; Stauffer, John R.; Velusamy, Thangasamy

    2004-01-01

    The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

  2. ISOPHOT Observations of the Circumstellar Environment of Young Stars

    NASA Astrophysics Data System (ADS)

    brahm, P.; Leinert, Ch.; Lemke, D.; Burkert, A.; Henning, T. H.

    The young pre-main sequence T Tau and Herbig Ae/Be stars are associated with circumstellar dust, whose thermal emission can be observed at infrared wavelengths. We report on 3.6-200 micron photometric observations performed with ISOPHOT, the photometer on-board the Infrared Space Observatory. Seven Herbig Ae/Be stars were observed at mid- and far-infrared wavelengths. At ??25?m the emission mainly arises from a compact circumstellar region, and the observed spectral energy distributions follow the power-law relationship F???-n with n typically around 1. The peak of the SEDs (in F?) is at 60-100?m, corresponding to temperatures of around 50 K. At longer wavelengths the observed emission is spatially extended, and at ?>100?m the emission observed by ISOPHOT is never dominated by the Herbig Ae/Be stars. The most likely sources of the far-infrared radiation are arcminute size dust cores located in the vicinity of the stars, and probably related to the star forming process. We also analysed ISOPHOT observations of 16 binary T Tau stars. For the 7 brightest objects the broad-band photometry was supplemented by 2.5-11.7?m spectrophotometry obtained by the PHT-S subinstrument. In most cases strong silicate emission at 10?m was detected with some indications for the presence of crystalline silicate. The comparison of the derived SEDs with those of single T Tau stars will help to understand how the presence of companions could affect the evolution of the circumstellar disks.

  3. Young Stars and Their Companions in NGC 2362

    NASA Astrophysics Data System (ADS)

    Weiss, Lauren M.; Hodgkin, S. T.; Irwin, M.; Irwin, J.; Birkby, J. L.; Jackson, R.; Jeffries, R.

    2011-09-01

    The mass-radius relation of young, low-mass (M < M⊙) stars is poorly understood due to a dearth of observations. Better measurements of the masses and radii of these stars would enable a fuller understanding of how low-mass stars form and better characterization of planets orbiting such stars. We investigate velocities of 116 cool (K-type and later), small (0.1 < M/M⊙ < 1.2) stars with magnitude 14 < I < 19 in the ˜ 5 Myr open cluster NGC 2362 with the aims of: (1) Identifying cluster members by finding the velocity and velocity dispersion of the cluster. (2) Constraining the masses and radii of candidate occulting systems by examining their radial velocities at multiple epochs. We obtained time-series photometry of 1180 candidate cluster members at the CTIO 4-m Blanco telescope with the Mosaic-II detector between January and December 2006. Multi- epoch spectra of 116 stars were obtained from the ESO/VLT using the GIRAFFE/FLAMES multi-fibre spectrograph in December 2007. We measured radial velocities of 93 cluster can- didates, 81 of which are within 3σ of the cluster velocity (39.7±1.58 km/s). One M dwarf displays eclipse depths of 5%, although the double-lined spectrum of this object suggest that it is an M dwarf binary. We calculate upper and lower limits on the masses and radii of the primary star and its companion: 0.34 < M1/M⊙ < 0.53; 1.0 < R1/R⊙ < 1.25; 0.035 < M2/M⊙ < 0.34; 0.28 < R2/R⊙ < 1.0. This system is ideal for follow-up with high cadence photometry and high resolution spectroscopy at quadrature. These measurements would allow the solution of the primary and secondary masses and radii and adding to the sparse existing measurements of the masses and radii of young, low-mass stars.

  4. Multiplicity among Young Brown Dwarfs and Very Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Ahmic, Mirza; Jayawardhana, Ray; Brandeker, Alexis; Scholz, Alexander; van Kerkwijk, Marten H.; Delgado-Donate, Eduardo; Froebrich, Dirk

    2007-12-01

    We report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and very low mass (VLM) stars, 28 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope. We resolve the suspected 0.16'' (~26 AU) binary Cha H? 2 and present two new binaries, Hn 13 and CHXR 15, with separations of 0.13'' (~20 AU) and 0.30'' (~50 AU), respectively; the latter is one of the widest VLM systems known. We find a binary frequency of 11+9-6%, thus confirming the trend for a lower binary frequency with decreasing mass. By combining our work with previous surveys, we arrive at the largest sample of young VLM objects (72) with high angular resolution imaging to date. Its multiplicity fraction is in statistical agreement with that for VLM objects in the field. Furthermore, we note that many field stellar binaries with lower binding energies and/or wider cross sections have survived dynamical evolution and that statistical models suggest tidal disruption by passing stars is unlikely to affect the binary properties of our systems. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars in OB and T associations between a few megayears to several gigayears. Instead, the observations so far suggest that VLM objects are either less likely to be born in fragile multiple systems than solar-mass stars or such systems are disrupted very early. We dedicate this paper to the memory of our coauthor, Eduardo Delgado-Donate, who died in a hiking accident in Tenerife earlier this year.

  5. FAST STAR, SLOW STAR; OLD STAR, YOUNG STAR: SUBGIANT ROTATION AS A POPULATION AND STELLAR PHYSICS DIAGNOSTIC

    SciTech Connect

    Van Saders, Jennifer L.; Pinsonneault, Marc H.

    2013-10-20

    Stellar rotation is a strong function of both mass and evolutionary state. Missions such as Kepler and CoRoT provide tens of thousands of rotation periods, drawn from stellar populations that contain objects at a range of masses, ages, and evolutionary states. Given a set of reasonable starting conditions and a prescription for angular momentum loss, we address the expected range of rotation periods for cool field stellar populations (∼0.4-2.0 M{sub ☉}). We find that cool stars fall into three distinct regimes in rotation. Rapid rotators with surface periods less than 10 days are either young low-mass main sequence (MS) stars, or higher mass subgiants which leave the MS with high rotation rates. Intermediate rotators (10-40 days) can be either cool MS dwarfs, suitable for gyrochronology, or crossing subgiants at a range of masses. Gyrochronology relations must therefore be applied cautiously, since there is an abundant population of subgiant contaminants. The slowest rotators, at periods greater than 40 days, are lower mass subgiants undergoing envelope expansion. We identify additional diagnostic uses of rotation periods. There exists a period-age relation for subgiants distinct from the MS period-age relations. There is also a period-radius relation that can be used as a constraint on the stellar radius, particularly in the interesting case of planet host stars. The high-mass/low-mass break in the rotation distribution on the MS persists onto the subgiant branch, and has potential as a diagnostic of stellar mass. Finally, this set of theoretical predictions can be compared to extensive datasets to motivate improved modeling.

  6. Surface deformation and seismic signatures associated with the eruption cycle of Lone Star Geyser, Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Gomez, F. G.; Johnson, H. E., III; LeWinter, A. L.; Finnegan, D. C.; Sandvol, E. A.; Nayak, A.; Hurwitz, S.

    2014-12-01

    Geysers are important subjects for studying processes involved with multi-phase eruptions. As part of a larger field effort, this study applies imaging geodesy and seismology to study eruptive cycles of the Lone Star Geyser in Yellowstone National Park. Lone Star Geyser is an ideal candidate for such study, as it erupts with a nearly regular period of approximately 3 hours. The geyser includes a 5 m diameter cone that rises 2 meters above the sinter terrace, and the entire system can be viewed from a nearby hillside. Fieldwork was accomplished during April 2014. Ground-based interferometric radar (GBIR) and terrestrial laser scanning (TLS) were used to image possible surface deformations associated with Lone Star Geyer's eruption cycles. Additional observations were provided by global positioning system (GPS) measurements and six broad-band seismometers deployed in the immediate vicinity of the geyser. The GBIR and TLS were deployed approximately 65 meters from the sinter cone of the geyser. The GBIR involves a ku-band radar (1.7 cm wavelength) that is sensitive to approximately half-millimeter changes in the line-of-sight distance. Radar images were acquired every minute for 3 or more eruptions per day. Temporally redundant, overlapping interferograms were used to improve the sensitivity and interpolate a minute-wise time series of line-of-sight displacement, and efforts were made to account for possible path-delay effects resulting from water vapor around the geyser cone. Repeat (every minute) high-speed TLS scans were acquired for multiple eruption cycles over the course of two-days. Resulting measurement point spacing on the sinter cone was ~3cm. The TLS point-clouds were geo-referenced using static surveyed reflectors and scanner positions. In addition to measuring ground deformation, filtering and classification of the TLS point cloud was used to construct a mask that allows radar interferometry to exclude non-ground areas (vegetation, snow, sensors). Preliminary results suggest deformations are very small, with possible uplift around the sinter cone of up to 1 cm. Ongoing analysis is examining temporal variations in the seismological data that may correlate with apparent temporal and spatial patterns of surface displacement.

  7. Dust around young stars. Photopolarimetric activity of the classical Herbig Ae/Be star RR Tauri.

    NASA Astrophysics Data System (ADS)

    Rostopchina, A. N.; Grinin, V. P.; Okazaki, A.; The, P. S.; Kikuchi, S.; Shakhovskoy, D. N.; Minikhulov, N. Kh.

    1997-11-01

    The classical Herbig Ae/Be (HAeBe) star RR Tau is known as a highly variable young star with an amplitude of variability of about 4mag in the V pass-band. In this paper we present the results of coordinated Crimea-Dodaira multi-band photo-polarimetric observations of this star which cover fully the observed interval of its brightness changes. Within the observed interval of its light variations the linear polarization of RR Tau anti-correlates with its brightness changes. The dependence of the linear polarization on the stellar magnitude agrees well with the model according to which the main source of the intrinsic polarization of RR Tau is scattered radiation by the circumstellar (CS) disk-like dust envelope (probably the protoplanetary disk) seen edge-on or under a small inclination to the line-of-sight, and that the brightness variations are caused by variable obscuration of the star by revolving circumstellar dust clouds. A comparison with previous photo-polarimetric observations of this star shows that the Stokes parameters of its polarized radiation are quite stable on a time scale of about 7 years. By using this fact we have separated the interstellar and intrinsic components of the observed polarization. The numerical modeling of the intrinsic linear polarization together with the colour-magnitude diagrams of RR Tau show that the circumstellar disk-like envelope around this star is strongly flattened and that the characteristic size of the grains is intermediate between that of interstellar dust and dust in the old protoplanetary disk of ? Pictoris. We assume on the basis of this analysis that RR Tau is surrounded by a young protoplanetary disk and that it can be considered as a young progenitor of ? Pictoris.

  8. DISK-RELATED BURSTS AND FADES IN YOUNG STARS

    SciTech Connect

    Findeisen, Krzysztof; Hillenbrand, Lynne; Levitan, David; Sesar, Branimir; Ofek, Eran; Laher, Russ; Surace, Jason E-mail: lah@astro.caltech.edu

    2013-05-01

    We present first results from a new, multiyear, time domain survey of young stars in the North America Nebula complex using the Palomar Transient Factory. Our survey is providing an unprecedented view of aperiodic variability in young stars on timescales of days to years. The analyzed sample covers R{sub PTF} Almost-Equal-To 13.5-18 and spans a range of mid-infrared color, with larger-amplitude optical variables (exceeding 0.4 mag root mean squared) more likely to have mid-infrared evidence for circumstellar material. This paper characterizes infrared excess stars with distinct bursts above or fades below a baseline of lower-level variability, identifying 41 examples. The light curves exhibit a remarkable diversity of amplitudes, timescales, and morphologies, with a continuum of behaviors that cannot be classified into distinct groups. Among the bursters, we identify three particularly promising sources that may represent theoretically predicted short-timescale accretion instabilities. Finally, we find that fading behavior is approximately twice as common as bursting behavior on timescales of days to years, although the bursting and fading duty cycle for individual objects often varies from year to year.

  9. HUBBLE PICTURES SHOW HOT GAS BUBBLE EJECTED BY YOUNG STAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These images taken with the Hubble Space Telescope's Wide Field and Planetary Camera 2 reveal the evolution of bubbles of glowing gas being blown out from the young binary star system XZ Tauri. Gas from an unseen disk around one or both of the stars is channeled through magnetic fields surrounding the binary system and then is forced out into space at nearly 300,000 miles per hour (540,000 kilometers per hour). This outflow, which is only about 30 years old, extends nearly 60 billion miles (96 billion kilometers). Hubble first discovered this unique bubble in 1995, and additional observations were made between 1998 and 2000. These images show that there was a dramatic change in its appearance between 1995 and 1998. In 1995, the bubble's edge was the same brightness as its interior. However, when Hubble took another look at XZ Tauri in 1998, the edge was suddenly brighter. This brightening is probably caused by the hot gas cooling off, which allows electrons in the gas to recombine with atoms, a process that gives off light. This is the first time that astronomers have seen such a cooling zone 'turn on.' These images provide an unprecedented opportunity to study the development of a very recent outflow from young (about 1 million years old) stars. Credits: NASA, John Krist (Space Telescope Science Institute), Karl Stapelfeldt (Jet Propulsion Laboratory), Jeff Hester (Arizona State University), Chris Burrows (European Space Agency/Space Telescope Science Institute)

  10. Exploring Dynamical Evolution of Young Star Clusters: Observed Fractal Statistics

    NASA Astrophysics Data System (ADS)

    Hetem, Annibal

    2015-08-01

    The studies of young nearby clusters are fundamental steps toward a unified picture of star formation in the Universe. In previous studies, we measured the Q parameter for a set of young stars clusters. The results show that almost half of that sample tends to follow a theoretically expected relation with the fractal dimension of the probable parental cloud. Similar to the clusters observed in the nearby clouds, these clusters have such Q values that indicates the presence of substructures in the parental clouds. However, other clusters present a radial distribution of stars that does not coincide with the structure of the clouds. Eventually, these properties can lead to significant conclusions on the initial conditions for cluster formation (bound or unbound), evolution (cold collapse or warm collapse) and their future interaction with other components of the Galaxy. Nevertheless, all possible conclusions are blurred by the estimates of the deviations on Q, fractal dimensions and core radius. In the bibliography, it is usual to use some artificial methods to estimate deviation and variance, that are valid when the object is an artificially generate cluster. However, if one deals with observational data it is possible to apply the traditional error propagations technics, what yields to the correct error bars for the measures.

  11. X-Ray Spectroscopy of Accretion Shocks in Young Stars

    NASA Astrophysics Data System (ADS)

    Brickhouse, Nancy S.

    2011-01-01

    High resolution X-ray spectroscopy of accreting young stars is providing new insights into the physical conditions of the shocked plasma. While young stars exhibit exceedingly active coronae (>10 MK) with highly energetic flares, the relatively low temperature ( 3 MK), high density (>1012 cm-3) accretion shock can only be clearly distinguished at high spectral resolution. The nearby Classical T Tauri star TW Hydrae was the first to show evidence of accretion using 50 ks with the Chandra High Energy Transmission Grating (HETG). More recently a Chandra HETG Large Program (489 ks obtained over the course of one month) on TW Hydrae has found evidence for a new type of coronal structure. In the standard model, the accreting gas shocks near the atmosphere of the star and gently settles onto the surface as it slows down and cools. On TW Hydrae the observed post-shock region is not this predicted settling flow, since its mass is 30 times the mass of material that passes through the shock. Instead the stellar atmosphere must be heated to soft X-ray emitting temperatures. Of the CTTS systems observed with the gratings on Chandra and XMM-Newton not all show the accretion shock signature; however, all of them show excess soft X-ray emission related to accretion. The production of highly charged ions in the proximity of both open and closed magnetic field lines has important implications for coronal heating, winds and jets in the presence of accretion. This work is supported by the Chandra X-ray Observatory through a NASA contract with the Smithsonian Astrophysical Observatory.

  12. The variable stars of the young LMC cluster NGC 2164

    NASA Technical Reports Server (NTRS)

    Welch, Douglas L.; Mateo, Mario; Olszewski, Edward W.; Fischer, Philippe; Takamiya, Marianne

    1993-01-01

    The present search of the LMC cluster NGC 2164 for variable stars has uncovered one new member classical Cepheid variable with 3.772-day period; attention is also given to photometry for a previously unknown field overtone Cepheid variable with 3.4626-day period, and the 10.6878-day period HV 12078, which may be a member of the young NGC 2156 cluster. The clear separation of fundamental and overtone pulsators in the period-luminosity-color relation of known LMC cluster Cepheids establishes that the NGC 2164 member is a true overtone.

  13. Gamma-ray emission from young neutron stars

    NASA Technical Reports Server (NTRS)

    Hartmann, Dieter H.; Liang, Edison P.; Cordes, J. M.

    1991-01-01

    The emission models of Cheng et al. (1986) and Harding (1981) are employed to determine likely candidates for pulsed gamma-ray emission on the basis of recent radio data of pulsars. The recent detection of pulsed gamma rays from PSR 1951+32 lends observational support to the scenario of Cheng et al. which also suggests that PSR 1855+09 might be another excellent gamma-ray pulsar candidate. The possible contribution of young neutron stars to the diffuse high energy glow is also discussed.

  14. Mandibular canine tooth impaction in a young dog--treatment and subsequent eruption: a case report.

    PubMed

    Stapleton, B L; Clarke, L L

    1999-09-01

    Extraction of an embedded supranumerary incisor tooth and surgical exposure of the crown of an impacted left mandibular canine tooth were performed in a 5 month-old Doberman Pinscher dog. Six months following surgery, the canine tooth was fully erupted and in normal occlusion. A review of tooth eruption in the dog is provided. PMID:10863519

  15. Probing triggered star formation: young stars associated with AFGL333 in W3

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Jose, J.; Sherry, W. H.; Meyer, M.

    2014-03-01

    We present our observational studies on star formation associated with the AFGL333 complex and W3-south cluster in the high density layer (HDL) region located in between the W3 giant molecular cloud and W4 H II region. This region is suggested to be experiencing triggered/assisted mode of star formation. We have conducted a multi-wavelength study of the region using optical, near- and mid-IR data. Using Spitzer data and from our deep near-IR observations we identified and classified young stellar objects. We present preliminary results on census of young stellar population, extinction map, stellar density, and spatial distribution of the young stars in the region. We find about 580 YSOs associated with AFGL333. The ages of YSO candidates range between 0.1-5 Myr with wide age spread. Spatial distribution of class I and class II sources suggests that the IR dark cloud (IRDC) region harbors more class I sources than its surrounding area, suggesting relatively younger YSO population.

  16. Multiplicity study of young pre-main sequence stars in the Lupus star-forming Region

    NASA Astrophysics Data System (ADS)

    Vogt, Nikolaus; Mugrauer, Markus; Schmidt, Tobias O. B.; Neuhaeuser, Ralph; Ginski, Christian

    2013-07-01

    We have conducted a high contrast imaging search for (sub)stellar companions among 63 young pre-main sequence stars in the Lupus star forming region, using the adaptive optics imager NACO at UT4 of the ESO Paranal observatory. We detected faint co-moving companions around our targets at angular separations between about 0.1 up to several arc seconds (binaries and triple systems). Some of these companions are in the sub stellar mass regime, according to their apparent near infrared photometry at the distance of the Lupus star forming region (about 140pc). We give a progress report to our long-term project, still in execution with the follow-up spectroscopy of detected substellar companion-candidates, and present some first results.

  17. Young viscous flows in the Lowell crater of Orientale basin, Moon: Impact melts or volcanic eruptions?

    NASA Astrophysics Data System (ADS)

    Srivastava, N.; Kumar, D.; Gupta, R. P.

    2013-10-01

    Topographical, morphological and spectral reflectance studies have been carried out for a distinct resurface event inside Copernican aged Lowell crater (13.00°S 103.40°W), Orientale basin, using high resolution TC, MI-VIS, LROC-NAC, and M3 data from Kaguya, Lunar Reconnaissance Orbiter (LRO) and Chandrayaan-1 missions. The resurfacing is predominantly gabbroic/basaltic in composition and is confined to nearly a linear ~17 km long, a 3-6 km wide and a ~100 m deep channel, possibly a graben. It is characterised with distinct surface features such as small uplift with melt pond, several lava-like flows, cracks going up to decimetre size, 20-80 m pits/craters with small central uplifts or depressions and ~100 m craters that emanate liquid. A minimum of three generations of flows have been identified within the unit, the oldest one being less viscous and the subsequent younger ones showing well developed lobes due to the high viscosity. There is a conspicuous absence of unambiguously identified primary impact craters on these flows suggesting their fresh nature. On the basis of these integrated observations we hypothesise that at least the younger portions of this amazingly carved resurfaced unit might be composed of volcanic flows erupted from single or multiple sources subsequent to the emplacement of impact melts from a ~9 km diameter crater on the edge of Lowell crater. Gabbroic/basaltic signatures have also been identified at several other locations inside Lowell crater indicating that it would have impacted on a pre-existing basaltic surface or on a gabbroic pluton. These findings have implications to lunar magmatism and understanding of the genesis of young flows on the lunar surface.

  18. Young Star May Be Belching Spheres of Gas, Astronomers Say

    NASA Astrophysics Data System (ADS)

    2001-05-01

    A young star more than 2,000 light-years away in the constellation Cepheus may be belching out spheres of gas, say astronomers who observed it with the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope. Not only is the star ejecting spheres of gas, the researchers say, but it also may be ejecting them repeatedly, phenomena not predicted by current theories of how young stars shed matter. Cepheus A star-forming region with blowups of detail In order to remain stable while accumulating matter, young stars have to throw off some of the infalling material to avoid "spinning up" so fast they would break apart, according to current theories. Infalling matter forms a thin spinning disk around the core of the new star, and material is ejected in twin "jets" perpendicular to the plane of the disk. "Twin jets have been seen emerging from many young stars, so we are quite surprised to see evidence that this object may be ejecting not jets, but spheres of gas," said Paul T.P. Ho, an astronomer at the Harvard-Smithsonian Center for Astrophysics. The research is reported in the May 17 edition of the scientific journal Nature. The astronomers observed a complex star-forming region in Cepheus and found an arc of water molecules that act like giant celestial amplifiers to boost the strength of radio signals at a frequency of 22 GHz. Such radio-wave amplifiers, called masers, show up as bright spots readily observed with radio telescopes. "With the great ability of the VLBA to show fine detail, we could track the motions of these maser spots over a period of weeks, and saw that this arc of water molecules is expanding at nearly 20,000 miles per hour," said Ho. "This was possible because we could detect detail equivalent to seeing Lincoln's nose on a penny in Los Angeles from the distance of New York," Ho added. "These observations pushed the tremendous capabilities of the VLBA and of modern computing power to their limits. This is an extremely complex observational project," said Luis F. Rodriguez, of Mexico's National Autonomous University. The arc of water masers can be fit to a nearly-perfect circle to within one part in a thousand. That, the researchers say, means that the water vapor in the arc most likely is part of a complete sphere. "The arc we see fits a circle so well that it is unlikely that any geometry other than that of a sphere would produce it," Ho said. The sphere would be about 1.5 times the size of the Solar System. Because the arc, and presumably the sphere of which it is part, is so thin and so uniform, the researchers say that it came from a single, short-lived ejection. In addition, other evidence suggests that the sphere from an earlier ejection now is being overtaken by a newer spherical bubble that took only about 33 years after being ejected to reach its observed size. "We now have at least one case, we believe, in which a young star has repeatedly ejected mass spherically in short bursts," Guillem Anglada, of the Institute of Astrophysics of Andalucia (CSIC), in Granada, Spain, said. "In light of our current understanding of star formation, we don't yet understand how this can happen, so we have an exciting new scientific challenge. It is surprising that nature can maintain such perfect symmetry, especially since the environment around the young star must be so varied. This appears to be a triumph of order over chaos," he added. The researchers, in addition to Rodriguez, Ho and Anglada, are: Jose M. Torrelles, Institute for Space Studies of Catalonia (IEEC)-Spanish Research Council (CSIC), Spain; Nimesh A. Patel and Lincoln Greenhill, of the Harvard-Smithsonian Center for Astrophysics; Jose F. Gomez, Laboratory for Space Astrophysics and Theoretical Physics of the National Institute for Aerospace Technology, Madrid, Spain; Salvador Curiel and Jorge Canto, of Mexico's National Autonomous University; and Guido Garay, Department of Astronomy of the University of Chile. The VLBA is part of the National Radio Astronomy Observatory. It consists of ten radio-telescope antennas, each 82 feet (25 meters) in diameter, spread across the U.S. from Hawaii to the U.S. Virgin Islands. Operated from Socorro, New Mexico, the VLBA provides astronomers with the greatest angular resolution, or ability to see fine detail, of any telescope on Earth or in space. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. Some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies.

  19. JET FORMATION FROM MASSIVE YOUNG STARS: MAGNETOHYDRODYNAMICS VERSUS RADIATION PRESSURE

    SciTech Connect

    Vaidya, Bhargav; Porth, Oliver; Fendt, Christian; Beuther, Henrik E-mail: fendt@mpia.de

    2011-11-20

    Observations indicate that outflows from massive young stars are more collimated during their early evolution compared to later stages. Our paper investigates various physical processes that impact the outflow dynamics, i.e., its acceleration and collimation. We perform axisymmetric magnetohydrodynamic (MHD) simulations particularly considering the radiation pressure exerted by the star and the disk. We have modified the PLUTO code to include radiative forces in the line-driving approximation. We launch the outflow from the innermost disk region (r < 50 AU) by magnetocentrifugal acceleration. In order to disentangle MHD effects from radiative forces, we start the simulation in pure MHD and later switch on the radiation force. We perform a parameter study considering different stellar masses (thus luminosity), magnetic flux, and line-force strength. For our reference simulation-assuming a 30 M{sub Sun} star-we find substantial de-collimation of 35% due to radiation forces. The opening angle increases from 20 Degree-Sign to 32 Degree-Sign for stellar masses from 20 M{sub Sun} to 60 M{sub Sun }. A small change in the line-force parameter {alpha} from 0.60 to 0.55 changes the opening angle by {approx}8 Degree-Sign . We find that it is mainly the stellar radiation that affects the jet dynamics. Unless the disk extends very close to the star, its force is too small to have much impact. Essentially, our parameter runs with different stellar masses can be understood as a proxy for the time evolution of the star-outflow system. Thus, we have shown that when the stellar mass (thus luminosity) increases with age, the outflows become less collimated.

  20. NEW YOUNG STAR CANDIDATES IN BRC 27 AND BRC 34

    SciTech Connect

    Rebull, L. M.; Laher, R.; Legassie, M.; Gibbs, J. C.; Aryal, S.; Canakapalli, T. S.; Linahan, M.; Ezyk, N.; Fagan, J.; Sartore, D.; Badura, K. S.; Armstrong, J. D.; Allen, L. E.; McGehee, P.; and others

    2013-01-01

    We used archival Spitzer Space Telescope mid-infrared data to search for young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These regions both appear to be actively forming young stars, perhaps triggered by the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of the 26 YSOs or YSO candidates identified in the literature, and identify 16 new YSO candidates that appear to have IR excesses. In BRC 34, the one literature-identified YSO has an IR excess, and we suggest 13 new YSO candidates in this region, including a new Class I object. Considering the entire ensemble, both BRCs are likely of comparable ages, within the uncertainties of small number statistics and without spectroscopy to confirm or refute the YSO candidates. Similarly, no clear conclusions can yet be drawn about any possible age gradients that may be present across the BRCs.

  1. New Young Star Candidates in BRC 27 and BRC 34

    NASA Astrophysics Data System (ADS)

    Rebull, L. M.; Johnson, C. H.; Gibbs, J. C.; Linahan, M.; Sartore, D.; Laher, R.; Legassie, M.; Armstrong, J. D.; Allen, L. E.; McGehee, P.; Padgett, D. L.; Aryal, S.; Badura, K. S.; Canakapalli, T. S.; Carlson, S.; Clark, M.; Ezyk, N.; Fagan, J.; Killingstad, N.; Koop, S.; McCanna, T.; Nishida, M. M.; Nuthmann, T. R.; O'Bryan, A.; Pullinger, A.; Rameswaram, A.; Ravelomanantsoa, T.; Sprow, H.; Tilley, C. M.

    2013-01-01

    We used archival Spitzer Space Telescope mid-infrared data to search for young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These regions both appear to be actively forming young stars, perhaps triggered by the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of the 26 YSOs or YSO candidates identified in the literature, and identify 16 new YSO candidates that appear to have IR excesses. In BRC 34, the one literature-identified YSO has an IR excess, and we suggest 13 new YSO candidates in this region, including a new Class I object. Considering the entire ensemble, both BRCs are likely of comparable ages, within the uncertainties of small number statistics and without spectroscopy to confirm or refute the YSO candidates. Similarly, no clear conclusions can yet be drawn about any possible age gradients that may be present across the BRCs.

  2. Properties of Young Stars in Nearby SFRs: Cepheus, Ophiuchus and Taurus

    NASA Astrophysics Data System (ADS)

    Allen, Thomas; Prchlik, Jakub; Megeath, S. Thomas; Wolk, Scott J.; Gutermuth, Robert A.; Pipher, Judith; Prato, Lisa A.; Mclane, Jacob Noel; Biddle, Lauren; Wright-Garba, Nuria Meilani Laure; Muzzio, Ryan; Avilez, Ian

    2016-01-01

    We study the properties of young stars in several nearby star formation regions. Our approach examines both the aggregate properties of large samples of young stars and the detailed properties of a smaller sample of individual stars. The large aggregate sample helps our statistical understanding of how while studying individual young stars in detail informs our interpretation of the larger data set. The specific star formation regions we have been studying include Cep OB3b, a large cluster of thousands of young stars as well as Taurus and Ophiuchus, both smaller star formation regions that are close enough to examine individual stars in detail. We use a number of instruments that span much of the electromagnetic spectrum including the Discovery Channel Telescope in the ultraviolet and visible and Keck in the infrared. For the young stars in the Cep OB3b region we examine the X-ray and accretion properties. For the young stars in Taurus and Ophiuchus, we estimate properties, such as vsini, magnetic field strength, effective temperature and presence (or lack) of a disk.

  3. Empirical Isochrones for Low Mass Stars in Nearby Young Associations

    NASA Astrophysics Data System (ADS)

    Herczeg, Gregory J.; Hillenbrand, Lynne A.

    2015-07-01

    Absolute ages of young stars are important for many issues in pre-main-sequence stellar and circumstellar evolution but long have been recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in Hertzsprung-Russell diagrams for low mass stars and brown dwarfs in the η Cha, ɛ Cha, and TW Hya Associations and the β Pic and Tuc-Hor Moving Groups. A successful theory of pre-main-sequence evolution should match the shapes of the stellar loci for these groups of young stars. However, when comparing the combined empirical isochrones to isochrones predicted from evolutionary models, discrepancies lead to a spectral type (mass) dependence in stellar age estimates. Improved prescriptions for convection and boundary conditions in the latest models of pre-main-sequence evolution lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncertainties or by model limitations. Independent of model predictions, linear fits to combined stellar loci of these regions provide a simple empirical method to order clusters by luminosity with a reduced dependence on spectral type. Age estimates calculated from various sets of modern models that reproduce Li depletion boundary ages of the β Pic Moving Group also imply a ˜4 Myr age for the low mass members of the Upper Sco OB Association, which is younger than the 11 Myr age that has been recently estimated for intermediate and high mass members.

  4. The star-formation history of very young clusters

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.

    1985-01-01

    The popular idea that star formation has proceeded sequentially from lowest to highest mass members in open clusters is examined critically. For extremely young clusters, such as NGC 2264 and NGC 6530, this sequential hypothesis is a consequence of the assignment of pre-main-sequence contraction ages to all member stars. However, such ages yield a formation history which is implausible from a physical point of view, since the critical time for the onset of formation at any stellar mass is equal to the pre-main-sequence contraction time for that mass. Moreover, these ages are in conflict with the strong observational evidence that a substantial fraction of cluster members have already reached the main sequence. After reconsideration of the probable main-sequence members, the stellar ages in NGC 2264 and NGC 6530 are consistent with a variety of formation histories, and, in particular, with the view that all stellar masses form in approximately the same interval of time within a given cluster, i.e., that there is no mass-age correlation. A notion closely related to the sequential hypothesis, that the total star-formation rate increases exponentially with time, is subject to the same criticism.

  5. Transformed photometry of young stars in Cha requested

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.

    2013-01-01

    Dr. Peter Abraham (Konkoly Observatory, Budapest, Hungary) requested the assistance of AAVSO observers in monitoring eight young stars in Chamaeleon in support of photometry he and his colleagues will be obtaining with the VLT/ISAAC (infrared) and Herschel Space Observatory (far-infrared) during January-February 2013. The targets are CR Cha, CT Cha, HP Cha (Glass I), VW Cha, VZ Cha, WW CHa, WX Cha, XX Cha. Calibrated, transformed VRI photometry is requested to precisely monitor changes in the optical brightness and colors of these objects. Calibration and transformation of the photometry is crucial - if all of the data are not on the same system and particularly if the colors are not transformed, it will be extremely difficult to correlate the data usefully. Previous observations indicate that the stars are highly variable. Brightness changes can be expected from a few tenths of a magnitude to up to 1-2 magnitudes on a timescale of a few days to a few weeks. Observers are asked to try to obtain one to two sets of VRI images per night. Finder charts with sequences may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details.

  6. Bright Young Star Clusters in NGC5253 with LEGUS

    NASA Astrophysics Data System (ADS)

    Calzetti, Daniela; Johnson, Kelsey E.; Adamo, Angela; Gallagher, John S.; Andrews, Jennifer E.; Smith, Linda J.; Clayton, Geoffrey C.; Lee, Janice C.; Sabbi, Elena; Ubeda, Leonardo; Kim, Hwihyun; Ryon, Jenna E.; Thilker, David A.; Bright, Stacey N.; Zackrisson, Erik; Kennicutt, Robert; de Mink, Selma E.; Whitmore, Bradley C.; Aloisi, Alessandra; Chandar, Rupali; Cignoni, Michele; Cook, David; Dale, Daniel A.; Elmegreen, Bruce; Elmegreen, Debra M.; Evans, Aaron S.; Fumagalli, Michele; Gouliermis, Dimitrios; Grasha, Kathryn; Grebel, Eva; Krumholz, Mark R.; Walterbos, Rene A. M.; Wofford, Aida; Brown, Thomas M.; Christian, Carol A.; Dobbs, Claire; Herrero-Davo`, Artemio; Kahre, Lauren; Messa, Matteo; Nair, Preethi; Nota, Antonella; Östlin, Göran; Pellerin, Anne; Sacchi, Elena; Schaerer, Daniel; Tosi, Monica

    2016-01-01

    Using UV-to-H broad and narrow-band HST imaging, we derive the ages and masses of the 11 brightest star clusters in the dwarf galaxy NGC5253. This galaxy, located at ~3 Mpc, hosts an intense starburst, which includes a centrally-concentrated dusty region with strong thermal radio emission (the `radio nebula'). The HST imaging includes data from the Cycle 21 Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), in addition to narrow--band H-alpha (6563 A), P-beta (12820 A), and P-alpha (18756 A). The bright clusters have ages ~1-15 Myr and masses ~1E4 - 2.5E5 Msun. Two of the 11 star clusters are located within the radio nebula, and suffer from significant dust attenuation. Both are extremely young, with a best-fit age around 1 Myr, and masses ~7.5E4 and ~2.5E5 Msun, respectively. The most massive of the two `radio nebula' clusters is 2-4 times less massive than previously estimated and is embedded within a cloud of dust with A_V~50 mag. The two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.

  7. SPIN EVOLUTION OF ACCRETING YOUNG STARS. I. EFFECT OF MAGNETIC STAR-DISK COUPLING

    SciTech Connect

    Matt, Sean P.; Greene, Thomas P.; Pinzon, Giovanni; De la Reza, Ramiro E-mail: thomas.p.greene@nasa.go E-mail: delareza@on.b

    2010-05-10

    We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and radius and a decreasing accretion rate. The model also includes, for the first time in a spin evolution model, the opening of the stellar magnetic field lines, as expected to arise from twisting via star-disk differential rotation. In order to isolate the effect that this has on the star-disk interaction torques, we neglect the influence of torques that may arise from open field regions connected to the star or disk. For a range of magnetic field strengths, accretion rates, and initial spin rates, we compute the stellar spin rates of pre-main-sequence stars as they evolve on the Hayashi track to an age of 3 Myr. How much the field opening affects the spin depends on the strength of the coupling of the magnetic field to the disk. For the relatively strong coupling (i.e., high magnetic Reynolds number) expected in real systems, all models predict spin periods of less than {approx}3 days, in the age range of 1-3 Myr. Furthermore, these systems typically do not reach an equilibrium spin rate within 3 Myr, so that the spin at any given time depends upon the choice of initial spin rate. This corroborates earlier suggestions that, in order to explain the full range of observed rotation periods of approximately 1-10 days, additional processes, such as the angular momentum loss from powerful stellar winds, are necessary.

  8. Vertical Structure of Magnetized Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    Lizano, S.; Tapia, C.; Boehler, Y.; D'Alessio, P.

    2016-01-01

    We model the vertical structure of the magnetized accretion disks that are subject to viscous and resistive heating and irradiation by the central star. We apply our formalism to the radial structure of the magnetized accretion disks that are threaded by the poloidal magnetic field dragged during the process of star formation, which was developed by Shu and coworkers. We consider disks around low-mass protostars, T Tauri, and FU Orionis stars, as well as two levels of disk magnetization: {λ }{sys}=4 (strongly magnetized disks) and {λ }{sys}=12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk, and the T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, which is consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (˜90%-95%) is in the disk midplane. With the advent of ALMA one expects direct measurements of magnetic fields and their morphology at disk scales. It will then be possible to determine the mass-to-flux ratio of magnetized accretion disks around young stars, an essential parameter for their structure and evolution. Our models contribute to the understanding of the vertical structure and emission of these disks.

  9. YoungStar in Wisconsin: An Initial Progress Report as of July 2011

    ERIC Educational Resources Information Center

    Edie, Dave

    2011-01-01

    YoungStar is a program of the Department of Children and Families (DCF) created to improve the quality of child care for Wisconsin children. YoungStar is designed to: (1) Evaluate and rate the quality of care given by child care providers; (2) Help parents choose the best child care for their kids; (3) Support providers with tools and training to…

  10. YoungStar in Milwaukee County: An Initial Progress Report as of July 2011

    ERIC Educational Resources Information Center

    Edie, Dave

    2011-01-01

    YoungStar is a program of the Department of Children and Families (DCF) created to improve the quality of child care for Wisconsin children. YoungStar is designed to: (1) Evaluate and rate the quality of care given by child care providers; (2) Help parents choose the best child care for their kids; (3) Support providers with tools and training to…

  11. Where to Find Young Bright Stars in Geosciences: GGD, NSU

    NASA Astrophysics Data System (ADS)

    Rakhmenkoulova, I. F.; Sharapov, V. N.

    2004-12-01

    Geology and Geophysics Department (GGD) of Novosibirsk State University (NSU) can be regarded as infant, because it was founded in 1962. On the other hand, if to judge by what have been done - it is not only full-fledged, but well-known department. The unique location and specific educational and scientific traditions make GGD a famous school not only in Siberia, but in Russia, and all over the world. What are the tips to prepare bright stars in geosciences? 1.NSU is located in Academgorodok (Novosibirsk scientific center), unique place in Siberia, where more than 20 scientific institutions are located. This makes the University different from other schools in Russia. Famous Russian scientists, including members of RAS, together with foreign professors give lectures and seminars for NSU students. 2.The bright star hunting starts far below the NSU level. Each year in April there is a special event in Academgorodok -`Geologic Olympiad', where children of all Russian regions, as well as ex-Soviet republics are gathered together to submit their papers, to discuss most interesting geoscience problems and to win prizes for their knowledge. The youngest stars happen to be only 6-7 years old. The event is sponsored by NSU, UIGGM, and the Ministry of Natural Resources. The brightest geostars are grown from `Geologic Olympiad' participants. 3.There is special physics-mathematical high school in Academgorodok. Each summer this school gathers young stars from farthest Siberian and Far East regions and gives classes and seminars in mathematics, physics, chemistry and geology. As the result the most talented children become the students of this school (for two years). The school in turn supplies GGD with the students. 4.NSU has the study curriculum different from other universities in Russia. That is why the entrance examinations are much more difficult as compared to other schools and are taken in July (a month earlier then at other universities). However the entrance examinations are based on free competition and education at GGD is free. For example, to become a student of oil and gas geochemistry a young star should win a competition between nine young persons. 5.GGD scientific research program starts from course paper (second year of study), the next steps being Bachelor's and Master's dissertations and postgraduate course. The scientific advisors are most famous scientists from Academgorodok. Moreover, the GGD students have a possibility to take unique exclusive electives of most modern fields of science. 6.GGD is equipped by a good computer class and SGG workstation. Most computers were granted by Schlumberger, as a sign that best graduates in geosciences in Russia are from GGD NSU. So the students have free Internet access as well as they can use online web educational resources of GGD. The educational system of GGD does not use a conception `to teach something', but the conception `to teach how to learn'. At GGD a tutor has 5-6 students. For some electives and specialties there is one student - one tutor system. GGD students are able to have field practice in all Siberian and Far East regions, huge territory with unique geology. The NSU educational system is flexible enough, so that the graduates are able to adapt to any interdisciplinary science and can successfully work in other fields. The graduators work not only in oil companies and scientific institutions in Russia, but in such companies as Schlumberger, Halliburton, Shell, Total, De Beers, and others. The brightest GGD stars are even head-hunted. The NSU slogan is `WE WILL NOT MAKE YOU SMARTER, WE WILL TEACH YOU HOW TO THINK!'

  12. Activity trends in young solar-type stars

    NASA Astrophysics Data System (ADS)

    Lehtinen, J.; Jetsu, L.; Hackman, T.; Kajatkari, P.; Henry, G. W.

    2016-04-01

    Aims: We study a sample of 21 young and active solar-type stars with spectral types ranging from late F to mid K and characterize the behaviour of their activity. Methods: We apply the continuous period search (CPS) time series analysis method on Johnson B- and V-band photometry of the sample stars, collected over a period of 16 to 27 years. Using the CPS method, we estimate the surface differential rotation and determine the existence and behaviour of active longitudes and activity cycles on the stars. We supplement the time series results by calculating new log R'HK = log F'HK/σTeff4 emission indices for the stars from high resolution spectroscopy. Results: The measurements of the photometric rotation period variations reveal a positive correlation between the relative differential rotation coefficient and the rotation period as k ∝ Prot1.36, but do not reveal any dependence of the differential rotation on the effective temperature of the stars. Secondary period searches reveal activity cycles in 18 of the stars and temporary or persistent active longitudes in 11 of them. The activity cycles fall into specific activity branches when examined in the log Prot/Pcyc vs. log Ro-1, where Ro-1 = 2Ωτc, or log Prot/Pcyc vs. log R'HK diagram. We find a new split into sub-branches within this diagram, indicating multiple simultaneously present cycle modes. Active longitudes appear to be present only on the more active stars. There is a sharp break at approximately log R'HK = -4.46 separating the less active stars with long-term axisymmetric spot distributions from the more active ones with non-axisymmetric configurations. In seven out of eleven of our stars with clearly detected long-term non-axisymmetric spot activity the estimated active longitude periods are significantly shorter than the mean photometric rotation periods. This systematic trend can be interpreted either as a sign of the active longitudes being sustained from a deeper level in the stellar interior than the individual spots or as azimuthal dynamo waves exhibiting prograde propagation. Based on observations made as part of the automated astronomy program at Tennessee State University and with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.Photometric data and results are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A38

  13. Interactions of flares, accretion and wind in young stars

    NASA Astrophysics Data System (ADS)

    Moritz Guenther, Hans

    2010-10-01

    Young stars can produce X-rays by different mechanisms: Coronal activity, accretion shocks and shocks in outflows. We propose to observe two targets within one field-of-view (FOV): SU Aur is accreting mass from a disk and shows violent coronal activity. We will study the time evolution of stellar flares on time scales from seconds to minutes using the high count rate in the EPIC and the OM to discover interactions with the accretion streams: The signature of the flare onset will differ in X-rays and UV between flares on coronal loops and flares on those field lines, which carry the accretion stream from the disk. AB Aur is more massive, it shows a tentative modulation in the X-ray luminosity apparently without spectral changes and contrary to model expectations.

  14. X-raying Circumstellar Material around Young Stars

    NASA Astrophysics Data System (ADS)

    Schneider, P. C.; Günther, H. M.

    2016-01-01

    Young stars are surrounded by copious amounts of circumstellar material. Its composition, in particular its gas-to-dust ratio, is an important parameter. However, measuring this ratio is challenging, because gas mass estimates are often model dependent. X-ray absorption is sensitive to the gas along the line-of-sight while optical/near-IR extinction depends on the dust. Therefore, the absorber's gas-to-dust ratio is directly given by the ratio between X-ray and optical/near-IR extinction. We present three systems where we used X-ray and optical/near-IR data to constrain the gas-to-dust ratio of circumstellar material; from a dust rich debris disk to gaseous protoplanetary disks.

  15. Radiological age estimation: based on third molar mineralization and eruption in Turkish children and young adults.

    PubMed

    Karadayi, Beytullah; Kaya, Ahsen; Kolusayın, Melek Ozlem; Karadayi, Sükriye; Afsin, Hüseyin; Ozaslan, Abdi

    2012-11-01

    Radiographic evaluation of mineralization and eruption stages of third molars using dental panoramic radiographies can be an efficient tool for chronological age estimation in both forensic sciences and legal medicine. The third molar tooth is utilized for dental age estimation about the age span of 15-23 years because it represents the only tooth still in development. The aim of this study is to obtain and analyze data regarding third molar development and eruption in Turkish population for dental age estimation. A total of 744 dental panoramic radiographies of 394 female and 350 male subjects aged between 8 and 22 years were examined. Third molar development was determined according to the Nolla classification system, and eruption was assessed relative to the alveolar bone level. Mandibular and maxillary third molars were generally found at similar stages of development on both sides. Nolla stage 6 (completed crown calcification) was reached at around the age of 15 in both maxillary and mandibular third molars in both sexes. Alveolar emergence was at around the age of 16 in males and around age of 17 in females. Although third molars' eruption shows greater variability than development of third molars, data which were obtained from this study about eruption of these teeth can be supportive to development data for age estimation. PMID:23010906

  16. An Infrared Examination of Young Stars in Upper Centaurus Lupus

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Linahan, M.; Barge, J.; Rebull, L. M.; Aranda, D.; Canlas, N. G.; Donahoe, K. E.; Ernst, M. K.; Ford, S.; Fox, M. E.; Gutierrez, E.; Haecker, L. W.; Hibbs, C. A.; Maddaus, M. R.; Martin, T. A.; Ng, E.; Niedbalec, A. P.; O'Bryan, S. E.; Searls, E. F.; Zeidner, A. B.; Zegeye, D.

    2014-01-01

    Optical studies of the Upper Centaurus Lupus (UCL) region of the Scorpius-Centaurus (Sco-Cen) complex have found many young stellar objects. The nearby G/K/M Sco-Cen members have been estimated to be much younger 10 Myr) than similar star associations (Song, et al 2012). We have assembled infrared data for the objects thought to be members of UCL by mining various archives including the 2-Micron All-Sky Survey (2MASS), the Spitzer Heritage Archive (SHA), specifically the Spitzer Enhanced Imaging Products Source List, and the Wide-field Infrared Survey Explorer (WISE) all-sky source catalog. We created spectral energy distributions (SEDs) and color-magnitude diagrams (CMDs) with multiple wavelengths to identify infrared excesses and determine what fraction of these stars have circumstellar disks. Students from three high schools collaborated on this project, which is a follow-up project made possible through the NASA/IPAC Teacher Archive Research Project (NITARP; http://nitarp.ipac.caltech.edu).

  17. SpS1-Measuring magnetic fields on young stars

    NASA Astrophysics Data System (ADS)

    Johns-Krull, Christopher M.; Valenti, Jeff A.

    2010-11-01

    T Tauri stars (TTSs) are young (~few Myr) late type stars that have only recently emerged from their natal molecular cloud material to become visible at optical wavelengths. It is now generally accepted that accretion of circumstellar disk material onto the surface of a TTS is controlled by a strong stellar magnetic field (e.g. see review by Bouvier et al. 2007). The stellar field appears critical for explaining the rotational properties of TTSs (Bouvier et al. 2007, Herbst et al. 2007) and may also play a critical role in driving the outflows seen from many of these sources (e.g. Shang et al. 2007, Mohanty & Shu 2008). As a result, there is a great deal of interest in measuring the magnetic field properties of TTSs (e.g. Johns-Krull 2007, Donati et al. 2008). In particular, disk locking theories predict that an equilibrium is established where the disk is trunctated at or close to corotation and the stellar rotation rate depends only on the (assumed) dipolar magnetic field strength, the stellar mass, radius, and the mass accretion rate in the disk (see Bouvier et al. 2007).

  18. Fourth Day of Creation: The Proto-history of Young Stars, Star Streams, and Exoplanets Near the Sun

    NASA Astrophysics Data System (ADS)

    Trimble, Virginia

    2016-01-01

    Items of scientific knowledge at any moment in time have pre-histories when they were debated, doubted, or absolutely denied. The examples considered here are the admitted facts that star formation is an on-going process in the Milky Way, that there are young moving groups (the products of young star clusters in the process of dissolution and perhaps more complex processes), and that planets orbiting other stars are common. It is hard to imagine any of these ceasing to be part of core astronomical knowledge, but you are advised not to place large bets on this.

  19. Fossil magnetic field of accretion disks of young stars

    NASA Astrophysics Data System (ADS)

    Dudorov, A. E.; Khaibrakhmanov, S. A.

    2014-07-01

    We elaborate the model of accretion disks of young stars with the fossil large-scale magnetic field in the frame of Shakura and Sunyaev approximation. Equations of the MHD model include Shakura and Sunyaev equations, induction equation and equations of ionization balance. Magnetic field is determined taking into account ohmic diffusion, magnetic ambipolar diffusion and buoyancy. Ionization fraction is calculated considering ionization by cosmic rays and X-rays, thermal ionization, radiative recombinations and recombinations on the dust grains. Analytical solution and numerical investigations show that the magnetic field is coupled to the gas in the case of radiative recombinations. Magnetic field is quasi-azimuthal close to accretion disk inner boundary and quasi-radial in the outer regions. Magnetic field is quasi-poloidal in the dusty "dead" zones with low ionization degree, where ohmic diffusion is efficient. Magnetic ambipolar diffusion reduces vertical magnetic field in 10 times comparing to the frozen-in field in this region. Magnetic field is quasi-azimuthal close to the outer boundary of accretion disks for standard ionization rates and dust grain size a d=0.1 ?m. In the case of large dust grains ( a d>0.1 ?m) or enhanced ionization rates, the magnetic field is quasi-radial in the outer regions. It is shown that the inner boundary of dusty "dead" zone is placed at r=(0.1-0.6) AU for accretion disks of stars with M=(0.5-2) M ?. Outer boundary of "dead" zone is placed at r=(3-21) AU and it is determined by magnetic ambipolar diffusion. Mass of solid material in the "dead" zone is more than 3 M ? for stars with M?1 M ?.

  20. SUPERSONIC LINE BROADENING WITHIN YOUNG AND MASSIVE SUPER STAR CLUSTERS

    SciTech Connect

    Tenorio-Tagle, Guillermo; Silich, Sergiy; Wuensch, Richard; Munoz-Tunon, Casiana; Palous, Jan E-mail: richard@wunsch.c E-mail: cmt@ll.iac.e

    2010-01-10

    The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters is discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines here are shown to occur in clusters that undergo a bimodal hydrodynamic solution, that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass versus the size of the cluster plane. A plethora of RSs is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster heating efficiency (eta). Based on our two-dimensional simulations we calculate the line profiles that result from several models and confirm our analytical predictions. From a comparison between the predicted and observed values of the half-width zero intensity of the two line components, we conclude that the thermalization efficiency in young super star clusters above the threshold line must be lower than 20%.

  1. The Brightest Young Star Clusters in NGC 5253.

    NASA Astrophysics Data System (ADS)

    Calzetti, D.; Johnson, K. E.; Adamo, A.; Gallagher, J. S., III; Andrews, J. E.; Smith, L. J.; Clayton, G. C.; Lee, J. C.; Sabbi, E.; Ubeda, L.; Kim, H.; Ryon, J. E.; Thilker, D.; Bright, S. N.; Zackrisson, E.; Kennicutt, R. C.; de Mink, S. E.; Whitmore, B. C.; Aloisi, A.; Chandar, R.; Cignoni, M.; Cook, D.; Dale, D. A.; Elmegreen, B. G.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Krumholz, M. R.; Walterbos, R.; Wofford, A.; Brown, T. M.; Christian, C.; Dobbs, C.; Herrero, A.; Kahre, L.; Messa, M.; Nair, P.; Nota, A.; Östlin, G.; Pellerin, A.; Sacchi, E.; Schaerer, D.; Tosi, M.

    2015-10-01

    The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (MV < -8.8) and the two young radio nebula clusters. The clusters have ages ˜1-15 Myr and masses ˜1 × 104-2.5 × 105 M⊙. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ˜15 Myr. The most massive cluster is in the radio nebula; with a mass ˜2.5 × 105 M⊙ and an age ˜1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV ˜ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ˜1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  2. Eruptive disseminated Spitz naevus (EDSN) in a young girl of Indian origin.

    PubMed

    Sharma, Niyati; Ho, Stephanie; Bing, Tan Kong; McCormack, Chris; Scolyer, Richard; Lee, Joyce

    2015-05-01

    Eruptive disseminated Spitz naevus (EDSN) is a rare entity and has never been documented in a South-east Asian individual (of Indian origin) previously. We report an adolescent with this condition which, to our knowledge, has only been previously reported a few times. PMID:25482351

  3. Young Stars in NGC 6231 and the Sco OB1 Association

    NASA Astrophysics Data System (ADS)

    Reipurth, B.

    2008-12-01

    NGC 6231 is a young cluster in the southern sky, around 3-5 Myr old, located at a distance of about 1.6 kpc at the near side of the Sagittarius spiral arm. It forms the nucleus of the extended Sco OB1 association. The cluster is very rich, with more than 100 massive stars, among them 15 O-stars. Radial velocity studies have revealed a very large binary fraction among these OB stars. The young low-mass population has recently been identified using deep X-ray observations. Within the large HII region Gum 55 that surrounds NGC 6231 there exists a major elephant trunk, which shows evidence for recent second-generation star formation in the form of young B-stars surrounded by reflection nebulae and a number of low-mass Hα emission stars.

  4. Structure, stratigraphy, and eruption dynamics of a young tuff ring: Hanauma Bay, O'ahu, Hawai'i

    NASA Astrophysics Data System (ADS)

    Rottas, K. M.; Houghton, B. F.

    2012-09-01

    The Hanauma Bay-Koko Head complex is one of several young volcanic landforms along the Koko fissure, in southeastern O'ahu. The Hanauma Bay region of the complex comprises two nested tuff rings, inner and outer Hanauma Bay, and multiple smaller vents. The internal structure of the inner tuff ring, well exposed due to subsequent breaching by the ocean and wave erosion, indicates that it formed during a minimum of five distinct phases of deposition that produced five mappable units. Significant inward collapses generated major unconformities that separate the units exposed in the inner wall. The planes of failure are cut by narrow steep-walled, locally overhung channels and gullies, suggesting that the collapse events were each followed by short time breaks during which the deposits were eroded by rainfall runoff. Within each pyroclastic unit, there are many local slump scars and unconformities, suggesting that minor instability of the inner wall was a near-constant feature. From bedding sags and surge bed forms, it is apparent that the vent shifted at least twice during tuff ring growth. Ballistic blocks in the youngest unit indicate that the eruption overlapped in time with a separate eruption to the north, most likely to be that of the Kahauloa tuff ring 880 m away.

  5. FAKE STAR FORMATION BURSTS: BLUE HORIZONTAL BRANCH STARS MASQUERADE AS YOUNG MASSIVE STARS IN OPTICAL INTEGRATED LIGHT SPECTROSCOPY

    SciTech Connect

    Ocvirk, P.

    2010-01-20

    Model color-magnitude diagrams of low-metallicity globular clusters (GCs) usually show a deficit of hot evolved stars with respect to observations. We investigate quantitatively the impact of such modeling inaccuracies on the significance of star formation history reconstructions obtained from optical integrated spectra. To do so, we analyze the sample of spectra of galactic globular clusters of Schiavon et al. with STECKMAP (Ocvirk et al.), and the stellar population models of Vazdekis et al. and Bruzual and Charlot, and focus on the reconstructed stellar age distributions. First, we show that background/foreground contamination correlates with E(B - V), which allows us to define a clean subsample of uncontaminated GCs, on the basis of an E(B - V) filtering. We then identify a 'confusion zone' where fake young bursts of star formation pop up in the star formation history although the observed population is genuinely old. These artifacts appear for 70%-100% of cases depending on the population model used, and contribute up to 12% of the light in the optical. Their correlation with the horizontal branch (HB) ratio indicates that the confusion is driven by HB morphology: red HB clusters are well fitted by old stellar population models while those with a blue HB require an additional hot component. The confusion zone extends over [Fe/H] = [ - 2, - 1.2], although we lack the data to probe extreme high and low metallicity regimes. As a consequence, any young starburst superimposed on an old stellar population in this metallicity range could be regarded as a modeling artifact, if it weighs less than 12% of the optical light, and if no emission lines typical of an H II region are present. This work also provides a practical method for constraining HB morphology from high signal to noise integrated light spectroscopy in the optical. This will allow post-asymptotic giant branch evolution studies in a range of environments and at distances where resolving stellar populations is impossible with current and planned telescopes.

  6. SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG STARS IN IC 348: THE ROLE OF DISKS IN ANGULAR MOMENTUM EVOLUTION OF YOUNG, LOW-MASS STARS

    SciTech Connect

    Le Blanc, Thompson S.; Stassun, Keivan G.; Covey, Kevin R.

    2011-08-15

    Theoretical work suggests that a young star's angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these 'disk-locking' theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young stars' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating stars possess close-in disks that enforce the star's slow rotation, whereas rapidly rotating stars possess anemic or evacuated inner disks that are unable to brake the stars and instead the stars spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young stars in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each star, we match the observed SED, typically sampling 0.6-8.0 {mu}m, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the star's measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.

  7. Spectral Energy Distributions of Young Stars in IC 348: The Role of Disks in Angular Momentum Evolution of Young, Low-mass Stars

    NASA Astrophysics Data System (ADS)

    Le Blanc, Thompson S.; Covey, Kevin R.; Stassun, Keivan G.

    2011-08-01

    Theoretical work suggests that a young star's angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these "disk-locking" theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young stars' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating stars possess close-in disks that enforce the star's slow rotation, whereas rapidly rotating stars possess anemic or evacuated inner disks that are unable to brake the stars and instead the stars spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young stars in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each star, we match the observed SED, typically sampling 0.6-8.0 μm, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the star's measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.

  8. Reconstructing the Initial Relaxation Time of Young Star Clusters in the Large Magellanic Cloud: The Evolution of Star Clusters

    NASA Astrophysics Data System (ADS)

    Portegies Zwart, S. F.; Chen, H.-C.

    2008-06-01

    We reconstruct the initial two-body relaxation time at the half mass radius for a sample of young ⪉ 300 Myr star clusters in the Large Magellanic cloud. We achieve this by simulating star clusters with 12288 to 131072 stars using direct N-body integration. The equations of motion of all stars are calculated with high precision direct N-body simulations which include the effects of the evolution of single stars and binaries. We find that the initial relaxation times of the sample of observed clusters in the Large Magellanic Cloud ranges from about 200 Myr to about 2 Gyr. The reconstructed initial half-mass relaxation times for these clusters have a much narrower distribution than the currently observed distribution, which ranges over more than two orders of magnitude.

  9. Multi-dimensional structure of accreting young stars

    NASA Astrophysics Data System (ADS)

    Geroux, C.; Baraffe, I.; Viallet, M.; Goffrey, T.; Pratt, J.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.

    2016-04-01

    This work is the first attempt to describe the multi-dimensional structure of accreting young stars based on fully compressible time implicit multi-dimensional hydrodynamics simulations. One major motivation is to analyse the validity of accretion treatment used in previous 1D stellar evolution studies. We analyse the effect of accretion on the structure of a realistic stellar model of the young Sun. Our work is inspired by the numerical work of Kley & Lin (1996, ApJ, 461, 933) devoted to the structure of the boundary layer in accretion disks, which provides the outer boundary conditions for our simulations. We analyse the redistribution of accreted material with a range of values of specific entropy relative to the bulk specific entropy of the material in the accreting object's convective envelope. Low specific entropy accreted material characterises the so-called cold accretion process, whereas high specific entropy is relevant to hot accretion. A primary goal is to understand whether and how accreted energy deposited onto a stellar surface is redistributed in the interior. This study focusses on the high accretion rates characteristic of FU Ori systems. We find that the highest entropy cases produce a distinctive behaviour in the mass redistribution, rms velocities, and enthalpy flux in the convective envelope. This change in behaviour is characterised by the formation of a hot layer on the surface of the accreting object, which tends to suppress convection in the envelope. We analyse the long-term effect of such a hot buffer zone on the structure and evolution of the accreting object with 1D stellar evolution calculations. We study the relevance of the assumption of redistribution of accreted energy into the stellar interior used in the literature. We compare results obtained with the latter treatment and those obtained with a more physical accretion boundary condition based on the formation of a hot surface layer suggested by present multi-dimensional simulations. One conclusion is that, for a given amount of accreted energy transferred to the accreting object, a treatment assuming accretion energy redistribution throughout the stellar interior could significantly overestimate the effects on the stellar structure and, in particular, on the resulting expansion.

  10. Magnetic field of the young star RW Aur

    NASA Astrophysics Data System (ADS)

    Dodin, A. V.; Lamzin, S. A.; Chuntonov, G. A.

    2012-03-01

    Results of ourmeasurements of the longitudinal magnetic field B z for the young star RWAur A are presented. B z measured from the so-called narrow component of the He I 5876 line varies in the range from -1.47 ± 0.15 to +1.10 ± 0.15 kG. Our data are consistent with a stellar rotation period of }~5.6 days and the model of two hot spots with opposite magnetic field polarities spaced about 180° apart in longitude. Relative to the Earth, the spot with B z < 0 lies in the hemisphere above the midplane of the accretion disk, while the spot with B z > 0 is below the midplane. The upper limit for B z (at the 3 σ level) obtained by averaging all observations is 180 G for the photosphere and 220 and 230 G for the H α and [OI] 6300 line formation regions, respectively. We have also failed to detect a field in the formation region of broad emission line components: the upper limit for B z is 600 G. In two of 11 cases, we have detected a magnetic field in the formation region of the blue absorption wing of the Na I D doublet lines, i.e., in the wind from RW Aur A: B z = -180 ± 50 and -810 ± 80 G. The radial velocity of the photospheric lines in RW Aur A averaged over all our observations is }~+10.5 km s-1, i.e., a value lower than that obtained by Petrov et al. (2001) ten years earlier by 5.5 km s-1. Therefore, we discuss the possibility that RW Aur is not a binary but a triple system.

  11. X-Rays from Young Stars and Eggs in the Eagle Nebula (M16)

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.; Gagne, Marc; Mytyk, Anna

    The Chandra X-ray Observatory observed the Eagle Nebula (M16) a young star forming region containing the dark columns of dust and cold molecular gas known as the ""Pillars of Creation"" or ""elephant trunks"". We identify more than 1000 X-ray sources coincident with K-band stars that are premain sequence stars ranging in spectral type from O to M. A handful of the hard X-ray sources in the pillars are spatially coincident with deeply embedded young stellar objects seen in JHK images. However none of the X-ray sources are associated with the evaporating gaseous globules (EGGs) first observed by Hester et al. (1996).

  12. Discovery at Young Star Hints Magnetism Common to All Cosmic Jets

    NASA Astrophysics Data System (ADS)

    2010-11-01

    Astronomers have found the first evidence of a magnetic field in a jet of material ejected from a young star, a discovery that points toward future breakthroughs in understanding the nature of all types of cosmic jets and of the role of magnetic fields in star formation. Throughout the Universe, jets of subatomic particles are ejected by three phenomena: the supermassive black holes at the cores of galaxies, smaller black holes or neutron stars consuming material from companion stars, and young stars still in the process of gathering mass from their surroundings. Previously, magnetic fields were detected in the jets of the first two, but until now, magnetic fields had not been confirmed in the jets from young stars. "Our discovery gives a strong hint that all three types of jets originate through a common process," said Carlos Carrasco-Gonzalez, of the Astrophysical Institute of Andalucia Spanish National Research Council (IAA-CSIC) and the National Autonomous University of Mexico (UNAM). The astronomers used the National Science Foundation's Very Large Array (VLA) radio telescope to study a young star some 5,500 light-years from Earth, called IRAS 18162-2048. This star, possibly as massive as 10 Suns, is ejecting a jet 17 light-years long. Observing this object for 12 hours with the VLA, the scientists found that radio waves from the jet have a characteristic indicating they arose when fast-moving electrons interacted with magnetic fields. This characteristic, called polarization, gives a preferential alignment to the electric and magnetic fields of the radio waves. "We see for the first time that a jet from a young star shares this common characteristic with the other types of cosmic jets," said Luis Rodriguez, of UNAM. The discovery, the astronomers say, may allow them to gain an improved understanding of the physics of the jets as well as of the role magnetic fields play in forming new stars. The jets from young stars, unlike the other types, emit radiation that provides information on the temperatures, speeds, and densities within the jets. This information, combined with the data on magnetic fields, can improve scientists' understanding of how such jets work. "In the future, combining several types of observations could give us an overall picture of how magnetic fields affect the young star and all its surroundings. This would be a big advance in understanding the process of star formation," Rodriguez said. Carrasco-Gonzalez and Rodriguez worked with Guillem Anglada and Mayra Osorio of the Astrophysical Institute of Andalucia, Josep Marti of the University of Jaen in Spain, and Jose Torrelles of the University of Barcelona. The scientists reported their findings in the November 26 edition of Science.

  13. Chromospherically active stars. II - HD 82558, a young single BY Draconis variable

    NASA Technical Reports Server (NTRS)

    Fekel, Francis C.; Bopp, Bernard W.; Africano, John L.; Goodrich, Bret D.; Palmer, Leigh Hunter

    1986-01-01

    It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, which appears to have been stable for several hundred rotation cycles, is reminiscent of that of the young, rapidly rotating, single K V variable H II 1883 in the Pleiades; this stability may be characteristic of young, single, chromospherically active stars.

  14. Lithium Depletion Boundary Ages of Young Stars: Inconsistencies in Pre-Main Sequence Models

    NASA Astrophysics Data System (ADS)

    Song, Inseok

    2016-01-01

    For proper interpretations of various phenomena in young stars and planetary systems, knowledge of accurate stellar ages is very important. Among a handful of age dating methods commonly used for young (<~500 Myr) stars, lithium depletion boundary (LDB) ages have recently become the most cited and accepted age estimates. However, because of inconsistencies in theoretical evolutionary models, especially for lithium depletion calculations, one has to be cautious in using LDB ages. For a given luminosity, the lithium depletion process is too slow, causing LDB ages to appear older. Various stellar processes affect the surface lithium abundance, and these effects include star spots, accretion history, and magnetic fields. Until we have a self-consistent theoretical evolutionary model for young stars including all relevant stellar effects, caution should be taken when LDB ages are used.

  15. Connecting the Dense Gas and Young Stars in the CARMA Large Area Star Formation Survey

    NASA Astrophysics Data System (ADS)

    Mundy, Lee G.; Storm, Shaye; Looney, Leslie; Lee, Katherine I.; Fernandez Lopez, Manuel; Ostriker, Eve C.; Chen, Che-Yu; CLASSy Team

    2016-01-01

    The CARMA Large Area Star Formation Survey (CLASSy) imaged the dense gas structure and kinematics in five, roughly 1 pc scale regions in the Serpens and Perseus clouds with 7" angular resolution. The spatial distribution and Class of the young stellar population (YSOs) is available for these regions from the Spitzer c2d and Gould Belt surveys, with added sources from the Herschel 70 micron images. Together, these datasets allow us to compare, for the first time at similar spatial resolutions, the distributions of the dense gas and YSOs over regions containing up to 90 identified YSOs. This enables a detailed look at the separation between YSOs and the nearest dense gas peak and a measure of overall relationship between the YSO and dense gas distributions. We find that most Class 0 YSOs are forming in the highest column density regions: leaves in the dendrogram analysis utilized by CLASSy. In Serpens and Perseus, we find that 29% and 38%, respectively, of the leaves have identified embedded YSOs. Class 1 sources are less confined to leaf locations; Class II sources are distributed throughout regions, mostly away from hierarchical peaks. This trend could be due to a modest (0.1 km/sec) velocity difference between YSOs and their natal cores, or due to the YSOs consuming or dispersing their natal cores.

  16. KMOS view of the Galactic centre. I. Young stars are centrally concentrated

    NASA Astrophysics Data System (ADS)

    Feldmeier-Krause, A.; Neumayer, N.; Schödel, R.; Seth, A.; Hilker, M.; de Zeeuw, P. T.; Kuntschner, H.; Walcher, C. J.; Lützgendorf, N.; Kissler-Patig, M.

    2015-12-01

    Context. The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also ≳100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8 Myr old. Aims: Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and growth of the nuclear star cluster. Methods: We cover the central >4 pc2 (0.75 sq. arcmin) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Results: Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is ≳12 000 M⊙. The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. Conclusions: The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or that the disk is dissolving rapidly. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (60.A-9450(A)).Appendices are available in electronic form at http://www.aanda.orgThe extracted spectra as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A2

  17. Nuclear ashes and outflow in the eruptive star Nova Vul 1670

    NASA Astrophysics Data System (ADS)

    Kamiński, Tomasz; Menten, Karl M.; Tylenda, Romuald; Hajduk, Marcin; Patel, Nimesh A.; Kraus, Alexander

    2015-04-01

    CK Vulpeculae was observed in outburst in 1670-1672 (ref. 1), but no counterpart was seen until 1982, when a bipolar nebula was found at its location. Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but its similarity to `red transients', which are more luminous than classical novae and thought to be the results of stellar collisions, has re-opened the question of CK Vul's status. Red transients cool to resemble late M-type stars, surrounded by circumstellar material rich in molecules and dust. No stellar source has been seen in CK Vul, though a radio continuum source was identified at the expansion centre of the nebula. Here we report that CK Vul is surrounded by chemically rich molecular gas in the form of an outflow, as well as dust. The gas has peculiar isotopic ratios, revealing that CK Vul's composition was strongly enhanced by the nuclear ashes of hydrogen burning. The chemical composition cannot be reconciled with a nova or indeed any other known explosion. In addition, the mass of the surrounding gas is too large for a nova, though the conversion from observations of CO to a total mass is uncertain. We conclude that CK Vul is best explained as the remnant of a merger of two stars.

  18. Nuclear ashes and outflow in the eruptive star Nova Vul 1670.

    PubMed

    Kamiński, Tomasz; Menten, Karl M; Tylenda, Romuald; Hajduk, Marcin; Patel, Nimesh A; Kraus, Alexander

    2015-04-16

    CK Vulpeculae was observed in outburst in 1670-1672 (ref. 1), but no counterpart was seen until 1982, when a bipolar nebula was found at its location. Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but its similarity to 'red transients', which are more luminous than classical novae and thought to be the results of stellar collisions, has re-opened the question of CK Vul's status. Red transients cool to resemble late M-type stars, surrounded by circumstellar material rich in molecules and dust. No stellar source has been seen in CK Vul, though a radio continuum source was identified at the expansion centre of the nebula. Here we report that CK Vul is surrounded by chemically rich molecular gas in the form of an outflow, as well as dust. The gas has peculiar isotopic ratios, revealing that CK Vul's composition was strongly enhanced by the nuclear ashes of hydrogen burning. The chemical composition cannot be reconciled with a nova or indeed any other known explosion. In addition, the mass of the surrounding gas is too large for a nova, though the conversion from observations of CO to a total mass is uncertain. We conclude that CK Vul is best explained as the remnant of a merger of two stars. PMID:25799986

  19. Young Brown Dwarfs and Giant Planets as Companions to Weak-Line T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Brandner, Wolfgang; Frink, Sabine; Kohler, Rainer; Kunkel, Michael

    Weak-line T Tauri stars, contrary to classical T Tauri stars, no longer possess massive circumstellar disks. In weak-line T Tauri stars, the circumstellar matter was either accreted onto the T Tauri star or has been redistributed. Disk instabilities in the outer disk might result in the formation of brown dwarfs and giant planets. Based on photometric and spectroscopic studies of ROSAT sources, we have selected an initial sample of 200 weak-line T Tauri stars in the Chamaeleon T association and the Scorpius-Centaurus OB association. In the course of follow-up observations, we identified visual and spectroscopic binary stars and excluded them from our final list, as the complex dynamics and gravitational interaction in binary systems might aggravate or even completely inhibit the formation of planets (depending on physical separation of the binary components and their mass ratio). The membership of individual stars to the associations was established from proper motion studies and radial velocity surveys. Our final sample consists of 70 single weak-line T Tauri stars. We have initiated a program to spatially resolve young brown dwarfs and young giant planets as companions to single weak-line T Tauri stars using adaptive optics at the ESO 3.6 m telescope and HST/NICMOS. In this poster we describe the observing strategy and present first results of our adaptive optics observations. An update on the program status can be found at http://www.astro.uiuc.edu/~brandner/text/bd/bd.html

  20. Open Clusters as Laboratories: The Angular Momentum Evolution of Young Stars

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.

    1998-01-01

    The core group concentrated on three primary research topics: (1) ROSAT observation of the coronal activity of low mass stars in young open clusters; (2) the determination of stellar ages and the determination of the timescale for dissipation of circumstellar disks around young stars; and (3) the determination of rotation velocities of low mass stars in young open cluster and the inferred angular momentum evolution of low mass stars. With accurate ages for the clusters, we can then derive an independent estimate of the timescale for debris disks to dissipate. As the second half of that project, we are using the Caltech/UC/NASA Keck telescopes to obtain spectra of brown dwarf candidates in a number of nearby, young open clusters, from which we can determine new and accurate cluster ages. The final primary program that we have addressed was the determination of rotational velocities for low mass stars in our target open clusters. Our group has obtained rotational velocities for a large number of stars in several open clusters during this LTSA program, and we have published the results in several papers. One particularly time-consuming aspect of our program was the development of a database of the photometry and rotational velocities for nearby open clusters, which we have made available to the community.

  1. ACCRETION RATES ON PRE-MAIN-SEQUENCE STARS IN THE YOUNG OPEN CLUSTER NGC 6530

    SciTech Connect

    Gallardo, Jose; Del Valle, Luciano; Ruiz, Maria Teresa E-mail: ldelvall@das.uchile.cl

    2012-01-15

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first {approx}1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the H{sub {alpha}} emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad H{sub {alpha}} emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR.

  2. Spectroscopic Confirmation of Young Stars in the Serpens Molecular Cloud: Placing Spitzer and Chandra in Context

    NASA Astrophysics Data System (ADS)

    Erickson, Kristen; Wilking, Bruce; Meyer, Michael; Sherry, William; Kim, Serena

    2010-02-01

    We propose to complete the first comprehensive spectroscopic survey of young stellar objects associated with the Serpens Main cluster. Already we have obtained optical spectra for 27 Serpens objects with X- ray emission and for the 23 optically brightest objects in the field. An additional 88 spectra have been taken using the WIYN telescope in June of 2009; these spectra are currently undergoing analysis for temperature and surface gravity. Utilizing our deep CCD images of the region obtained in 2007, we have selected 250 candidate young stellar objects, which form an unbiased extinction-limited sample. By observing objects with both blue and red grating settings, we can derive effective temperatures and constrain surface gravities for candidate young stars complete down to 0.3 M_sun with extinctions A_v≤ 5 mag. Using our BVR photometry, we can then derive bolometric luminosities and through comparisons with theoretical tracks and isochrones for young stars, ages and masses. When combined with recent X-ray, infrared and optical surveys of the Serpens region, we will be able to assemble a complete census of young stars, reconstruct the star formation history, estimate disk survival times, and begin investigations into the mass function of this young cluster.

  3. STAR FORMATION HISTORY OF A YOUNG SUPER-STAR CLUSTER IN NGC 4038/39: DIRECT DETECTION OF LOW-MASS PRE-MAIN SEQUENCE STARS

    SciTech Connect

    Greissl, Julia; Meyer, Michael R.; Christopher, Micol H.; Scoville, Nick Z.

    2010-02-20

    We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of {approx}90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.

  4. Star Formation History of a Young Super-Star Cluster in NGC 4038/39: Direct Detection of Low-Mass Pre-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Greissl, Julia; Meyer, Michael R.; Christopher, Micol H.; Scoville, Nick Z.

    2010-02-01

    We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of ≈90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.

  5. A KINEMATIC AND PHOTOMETRIC STUDY OF THE GALACTIC YOUNG STAR CLUSTER NGC 7380

    SciTech Connect

    Chen, W. P.; Chen, C. W.; Pandey, A. K.; Sharma, Saurabh; Chen Li; Sperauskas, J.; Ogura, K.; Chuang, R. J.; Boyle, R. P.

    2011-09-15

    We present proper motions, radial velocities, and a photometric study of the Galactic open cluster NGC 7380, which is associated with prominent emission nebulosity and dark molecular clouds. On the basis of the sample of highly probable member stars, the star cluster is found to be at a distance of 2.6 {+-} 0.4 kpc, has an age of around 4 Myr, and a physical size of {approx}6 pc across with a tidal structure. The binary O-type star DH Cep is a member of the cluster in its late stage of clearing the surrounding material, and may have triggered the ongoing star formation in neighboring molecular clouds which harbor young stars that are coeval and comoving with, but not gravitationally bound by, the star cluster.

  6. Star Formation and Young Stellar Content in the W3 Giant Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Rivera-Ingraham, Alana; Martin, Peter G.; Polychroni, Danae; Moore, Toby J. T.

    2011-12-01

    In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the "Class" scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSO population. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR 140.

  7. Planetary science: Preventing stars from eating their young

    NASA Astrophysics Data System (ADS)

    Duncan, Martin J.

    2015-04-01

    Researchers have found a mechanism that prevents newly forming giant-planet cores from spiralling in towards their parent stars. The result may explain why planets such as Saturn and Jupiter are where they are today. See Letter p.63

  8. On the origin of young stars at the Galactic center

    NASA Astrophysics Data System (ADS)

    Madigan, Ann-Marie; Pfuhl, Oliver; Levin, Yuri; Gillessen, Stefan; Genzel, Reinhard; Perets, Hagai B.

    2014-05-01

    The center of our Galaxy is home to a massive black hole, Sgr A*, and a nuclear star cluster containing stellar populations of various ages. While the late type stars may be too old to have retained memory of their initial orbital configuration, and hence formation mechanism, the kinematics of the early type stars should reflect their original distribution. In this contribution we present a new statistic which uses directly-observable kinematic stellar data to infer orbital parameters for stellar populations, and is capable of distinguishing between different origin scenarios. We use it on a population of B-stars in the Galactic center that extends out to large radii (˜0.5 pc) from the massive black hole. We find that the high K-magnitude population (≲15 M⊙) form an eccentric distribution, suggestive of a Hills binary-disruption origin.

  9. The Mass-Radius Relation of Young Stars from K2

    NASA Astrophysics Data System (ADS)

    Kraus, Adam L.; Cody, Ann Marie; Covey, Kevin R.; Rizzuto, Aaron C.; Mann, Andrew; Ireland, Michael; Jensen, Eric L. N.; Muirhead, Philip Steven

    2016-01-01

    Evolutionary models of pre-main sequence stars remain largely uncalibrated, especially for masses below that of the Sun, and dynamical masses and radii pose valuable tests of these theoretical models. Stellar mass dependent features of star formation (such as disk evolution, planet formation, and even the IMF) are fundamentally tied to these models, which implies a systematic uncertainty that can only be improved with precise measurements of calibrator stars. We will describe the discovery and characterization of ten eclipsing binary systems in the Upper Scorpius star-forming region from K2 Campaign 2 data, spanning from B stars to the substellar boundary. We have obtained complementary RV curves, spectral classifications, and high-resolution imaging for these targets; the combination of these data yield high-precision masses and radii for the binary components, and hence a dense sampling of the (nominally coeval) mass-radius relation of 10 Myr old stars. We already reported initial results from this program for the young M4.5 eclipsing binary UScoCTIO 5 (Kraus et al. 2015), demonstrating that theoretically predicted masses are discrepant by ~50% for low-mass stars. K2's unique radius measurements allow us to isolate the source of the discrepancy: models of young stars do not predict luminosities that are too low, as is commonly thought, but rather temperatures that are too warm.

  10. Optically visible post-AGB stars, post-RGB stars and young stellar objects in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2015-12-01

    We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) stars in the Large Magellanic Cloud (LMC). First, we selected candidates with a mid-IR excess and then obtained their optical spectra. We disentangled contaminants with unique spectra such as M stars, C stars, planetary nebulae, quasi-stellar objects and background galaxies. Subsequently, we performed a detailed spectroscopic analysis of the remaining candidates to estimate their stellar parameters such as effective temperature, surface gravity (log g), metallicity ([Fe/H]), reddening and their luminosities. This resulted in a sample of 35 likely post-AGB candidates with late-G to late-A spectral types, low log g, and [Fe/H] < -0.5. Furthermore, our study confirmed the existence of the dusty post-red giant branch (post-RGB) stars, discovered previously in our Small Magellanic Cloud survey, by revealing 119 such objects in the LMC. These objects have mid-IR excesses and stellar parameters (Teff, log g, [Fe/H]) similar to those of post-AGB stars except that their luminosities (< 2500 L⊙), and hence masses and radii, are lower. These post-RGB stars are likely to be products of binary interaction on the RGB. The post-AGB and post-RGB objects show spectral energy distribution properties similar to the Galactic post-AGB stars, where some have a surrounding circumstellar shell, while some others have a surrounding stable disc similar to the Galactic post-AGB binaries. This study also resulted in a new sample of 162 young stellar objects, identified based on a robust log g criterion. Other interesting outcomes include objects with an UV continuum and an emission line spectrum; luminous supergiants; hot main-sequence stars; and 15 B[e] star candidates, 12 of which are newly discovered in this study.

  11. Chemical Composition of the Magellanic Clouds, from Young to Old Stars

    NASA Astrophysics Data System (ADS)

    Hill, Vanessa

    I review the current state of our knowledge of the detailed chemical composition of the Magellanic Clouds, concentrating on the best probes of detailed elemental abundances, namely individual stars observed by means of high-resolution spectroscopy, probing stellar population of all ages from the oldest (>10 Gyr) stellar generations, intermediate-age populations (1--10 Gyr), and young massive stars, complemented by H ii region abundances.

  12. Star formation in the vicinity of nuclear black holes: young stellar objects close to Sgr A*

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Pelupessy, F. I.; Eckart, A.; Portegies Zwart, S.; Sabha, N.; Borkar, A.; Moultaka, J.; Mui?, K.; Moser, L.

    2014-10-01

    It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across the entire nuclear star cluster of the Milky Way including the region close (<0.5 pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects (<1 Myr). We perform three-dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a 4 106 M? black hole, to constrain the formation and the physical conditions of such groups. The molecular clumps in our models are assumed to be isothermal containing 100 M? in <0.2 pc radius. Such molecular clumps exist in the circumnuclear disc of the Galaxy. In our highly eccentrically orbiting clump, the strong orbital compression of the clump along the orbital radius vector and perpendicular to the orbital plane causes the gas densities to increase to values higher than the tidal density of Sgr A*, which are required for star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust-enshrouded star that may have been formed recently through the mechanism supported by our models.

  13. Simultaneous Spitzer and K2 monitoring of young stars in the Lagoon Nebula

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie; Stauffer, John; Rebull, Luisa; Howell, Steve; Barentsen, Geert; Douglas, Stephanie

    2015-10-01

    We propose to obtain 17 days of Spitzer/IRAC monitoring on disk-bearing members of the 1--2 Myr Lagoon Nebula star cluster (M8), simultaneous with the K2 optical campaign 9 on the same objects June/July 2016. Young stars in this age range are dynamic objects, with highly variable emission at many wavelengths from X-ray to infrared. Variability on day to month timescales originates from the stellar surface, accretion columns, and the inner disk (r~0.1-1 AU), and provides a way to infer structural features that are inaccessible to direct imaging. We aim to monitor a set of several hundred young stars in the optical and infrared at continuous sub-day cadence and 1% or better precision-- a set-up that is only possible with space telescopes. Despite similarity to the Young Stellar Object Variability Project (YSOVAR; cycle 6) and Coordinated Synoptic Investigation of NGC 2264 (CSI 2264; cycle 8), this program is the only one to obtain high quality light curves on higher mass Herbig AeBe stars. In this mass regime, the inner disk and its relationship to the star may be substantially different from the lower mass T Tauri stars previously monitored with Spitzer. We will use the acquired data to determine how variability processes-- and hence inner disk structure-- vary with mass. With the required 2x/day cadence, we request a total of 33.0 hours for this program.

  14. The Dispersal of Young Stars and the Greater Sco-Cen Association

    NASA Astrophysics Data System (ADS)

    Mamajek, E. E.; Feigelson, E. D.

    We review topics related to the dispersal of young stars from their birth-sites, and focus in particular on the entourage of young stars related to the ongoing star-formation event in the Sco-Cen OB association. We conduct a follow-up kinematic study to that presented in Mamajek, Lawson, & Feigelson (2000; ApJ 544, 356) amongst nearby, isolated, young stars. In addition to the eta Cha and TW Hya groups, we find several more intriguing Sco-Cen outlier candidates: most notably β Pic, PZ Tel, HD 199143, and HD 100546. We discuss the connection between Sco-Cen and the southern ``150 pc Conspiracy'' molecular clouds, and in particular, Corona Australis. The kinematic evidence suggests that many of the nearby, isolated ~10 Myr-old stars were born near Sco-Cen during the UCL and LCC starbursts 10-15 Myr ago. We hypothesize that these stars inherited 5-10 km/s velocities moving away from Sco-Cen, either through molecular cloud turbulence, or through formation in molecular clouds associated with the expanding Sco-Cen superbubbles (e.g. Loop I).

  15. M-dwarf rapid rotators and the detection of relatively young multiple M-star systems

    SciTech Connect

    Rappaport, S.; Joss, M.; Sanchis-Ojeda, R. E-mail: mattjoss@mit.edu; and others

    2014-06-20

    We have searched the Kepler light curves of ∼3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, 'sonograms', and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P {sub rot}, of <2 days, and 110 with P {sub rot} < 1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have 3 or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M stars, this could prove a valuable way discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ∼5% occurrence rate of rapid rotation among the ∼3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days.

  16. Buoyancy and g-modes in young superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Passamonti, A.; Andersson, N.; Ho, W. C. G.

    2016-01-01

    We consider the local dynamics of a realistic neutron-star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We derive the equations that govern this problem in full detail, paying particular attention to the input that needs to be provided through the equation of state and distinguishing between normal and superfluid regions. The analysis highlights a number of key issues that should be kept in mind whenever equation of state data is compiled from nuclear physics for use in neutron-star calculations. We provide explicit results for a particular stellar model and a specific nucleonic equation of state, making use of cooling simulations to show how the local wave spectrum evolves as the star ages. Our results show that the composition gradient is effectively dominated by the muons whenever they are present. When the star cools below the superfluid transition, the support for g-modes at lower densities (where there are no muons) is entirely thermal. We confirm the recent suggestion that the g-modes in this region may be unstable, but our results indicate that this instability will be weak and would only be present for a brief period of the star's life. Our analysis accounts for the presence of thermal excitations encoded in entrainment between the entropy and the superfluid component. Finally, we discuss the complete spectrum, including the normal sound waves and, in superfluid regions, the second sound.

  17. Constraints on the low-mass IMF in young super-star clusters in starburst galaxies

    NASA Astrophysics Data System (ADS)

    Greissl, Julia Jennifer

    2010-12-01

    As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (≤ 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field. The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of ≈ 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (≤ 1 M⊙ ) in either of these galaxies.

  18. Young star clusters in the circumnuclear region of NGC 2110

    SciTech Connect

    Durré, Mark; Mould, Jeremy

    2014-03-20

    High-resolution observations in the near infrared show star clusters around the active galactic nucleus (AGN) of the Seyfert 1 NGC 2110, along with a 90 × 35 pc bar of shocked gas material around its nucleus. These are seen for the first time in our imaging and gas kinematics of the central 100 pc with the Keck OSIRIS instrument with adaptive optics. Each of these clusters is two to three times brighter than the Arches cluster close to the center of the Milky Way. The core star formation rate is 0.3 M {sub ☉} yr{sup –1}. The photoionized gas (He I) dynamics imply an enclosed mass of 3-4 × 10{sup 8} M {sub ☉}. These observations demonstrate the physical linkage between AGN feedback, which triggers star formation in massive clusters, and the resulting stellar (and supernovae) winds, which cause the observed [Fe II] emission and feed the black hole.

  19. GRAVITATIONAL SLINGSHOT OF YOUNG MASSIVE STARS IN ORION

    SciTech Connect

    Chatterjee, Sourav; Tan, Jonathan C. E-mail: jt@astro.ufl.edu

    2012-08-01

    The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's {approx}1000 members are: {theta}{sup 1} Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M{sub Sun }; the Becklin-Neugebauer (BN) object, a 30 km s{sup -1} runaway star of {approx}8 M{sub Sun }; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, {approx}15 M{sub Sun} object still accreting gas while also driving a powerful, apparently 'explosive' outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using {approx}10{sup 7} numerical experiments of gravitational interactions of the {theta}{sup 1}C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for {theta}{sup 1}C. Five other observed properties of {theta}{sup 1}C are also consistent with it having ejected BN and altogether we estimate that there is only a {approx}< 10{sup -5} probability that {theta}{sup 1}C has these properties by chance. We conclude that BN was dynamically ejected from the {theta}{sup 1}C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.

  20. HUBBLE IMAGES REVEAL A YOUNG STAR'S DYNAMIC DISK AND JETS

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These images of HH 30 show changes over only a five-year period in the disk and jets of this newborn star, which is about half a million years old. The pictures were taken between 1995 and 2000 with the Wide Field and Planetary Camera 2 aboard NASA's Hubble Space Telescope. Astronomers are interested in the disk because it is probably similar to the one from which the Sun and the planets in our solar system formed. Hubble reveals an edge-on disk (located at the bottom of the images), which appears as a flattened cloud of dust split into two halves by a dark lane. The disk blocks light from the central star. All that is visible is the reflection of the star's light by dust above and below the plane of the disk. The disk's diameter is 450 astronomical units (one astronomical unit equals the Earth-Sun distance). Shadows billions of miles in size can be seen moving across the disk. In 1995 and 2000, the left and right sides of the disk were about the same brightness, but in 1998 the right side was brighter. These patterns may be caused by bright spots on the star or variations in the disk near the star. The dust cloud near the top of these frames is illuminated by the star and reflects changes in its brightness. The star's magnetic field plays a major role in forming the jets (located above and below the disk), which look like streams of water from a fire hose. The powerful magnetic field creates the jets by channeling gas from the disk along the magnetic poles above and below the star. The gaps between the compact knots of gas seen in the jet above the disk indicate that this is a sporadic process. By tracking the motion of these knots over time, astronomers have measured the jet's speed at between 200,000 to 600,000 miles per hour (160,000 and 960,000 kilometers per hour). Oddly, the jet below the disk is moving twice as fast as the one above it. Credits: NASA, Alan Watson (Universidad Nacional Autonoma de Mexico), Karl Stapelfeldt (Jet Propulsion Laboratory), John Krist and Chris Burrows (European Space Agency/Space Telescope Science Institute)

  1. X-RAY VARIABILITY OF {sigma} ORIONIS YOUNG STARS AS OBSERVED WITH ROSAT

    SciTech Connect

    Caballero, J. A.; Lopez-Santiago, J.; De Castro, E.; Cornide, M.

    2009-06-15

    We used the Aladin Virtual Observatory tool and High Resolution Imager ROSAT archival data to search for X-ray variability in scale of days in 23 young stars in the {sigma} Orionis cluster and a background galaxy. Five stars displayed unambiguous flares and had probabilities p {sub var}>> 99% of being actual variables. Two of the detected flares were violent and long lasting, with maximum duration of six days and amplitude of eight times above the quiescent level. We classified another four stars as possible X-ray variables, including the binary system formed by the B2Vp star {sigma} Ori E and its close late-type companion. This makes a minimum frequency of high-amplitude X-ray variability in excess of a day of 39% among {sigma} Orionis stars. The incidence of this kind of X-ray variability seems to be lower among classical T Tauri stars with mid-infrared flux excesses than among fast-rotating, disk-less young stars.

  2. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    SciTech Connect

    Matt, Sean P.; Greene, Thomas P.; Pudritz, Ralph E. E-mail: thomas.p.greene@nasa.gov E-mail: pudritz@physics.mcmaster.ca

    2012-01-20

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  3. Workshop on Physics of Accretion Disks Around Compact and Young Stars

    NASA Technical Reports Server (NTRS)

    Liang, E (Editor); Stepinski, T. F. (Editor)

    1995-01-01

    The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster presentations, and a list of workshop participants. Accretion disks are believed to surround many stars. Some of these disks form around compact stars, such as white dwarfs, neutron stars, or black holes that are members of binary systems and reveal themselves as a power source, especially in the x-ray and gamma regions of the spectrum. On the other hand, protostellar disks are believed to be accretion disks associated with young, pre-main-sequence stars and manifest themselves mostly in infrared and radio observations. These disks are considered to be a natural outcome of the star formation process. The focus of this workshop included theory and observations relevant to accretion disks around compact objects and newly forming stars, with the primary purpose of bringing the two communities together for intellectual cross-fertilization. The nature of the workshop was exploratory, to see how much interaction is possible between distinct communities and to better realize the local potential in this subject. A critical workshop activity was identification and documentation of key issues that are of mutual interest to both communities.

  4. High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

    PubMed

    Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

    2010-02-11

    Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies. PMID:20148033

  5. An Investigation of Three Methods for Determining Young Star Spectral Types

    NASA Astrophysics Data System (ADS)

    Bruhns, Sara; Prato, Lisa A.

    2015-01-01

    We present an investigation of several spectral typing techniques applied to 6 young, low-mass binary systems in the Taurus star-forming region (2 Myr). Spectra of resolution ~2000 were taken in the K band at Keck II using NIRC2 in grism spectroscopy mode where adaptive optics allowed us to resolve subarcsecond separations. We tested three different methods to determine spectral type to compare and contrast the strengths and weaknesses of each method. First, we used fits to standard star spectra to determine spectral types, extinctions, and K-band excesses. This method resulted in anomalously high extinctions not supported in the literature. It was also often difficult to distinguish between best fits. Second, we used the equivalent width ratios of IRTF SpeX standards to determine linear relationships onto which we plotted the equivalent width ratios of our sample stars. This method was complicated by low signal to noise in weak lines and the presence of significant circumstellar material around some of our sample of young stars, which may have inconsistently veiled and skewed our results. Third, we used K-band spectral indices and solar metallicity models to infer effective temperatures for our sample. This promising approach, applicable for the M-type stars in our sample, yields effective temperatures of several hundred degrees Kelvin lower than the other methods. Our main goal in this work is to highlight the uncertainties inherent in the typical procedures used for determining young star spectral types and encourage a concerted effort to define a more accurate and precise approach to the measurement of pre-main sequence effective temperature. Temperature is a fundamental stellar property without which our calibration of young star evolution, and by inference planet formation, is highly uncertain, even in the face of precisely measured stellar masses.

  6. SIM PlanetQuest Key Project Precursor Observations to Detect Gas Giant Planets Around Young Stars

    NASA Technical Reports Server (NTRS)

    Tanner, Angelle; Beichman, Charles; Akeson, Rachel; Ghez, Andrea; Grankin, Konstantin N.; Herbst, William; Hillenbrand, Lynne; Huerta, Marcos; Konopacky, Quinn; Metchev, Stanimir; Mohanty, Subhanjoy; Prato, L.; Simon, Michal

    2008-01-01

    We present a review of precursor observing programs for the SIM PlanetQuest Key project devoted to detecting Jupiter mass planets around young stars. In order to ensure that the stars in the sample are free of various sources of astrometric noise that might impede the detection of planets, we have initiated programs to collect photometry, high contrast images, interferometric data and radial velocities for stars in both the Northern and Southern hemispheres. We have completed a high contrast imaging survey of target stars in Taurus and the Pleiades and found no definitive common proper motion companions within one arcsecond (140 AU) of the SIM targets. Our radial velocity surveys have shown that many of the target stars in Sco-Cen are fast rotators and a few stars in Taurus and the Pleiades may have sub-stellar companions. Interferometric data of a few stars in Taurus show no signs of stellar or sub-stellar companions with separations of <5 mas. The photometric survey suggests that approximately half of the stars initially selected for this program are variable to a degree (1(sigma) >0.1 mag) that would degrade the astrometric accuracy achievable for that star. While the precursor programs are still a work in progress, we provide a comprehensive list of all targets ranked according to their viability as a result of the observations taken to date. By far, the observable that removes the most targets from the SIM-YSO program is photometric variability.

  7. Infrared Observational Manifestations of Young Dusty Super Star Clusters

    NASA Astrophysics Data System (ADS)

    Martínez-González, Sergio; Tenorio-Tagle, Guillermo; Silich, Sergiy

    2016-01-01

    The growing evidence pointing at core-collapse supernovae as large dust producers makes young massive stellar clusters ideal laboratories to study the evolution of dust immersed in a hot plasma. Here we address the stochastic injection of dust by supernovae, and follow its evolution due to thermal sputtering within the hot and dense plasma generated by young stellar clusters. Under these considerations, dust grains are heated by means of random collisions with gas particles which result in the appearance of infrared spectral signatures. We present time-dependent infrared spectral energy distributions that are to be expected from young stellar clusters. Our results are based on hydrodynamic calculations that account for the stochastic injection of dust by supernovae. These also consider gas and dust radiative cooling, stochastic dust temperature fluctuations, the exit of dust grains out of the cluster volume due to the cluster wind, and a time-dependent grain size distribution.

  8. Young and intermediate-age massive star clusters.

    PubMed

    Larsen, Søren S

    2010-02-28

    An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10(5) M(o)) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, dN/dM proportional to M(-2), but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M > 2 x 10(5) M(o). In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several x10(6) M(o). The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation. PMID:20083510

  9. Initial Results From The AO International Deep Planet Search Around Young A Stars

    NASA Astrophysics Data System (ADS)

    Vigan, Arthur; Patience, J.; Galicher, R.; Marois, C.; Macintosh, B.; Song, I.; Doyon, R.; Zuckerman, B.; Lafrenière, D.; Barman, T.

    2011-09-01

    Throughout their evolution, A stars exhibit favorable physical conditions and indirect evidence of planet formation, such as extended protoplanetary disks at the pre-main sequence stage and debris disks in the main sequence phase. Recent breakthrough discoveries of planetary companions around young, dusty A stars have identified the first massive planets at wide orbital separation. In order to understand the frequency of such systems -- an important factor for formation scenarios -- we are conducting a near-infrared adaptive optics search for giant planets around nearby A stars, part the on-going International Deep Planet Search (IDPS). We present the preliminary results of this survey of 40 stars: 28 of them are nearby (<65 pc) young (<200 Myr) A stars, and the others are star identified as extremely young (<20 Myr) from spectral analysis. The observations were obtained with 8 meter-class telescopes (VLT and Gemini). The Locally Optimized Combination of Images (LOCI) was used to suppress the speckle noise of the central star and reach the detection level of giant planets and low-mass brown dwarfs at wide orbital separation. The median 5-sigma sensitivity of our observations is 9.5 mag at 0.5 arcseconds and 14 mag at separations of a few arcseconds, allowing us to reach limits 1 to 20 Mjup, depending on the target mass and age. We present an overview of the observations, data analysis and performance, followed by a statistical analysis of the survey results, which provide upper limits on the fractions of stars with giant planet and low mass brown dwarf companions.

  10. On the velocity dispersion of young star clusters: super-virial or binaries?

    NASA Astrophysics Data System (ADS)

    Gieles, M.; Sana, H.; Portegies Zwart, S. F.

    2010-03-01

    Many young extra-galactic clusters have a measured velocity dispersion that is too high for the mass derived from their age and total luminosity, which has led to the suggestion that they are not in virial equilibrium. Most of these clusters are confined to a narrow age range centred around 10Myr because of observational constraints. At this age, the cluster light is dominated by luminous evolved stars, such as red supergiants, with initial masses of ~13-22Msolar for which (primordial) binarity is high. In this study, we investigate to what extent the observed excess velocity dispersion is the result of the orbital motions of binaries. We demonstrate that estimates for the dynamical mass of young star clusters, derived from the observed velocity dispersion, exceed the photometric mass by up to a factor of 10 and are consistent with a constant offset in the square of the velocity dispersion. This can be reproduced by models of virialized star clusters hosting a massive star population of which ~25 per cent is in binaries, with typical mass ratios of ~0.6 and periods of ~1000 d. We conclude that binaries play a pivotal role in deriving the dynamical masses of young (~10Myr), moderately massive and compact (<~105Msolar >~1pc) star clusters.

  11. Photometry and Polarization of the UXor Type Young Star GM Cep

    NASA Astrophysics Data System (ADS)

    Huang, Po-Chieh; Chen, Chang-Yao; Hu, Chia-Ling; Chen, Wen-Ping

    2015-08-01

    UX Orionis stars, or UXORs, are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such a UXOR in the young (~4 Myr) open cluster Trumper 37 at ~900 pc, showing prominent infrared access, H-alpha emission, and abrupt brightness variation. Here we present intense multi-color photometric monitoring from 2009 to 2015, together with the century-long photometric behavior reported in the literature, to add to the study by Chen et al. (2012) that GM Cep showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual “blueing” phenomena near the brightness minima when the star appeared bluer when dimmer. The occultation events may be caused by a dust clump, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. We present evidence of possible radial drift of the clump toward the star, stretching longer along the orbit and thinner in the line of sight. GM Cep is moderately polarized, from 4% to 9% in g, r, and i bands, with the level of polarization anticorrelated with the brightness in the bright state, during which the dust clump is back-scattering stellar light.

  12. Analysis of MOST light curves of five young stars in Taurus-Auriga and Lupus 3 star-forming regions

    NASA Astrophysics Data System (ADS)

    Siwak, Michal; Rucinski, Slavek M.; Matthews, Jaymie M.; Kuschnig, Rainer; Guenther, David B.; Moffat, Anthony F. J.; Sasselov, Dimitar; Weiss, Werner W.

    2011-08-01

    Continuous photometric observations of five young stars obtained by the MOST satellite in 2009 and 2010 in the Taurus and Lupus star formation regions are presented. Using light-curve modelling under the assumption of internal invariability of spots, we obtained small values of the solar-type differential-rotation parameter (k = 0.0005-0.009) for three spotted weak-line T Tauri stars, V410 Tau, V987 Tau and Lupus 3-14; for another spotted weak-line T Tauri star (WTTS), Lupus 3-48, the data are consistent with a rigidly rotating surface (k = 0). Three flares of similar rise (4 min and 30 s) and decay (1 h and 45 min) times were detected in the light curve of Lupus 3-14. The brightness of the classical T Tauri star RY Tau continuously decreased over 3 weeks of its observations with a variable modulation not showing any obvious periodic signal. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute of Aerospace Studies and the University of British Columbia, with the assistance of the University of Vienna.

  13. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    SciTech Connect

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

    2010-09-10

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with H{alpha} excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with H{alpha} excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  14. Accretion Disks around Young Stars: An Observational Perspective

    NASA Astrophysics Data System (ADS)

    Ménard, F.; Bertout, C.

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today to understand the mechanism leading to the formation of planets.

  15. A NEW SUB-STELLAR COMPANION AROUND THE YOUNG STAR HD 284149

    SciTech Connect

    Bonavita, Mariangela; Desidera, Silvano; Daemgen, Sebastian; Jayawardhana, Ray; Janson, Markus; Lafrenire, David

    2014-08-20

    Even though only a handful of sub-stellar companions have been found via direct imaging, each of these discoveries has had a tremendous impact on our understanding of the star formation process and the physics of cool atmospheres. Young stars are prime targets for direct imaging searches for planets and brown dwarfs due to the favorable brightness contrast expected at such ages and also because it is often possible to derive relatively good age estimates for these primaries. Here we present the direct imaging discovery of HD 284149 b, a 18-50 M {sub Jup} companion at a projected separation of 400AU from a young (25{sub 10}{sup +25}Myr) F8 star, with which it shares common proper motion.

  16. Is the 1.5-ms pulsar a young neutron star?

    NASA Technical Reports Server (NTRS)

    Blondin, John M.; Freese, Katherine

    1986-01-01

    It is proposed that PSR1937 + 214 is a young neutron star spun up by accretion from a high-mass companion in a close binary system. The supercritical mass transfer rates expected in such a binary system should allow the neutron star to be spun up in the comparatively short time of about 10,000 yr. The accretion process will also power thermomagnetic effects that could remove the strong magnetic field of a young pulsar from the crust of the star in a similarly short timescale. Such a high-mass binary system is expected to disrupt when the companion explodes in a supernova. Thus a spin-up model in a high-mass system can explain the lack of a companion, low magnetic field, and high spin rate of PSR1937 + 214.

  17. COOL YOUNG STARS IN THE NORTHERN HEMISPHERE: {beta} PICTORIS AND AB DORADUS MOVING GROUP CANDIDATES

    SciTech Connect

    Schlieder, Joshua E.; Simon, Michal; Lepine, Sebastien E-mail: schlieder@mpia-hd.mpg.de

    2012-04-15

    As part of our continuing effort to identify new, low-mass members of nearby, young moving groups (NYMGs), we present a list of young, low-mass candidates in the northern hemisphere. We used our proven proper-motion selection procedure and ROSAT X-ray and GALEX-UV activity indicators to identify 204 young stars as candidate members of the {beta} Pictoris and AB Doradus NYMGs. Definitive membership assignment of a given candidate will require a measurement of its radial velocity and distance. We present a simple system of indices to characterize the young candidates and help prioritize follow-up observations. New group members identified in this candidate list will be high priority targets for (1) exoplanet direct imaging searches, (2) the study of post-T-Tauri astrophysics, (3) understanding recent local star formation, and (4) the study of local galactic kinematics. Information available now allows us to identify eight likely new members in the list. Two of these, a late-K and an early-M dwarf, we find to be likely members of the {beta} Pic group. The other six stars are likely members of the AB Dor moving group. These include an M dwarf triple system, and three very cool objects that may be young brown dwarfs, making them the lowest-mass, isolated objects proposed in the AB Dor moving group to date.

  18. Distances with <4% precision from type Ia supernovae in young star-forming environments.

    PubMed

    Kelly, Patrick L; Filippenko, Alexei V; Burke, David L; Hicken, Malcolm; Ganeshalingam, Mohan; Zheng, WeiKang

    2015-03-27

    The luminosities of type Ia supernovae (SNe), the thermonuclear explosions of white-dwarf stars, vary systematically with their intrinsic color and the rate at which they fade. From images taken with the Galaxy Evolution Explorer (GALEX), we identified SNe Ia that erupted in environments that have high ultraviolet surface brightness and star-formation surface density. When we apply a steep model extinction law, we calibrate these SNe using their broadband optical light curves to within ~0.065 to 0.075 magnitude, corresponding to <4% in distance. The tight scatter, probably arising from a small dispersion among progenitor ages, suggests that variation in only one progenitor property primarily accounts for the relationship between their light-curve widths, colors, and luminosities. PMID:25814580

  19. Infrared Spectroscopic Studies of Water and Organics in Protoplanetary Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin; Forrest, William; Watson, Dan M.; Calvet, Nuria; Furlan, Elise; Kim, Kyoung-Hee; Green, Joel; Pontoppidan, Klaus Martin; Tayrien, Cyprian

    2015-08-01

    The building blocks of planets in planet-forming ("protoplanetary") disks are assembled early in the lifetime of a young star. The gas disks are relatively short-lived, with a half-life of about 3 million years, as chemical reactions modify the reservoir of material from the natal molecular cloud. 5 - 7.5 ?m wavelength Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of about a dozen T Tauri stars in the Taurus-Auriga star-forming region showing emission from water vapor and absorption from other gases in these stars' protoplanetary disks will be presented. Some of these stars' spectra show a strong emission manifold at 6.6 ?m due to the nu2 = 1 - 0 bending mode of water vapor, with the shape of the spectrum suggesting water vapor temperatures > 500 K. Other stars' spectra show a strong absorption band, peaking in strength at 5.6 - 5.7 ?m, which appears consistent in some cases with gaseous formaldehyde (H2CO) and in other cases with formic acid (HCOOH). Modeling of these stars' spectra suggests these gases are present in the inner few AU -- i.e., in the planet-forming regions -- of their disks. How the gaseous features observed between 5 - 7.5 ?m relate to those at other wavelengths will be discussed. Future directions for this research, including both pursuing confirmation of HCOOH and H2CO features at these and other wavelengths and modeling of the gas features at these wavelengths in other Spitzer-IRS spectra of protoplanetary disks around young stars, will also be discussed. This work suggests that water and organic molecules, which are crucial for life as we know it, are present in the habitable zones of stars at a very early age [of 1-3 million years].

  20. Magnetic fields on young, moderately rotating Sun-like stars - I. HD 35296 and HD 29615

    NASA Astrophysics Data System (ADS)

    Waite, I. A.; Marsden, S. C.; Carter, B. D.; Petit, P.; Donati, J.-F.; Jeffers, S. V.; Boro Saikia, S.

    2015-05-01

    Observations of the magnetic fields of young solar-type stars provide a way to investigate the signatures of their magnetic activity and dynamos. Spectropolarimetry enables the study of these stellar magnetic fields and was thus employed at the Télescope Bernard Lyot and the Anglo-Australian Telescope to investigate two moderately rotating young Sun-like stars, namely HD 35296 (V119 Tau, HIP 25278) and HD 29615 (HIP 21632). The results indicate that both stars display rotational variation in chromospheric indices consistent with their spot activity, with variations indicating a probable long-term cyclic period for HD 35296. Additionally, both stars have complex, and evolving, large-scale surface magnetic fields with a significant toroidal component. High levels of surface differential rotation were measured for both stars. For the F8V star HD 35296 a rotational shear of ΔΩ = 0.22^{+0.04}_{-0.02} rad d- 1 was derived from the observed magnetic profiles. For the G3V star HD 29615, the magnetic features indicate a rotational shear of ΔΩ = 0.48_{-0.12}^{+0.11} rad d- 1, while the spot features, with a distinctive polar spot, provide a much lower value of ΔΩ of 0.07_{-0.03}^{+0.10} rad d- 1. Such a significant discrepancy in shear values between spot and magnetic features for HD 29615 is an extreme example of the variation observed for other lower mass stars. From the extensive and persistent azimuthal field observed for both targets, it is concluded that a distributed dynamo operates in these moderately rotating Sun-like stars, in marked contrast to the Sun's interface-layer dynamo.

  1. Vertical Structure of Magnetized Accretion Disks Around Young Stars

    NASA Astrophysics Data System (ADS)

    Tapia, Carlos; Lizano, Susana

    2016-01-01

    We model the vertical structure of magnetized accretion disks subject to viscous and resistive heating, and irradiation by the central star. We apply our formalism to the radial structure of magnetized accretion disks threaded by a poloidal magnetic field dragged during the process of star formation developed by Shu and coworkers. We consider disks around low mass protostars, T Tauri, and FU Orionis stars. We consider two levels of disk magnetization, λsys = 4 (strongly magnetized disks), and λsys = 12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk. The T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (~ 90 - 95 %) is in the disk midplane.

  2. Star formation triggered by supernova explosions in young galaxies

    NASA Astrophysics Data System (ADS)

    Nagakura, Takanori; Hosokawa, Takashi; Omukai, Kazuyuki

    2009-11-01

    We study the evolution of supernova remnants in a low-metallicity medium Z/Zsolar = 10-4 to 10-2 in the early universe, using one-dimensional hydrodynamics with non-equilibrium chemistry. Once a post-shock layer is able to cool radiatively, a dense shell forms behind the shock. If this shell becomes gravitationally unstable and fragments into pieces, next-generation stars are expected to form from these fragments. To explore the possibility of this triggered star formation, we apply a linear perturbation analysis of an expanding shell to our results and constrain the parameter range of ambient density, explosion energy and metallicity where fragmentation of the shell occurs. For the explosion energy of 1051 erg (1052 erg), the shell fragmentation occurs for ambient densities higher than >~102 cm-3 (10 cm-3), respectively. This condition depends little on the metallicity in the ranges we examined. We find that the mode of star formation triggered occurs only in massive (>~108Msolar) haloes.

  3. Determining the Locations of Brown Dwarfs in Young Star Clusters

    NASA Technical Reports Server (NTRS)

    Porter, Lauren A.

    2005-01-01

    Brown dwarfs are stellar objects with masses less than 0.08 times that of the Sun that are unable to sustain nuclear fusion. Because of the lack of fusion, they are relatively cold, allowing the formation of methane and water molecules in their atmospheres. Brown dwarfs can be detected by examining stars' absorption spectra in the near-infrared to see whether methane and water are present. The objective of this research is to determine the locations of brown dwarfs in Rho Ophiuchus, a star cluster that is only 1 million years old. The cluster was observed in four filters in the near-infrared range using the Wide-Field Infra-Red Camera (WIRC) on the 100" DuPont Telescope and Persson's Auxiliary Nasymith Infrared Camera (PANIC) on the 6.5-m Magellan Telescope. By comparing the magnitude of a star in each of the four filters, an absorption spectrum can be formed. This project uses standard astronomical techniques to reduce raw frames into final images and perform photometry on them to obtain publishable data. Once this is done, it will be possible to determine the locations and magnitudes of brown dwarfs within the cluster.

  4. THE NEARBY, YOUNG, ISOLATED, DUSTY STAR HD 166191

    SciTech Connect

    Schneider, Adam; Song, Inseok; Hufford, Tara; Melis, Carl; Zuckerman, B.; Bessell, Mike; Hinkley, Sasha E-mail: song@physast.uga.edu E-mail: cmelis@ucsd.edu E-mail: bessell@mso.anu.edu.au

    2013-11-01

    We report an in-depth study of the F8-type star HD 166191, identified in an ongoing survey for stars exhibiting infrared emission above their expected photospheres in the Wide-field Infrared Survey Explorer all-sky catalog. The fractional IR luminosity measured from 3.5 to 70 μm is exceptionally high (L{sub IR}/L{sub bol} ∼ 10%). Near-diffraction-limited imaging observations with the T-ReCS Si filter set on the Gemini South telescope and adaptive optics imaging with the NIRC2 Lp filter on the Keck II telescope confirmed that the excess emission coincides with the star. Si-band images show a strong solid-state emission feature at ∼10 μm. Theoretical evolutionary isochrones and optical spectroscopic observations indicate a stellar age in the range 10-100 Myr. The large dust mass seen in HD 166191's terrestrial planet zone is indicative of a recent collision between planetary embryos or massive ongoing collisional grinding associated with planet building.

  5. The Nearby, Young, Isolated, Dusty Star HD 166191

    NASA Astrophysics Data System (ADS)

    Schneider, Adam; Song, Inseok; Melis, Carl; Zuckerman, B.; Bessell, Mike; Hufford, Tara; Hinkley, Sasha

    2013-11-01

    We report an in-depth study of the F8-type star HD 166191, identified in an ongoing survey for stars exhibiting infrared emission above their expected photospheres in the Wide-field Infrared Survey Explorer all-sky catalog. The fractional IR luminosity measured from 3.5 to 70 μm is exceptionally high (L IR/L bol ~ 10%). Near-diffraction-limited imaging observations with the T-ReCS Si filter set on the Gemini South telescope and adaptive optics imaging with the NIRC2 Lp filter on the Keck II telescope confirmed that the excess emission coincides with the star. Si-band images show a strong solid-state emission feature at ~10 μm. Theoretical evolutionary isochrones and optical spectroscopic observations indicate a stellar age in the range 10-100 Myr. The large dust mass seen in HD 166191's terrestrial planet zone is indicative of a recent collision between planetary embryos or massive ongoing collisional grinding associated with planet building.

  6. An Infrared Radial Velocity Search for 'Hot Jupiters' Around Young Stars

    NASA Astrophysics Data System (ADS)

    Cantrell, Justin R.; White, Russel; Ira Bailey, John

    2016-01-01

    We present initial findings from our infrared RV survey of young stars in search of young hot Jupiters utilizing high dispersion IR (2.3micron) spectra from Gemini South Phoenix, VLT CRIRES and Keck NIRSPEC. Our technique uses telluric features as an absolute wavelength reference, allowing us to achieve a precision of ~40m/s for slowly rotating field stars. Although RV jitter is lower at IR wavelengths, it is still ~100m/s, thus limiting our sensitivity to hot Jupiters. With this survey of young (8-12Myr) associations using multi-epoch RV data, we hope to to put constraints on the current theories of formation and early migration as it allows for the detection of planets in the process of formation, or soon after they have formed.

  7. BAYESIAN ANALYSIS TO IDENTIFY NEW STAR CANDIDATES IN NEARBY YOUNG STELLAR KINEMATIC GROUPS

    SciTech Connect

    Malo, Lison; Doyon, Rene; Lafreniere, David; Artigau, Etienne; Gagne, Jonathan; Baron, Frederique; Riedel, Adric E-mail: doyon@astro.umontreal.ca E-mail: artigau@astro.umontreal.ca E-mail: baron@astro.umontreal.ca

    2013-01-10

    We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the {beta} Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as H{alpha} and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in {beta} Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for {beta} Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 A equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the {beta} Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.

  8. Accretion Rates on Pre-main-sequence Stars in the Young Open Cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    Gallardo, José; del Valle, Luciano; Ruiz, María Teresa

    2012-01-01

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first ~1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the Hα emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad Hα emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  9. PRECISE HIGH-CADENCE TIME SERIES OBSERVATIONS OF FIVE VARIABLE YOUNG STARS IN AURIGA WITH MOST

    SciTech Connect

    Cody, Ann Marie; Tayar, Jamie; Hillenbrand, Lynne A.; Matthews, Jaymie M.; Kallinger, Thomas

    2013-03-15

    To explore young star variability on a large range of timescales, we have used the MOST satellite to obtain 24 days of continuous, sub-minute cadence, high-precision optical photometry on a field of classical and weak-lined T Tauri stars (TTSs) in the Taurus-Auriga star formation complex. Observations of AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal brightness fluctuations at the 1%-10% level on timescales of hours to weeks. We have further assessed the variability properties with Fourier, wavelet, and autocorrelation techniques, identifying one significant period per star. We present spot models in an attempt to fit the periodicities, but find that we cannot fully account for the observed variability. Rather, all stars exhibit a mixture of periodic and aperiodic behavior, with the latter dominating stochastically on timescales less than several days. After removal of the main periodicity, periodograms for each light curve display power-law trends consistent with those seen for other young accreting stars. Several of our targets exhibited unusual variability patterns not anticipated by prior studies, and we propose that this behavior originates with the circumstellar disks. The MOST observations underscore the need for investigation of TTS light variations on a wide range of timescales in order to elucidate the physical processes responsible; we provide guidelines for future time series observations.

  10. YOUNG STARS IN AN OLD BULGE: A NATURAL OUTCOME OF INTERNAL EVOLUTION IN THE MILKY WAY

    SciTech Connect

    Ness, M.; Debattista, Victor P.; Cole, D. R.; Bensby, T.; Feltzing, S.; Roškar, R.; Johnson, J. A.; Freeman, K.

    2014-06-01

    The center of our disk galaxy, the Milky Way, is dominated by a boxy/peanut-shaped bulge. Numerous studies of the bulge based on stellar photometry have concluded that the bulge stars are exclusively old. The perceived lack of young stars in the bulge strongly constrains its likely formation scenarios, providing evidence that the bulge is a unique population that formed early and separately from the disk. However, recent studies of individual bulge stars using the microlensing technique have reported that they span a range of ages, emphasizing that the bulge may not be a monolithic structure. In this Letter we demonstrate that the presence of young stars that are located predominantly nearer to the plane is expected for a bulge that has formed from the disk via dynamical instabilities. Using an N-body+ smoothed particle hydrodynamics simulation of a disk galaxy forming out of gas cooling inside a dark matter halo and forming stars, we find a qualitative agreement between our model and the observations of younger metal-rich stars in the bulge. We are also able to partially resolve the apparent contradiction in the literature between results that argue for a purely old bulge population and those that show a population comprised of a range in ages; the key is where to look.

  11. Young Stars in an Old Bulge: A Natural Outcome of Internal Evolution in the Milky Way

    NASA Astrophysics Data System (ADS)

    Ness, M.; Debattista, Victor P.; Bensby, T.; Feltzing, S.; Roškar, R.; Cole, D. R.; Johnson, J. A.; Freeman, K.

    2014-06-01

    The center of our disk galaxy, the Milky Way, is dominated by a boxy/peanut-shaped bulge. Numerous studies of the bulge based on stellar photometry have concluded that the bulge stars are exclusively old. The perceived lack of young stars in the bulge strongly constrains its likely formation scenarios, providing evidence that the bulge is a unique population that formed early and separately from the disk. However, recent studies of individual bulge stars using the microlensing technique have reported that they span a range of ages, emphasizing that the bulge may not be a monolithic structure. In this Letter we demonstrate that the presence of young stars that are located predominantly nearer to the plane is expected for a bulge that has formed from the disk via dynamical instabilities. Using an N-body+ smoothed particle hydrodynamics simulation of a disk galaxy forming out of gas cooling inside a dark matter halo and forming stars, we find a qualitative agreement between our model and the observations of younger metal-rich stars in the bulge. We are also able to partially resolve the apparent contradiction in the literature between results that argue for a purely old bulge population and those that show a population comprised of a range in ages; the key is where to look.

  12. Modeling tracers of young stellar population age in star-forming galaxies

    SciTech Connect

    Levesque, Emily M.; Leitherer, Claus

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  13. Young Stellar Objects in the Massive Star-forming Region W49

    NASA Astrophysics Data System (ADS)

    Saral, G.; Hora, J. L.; Willis, S. E.; Koenig, X. P.; Gutermuth, R. A.; Saygac, A. T.

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color-color and color-magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

  14. Formation of new stellar populations from gas accreted by massive young star clusters.

    PubMed

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters. PMID:26819043

  15. Formation of new stellar populations from gas accreted by massive young star clusters

    NASA Astrophysics Data System (ADS)

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M.; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-01

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old ‘globular’ clusters—those with ages greater than ten billion years and masses several hundred thousand times that of the Sun—often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies’ gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  16. Are superluminous supernovae and long GRBs the products of dynamical processes in young dense star clusters?

    SciTech Connect

    Van den Heuvel, E. P. J.; Portegies Zwart, S. F.

    2013-12-20

    Superluminous supernovae (SLSNe) occur almost exclusively in small galaxies (Small/Large Magellanic Cloud (SMC/LMC)-like or smaller), and the few SLSNe observed in larger star-forming galaxies always occur close to the nuclei of their hosts. Another type of peculiar and highly energetic supernovae are the broad-line Type Ic SNe (SN Ic-BL) that are associated with long-duration gamma-ray bursts (LGRBs). Also these have a strong preference for occurring in small (SMC/LMC-like or smaller) star-forming galaxies, and in these galaxies LGRBs always occur in the brightest spots. Studies of nearby star-forming galaxies that are similar to the hosts of LGRBs show that these brightest spots are giant H II regions produced by massive dense young star clusters with many hundreds of O- and Wolf-Rayet-type stars. Such dense young clusters are also found in abundance within a few hundred parsecs from the nucleus of larger galaxies like our own. We argue that the SLSNe and the SNe Ic-BL/LGRBs are exclusive products of two types of dynamical interactions in dense young star clusters. In our model the high angular momentum of the collapsing stellar cores required for the engines of an SN Ic-BL results from the post-main-sequence mergers of dynamically produced cluster binaries with almost equal-mass components. The merger produces a critically rotating single helium star with sufficient angular momentum to produce an LGRB; the observed 'metal aversion' of LGRBs is a natural consequence of the model. We argue that, on the other hand, SLSNe could be the products of runaway multiple collisions in dense clusters, and we present (and quantize) plausible scenarios of how the different types of SLSNe can be produced.

  17. Stellar Masses in the Mysterious Young Triple Star System AS 205

    NASA Astrophysics Data System (ADS)

    Encalada, Frankie; Rosero, Viviana A.; Prato, Lisa A.; Bruhns, Sara

    2015-01-01

    The lack of accurate absolute mass measurements for young, low-mass pre-main sequence stars is problematic for the calibration of stellar evolutionary track models. An on-going program to increase the sample of young star masses begins with mass ratio measurements in spectroscopic binaries. By the end of its 5-year duration, the GAIA all-sky mission will provide new astrometric measurements for young spectroscopic binaries down to separations of tens of microarcseconds, yielding absolute masses for double-lined systems. We obtain mass ratios by taking high-resolution spectra of young double-lined spectroscopic binaries over a few epochs to construct a radial velocity versus phase diagram. For the young spectroscopic binary AS 205B, using eight of our own spectra supplied by the CSHELL instrument on the IRTF at Mauna Kea, plus one from the literature, we estimate a period of approximately 140 days, an eccentricity of 0.7, and a mass-ratio of 0.5. This spectroscopic system comprises the secondary in a 1.4'' visual binary in which both the A and B components are surrounded by optically thick, actively accreting disks, making AS 205B a member of that rare class of young spectroscopic binaries with a primordial circumbinary disk.

  18. A M2FS Spectroscopic Study of Low-mass Young Stars in Orion OB1

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

    2015-01-01

    Surveys of pre-main sequence stars in the ~4-10 Myr range provide a window into the decline of the accretion phase of stars and the formation of planets. Nearby star clusters and stellar associations allow for the study of these young stellar populations all the way down to the lowest mass members. One of the best examples of nearby 4-10 Myr old stellar populations is the Orion OB1 association. The CIDA Variability Survey of Orion OB1 (CVSO - Briceño et al. 2001) has used the variability properties of low-mass pre-main-sequence (PMS) stars to identify hundreds of K and M-type stellar members of the Orion OB1 association, a number of them displaying IR-excess emission and thought to be representative of more evolved disk-bearing young stars. Characterizing these young, low-mass objects using spectroscopy is integral to understanding the accretion phase in young stars. We present preliminary results of a spectroscopic survey of candidate and confirmed Orion OB1 low-mass members taken during November 2014 and February 2014 using the Michigan/Magellan Fiber Spectrograph (M2FS), a PI instrument on the Magellan Clay Telescope (PI: M. Matteo). Target fields located in the off-cloud regions of Orion were identified in the CVSO, and observed using the low and high-resolution modes of M2FS. Both low and high-resolution spectra are needed in order to confirm membership and derive masses, ages, kinematics and accretion properties. Initial analysis of these spectra reveal many new K and M-type members of the Orion OB1 association in these low extinction, off-cloud areas. These are the more evolved siblings of the youngest stars still embedded in the molecular clouds, like those in the Orion Nebula Cluster. With membership and spectroscopic indicators of accretion we are building the most comprehensive stellar census of this association, enabling us to derive a robust estimate of the fraction of young stars still accreting at a various ages, a key constraint for the end of accretion and the formation of giant planets.

  19. The ultraviolet spectra of the O and B stars in the young galactic cluster NGC 6530

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.; Hodge, P.; Boggs, D.

    1984-01-01

    The UV spectra between 1200 and 3000 A of stars in the young galactic cluster NGC 6530 and the surrounding association are studied. From the UBV colors and empirical as well as theoretical calibrations, the T(eff) and L for those stars which follow a sequence in the H-R diagram corresponding to the main sequence are determined. From a comparison with theoretical evolutionary tracks, the age of the cluster is estimated to be 5 + or - 2 x 10 to the 6th yr, with a very small scatter for the different stars. The UV extinction is determined for the stars from a comparison of theoretical model energy distributions for the stellar T(eff)s and the observed energy distributions. The stellar wind lines are studied, and strong stellar winds are found for bolometric magnetidues less than -8.

  20. Mass Ejection from Old and Young Stars and the Sun

    NASA Astrophysics Data System (ADS)

    Jatenco-Pereira, V.; Opher, R.

    1990-11-01

    RESUMEN. Para poder explicar: 1) la enorme cantidad de perdida de masa y la baja velocidad asint5tica de las estrellas gigantes de o, y 2) los flujos de masa observados en protoestrellas, se sugiere un modelo para Ia perdida de masa, en donde se usa un flujo de ondas de Alfvencomo un mecanismo de aceleraci6n para los vientos de estrellas de tipo y vientos en protoestrellas. Se estudian los mecanismos de disipaci5n de las ondas de Alfven: los amortiguamientos no lineal, de superficie reso- nante y turbulento. En nuestro modelo se usa una divergente A(r) = A(R0) (r/r0)5 (donde A(r) es el area a una distancia radial r, y (A(r)/r2)max/(A(ro)/r02 - 10). Tambien se sugiere un modelo para una de hoyo coronal en el Sol. Se muestra que para satisfacer los datos observacionales en el Sol, tomando en cuenta la deposici6n del momento de las ondas de Alfven sobre el viento, se necesita: (a) una divergencia lenta en un hoyo coronal hasta una altura de 0.01 - 0.1 R seguido de (b) una divergencia rap ida de hasta una altura aproximada de 1 R . ABSTRACT: In order to explain (1) a large mass-loss rate and a small asymptotic flow speed of late-type giant stars and (2) the observed protostellar mass outflows, we suggest a model for mass loss, where we use a flux of Alfven waves as a mechanism of acceleration for late-type giant star winds and protostellar winds. We study the Alfven wave dissipation mechanisms: nonlinear damping, resonant surface damping, and turbulent damping. In our model we use a diverging geometry A(r) = A(r0) (r I r )S (where A(r) is the cross sectional area of the geometry at a radial distance r, and(A(r) I r2)max/(A(r0)/r02) = 10). We also suggest a model for a coronal hole geometry in the sun. We show that in order to satisfy the observational data of the sun, taking into account Alfven wave momentum deposition in the wind, we need: (a) a slow divergence in a coronal hole up t6 a height of 0.01 - 0.1 followed by (b) a rapid divergence up to a height of approximately 1 Re Key : '? #TICS - STARS-LATE TYPE - STARS- LOSS

  1. Deep HST/ACS Photometry of an Arc of Young Stars in the Southern Halo of M82

    NASA Astrophysics Data System (ADS)

    Suwannajak, Chutipong

    2016-01-01

    We present deep HST/ACS photometry of an arclike, overdense region of stars in the southern halo of M82, located approximately 5 kpc from its disk. This arc feature was originally identified about a decade ago. The early ground-based studies suggested that it contains young stars with ages and metallicities similar to those that formed in the tidal tails between M81, M82, and NGC3077 during their interactions. The arc is clearly presented in the spatial distribution of stars in our field with significantly higher stellar density than the background M82 halo stars. The location of the tip of the red giant branch (RGB) reveals the arc to have a similar distance to M81 and M82, therefore confirming that it belongs to this interacting system. Combining our data with those from the ACS Nearby Galaxy Survey Treasury (ANGST), we construct a color-magnitude diagram (CMD) for the arc. A sequence of young stars is clearly presented on its CMD. This young main sequence is not seen in other parts of the M82 halo. Single-metallicity isochrones are used to derive the age of the young stars in the arc. We confirm that these stars exhibit ages consistent with young stars found in the HI bridges between M81, M82 and NGC3077. Furthermore, the mean metallicity of the RGB stars is also derived from their metallicity distribution function and found to be similar to that found in the HI bridges.

  2. Uncovering the Properties of Young Neutron Stars and their Surrounding Supernova Remnants

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald J. (Technical Monitor); Slane, Patrick O.

    2004-01-01

    This five-year grant involves the study of young neutron stars, particularly those in supernova remnants.In the fourth year of this program, the following studies have been undertaken in support of this effort: 1.CTA 1: Following up on our ROSAT and ASCA studies of this SNR, we obtained observations with the XMM-Newton observatory to investigate the central compact source and surrounding nebula. 2. 3C 58: Based upon our earlier Chandra observations, we submitted a successful Chandra Large Project proposal for a 350 ks observation of this young neutron star and its wind nebula. 3. G347.3 - - 0.5: Our Chandra observations of portions of this SNR were aimed at studying the nonthermal X-ray emission from the remnant shell. 4. Chandra Survey for Compact Objects in Supernova Remnants: We have formed a collaboration to carry out an extensive search for young neutron stars in nearby supernova remnants. Using X-ray observations from an approved Chandra Large Project, as well as from additional approved XMM observations, we are investigating a volume-limited sample of SNRs for which there is currently no evidence of associated neutron stars.

  3. Spitzer and Variable Young Stars: Shining a Spotlight on Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie; CSI 2264 Team

    2014-01-01

    Since its launch in 2003, the Spitzer Space Telescope has helped to uncover hundreds of disk bearing young stars in clusters by detecting their infrared excesses. Study of the spectral energy distributions of these objects has shed light on disk evolution, dispersal, and the relationship to planet formation. With the start of the Warm Spitzer Mission, mid-infrared time series observations have opened up a new window into the dynamic nature of these systems. Not only are young stellar objects (YSOs) highly variable, but so are their disks! I will review recent findings on mid-infrared variability in young stars, highlighting the Young Stellar Object Variability project and the joint Spitzer/CoRoT Coordinated Synoptic Investigation of NGC 2264. These efforts have resulted in a comprehensive census and categorization of YSO flux behavior at 0.5 through 4.5 microns, on timescales from hours to months. We now have evidence for multiple simultaneous variability mechanisms, supporting the picture of a highly dynamic star-disk system.

  4. YOUNG STELLAR OBJECTS AND TRIGGERED STAR FORMATION IN THE VULPECULA OB ASSOCIATION

    SciTech Connect

    Billot, N.; Latter, W.; Noriega-Crespo, A.; Carey, S.; Guieu, S.; Shenoy, S.; Paladini, R.

    2010-04-01

    The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of young stellar objects (YSOs) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous-ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be {approx}8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.

  5. Main-sequence Stars Masquerading as Young Stellar Objects in the Central Molecular Zone

    NASA Astrophysics Data System (ADS)

    Koepferl, Christine M.; Robitaille, Thomas P.; Morales, Esteban F. E.; Johnston, Katharine G.

    2015-01-01

    In contrast to most other galaxies, star formation rates in the Milky Way can be estimated directly from young stellar objects (YSOs). In the central molecular zone the star formation rate calculated from the number of YSOs with 24 ?m emission is up to an order of magnitude higher than the value estimated from methods based on diffuse emission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or both star formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOs could be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfer models of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objects can indeed mimic YSOs at 24 ?m. However, we show that in some cases the main-sequence models can be marginally resolved at 24 ?m, whereas the YSO models are always unresolved. Based on the fraction of resolved MIPS 24 ?m sources in the sample of YSOs previously used to compute the star formation rate, we estimate the fraction of misclassified "YSOs" to be at least 63%, which suggests that the star formation rate previously determined from YSOs is likely to be at least a factor of three too high.

  6. MAIN-SEQUENCE STARS MASQUERADING AS YOUNG STELLAR OBJECTS IN THE CENTRAL MOLECULAR ZONE

    SciTech Connect

    Koepferl, Christine M.; Robitaille, Thomas P.; Morales, Esteban F. E.; Johnston, Katharine G.

    2015-01-20

    In contrast to most other galaxies, star formation rates in the Milky Way can be estimated directly from young stellar objects (YSOs). In the central molecular zone the star formation rate calculated from the number of YSOs with 24 μm emission is up to an order of magnitude higher than the value estimated from methods based on diffuse emission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or both star formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOs could be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfer models of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objects can indeed mimic YSOs at 24 μm. However, we show that in some cases the main-sequence models can be marginally resolved at 24 μm, whereas the YSO models are always unresolved. Based on the fraction of resolved MIPS 24 μm sources in the sample of YSOs previously used to compute the star formation rate, we estimate the fraction of misclassified ''YSOs'' to be at least 63%, which suggests that the star formation rate previously determined from YSOs is likely to be at least a factor of three too high.

  7. Spitzer Observations of Young Stars in the Witch Head Nebula (IC2118)

    NASA Astrophysics Data System (ADS)

    Spuck, T. S.; Bowser, D. H., II; Ehrhart, B. R.; Maranto, A. R.; Greer, M. T.; Preis, J. V.; Weston, P. D.; Rebull, L. M.; Roelofsen, T. E.; Sepulveda, B.; Hughes, A. S.; Sharma, N. D.; Weehler, C. R.; Herrera, J. M.

    2005-12-01

    Two high-Galactic latitude molecular clouds (HLC) in the region of IC 2118, the Witch Head Nebula, appear to be forming stars (Kun et al. 2004). Star formation in HLCs, while rare, may be the origin of some of the apparently isolated T Tauri stars revealed by ROSAT. At only 210 pc away, the clouds in IC 2118 are thought to be excited by Rigel. Kun et al. (2004) reported the discovery of several T Tauri stars in this region and estimated their ages to be 2.5 Myr. We observed a 15'}15{' region centered on the head of the northernmost cloud with Spitzer, using IRAC (3.6, 4.5, 5.8, and 8 microns) and MIPS (24, 70, and 160 microns). We have approximately quadrupled the number of known or suspected young objects in this region. In this poster, we will present color-color plots and SEDs of these stars, and we will compare the properties of these stars to those of other star-forming regions. These observations are part of the Spitzer Space Telescope Research Program for Teachers and Students, so these data are also being used for educational purposes; please see our companion educational poster by Weehler et al.

  8. The Young Star Clusters in the Antennae Galaxies (NGC4038/9)

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Fall, S. M.; Whitmore, B. C.

    2000-12-01

    We present new results from our study of young star clusters in the merging galaxy NGC 4038/9 ("the Antennae" galaxies). With the high-resolution HST WFPC2 observations, we obtained a large sample of star clusters located in the central disks of NGC 4038/9. The clusters formed during the merging process and have a variety of ages ranging from a few to several hundred million years. The young star clusters have properties that are consistent with old globular clusters (e.g., their mass and size). However, we find that both their luminosity function and their mass function are, to first order, described by power-laws with indices close to -2, rather than bell-shaped distributions appropriate for old globular clusters. We construct simple and largely analytical models to explore the evolutionary connection between the young star clusters and old globular clusters. We compute the effects of disruption on the mass function, including evaporation by two-body relaxation, disk shocks, and mass loss by stellar evolution. We find that for a wide variety of initial conditions the mass function develops a turnover or peak, and that after 12 Gyr the distribution is remarkably close to the observed peak for old globular clusters (i.e. MV=-7.2 mag and M=2 105 solar masses). Finally, we explore the relationship between the positions of the young star clusters in the Antennae and the properties of the interstellar medium, as defined by both intensity maps (covering a range of wavelengths from X-rays to radio waves) and velocity fields (from H-alpha, CO, and HI). Support for this work is provided in part by NASA through grant number GO-07468 from STScI.

  9. Probing the circumstellar environments of very young low-mass stars using water masers

    NASA Technical Reports Server (NTRS)

    Terebey, S.; Vogel, S. N.; Myers, P. C.

    1992-01-01

    The VLA is used to search nearby very young low-mass stars for water maser emission. The sample consists of 26 low-luminosity IRAS sources embedded in dense molecular cores, a class of sources suspected to be newly forming low-mass stars on the order of a few hundred thousand years old. Three sources were detected. High spatial resolution maps show the region of maser emission is generally confined to an area smaller than about 0.5 arcsec near the star, and the velocities of individual components span intervals ranging from 20 to 40 km/s. It is inferred from the fact that the maser velocities are too large to be due to gravitational motions in at least two of the sources that the masers are associated with the winds from the young low-mass stars. A comparison of the high spatial resolution maser data to lower-resolution CO data shows no evidence for higher collimation close to the star; the stellar wind cavity appears to have similar collimation at 10 exp 15 cm as at 10 exp 7 to 10 exp 18 cm.

  10. Testing the Generation of Jets in Young Stars with ALMA

    NASA Astrophysics Data System (ADS)

    Bacciotti, F.; Podio, L.; Codella, C.; Coffey, D.

    2015-12-01

    Jets are a crucial element in the star formation process, as they are thought to remove the excess angular momentum from the system. A firm detection of jet rotation could lend support to this statement. Jet rotation studies, however, are hindered by the requirement of simultaneous high spatial and spectral resolution, and as a matter of fact, the rotation interpretation is still debated. Soon, however, the improved spatial resolution of ALMA will allow us to firmly establish rotation patterns. At the same time the new ALMA polarimetric capabilities will permit the determination of the magnetic configuration in the system. The ALMA combined search for rotation properties and magnetic fields will be a powerful test of the proposed jet generation mechanisms.

  11. Identifying the Young Low-mass Stars within 25 pc. II. Distances, Kinematics, and Group Membership

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya L.; Anglada-Escudé, Guillem; Liu, Michael C.; Bowler, Brendan P.; Weinberger, Alycia J.; Boss, Alan P.; Reid, I. Neill; Tamura, Motohide

    2012-10-01

    We have conducted a kinematic study of 165 young M dwarfs with ages of lsim300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of lsim25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (lsim3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and β Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages lsim150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope, the du Pont Telescope at Las Campanas Observatory, and the Subaru Telescope. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. The CFHT is operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

  12. Young Stars and Planets Near the Sun: Explosive Phenomena from Falling Evaporating Bodies

    NASA Astrophysics Data System (ADS)

    Ibadov, Subhon; Ibodov, Firuz S.

    2016-01-01

    Impacts of falling evaporating bodies (FEBs) with stars and planets at velocities V >~ 10 - 20 km/s will be accompanied, due to aerodynamic effects such as crushing and transversal expansion of the crushed mass, by the FEB's ``explosion'' and the generation of a strong ``blast'' wave, resulting in FEB-generated explosive/flare phenomena. Multiwavelength monitoring of nearby young stars (and exoplanets) with dense protoplanetary disks rich in FEB's is hence of interest for identifying such FEB-related mechanisms possibly underlying their variability.

  13. Identifying Planet-Forming Disks Around Young Stars

    NASA Astrophysics Data System (ADS)

    Espaillat, C.

    2013-04-01

    In the past few years, several disks with inner holes that are relatively empty of small dust grains have been detected and are known as transitional disks. Spitzer identified a new class of “pre-transitional disks” with gaps; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. Here we review spectral observations which provided the first confirmations of gaps in the pre-transitional disks of LkCa 15 and UX Tau A. We also review the results of a Spitzer IRS study of variability in transitional and pre-transitional objects. The structure and behavior of pre-transitional and transitional disks may be a sign of young planets forming in these disks and future studies of these disks will provide constraints to aid in theoretical modeling of planet formation.

  14. Young Star Clusters in the Outer Disks of LITTLE THINGS Dwarf Irregular Galaxies

    NASA Astrophysics Data System (ADS)

    Hunter, Deidre A.; Elmegreen, Bruce G.; Gehret, Elizabeth

    2016-06-01

    We examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular (dIrr) and Blue Compact Dwarf galaxies to identify distinct young regions in their far outer disks. We use these data, obtained with the Galaxy Evolution Explorer satellite, to determine the furthest radius at which in situ star formation can currently be identified. The FUV knots are found at distances from the center of the galaxies of 1–8 disk scale lengths and have ages of ≤slant 20 Myr and masses of 20 M{}ȯ to 1 × 105M{}ȯ . The presence of young clusters and OB associations in the outer disks of dwarf galaxies shows that dIrrs do have star formation taking place there in spite of the extreme nature of the environment. Most regions are found where the H i surface density is ∼1 M{}ȯ pc‑2, though both the H i and dispersed old stars go out much further. This limiting density suggests a cutoff in the ability to form distinct OB associations and perhaps even stars. We compare the star formation rates in the FUV regions to the average rates expected at their radii and beyond from the observed gas, using the conventional correlation for gas-rich regions. The localized rates are typically 10% of the expected average rates for the outer disks. Either star formation in dIrrs at surface densities \\lt 1 {M}ȯ pc‑2 occurs without forming distinct associations, or the Kennicutt–Schmidt relation over-predicts the rate beyond this point. In the latter case, the stellar disks in the far-outer parts of dIrrs result from scattering of stars from the inner disk.

  15. Young Stars & Planets Near the Sun in 2015: Five Takeaways and Five Predictions

    NASA Astrophysics Data System (ADS)

    Liu, Michael C.

    2016-01-01

    I present a highly biased and skewed summary of IAU Symposium 314, ``Young Stars and Planets Near the Sun,'' held in May 2015. This summary includes some takeaway thoughts about the rapidly evolving state of the field, as well as some crowd-sourced predictions for progress over the next ~10 years. We predict the elimination of 1-2 of the currently recognized young moving groups, the addition of 3 or more new moving groups within 100 pc, the continued lack of a predictive theory of stellar mass, robust measurements of the gas and dust content of circumstellar disks, and an ongoing struggle to achieve a consensus definition for a planet.

  16. 30 Doradus - Relating Young Stars Imaged by Spitzer and Hubble to the CO Molecular Gas Observed with ALMA

    NASA Astrophysics Data System (ADS)

    Nayak, Omnarayani; Meixner, Margaret; Indebetouw, Remy; Sabbi, Elena; De Marchi, Guido; Panagia, Nino

    2016-01-01

    The majority of star have masses less than 8 solar mass and form in clumps that are less than 1 pc in size. The sub-parsec scales in which star formation takes place makes it difficult to resolve the effects star formation and the surrounding dense gas have on each other. The Magellanic Clouds are more active in forming high mass stars as compared to the Milky Way. The SAGE and Heritage surveys combined with the Hubble Tarantula Treasury Project provide us the opportunity to study high-mass (>15 solar masses) and low-mass (<1 solar mass) star formation. ALMA observations cover a 60 pc x 30 pc region of CO gas slightly north of the R136 cluster in 30 Doradus. We find 16 young stellar objects and about a 100 pre-main-sequence stars within the ALMA footprint. We define young stellar objects to be very early stage stars that are about 10,000 years old and whose SEDs peak in the infrared, and we use pre-main-sequence-stars to refer to slightly older stars that can be seen in the optical. I will use dendrograms to analyze both the high- and low-mass star properties with respect to the CO gas structure observed with ALMA. Preliminary results show that not all massive young stellar objects are associated with CO gas, higher mass clumps tend to form higher mass stars and are more likely to have multiple young stars, and lower mass clumps tend to not be gravitationally bound however the larger clouds are bound. Looking at the interplay between dense molecular gas and the newly forming stars in a stellar nursery will shed light on how these stars formed: monolithic collapse or competitive accretion.

  17. A multiwavelength study of star formation in the very young open cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    van den Ancker, M. E.; The, P. S.; Feinstein, A.; Vazquez, R. A.; de Winter, D.; Perez, M. R.

    1997-05-01

    The distance and formation history of the very young open cluster NGC 6530 were investigated by studying a total of 132 probable member stars of this open cluster. It was concluded that the distance to NGC 6530 is 1.8 +/- 0.2 kpc, and its interstellar reddening E(B-V) is 0\\fm30. Furthermore, we conclude that the extinction law of the intracluster material is normal (i.e. R_V = 3.1), but anomalous extinction laws were found for several more embedded stars in the cluster. Of the 132 stars included in this study, 11 are suspected to be variable, five show H? in emission and nine show an infrared excess. Among the member stars of NGC 6530, three were found to be part of the Herbig Ae/Be stellar class, whereas two others are possible members of this stellar group as well. Also, one cluster member is probably a new massive post-AGB star, whereas the same could possibly apply to another member star. Finally, from the distribution of post- and pre-main sequence stars in the cluster's HR-diagram, it was concluded that the process of star formation in NGC 6530 must have started a few times 10^7 years ago and, for the less massive stars, is probably still going on today. Based on observations collected at the European Southern Observatory, La Silla, Chile, on observations collected at Cerro Tololo Inter-American Observatory, and on spectral data obtained with the International Ultraviolet Explorer. Tables 1, 2 and 5 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

  18. The Mass Function of Young Star Clusters in the "Antennae" Galaxies.

    PubMed

    Zhang; Fall

    1999-12-20

    We determine the mass function of young star clusters in the merging galaxies known as the "Antennae" (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimate the intrinsic luminosity and age, and hence the mass, of each cluster. We find that the mass function of the young star clusters (with ages less, similar160 Myr) is well represented by a power law of the form psi&parl0;M&parr0;~M-2 over the range 104 less, similarM less, similar106 M middle dot in circle. This result may have important implications for our understanding of the origin of globular clusters during the early phases of galactic evolution. PMID:10577944

  19. The Einstein survey of the young stars in the Orion Nebula

    NASA Technical Reports Server (NTRS)

    Zoonematkermani, S.; Caillault, J.-P.

    1987-01-01

    The Orion Nebula is the best studied site of recent star formation in the Galaxy. The complete Einstein Observatory survey of the Orion Nebula covering a 2 deg x 2 deg region centered on the Trapezium is reported. An X-ray mosaic is presented for the Nebula along with a complete X-ray catalogue for this very young cluster. Approximately 150 distinct sources were found in this 4 sq deg region; spectral types and colors were obtained for about 1/2 of the optical counterparts of these sources. Comparison of the variability of the Orion X-ray sources with those found in the Rho Ophiuchi cloud leads to the conclusion that the Orion sources' variability is also likely to result from continual flaring activities. Eleven new late B stars associated with X-ray emission far exceeding that expected from early type stars were discovered. The X-rays may originate from pre-main sequence companions to these stars; a T-Tauri star of the same age would have the correct L sub x. Comparison of the solar type stars in Orion with those in the Pleiades, the Hyades, and the field suggests that the decay of activity with age is most appropriately described by an exponential, rather than a power law fit.

  20. The star-forming history of the young cluster NGC 2264

    NASA Technical Reports Server (NTRS)

    Adams, M. T.; Strom, K. M.; Strom, S. E.

    1983-01-01

    UBVRI H-alpha photographic photometry was obtained for a sample of low-mass stars in the young open cluster NGC 2264 in order to investigate the star-forming history of this region. A theoretical H-R diagram was constructed for the sample of probable cluster members. Isochrones and evolutionary tracks were adopted from Cohen and Kuhi (1979). Evidence for a significant age spread in the cluster was found amounting to over ten million yr. In addition, the derived star formation rate as a function of stellar mass suggests that the principal star-forming mass range in NGC 2264 has proceeded sequentially in time from the lowest to the highest masses. The low-mass cluster stars were the first cluster members to form in significant numbers, although their present birth rate is much lower now than it was about ten million yr ago. The star-formation rate has risen to a peak at successively higher masses and then declined.

  1. Propeller regime of the accretion onto young stars in the ballistic approach

    NASA Astrophysics Data System (ADS)

    Shulman, S. G.; Grinin, V. P.; Potravnov, I. S.

    2015-12-01

    The form of the outflows generated during the interaction of the accretion disc with the tilted stellar magnetosphere in the propeller regime is studied in the ballistic approach. The problem is solved analytically. Different ways of the flux expansion are considered. The results are applied to the description of the narrow absorption details observed in the spectra of young stars in a blue wing of the sodium D Na I resonance lines.

  2. Radiation-driven Warping of Circumbinary Disks around Eccentric Young Star Binaries

    NASA Astrophysics Data System (ADS)

    Hayasaki, Kimitake; Sohn, Bong Won; Okazaki, Atsuo T.; Jung, Taehyun; Zhao, Guangyao; Naito, Tsuguya

    2014-12-01

    We study a warping instability of a geometrically thin, non-self-gravitating, circumbinary disk around young binary stars on an eccentric orbit. Such a disk is subject to both the tidal torques due to a time-dependent binary potential and the radiative torques due to radiation emitted from each star. The tilt angle between the circumbinary disk plane and the binary orbital plane is assumed to be very small. We find that there is a radius within/beyond which the circumbinary disk is unstable to radiation-driven warping, depending on the disk density and temperature gradient indices. This marginally stable warping radius is very sensitive to viscosity parameters, a fiducial disk radius and the temperature measured there, the stellar luminosity, and the disk surface density at a radius where the disk changes from optically thick to thin for the irradiation from the central stars. On the other hand, it is insensitive to the orbital eccentricity and binary irradiation parameter, which is a function of the binary mass ratio and luminosity of each star. Since the tidal torques can suppress the warping in the inner part of the circumbinary disk, the disk starts to be warped in the outer part. While the circumbinary disks are most likely to be subject to the radiation-driven warping on an AU to kilo-AU scale for binaries with young massive stars more luminous than 104 L ⊙, the radiation-driven warping does not work for those around young binaries with the luminosity comparable to the solar luminosity.

  3. Radiation-driven warping of circumbinary disks around eccentric young star binaries

    SciTech Connect

    Hayasaki, Kimitake; Sohn, Bong Won; Jung, Taehyun; Zhao, Guangyao; Okazaki, Atsuo T.; Naito, Tsuguya

    2014-12-10

    We study a warping instability of a geometrically thin, non-self-gravitating, circumbinary disk around young binary stars on an eccentric orbit. Such a disk is subject to both the tidal torques due to a time-dependent binary potential and the radiative torques due to radiation emitted from each star. The tilt angle between the circumbinary disk plane and the binary orbital plane is assumed to be very small. We find that there is a radius within/beyond which the circumbinary disk is unstable to radiation-driven warping, depending on the disk density and temperature gradient indices. This marginally stable warping radius is very sensitive to viscosity parameters, a fiducial disk radius and the temperature measured there, the stellar luminosity, and the disk surface density at a radius where the disk changes from optically thick to thin for the irradiation from the central stars. On the other hand, it is insensitive to the orbital eccentricity and binary irradiation parameter, which is a function of the binary mass ratio and luminosity of each star. Since the tidal torques can suppress the warping in the inner part of the circumbinary disk, the disk starts to be warped in the outer part. While the circumbinary disks are most likely to be subject to the radiation-driven warping on an AU to kilo-AU scale for binaries with young massive stars more luminous than 10{sup 4} L {sub ☉}, the radiation-driven warping does not work for those around young binaries with the luminosity comparable to the solar luminosity.

  4. Mapping the circumstellar environment of a young very low mass star

    NASA Astrophysics Data System (ADS)

    Bozhinova, Inna; Scholz, Alexander; Wood, Kenneth; Starkey, David; Horne, Keith

    2015-10-01

    Young stellar objects exhibit variability due to surface features on the star, star-disk interaction, and inhomogenities in the inner disk. Over recent years, multi-band monitoring campaigns have proven to be an effective tool to map the complex environment of young stars and to investigate the physical processes associated with the formation of planets. Here we propose to use Spitzer, combined with ground-based telescopes, to monitor a young very low mass star simultaneous in the mid-infrared and optical. Our target has shown persistent high-level variability over more than a decade of optical monitoring. Our aim is to map the geometry of the inner disk and the accretion flow, for the first time for an object with a mass of only 0.1 Msol. There are clear indications that accretion and disk evolution are dependent on the mass of the central object. By targeting a very low mass star we can explore the physical processes in the inner disk in an extreme parameter regime. We plan to apply two different strategies to obtain spatial constraints. We will monitor over the rotational timescale of several days, to obtain azimuthal information about hot spots on the stellar surface and structures in the inner disk material. In addition, we will derive the inner radius of the disk by measuring the delay between optical and mid-infrared variations ('light echos') over timescales of one hour. In total, we ask for 10 hours of Spitzer/IRAC 4.5mu observing, spread over ten days. Guaranteed time at ground-based telescope will provide the simultaneous optical data. Our team combines the expertise for monitoring campaigns, radiative transfer modeling, and light echo modeling.

  5. Anatomy of a flaring proto-planetary disk around a young intermediate-mass star.

    PubMed

    Lagage, Pierre-Olivier; Doucet, Coralie; Pantin, Eric; Habart, Emilie; Duchêne, Gaspard; Ménard, François; Pinte, Christophe; Charnoz, Sébastien; Pel, Jan-Willem

    2006-10-27

    Although planets are being discovered around stars more massive than the Sun, information about the proto-planetary disks where such planets have built up is sparse. We have imaged mid-infrared emission from polycyclic aromatic hydrocarbons at the surface of the disk surrounding the young intermediate-mass star HD 97048 and characterized the disk. The disk is in an early stage of evolution, as indicated by its large content of dust and its hydrostatic flared geometry, indicative of the presence of a large amount of gas that is well mixed with dust and gravitationally stable. The disk is a precursor of debris disks found around more-evolved A stars such as beta-Pictoris and provides the rare opportunity to witness the conditions prevailing before (or during) planet formation. PMID:17008490

  6. Variability in young very low mass stars: Two surprises from spectrophotometric monitoring

    NASA Astrophysics Data System (ADS)

    Bozhinova, I.; Scholz, A.; Eislöffel, J.

    2016-03-01

    We present simultaneous photometric and spectroscopic observations of seven young and highly variable M dwarfs in star forming regions in Orion, conducted in 4 observing nights with FORS2 at ESO/VLT. All seven targets show significant photometric variability in the I-band, with amplitudes between 0.1-0.8 mag, The spectra, however, remain remarkably constant, with spectral type changes less than 0.5 subtypes. Thus, the brightness changes are not caused by veiling that `fills in' absorption features. Three objects in the σ Ori cluster (age ˜3 Myr) exhibit strong Hα emission and Hα variability, in addition to the continuum variations. Their behaviour is mostly consistent with the presence of spots with temperature of ˜300 K above the photosphere and filling factors between 0.2-0.4, in contrast to typical hot spots observed in more massive stars. The remaining targets near ɛ Ori, likely to be older, show eclipse-like lightcurves, no significant Hα activity and are better represented by variable extinction due to circumstellar material. Interestingly, two of them show no evidence of infrared excess emission. Our study shows that high-amplitude variability in young very low mass stars can be caused by different phenomena than in more massive T Tauri stars and can persist when the disk has disappeared and accretion has ceased.

  7. Variability in young very low mass stars: two surprises from spectrophotometric monitoring

    NASA Astrophysics Data System (ADS)

    Bozhinova, I.; Scholz, A.; Eislöffel, J.

    2016-05-01

    We present simultaneous photometric and spectroscopic observations of seven young and highly variable M dwarfs in star-forming regions in Orion, conducted in four observing nights with FOcal Reducer and low dispersion Spectrograph2 at European Southern Observatory/VLT. All seven targets show significant photometric variability in the I band, with amplitudes between 0.1-0.8 mag, The spectra, however, remain remarkably constant, with spectral type changes less than 0.5 subtypes. Thus, the brightness changes are not caused by veiling that `fills in' absorption features. Three objects in the σ Ori cluster (age ˜3 Myr) exhibit strong Hα emission and Hα variability, in addition to the continuum variations. Their behaviour is mostly consistent with the presence of spots with temperature of ˜300 K above the photosphere and filling factors between 0.2-0.4, in contrast to typical hotspots observed in more massive stars. The remaining targets near ɛ Ori, likely to be older, show eclipse-like light curves, no significant Hα activity and are better represented by variable extinction due to circumstellar material. Interestingly, two of them show no evidence of infrared excess emission. Our study shows that high-amplitude variability in young very low mass stars can be caused by different phenomena than in more massive T Tauri stars and can persist when the disc has disappeared and accretion has ceased.

  8. Signatures of multiple stellar populations in unresolved extragalactic globular/young massive star clusters

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.; Finzell, Thomas

    2013-06-01

    We present an investigation of potential signatures of the formation of multiple stellar populations in recently formed extragalactic star clusters. All of the Galactic globular clusters for which good samples of individual stellar abundances are available show evidence for multiple populations. This appears to require that multiple episodes of star formation and light element enrichment are the norm in the history of a globular cluster. We show that there are detectable observational signatures of multiple formation events in the unresolved spectra of massive, young extragalactic star clusters. We present the results of a pilot program to search for one of the cleanest signatures that we identify—the combined presence of emission lines from a very recently formed population and absorption lines from a somewhat older population. A possible example of such a system is identified in the Antennae galaxies. This source's spectrum shows evidence of two stellar populations with ages of 8 Myr and 80 Myr. Further investigation shows that these populations are in fact physically separated, but only by a projected distance of 59 pc. We show that the clusters are consistent with being bound and discuss the possibility that their coalescence could result in a single globular cluster hosting multiple stellar populations. While not the prototypical system proposed by most theories of the formation of multiple populations in clusters, the detection of this system in a small sample is both encouraging and interesting. Our investigation suggests that expanded surveys of massive young star clusters should detect more clusters with such signatures.

  9. Chandra Observations of a Young Embedded Magnetic B Star in the p Ophiuchus Cloud

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Kenji; Imanishi, Kensuke

    2002-01-01

    This paper reports the analysis of two Chandra X-ray observations of the young magnetic B star rho Ophiuchus S1. X-ray emission from the star was detected in both observations. The average flux is almost the same in both, but during each observation the flux shows significant time variations by a factor of two on timescales of 20-40 ksec. Each spectrum can be fit by either an absorbed power law model with a photon index of approx. -3 or a thin-thermal plasma model with a temperature of approx. 2 keV and an extremely low metal abundance (approx. less than 0.1 solar). The spectrum of the first observation has an apparent line feature at about 6.8 keV, which likely corresponds to highly ionized iron K alpha. In contrast, the spectrum of the second observation shows an anomalous edge absorption component at E approx. 1 keV. The continuum emission and log (L(sub X)/L(sub bol)) approx. -6 are similar to those of young intermediate-mass stars (Herbig Ae/Be stars) although the presence of the magnetic field inferred from the detection of non-thermal radio emission has drawn an analogy between rho Ophiuchus S1 and magnetic chemically peculiar (MCP) stars. If the X-ray emission is thermal, the highest plasma temperature observed is too high to be explained by the conventional theories of magnetic stars, and favors some kind of magnetic dynamo activity, while if the emission is nonthermal, it might be related to mass infall. The 6.8 keV line and 4 keV edge features are marginal but they give important information near the stellar body if they are real. Their physical interpretation is discussed.

  10. Precise High-cadence Time Series Observations of Five Variable Young Stars in Auriga with MOST

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie; Tayar, Jamie; Hillenbrand, Lynne A.; Matthews, Jaymie M.; Kallinger, Thomas

    2013-03-01

    To explore young star variability on a large range of timescales, we have used the MOST satellite to obtain 24 days of continuous, sub-minute cadence, high-precision optical photometry on a field of classical and weak-lined T Tauri stars (TTSs) in the Taurus-Auriga star formation complex. Observations of AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal brightness fluctuations at the 1%-10% level on timescales of hours to weeks. We have further assessed the variability properties with Fourier, wavelet, and autocorrelation techniques, identifying one significant period per star. We present spot models in an attempt to fit the periodicities, but find that we cannot fully account for the observed variability. Rather, all stars exhibit a mixture of periodic and aperiodic behavior, with the latter dominating stochastically on timescales less than several days. After removal of the main periodicity, periodograms for each light curve display power-law trends consistent with those seen for other young accreting stars. Several of our targets exhibited unusual variability patterns not anticipated by prior studies, and we propose that this behavior originates with the circumstellar disks. The MOST observations underscore the need for investigation of TTS light variations on a wide range of timescales in order to elucidate the physical processes responsible; we provide guidelines for future time series observations. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Systems Canada Inc. (MSCI), formerly part of Dynacon, Inc., the University of Toronto Institute for Aerospace Studies, and the University of British Columbia with the assistance of the University of Vienna.

  11. AGN feedback and star formation in young and old radio galaxies

    NASA Astrophysics Data System (ADS)

    Labiano , A.; García-Burillo, S.; Combes, F.; Usero, A.; Soria-Ruiz, R.; Piqueras López, J.; Tremblay, G.; Hunt, L.; Fuente, A.; Neri, R.; Oosterloo, T.

    2016-01-01

    Powerful radio galaxies show evidence of ongoing active galactic nuclei (AGN) feedback, mainly in the form of fast, massive outflows. Yet, it is not clear how these outflows affect the star formation of their hosts. We investigated the different manifestations of AGN feedback in the evolved 3C 293 radio source, and in the young, reactivated 3C 236. Both sources harbor young star-forming regions and fast outflows of \\hi and ionized gas. Due to the different evolution stages of these sources, they are expected to be at different phases of the AGNISM interaction process. Using high spatial resolution observations of CO lines taken with the IRAM Plateau de Bure interferometer, we studied the distribution and kinematics of the molecular gas in these sources, and compared the results with the dust and star-formation images of the host. We searched for signatures of outflow motions in the CO kinematics, and derived the star formation rate (SFR) and star formation efficiency (SFE) of the host with all available SFR tracers. Based on the gas mass derived from our observations and on the SFR estimates, we compared the star-formation efficiency of 3C 236 and 3C 293 against a sample of powerful radio galaxies. Our results suggest that the apparently low SFE of evolved radio galaxies is not necessarily due to AGN feedback, but may be caused by an underestimation of the SFR and/or an overestimation of the molecular gas densities in radio galaxies. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

  12. StarPals International Young Astronomers' Network Collaborative Projects for IYA

    NASA Astrophysics Data System (ADS)

    Kingan, Jessi

    2008-09-01

    StarPals is a nascent non-profit organization with the goal of providing opportunities for international collaboration between students of all ages within space science research. We believe that by encouraging an interest in the cosmos, the one thing that is truly Universal, from a young age, students will not only further their knowledge of and interest in science but will learn valuable teamwork and life skills. The goal is to foster respect, understanding and appreciation of cultural diversity among all StarPals participants, whether students, teachers, or mentors. StarPals aims to inspire students by providing opportunities in which, more than simply visualizing themselves as research scientists, they can actually become one. The technologies of robotic telescopes, videoconferencing, and online classrooms are expanding the possibilities like never before. In honor of IYA2009, StarPals would like to encourage 400 schools to participate on a global scale in astronomy/cosmology research on various concurrent projects. We will offer in-person or online workshops and training sessions to teach the teachers. We will be seeking publication in scientific journals for some student research. For our current project, the Double Stars Challenge, students use the robotic telescopes to take a series of four images of one of 30 double stars from a list furnished by the US Naval Observatory and then use MPO Canopus software to take distance and position angle measurements. StarPals provides students with hands-on training, telescope time, and software to complete the imaging and measuring. A paper will be drafted from our research data and submitted to the Journal of Double Star Observations. The kids who participate in this project may potentially be the youngest contributors to an article in a vetted scientific journal. Kids rapidly adapt and improve their computer skills operating these telescopes and discover for themselves that science is COOL!

  13. Similarities in Populations of Young Star Clusters: Evidence for Quasi-Universal Processes

    NASA Astrophysics Data System (ADS)

    Fall, Michael

    2015-08-01

    Star clusters are the link between interstellar clouds and star-forming galaxies - the topics of this symposium. They are important in the ecology of galaxies, as the sites of star formation and stellar feedback and as the building blocks of stellar populations. This talk presents observations of the mass functions of young star clusters (i.e., the spectrum of cluster masses) in different galaxies, including dwarf and giant, interacting and quiescent galaxies. These observations reveal some remarkable similarities in the mass functions of clusters in these different environments, analogous to the similarities in stellar initial mass functions (IMFs). Thus, we have evidence for universal or quasi-universal processes regulating the formation and early evolution of star clusters. This in turn is highly suggestive of universal or quasi-universal processes regulating the structure of the interstellar medium on the scales of protoclusters. This talk presents some theoretical explanations for these similarities. Specifically, we focus on the similarity of the mass functions of star clusters and their progenitor molecular clouds (protoclusters); both are power laws with indices near -2 (after correcting the observed distributions for life-time effects). This similarity indicates that the average efficiency of star formation in the protoclusters is independent of their masses (or nearly so), which in turn places interesting constraints on the dominant types of stellar feedback within the protoclusters. In particular, momentum-driven processes such as radiation pressure are favored. This talk also presents some theoretical explanations for the observed similarity of the mass functions of star clusters of different ages. These gas-free objects are affected primarily by stellar mass loss, tidal interactions with passing molecular clouds, and internal two-body relaxation. All these processes reduce the masses of clusters, progressively lowering the amplitude of their mass function. But, as explained here, this happens in a way largely independent of the masses of the clusters, thus preserving the power-law shape of their mass function.

  14. Spectroscopic characterization of X-ray emitting young stars associated with the Sh 2-296 nebula

    NASA Astrophysics Data System (ADS)

    Fernandes, B.; Gregorio-Hetem, J.; Montmerle, T.; Rojas, G.

    2015-03-01

    We studied a sample of stars associated with the Sh 2-296 nebula, part of the reflection nebulae complex in the region of Canis Major R1 (CMa R1). Our sample corresponds to optical counterparts of X-ray sources detected from observations with the XMM-Newton satellite, which revealed dozens of possible low-mass young stars not yet known in this region. A sample of 58 young star candidates were selected based on optical spectral features, mainly Hα and lithium lines, observed with multiobjects spectroscopy performed by the Gemini South telescope. Among the candidates, we find 41 confirmed T Tauri and 15 very likely young stars. Based on the Hα emission, the T Tauri stars were distinguished between classical (17 per cent) and weak-lined (83 per cent), but no significant difference was found in the age and mass distribution of these two classes. The characterization of the sample was complemented by near- and mid-infrared data, providing an estimate of ages and masses from the comparison with pre-main-sequence evolutionary models. While half of the young stars have an age of 1-2 Myr or less, only a small fraction (˜25 per cent) shows evidence of IR excess revealing the presence of circumstellar discs. This low fraction is quite rare compared to most young star-forming regions, suggesting that some external factor has accelerated the disc dissipation.

  15. Young Super Star Clusters in the Starburst of M82: The Catalog

    NASA Astrophysics Data System (ADS)

    Melo, V. P.; Muñoz-Tuñón, C.; Maíz-Apellániz, J.; Tenorio-Tagle, G.

    2005-01-01

    Recent results from the Hubble Space Telescope (HST) have resolved starbursts as collections of compact young stellar clusters. Here we present a photometric catalog of the young stellar clusters in the nuclear starburst of M82, observed with the HST WFPC2 in Hα (F656N) and in four optical broadband filters. We identify 197 young super stellar clusters. The compactness and high density of the sources led us to develop specific techniques to measure their sizes. Strong extinction lanes divide the starburst into five different zones, and we provide a catalog of young super star clusters for each of these. In the catalog we include relative coordinates, radii, fluxes, luminosities, masses, equivalent widths, extinctions, and other parameters. Extinction values have been derived from the broadband images. The radii range between 3 and 9 pc, with a mean value of 5.7+/-1.4 pc, and a stellar mass between 104 and 106 Msolar. The inferred masses and mean separation, comparable to the size of the super star clusters, together with their high volume density, provide strong evidence for the key ingredients postulated by Tenorio-Tagle and coworkers as required for the development of a supergalactic wind. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  16. Infrared Spectra of Young Stars Embedded in the R Coronae Australis Cloud

    NASA Astrophysics Data System (ADS)

    Meyer, Michael R.; Wilking, Bruce A.

    2009-04-01

    Infrared spectra are presented for a magnitude-limited (K < 12.5 mag) sample of stellar objects observed toward the R Coronae Australis molecular core. These spectra, which are used to identify young stellar objects in the cloud, include the wavelengths of emission lines from [Fe II] and H2, four of the Brackett series lines, the CO bandheads, as well as photospheric absorption lines of Al, Na, Mg, Si, and Ca. For a subset of the sample, the spectra are compared to those of infrared spectral standard stars to derive spectral types and luminosity classes. By comparing their placement in a Hertzsprung-Russell diagram with theoretical pre-main-sequence tracks and isochrones, we estimate the stellar masses and assess the evolutionary states of the members of this young aggregate. All of the sources classified via near-IR spectroscopy have masses in the range 0.2-2.5 Msolar. The locus of points in the H-R diagram is lower than observed for other embedded clusters (e.g., NGC 2024 and the ρ Oph core), suggesting either a more advanced evolutionary state or a difference in the intrinsic stellar birthline for very young clusters. We discuss the implications of our results for the shape of the initial mass function of the embedded young cluster and the star-forming history of the cloud.

  17. A Confirmed Directly Imaged Planet Orbiting a Nearby Young, Dusty Star

    NASA Astrophysics Data System (ADS)

    Currie, Thayne M.; Rameau, J.; Chauvin, G.; Lagrange, A.; Boccaletti, A.; Meshkat, T.; Quanz, S.; Girard, J.; Bonnefoy, M.; Kenworthy, M. A.

    2014-01-01

    We present new VLT/NaCo infrared (Lp/3.8 micron) high-contrast imaging observations of a nearby, young (13--21 Myr old) star known to be surrounded by a luminous Kuiper belt-like debris disk. Using multiple reduction pipelines, we unambiguously detect a faint companion located interior to the disk at a projected separation of ~55 AU in four separate data sets between 2012 and 2013. The companion’s astrometry is decisively inconsistent with that of a background object. Combining our Lp photometry with sensitive upper limits at shorter wavelengths shows that the companion has red colors characteristic of young jovian planets with an inferred mass of 3--7 Mj, making it potentially the lowest mass planet imaged thus far. This planet will be a benchmark for further physical and orbital characterization of young gas giants.

  18. Bayesian Analysis to Identify New Star Candidates in Nearby Young Stellar Kinematic Groups

    NASA Astrophysics Data System (ADS)

    Malo, Lison; Doyon, René; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan; Baron, Frédérique; Riedel, Adric

    2013-01-01

    We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the β Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as Hα and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in β Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for β Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 Å equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the β Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii.

  19. Uncovering The Properties of Young Neutron Stars and Their Surrounding Supernova A Remnants

    NASA Technical Reports Server (NTRS)

    Slane, Patrick O.; Oliversen, Ronald J. (Technical Monitor)

    2003-01-01

    In the third year of this program, the following studies have been undertaken in support of this effort: G292.0+1.8: In our previous work on this SNR, we discovered a young neutron star and its associated pulsar wind nebula. Radio observations by Camilo et al. (2002) have identified a young 136 ms pulsar in the direction of G292.0+1.8. We have used Chandra HRC observations of the central source to identify X-ray pulsations at the same period, thus establishing the neutron star as the radio pulsar counterpart. We have also set limits on the cooling of this young neutron star based on the unpulsed component of the X-ray emission. We find that the limit falls slightly below standard cooling models in which the modified Urca process is responsible for the bulk of the interior neutrino emission. A paper summarizing these results is currently being circulated amongst co-authors for review prior to publication. 3c 58: Our Chandra observations of this Crab-like SNR revealed the presence of a young, rapidly rotating pulsar as well as a central compact nebula which we interpret as a toroidal structure associated with the pulsar wind termination shock. Our modeling of this structure has allowed us to establish a temperature upper limit for the neutron star which falls well below predictions from standard cooling models, and implies the presence of exotic particles (such as pion condensates) or other processes that increase the neutrino production rate in the interior. A paper summarizing this work has been published in the Astrophysical Journal (Slane, Helfand, & Murray 2002, ApJ, 571, L45), and the results were the subject of a NASA Space Science Update (4/10/2002) which led to extensive media coverage. Based upon our initial observations, we submitted a successful Chandra Large Project proposal for a 350 ks observation of this young neutron star and its wind nebula. Kes 79: Our Chandra observations of this SNR reveal a compact central source which appears to be the neutron star formed in the explosion that produced the remnant. There is no evidence for a surrounding pulsar wind nebula. The source properties are similar to the central source in Cas A even though the Kes 79 remnant is considerably older. The results have been published in the Astrophysical Journal (Seward, Slane, Smith, and Sun 2003, ApJ, 584,414). Chandra Survey for Compact Objects in Supernova Remnants: We have formed a collaboration to carry out an extensive search for young neutron stars in nearby supernova remnants. Using X-ray observations from an approved Chandra Large Project, as well as from additional approved XMM observations, we are investigating a volume-limited sample of SNRs for which there is currently no evidence of associated neutron stars. We have obtained extensive optical and 1R data to complement the project, and analysis of these data is currently underway.

  20. As Eyes See Young Stars Assemble: Star and Planet Formation in the VLT Era

    NASA Astrophysics Data System (ADS)

    McCaughrean, Mark J.

    The river of time leading to this meeting on star and planet formation with the VLT can apparently be traced back to somewhere in the vicinity of Lake Geneva almost 25 years ago, in 1977. In this introductory talk, I attempt to navigate back upstream and locate the source of the river and in doing so, discover a rather surprising link to musical happenings elsewhere on the lake at the same time. The reader is free to decide whether they find the connection more than mere coincidence, let alone interesting.

  1. Commissioning COSMOS: Detection of Lithium in Young Stars in Lupus 3 through Multi-Object Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lackey, Kyle; Briceno, Cesar; Elias, Jonathan H.

    2015-01-01

    COSMOS, a multi-object spectrograph and imager, is a new instrument on the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory. In order to demonstrate the instrument's operations during commissioning, we used COSMOS, its red grism and three custom slit masks to conduct a spectroscopic survey of the star-forming core of the Lupus 3 dark cloud in an effort to detect the presence of Lithium in the T Tauri stars that have been previously identified in that region. We detected the Li I 6708 Angstrom resonance transition in several (but not all) stars that were observed, consistent with prior studies that have observed Lithium in other young stars at the center of the Lupus 3 dark cloud and in other star-forming regions. These results also demonstrate the ability of COSMOS to significantly reduce the time required to complete spectroscopic surveys, relative to single-object instruments.Lackey was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program (AST-1262829).

  2. The Cool Supergiant Population of the Massive Young Star Cluster RSGC1

    NASA Astrophysics Data System (ADS)

    Davies, Ben; Figer, Don F.; Law, Casey J.; Kudritzki, Rolf-Peter; Najarro, Francisco; Herrero, Artemio; MacKenty, John W.

    2008-04-01

    We present new high-resolution near-IR spectroscopy and OH maser observations to investigate the population of cool luminous stars of the young massive Galactic cluster RSGC1. Using the 2.293 μm CO band-head feature, we make high-precision radial velocity measurements of 16 of the 17 candidate red supergiants (RSGs) identified by Figer et al. We show that F16 and F17 are foreground stars, while we confirm that the rest are indeed physically associated RSGs. We determine that star F15, also associated with the cluster, is a yellow hypergiant based on its luminosity and spectroscopic similarity to ρ Cas. Using the cluster's radial velocity, we have derived the kinematic distance to the cluster and revisited the stars' temperatures and luminosities. We find a larger spread of luminosities than in the discovery paper, consistent with a cluster age 30% older than previously thought (12 +/- 2 Myr), and a total initial mass of (3 +/- 1) × 104 M⊙. The spatial coincidence of the OH maser with F13, combined with similar radial velocities, is compelling evidence that the two are related. Combining our results with recent SiO and H2O maser observations, we find that those stars with maser emission are the most luminous in the cluster. From this we suggest that the maser active phase is associated with the end of the RSG stage, when the luminosity-mass ratios are at their highest.

  3. Formation of massive black holes through runaway collisions in dense young star clusters.

    PubMed

    Zwart, Simon F Portegies; Baumgardt, Holger; Hut, Piet; Makino, Junichiro; McMillan, Stephen L W

    2004-04-15

    A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11. PMID:15085124

  4. Photoevaporating Disks around Young Stars: Ultracompact HII Regions and Protoplanetary Disks.

    NASA Astrophysics Data System (ADS)

    Johnstone, Douglas Ian

    1995-01-01

    Newly formed stars produce sufficient Lyman continuum luminosity phi to significantly alter the structure and evolution of the accretion disk surrounding them. In the absence of a stellar wind, a nearly static, photoionized, 10^4 K, disk atmosphere, with a scale height that increases with disk radius varpi as varpi^{3/2 }, forms inside the gravitational radius varpig ~ 1014(M_*/ M_odot) cm where M _* is the mass of the central star. This ionized atmosphere is maintained by both the direct radiation from the central star and the diffuse field produced in the disk atmosphere by the significant fraction of hydrogen recombinations directly to the ground state. Beyond varpig the material evaporated from the disk is capable of escaping from the system and produces an ionized disk wind. The mass-loss due to this disk wind peaks at varpig . The inclusion of a stellar wind into the basic picture reduces the height of the inner disk atmosphere and introduces a new scale radius varpi_ {w} where the thermal pressure of the material evaporated from the disk balances the ram pressure in the wind. In this case the mass-loss due to the disk wind peaks at varpiw and is enhanced over the no-wind case. The photoevaporation of disks around newly formed stars has significance to both ultracompact HII regions and the dispersal of solar-type nebulae. High mass stars are intrinsically hot and thus yield sufficient Lyman luminosity to create, even without a stellar wind, disk mass-loss rates of order 2 times 10 ^{-5}phi_sp{49} {1/2} M_odotyr ^{-1}, where phi 49 = phi/(10 49 Lyman continuum photons s^{-1}). This wind, which will last until the disk is dispersed, ~ 10^5 yrs if the disk mass is M_ {d}~0.3M_*, yields sizes, emission measures and ages consistent with observations of ultracompact HII regions. The well-observed high mass star MWC 349 may be the best example to date of an evaporating disk around a high mass star. On the other end of the stellar scale, many newly formed low-mass stars are known to have enhanced extreme ultraviolet luminosity suggested to be due to boundary layer accretion. Assuming that most low mass stars have such an enhanced Lyman luminosity phi ~ 1041 s ^{-1}, for ~ 3 times 10^7 yrs it is possible to remove most of the gas in the outer disk. A diagnostic of this mass loss may be the low-velocity forbidden oxygen, nitrogen, and sulphur line emission observed around young stars with disks. Photoevaporating disk models yield reasonable agreement with the flux seen in these lines. The process of photoevaporation also has implications for the formation of the giant planets within the solar nebula. Within young stellar clusters a few high mass stars may overwhelm the internal Lyman continuum flux from low mass stars and externally evaporated disks may result. The Trapezium region presents the best studied example of such a cluster. Photoionization due to high energy photons from the high mass stars erode the disks around nearby low mass stars. The resulting short destruction times for these disks constrain the gestation period for creating planets.

  5. Strong biases in estimating the time dependence of mass accretion rates in young stars

    NASA Astrophysics Data System (ADS)

    Da Rio, N.; Jeffries, R. D.; Manara, C. F.; Robberto, M.

    2014-04-01

    The temporal decay of mass accretion in young stars is a fundamental tracer of the early evolution of circumstellar discs. Through population syntheses, we study how correlated uncertainties between the estimated parameters of young stars (luminosity, temperature, mass and age) and mass accretion rates dot{M}_acc, as well as observational selection effects, can bias the temporal decay of mass accretion rates (dot{M}_acc∝ t^{-η }) inferred from a comparison of measured dot{M}_acc with isochronal ages in young stellar clusters. We find that the presence of realistic uncertainties reduces the measured value of η by up to a factor of 3, leading to the inference of shallower decays than the true value. This suggests a much faster temporal decay of dot{M}_acc than generally assumed. When considering the minimum uncertainties in ages affecting the Orion Nebula Cluster, the observed value η ˜ 1.4, typical of Galactic star-forming regions, can only be reproduced if the real decay exponent is η ≳ 4. This effect becomes more severe if one assumes that observational uncertainties are larger, as required by some fast star formation scenarios. Our analysis shows that while selection effects due to sample incompleteness do bias η, they cannot alter this main result and strengthen it in many cases. A remaining uncertainty in our work is that it applies to the most commonly used and simple relationship between dot{M}_acc, the accretion luminosity and the stellar parameters. We briefly explore how a more complex interplay between these quantities might change the results.

  6. Hot and Cold: A Study of H2 Jets and CO Molecular Outflows from Young Stars

    NASA Astrophysics Data System (ADS)

    Yu, K. C.

    2000-12-01

    The thesis examines outflows from young low-mass accreting protostars. The outflow phenomenon appears to be ubiquitous to all newborn stars, and is often the first observational evidence for embedded young stars. Outflows may be crucial for removing angular momentum from the accretion disk, thereby allowing material to accrete onto the stellar core. In addition, since they can transport supersonic gas over parsec-scale distances, outflows probably contribute to changing the chemistry of the molecular cloud, adding to the cloud's overall turbulence, and may even affect the efficiency of star formation by physically disrupting the infall environments around other protostars. New observations and interpretations are reported for two regions: the Barnard 5 cloud containing the IRS 1 flow, and the OMC-2 and OMC-3 cloud cores, containing a rich cluster of young stars and criss-crossing H2 jets. 12CO J=2--1 mapping, H2 and optical line imaging, and high resolution optical and NIR spectroscopy have revealed the locations of H2 emission; provided support for bow shock entrainment models for the acceleration of CO bearing gas; showed evidence for H2 heating by a magnetic precursor or HH-object-induced fluorescence; showed that many H2 knots can be described as bow shocks with forward and reverse shock line profiles; gave support to outflow models where both a jet and a wide angle wind emanate from the YSO or accretion disk; and revealed possible differences between how low and high mass YSOs entrain ambient gas into outflows as they evolve.

  7. Relations between the Luminosity, Mass, and Age Distributions of Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Fall, S. Michael

    2006-12-01

    We derive and interpret some relations between the luminosity, mass, and age distributions of star clusters, denoted here by φ(L), ψ(M), and χ(τ), respectively. Of these, φ(L) is the easiest to determine observationally, whereas ψ(M) and χ(τ) are more informative about formation and disruption processes. For a population of young clusters, with a relatively wide range of ages, φ(L) depends on both ψ(M) and χ(τ) and thus cannot serve as a proxy for ψ(M) in general. We demonstrate this explicitly by four illustrative examples with specific forms for either ψ(M) or χ(τ). In the special case in which ψ(M) is a power law and is independent of χ(τ), however, φ(L) is also a power law with the same exponent as ψ(M). We conclude that this accounts for the observed similarity between φ(L) and ψ(M) for the young clusters in the Antennae galaxies. This result reinforces our picture in which clusters form with ψ(M)~M-2 and are then disrupted rapidly at a rate roughly independent of their masses. The most likely disruptive process in this first stage is the removal of interstellar matter by the energy and momentum input from young stars (by photoionization, winds, jets, and supernovae). The few clusters that avoid this ``infant mortality'' are eventually disrupted in a second stage by the evaporation of stars driven by two-body relaxation, a process with a strong dependence on mass. We suspect this picture may apply to many, if not all, populations of star clusters, but this needs to be verified observationally by determinations of ψ(M) and χ(τ) in more galaxies.

  8. Angular momentum regulation in low-mass young stars surrounded by accretion disks

    NASA Technical Reports Server (NTRS)

    Edwards, Suzan; Strom, Stephen E.; Hartigan, Patrick; Strom, Karen M.; Hillenbrand, Lynne A.; Herbst, William; Attridge, Joanne; Merrill, K. M.; Probst, Ron; Gatley, Ian

    1993-01-01

    From study of a sample of 34 T Tauri stars with photometrically derived rotation periods and spectral types later than KS, we find that the observed periods appear to be related to the presence or absence of an accretion disk. Those stars which we infer to be surrounded by accretion disks have rotation periods P(rot) over 4 days with a most probable P(rot) of about 8.5 days, while those stars which lack accretion disk signatures cover a wide range of P(rot) from 1.5 to 16 days, including a significant number of objects with P(rot) less than 4 days. This suggests the possibility that the 'initial' angular momentum of a star is not established until it dissipates its circumstellar accretion disk. During the disk accretion phase, the stellar angular velocity appears to be regulated at a low value, countering the tendency of the star to spin up both from contraction toward the main sequence and from the accretion of inner disk material of high specific angular momentum. When the accretion disk is dissipated, this regulation mechanism will cease to function. At this point, the star is no longer maintained at a low angular velocity, but is 'free' to conserve its angular momentum, and thus to increase its angular velocity in response to contraction and changes in moment of inertia. This hypothesis, combined with a spread in disk dispersal time scales, provides a context for explaining the observed distribution of stellar rotational velocities for stars on the ZAMS in young clusters.

  9. The life-cycle of young star-clusters; the role of the galactic environment on cluster formation and evolution

    NASA Astrophysics Data System (ADS)

    Adamo, Angela

    2015-08-01

    Our understanding of star formation on galactic scales has been fairly grasped (e.g. the rate at which stars form scales proportionally to the molecular gas content) both in the local and high redshift universe. However, our knowledge on how star formation proceeds at small scales (e.g. the fraction of star formation happening in stellar clusters, the time-scales for star-forming regions to dissolve, the impact of the galactic environment on star and cluster formation) remains a challenge. Gravitationally bound young stellar clusters appear to be a commune product of star formation. There are tantalizing similarities between young star clusters and globular clusters, the latter formed by gravitationally bound ancient stellar populations. However, the young and globular cluster populations show statistical properties (mass functions, formation efficiencies, and survival times) that have been claimed incompatible, leaving the two populations being the results of distinct processes of formation. In my contribution, I will discuss the latest results produced with the analysis of the young cluster populations in several nearby galaxies. The use of new statistical methods, the link with dense gas fueling star formation, the access to homogenous datasets show, for the first time, clear evidence of the influence of the galactic environment in shaping the properties of young star cluster populations. After all, the differences between the two cluster populations may not be so pronounced, suggesting that the same physical formation process under different environmental conditions has been (and currently is) at work at high redshift (when globular clusters were formed) and in the local universe.

  10. Completing the census of young stars near the Sun with the FunnelWeb spectroscopic survey

    NASA Astrophysics Data System (ADS)

    Lawson, Warrick; Murphy, Simon; Tinney, Christopher G.; Ireland, Michael; Bessell, Michael S.

    2016-06-01

    From late 2016, the Australian FunnelWeb survey will obtain medium-resolution (R~2000) spectra covering the full optical range for 2 million of the brightest stars (I<12) in the southern sky. It will do so using an upgraded UK Schmidt Telescope at Siding Spring Observatory, equipped with a revolutionary, parallelizable optical fibre positioner ("Starbugs") and spectrograph. The ability to reconfigure a multi-fibre plate in less than 5 minutes allows FunnelWeb to observe more stars per night than any other competing multi-fibre spectrograph and enables a range of previously inefficient bright star science not attempted since the completion of the HD catalogues in the 1940s. Among its key science aims, FunnelWeb will obtain spectra for thousands of young and adolescent (<1 Gyr) stars near the Sun (<200 pc) across a wide range of spectral types. These spectra will include well-studied youth and activity indicators such as H-alpha, Li I 6708A, Ca II H&K, as well as surface gravity diagnostics (e.g. Na I, K I). In addition, FunnelWeb will obtain stellar parameters (Teff, logg, vsini), abundances (Fe/H, alpha/Fe) and radial velocities to 1-2 km/s for every star in the survey. When combined with high precision parallaxes and proper motions from the Gaia mission expected from 2017, this dataset will provide a near-complete census of adolescent stars in the solar neighbourhood. It will help reveal the typical formation environments of young solar-type stars, how such stars move from their stellar nurseries to their adult lives in the field, and identifying thousands of high-priority targets for follow-up direct imaging (GPI, SPHERE), transit (including TESS) and radial velocity exoplanet studies. In this poster contribution we introduce the FunnelWeb survey, its science goals and input catalogue, as well as provide an update on the status of the fibre positioner and spectrograph commissioning at Siding Spring.

  11. Magnetocentrifugally driven flows from young stars and disks. 1: A generalized model

    NASA Technical Reports Server (NTRS)

    Shu, Frank; Najita, Joan; Ostriker, Eve; Wilkin, Frank; Ruden, Steven; Lizano, Susana

    1994-01-01

    We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin of winds, jets, and bipolar outflows from young stellar objects. We consider the steady state dynamics of accretion of matter from a viscous and imperfectly conducting disk onto a young star with a strong magnetic field. For an aligned stellar magnetosphere, shielding currents in the surface layers of the disk prevent stellar field lines from penetrating the disk everywhere except for a range of radii about pi = R(sub x), where the Keplerian angular speed of rotation Omega(sub x) equals the angular speed of the star Omega(sub *). For the low disk accretion rates and high magnetic fields associated with typical T Tauri stars, R(sub x) exceeds the radius of the star R(sub *) by a factor of a few, and the inner disk is effectively truncated at a radius R(sub t) somewhat smaller than R(sub x). Where the closed field lines between R(sub t) and R(sub x) bow sufficiently inward, the accreting gas attaches itself to the field and is funneled dynamically down the effective potential (gravitational plus centrifugal) onto the star. Contrary to common belief, the accompanying magnetic torques associated with this accreting gas may transfer angular momentum mostly to the disk rather than to the star. Thus, the star can spin slowly as long as R(sub x) remains significantly greater than R(sub *). Exterior to R(sub x) field lines threading the disk bow outward, which makes the gas off the mid-plane rotate at super-Keplerian velocities. This combination drives a magnetocentrifugal wind with a mass-loss rate M(sub w) equal to a definite fraction f of the disk accretion rate M(sub D). For high disk accretion rates, R(sub x) is forced down to the stellar surface, the star is spun to breakup, and the wind is generated in a manner identical to that proposed by Shu, Lizano, Ruden, & Najita in a previous communication to this journal. In two companion papers (II and III), we develop a detailed but idealized theory of the magnetocentrifugal acceleration process.

  12. Search for associations containing young stars (SACY). VII. New stellar and substellar candidate members in the young associations

    NASA Astrophysics Data System (ADS)

    Elliott, P.; Bayo, A.; Melo, C. H. F.; Torres, C. A. O.; Sterzik, M. F.; Quast, G. R.; Montes, D.; Brahm, R.

    2016-04-01

    Context. The young associations offer us one of the best opportunities to study the properties of young stellar and substellar objects and to directly image planets thanks to their proximity (<200 pc) and age (≈5-150 Myr). However, many previous works have been limited to identifying the brighter, more active members (≈1 M⊙) owing to photometric survey sensitivities limiting the detections of lower mass objects. Aims: We search the field of view of 542 previously identified members of the young associations to identify wide or extremely wide (1000-100 000 au in physical separation) companions. Methods: We combined 2MASS near-infrared photometry (J, H, K) with proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the field of view of known members. We collated further photometry and spectroscopy from the literature and conducted our own high-resolution spectroscopic observations for a subsample of candidate members. This complementary information allowed us to assess the efficiency of our method. Results: We identified 84 targets (45: 0.2-1.3 M⊙, 17: 0.08-0.2 M⊙, 22: <0.08 M⊙) in our analysis, ten of which have been identified from spectroscopic analysis in previous young association works. For 33 of these 84, we were able to further assess their membership using a variety of properties (X-ray emission, UV excess, Hα, lithium and K I equivalent widths, radial velocities, and CaH indices). We derive a success rate of 76-88% for this technique based on the consistency of these properties. Conclusions: Once confirmed, the targets identified in this work would significantly improve our knowledge of the lower mass end of the young associations. Additionally, these targets would make an ideal new sample for the identification and study of planets around nearby young stars. Given the predicted substellar mass of the majority of these new candidate members and their proximity, high-contrast imaging techniques would facilitate the search for new low-mass planets. Based on FEROS observations obtained during CNTAC programme CN2015B-9 and observations made with the HERMES spectrograph mounted on the 1.2 m Mercator Telescope at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Full Table 4 (Appendix E) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A13

  13. NEAR-INFRARED VARIABILITY IN YOUNG STARS IN CYGNUS OB7

    SciTech Connect

    Rice, Thomas S.; Wolk, Scott J.; Aspin, Colin

    2012-08-10

    We present the first results from a 124 night J, H, K near-infrared monitoring campaign of the dark cloud L 1003 in Cygnus OB7, an active star-forming region. Using three seasons of UKIRT observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. On the basis of near-infrared excesses from disks, we identify 30 pre-main-sequence stars, including 24 which are newly discovered. We analyze those stars and find that the NIR excesses are significantly variable. All 9200 stars were monitored for photometric variability; among the field star population, {approx}160 exhibited near-infrared variability (1.7% of the sample). Of the 30 young stellar objects (YSOs), 28 of them (93%) are variable at a significant level. Of the 30 YSOs, twenty-five have near-infrared excess consistent with simple disk-plus-star classical T Tauri models. Nine of these (36%) drift in color space over the course of these observations and/or since Two Micron All Sky Survey observations such that they cross the boundary defining the NIR excess criteria; effectively, they have a transient near-infrared excess. Thus, time-series JHK observations can be used to obtain a more complete sample of disk-bearing stars than single-epoch JHK observations. About half of the YSOs have color-space variations parallel to either the classical T Tauri star locus or a hybrid track which includes the dust reddening trajectory. This indicates that the NIR variability in YSOs that possess accretion disks arises from a combination of variable extinction and changes in the inner accretion disk: either in accretion rate, central hole size, and/or the inclination of the inner disk. While some variability may be due to stellar rotation, the level of variability on the individual stars can exceed a magnitude. This is a strong empirical suggestion that protoplanetary disks are quite dynamic and exhibit more complex activity on short timescales than is attributable to rotation alone or captured in static disk models.

  14. Bolometric temperature and young stars in the Taurus and Ophiuchus complexes

    NASA Technical Reports Server (NTRS)

    Chen, H.; Myers, P. C.; Ladd, E. F.; Wood, D. O. S.

    1995-01-01

    We calculated bolometric temperature (T(sub bol)) and luminosity (L(sub bol)) for 128 young stellar objects (YSOs) in Taurus, 74 in the Ophiuchus 'core', and 33 in the Ophiuchus 'off-core' region. We have constructed the bolometric luminosity-temperature (BLT) diagram, the log-log plot of L(sub bol) versus T(sub bol), for the three samples. T(sub bol) is defined as the temperature of a blackbody having the same frequency as the observed continuum spectrum. It measures the redness (or coldness) of an astronomical source. The BLT diagram is analogous to the H-R diagram and allows for a direct and quantitative comparison of YSOs at a wide variety of evolutionary states, ranging from the most deeply embedded stars to T Tauri stars nearly on the main sequence. We found (1) T(sub bol) increases monotonically from embedded sources (approximately 60-500 K) to classical T Tauri stars (approximately 1000-3000 K) to weak-line T Tauri stars (approximately 2000-5000 K); (2) T(sub bol) correlates reasonably well with the age inferred from the evolutionary models of pre-main-sequence stars and protostars for embedded 'protostars' and weak-line T Tauri stars. There is no significant correlation for the classical T Tauri stars. These results can be understood in terms of dissipation of circumstellar dust envelope and disk during the early stages of stellar evolution. Sources in the three regions have different distributions in the BLT diagram. The Ophiuchus core has the highest fraction of cold sources among the three regions. These cold sources are also more luminous than the YSOs in the other regions. The Ophiuchus off-core sample is dominated by the more evolved pre-main-sequence stars. The Taurus sources have distributions intermediate in L(sub bol), T(sub bol), and age between the Ophiuchus core and off-core distributions. These may suggest differences in the star formation history, and possibly in the stellar masses and mass accretion rates in these star-forming regions.

  15. X-Ray and Infrared Observations of Embedded Young Stars in NGC 2264

    NASA Technical Reports Server (NTRS)

    Simon, Theordore; Dahm, S. E.

    2005-01-01

    Images of the NGC 2264 star-forming region, which we have acquired with the XMM-Newton spacecraft, reveal strong X-ray emission from three deeply embedded (Av > 10 mag) young stellar objects in the vicinity of Allen's infrared source (AFGL 989 = IRS 1) and Castelaz & Grasdalen s infrared source (RNO-EW = IRS 2). Thermal plasma models for the brightest source in X-rays, located 11 southwest of Allen's star, yield a quasi-steady luminosity of Lx = 10 ergs s-1 and an extraordinarily high X-ray temperature of 100 MK. The high temperature is consistent with the presence of emission lines of Fe xxv and Fe xxvi at photon energies of 6.7 and 6.9 keV, respectively. An even higher temperature of nearly 140 MK was observed during the rise phase of a powerful impulsive X-ray flare of another young star in the IRS 2 region. Moderate-resolution near-infrared (1-4 um) spectra of the embedded objects, obtained at the NASA Infrared Telescope Facility, exhibit deep water ice absorption bands, as well as a variety of emission and absorption features of H I, CO, and both neutral and ionized metals.

  16. Photoevaporation of Disks Around Young Stars: Application to Ultracompact HII Regions, Proplyds, and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    Young massive stars produce sufficient Lyman continuum photon luminosity to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 10' K atmosphere forms above the neutral disk, creating a photoevaporative flow from the outer parts of the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for greater than or approximately 10(exp 5) years for disk masses M(sub d) to approximately 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which axe externally illuminated by the UV photons from the nearby massive star theta(sup 1)C.

  17. Direct measurement of interstellar extinction toward young stars using atomic hydrogen Lyα absorption

    SciTech Connect

    McJunkin, Matthew; France, Kevin; Brown, Alexander; Schneider, P. C.; Herczeg, Gregory J.; Hillenbrand, Lynne; Schindhelm, Eric; Edwards, Suzan

    2014-01-10

    Interstellar reddening corrections are necessary to reconstruct the intrinsic spectral energy distributions (SEDs) of accreting protostellar systems. The stellar SED determines the heating and chemical processes that can occur in circumstellar disks. Measurement of neutral hydrogen absorption against broad Lyα emission profiles in young stars can be used to obtain the total H I column density (N(H I)) along the line of sight. We measure N(H I) with new and archival ultraviolet observations from the Hubble Space Telescope (HST) of 31 classical T Tauri and Herbig Ae/Be stars. The H I column densities range from log{sub 10}(N(H I)) ≈19.6-21.1, with corresponding visual extinctions of A{sub V} =0.02-0.72 mag, assuming an R{sub V} of 3.1. We find that the majority of the H I absorption along the line of sight likely comes from interstellar rather than circumstellar material. Extinctions derived from new HST blue-optical spectral analyses, previous IR and optical measurements, and new X-ray column densities on average overestimate the interstellar extinction toward young stars compared to the N(H I) values by ∼0.6 mag. We discuss possible explanations for this discrepancy in the context of a protoplanetary disk geometry.

  18. Millimeter continuum measurements of circumstellar dust around very young low-mass stars

    NASA Technical Reports Server (NTRS)

    Terebey, S.; Chandler, C. J.; Andre, P.

    1994-01-01

    We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) whose analysis of L1551 showed the millimeter continuum emission comes from both an unresolved circumstellar component, i.e., a disk and an extended cloud core. We model the dust continuum emission from the cloud core and show how it is important at 1.3 mm but negligible at 2.7 mm. Combining new 2.7 mm Owens Valley Interferometer data of IRAS-Dense cores with data from the literature we conclude that massive disks are also seen toward a number of other sources. However, 1.3 mm data from the IRAM 30 m telescope for a larger sample shows that massive disks are relatively rare, occurring around perhaps 5% of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. At 1.3 mm the median flux of IRAS-Dense cores is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass during the embedded phase is nearly the same or less than the typical disk mass during the T Tauri phase.

  19. VVV Study of the Young Milky Way Star Clusters: Mercer 35, 69 and 70

    NASA Astrophysics Data System (ADS)

    Kurtev, Radostin; Borissova, Jura; Bonatto, Charles; Peñaloza, Francisco; Ivanov, Valentin; Artigau, Étienne; Folkes, Stuart; Geisler, Douglas; Minniti, Dante; Lucas, Philip; Sale, Stuart

    Young massive clusters are usually deeply embedded in dust and gas. They represent excellent astrophysical laboratories for revealing the enigma of star formation processes and the early stages of stellar evolution. Wide-field infrared surveys are a modern tool for studying hidden clusters. "Vista variables in Vía Láctea - VVV" (Minniti et al. New Astron. 15:433, 2010) is an ESO/Chile/VISTA public deep near-IR survey, covering the Galactic Bulge and Southern Galactic disk. This is the next step of our systematic study of the cluster content of the inner Milky Way. Here we present our first analysis of the young hidden clusters Mercer 35, 69 and 70. It is based on VVV and SOFI/NTT { JHK} S photometry and follow-up NIR spectroscopy. All of the investigated clusters are young (t ≤ 10 Myr). The basic cluster parameters are obtained from photometry. The follow-up spectroscopy of probable cluster members shows that the brightest star in Mercer 35 presents characteristics of a red supergiant!

  20. Young Star Cluster Found Aglow With Mysterious X-Ray Cloud

    NASA Astrophysics Data System (ADS)

    2002-12-01

    A mysterious cloud of high-energy electrons enveloping a young cluster of stars has been discovered by astronomers using NASA's Chandra X-ray Observatory. These extremely high-energy particles could cause dramatic changes in the chemistry of the disks that will eventually form planets around stars in the cluster. Known as RCW 38, the star cluster covers a region about 5 light years across. It contains thousands of stars formed less than a million years ago and appears to be forming new stars even today. The crowded environment of a star cluster is thought to be conducive to the production of hot gas, but not high-energy particles. Such particles are typically produced by exploding stars, or in the strong magnetic fields around neutron stars or black holes, none of which is evident in RCW 38. "The RCW 38 observation doesn't agree with the conventional picture," said Scott Wolk of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, lead author of an Astrophysical Journal Letters paper describing the Chandra observation. "The data show that somehow extremely high-energy electrons are being produced there, although it is not clear how." RCW 38 RCW 38 X-ray, Radio, Infrared Composite Electrons accelerated to energies of trillions of volts are required to account for the observed X-ray spectrum of the gas cloud surrounding the ensemble of stars, which shows an excess of high-energy X-rays. As these electrons move in the magnetic field that threads the cluster, they produce X-rays. One possible origin for the high-energy electrons is a previously undetected supernova that occurred in the cluster. Although direct evidence for the supernova could have faded away thousands of years ago, a shock wave or a rapidly rotating neutron star produced by the outburst could be acting in concert with stellar winds to produce the high-energy electrons. "Regardless of the origin of the energetic electrons," said Wolk, "their presence would change the chemistry of proto-stellar disks in ways that could still be manifest billions of years later." For example, in our own solar system, we find evidence of certain short-lived radioactive nuclides (Aluminum 26 being the most well known). This implies the existence of a high-energy process late in the evolution of our solar system. If our solar system was immersed for a time in a sea of energetic particles, this could explain the rare nuclides present in meteorites found on the Earth today. RCW 38, at a distance of 6,000 light years from Earth, is one of the nearest star-forming regions with very young, hot stars. Other authors of the paper, which appeared in the 2002 December 1 issue of the Astrophysical Journal Letters, are Tyler Bourke, Randall Smith and Bradley Spitzbart of the Harvard-Smithsonian Center for Astrophysics, and Joao Alves of the European Southern Observatory in Garching, Germany. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science in Washington. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.

  1. The structure of accretion discs around low-mass young stars

    NASA Astrophysics Data System (ADS)

    Lachaume, R.

    2003-07-01

    It is nowadays widely accepted that low mass star formation initiated from a molecular cloud undergoes a phase where the central object is surrounded by a disc, in which planets may form later. The study of such a disc mainly aims at the understanding of the evolutionary sequence of star formation and of planet formation. Radiative transfer in this disc is of high importance, for it is heated by viscous dissipation or stellar irradiation for instance. The production and transportation of thermal energy in this disc therefore conditions its chemical and physical properties inside. It has countless consequences in terms of structure. I shall present a study of the discs based on a deep analytical description of the radiative transfer and a delay of the numerical implementation. This method allows a better grasp on processes and physical conditions in these objects. I shall constrain model parameters and establish a new diagnosis combining the spectral energy distribution and the visibilities obtained with optical long-baseline interferometers. The former observable is a well known technique, and the latter new and promising: it provides information at the scale of one astronomical unit for the closest star forming regions. I shall start a generalisation of the analytical studies of the radiative transfer in stellar atmospheres, with two striking discrepancies: viscous heating occurs everywhere in the disc and the surface is illuminated by the star. I apply this formalism in a numerical simulation of a disc heated by viscosity alone. I then develop a simplified version of this transfer in a two-layer disc: the surface is heated by the interior and by the star, and the interior by viscosity and by the surface. This simplification allow to derive a simplified analytical description of the physical conditions in a disc heated by the two processes mentioned above. I shall tackle the interpretation of observations in the end. I shall of the possibilities brought by interferometry concerning marginally resolved objects, as most young star will be. I then shall present best fits of the two-layer models for low mass young stars already observed by interferometers. The LaTeX and PDF files of the manuscript (in French with English appendices) are made available by the National Centre for Scientific Reasearch (CNRS) archive site (http://tel.ccsd.cnrs.fr/documents/archives0/00/00/64/74).

  2. Rotating models of young solar-type stars. Exploring braking laws and angular momentum transport processes

    NASA Astrophysics Data System (ADS)

    Amard, L.; Palacios, A.; Charbonnel, C.; Gallet, F.; Bouvier, J.

    2016-03-01

    Context. Understanding the angular momentum evolution of stars is one of the greatest challenges of modern stellar physics. Aims: We study the predicted rotational evolution of solar-type stars from the pre-main sequence to the solar age with 1D rotating evolutionary models including physical ingredients. Methods: We computed rotating evolution models of solar-type stars including an external stellar wind torque and internal transport of angular momentum following the method of Maeder and Zahn with the code STAREVOL. We explored different formalisms and prescriptions available from the literature. We tested the predictions of the models against recent rotational period data from extensive photometric surveys, lithium abundances of solar-mass stars in young clusters, and the helioseismic rotation profile of the Sun. Results: We find a best-matching combination of prescriptions for both internal transport and surface extraction of angular momentum. This combination provides a very good fit to the observed evolution of rotational periods for solar-type stars from early evolution to the age of the Sun. Additionally, we show that fast rotators experience a stronger coupling between their radiative region and the convective envelope. Regardless of the set of prescriptions, however, we cannot simultaneously reproduce surface angular velocity and the internal profile of the Sun or the evolution of lithium abundance. Conclusions: We confirm the idea that additional transport mechanisms must occur in solar-type stars until they reach the age of the Sun. Whether these processes are the same as those needed to explain recent asteroseismic data in more advanced evolutionary phases is still an open question.

  3. A CubeSat to Search for Transiting Planets Around the Young Star Beta Pictoris

    NASA Astrophysics Data System (ADS)

    Blake, Ameer; Roberge, Aki

    2016-01-01

    The goal of this project is to further our growing knowledge of exoplanets in the solar neighborhood. The nearby star Beta Pictoris, which is nearly twice the mass of the Sun, is encircled by a huge disk of dust and gas reaching out 500-800 AU from the star. This so-called "debris disk" is the product of collisions between large numbers of asteroids and comets orbiting this relatively young star. The presence of these small planetary bodies hinted that there might be planets in the disk as well, which was recently confirmed when a ground-based telescope directly imaged a super-Jupiter exoplanet orbiting the star.The debris disk of Beta Pic tells us that this planetary system is edge-on from our vantage point on Earth. Therefore, it is an ideal system to use transit photometry to search for additional planets. We hope to due so by monitoring the brightness of the star over a given period, using a telescope on small satellite (a CubeSat). A CubeSat is a very small satellite tasked with a single purpose and, in this case, a single target. The advantage of a CubeSat over a larger telescope is the low cost and fast development schedule. Since we wish to study only one star's system, a CubeSat is an economical choice, although the limited lifetime of a CubeSat means that only planets with relatively short (up to few month) periods may be found. Our preliminary calculations show that, in principle, we can discover planets from Jupiter-size down to Neptune-size around Beta Pic with a telescope sized to fit in a CubeSat.

  4. Ages and luminosities of young SMC/LMC star clusters and the recent star formation history of the Clouds

    NASA Astrophysics Data System (ADS)

    Glatt, K.; Grebel, E. K.; Koch, A.

    2010-07-01

    Aims: In this paper we discuss the age and spatial distribution of young (age < 1 Gyr) Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) clusters using data from the Magellanic Cloud Photometric Surveys. Luminosities are calculated for all age-dated clusters. Methods: The ages of 324 and 1193 populous star clusters in the SMC and the LMC were determined fitting Padova and Geneva isochrone models to their resolved color-magnitude diagrams. The clusters cover an age range between 10 Myr and 1 Gyr in each galaxy. For the SMC, a constant distance modulus of (m-M)_0 = 18.90 and a metallicity of Z = 0.004 were adopted. For the LMC, we used a constant distance modulus of (m-M)_0 = 18.50 and a metallicity of Z = 0.008. For both galaxies, we used a variable color excess to derive the cluster ages. Results: We find two periods of enhanced cluster formation in both galaxies at 160 Myr and 630 Myr (SMC) and at 125 Myr and 800 Myr (LMC). We present the spatially resolved recent star formation history of both Clouds based on young star clusters. The first peak may have been triggered by a close encounter between the SMC and the LMC. In both galaxies, the youngest clusters reside in the supergiant shells, giant shells, the intershell regions, and toward regions with a high Hα content, suggesting that their formation is related to expansion and shell-shell interaction. Most of the clusters are older than the dynamical age of the supergiant shells. No evidence of cluster dissolution was found. Computed V band luminosities show a trend toward fainter magnitudes with increasing age, as well as a trend toward brighter magnitudes with increasing apparent cluster radii. Full Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/517/A50

  5. MWC 297: a young high-mass star rotating at critical velocity

    NASA Astrophysics Data System (ADS)

    Acke, B.; Verhoelst, T.; van den Ancker, M. E.; Deroo, P.; Waelkens, C.; Chesneau, O.; Tatulli, E.; Benisty, M.; Puga, E.; Waters, L. B. F. M.; Verhoeff, A.; de Koter, A.

    2008-07-01

    Context: MWC 297 is a nearby young massive B[e] star. The central star is attenuated by 8 mag in the optical and has a high projected rotational velocity of 350 km s-1. Despite the wealth of published observations, the nature of this object and its circumstellar environment is not understood very well. Aims: With the present paper, we intend to shed light on the geometrical structure of the circumstellar matter that is responsible for the near- to mid-infrared flux excess. Methods: The H-band (1.6-2.0 ?m), K-band (2.0-2.5 ?m), and N-band (8-13 ?m) brightness distribution of MWC 297 was probed with the ESO interferometric spectrographs AMBER and MIDI, mounted on the VLTI in Paranal, Chile. We obtained visibility measurements on 3 AMBER and 12 MIDI baselines, covering a wide range of spatial frequencies. Different models (parametrized circumstellar disks, a dusty halo) were invoked to fit the data, all of which fail to do so in a satisfying way. We approximated the brightness distribution in H, K, and N with a geometric model consisting of three Gaussian disks with different extents and brightness temperatures. This model can account for the entire near- to mid-IR emission of MWC 297. Results: The circumstellar matter around MWC 297 is resolved on all baselines. The near- and mid-IR emission, including the silicate emission at 10 micron, emanates from a very compact region (FWHM < 1.5 AU) around the central star. Conclusions: We argue that the extinction towards the MWC 297 star+disk system is interstellar and most likely due to remnants of the natal cloud from which MWC 297 was formed. Furthermore, we argue that the circumstellar matter in the MWC 297 system is organized in a circumstellar disk, seen under moderate (i < 40) inclination. The disk displays no inner emission-free gap at the resolution of our interferometric observations. The low inclination of the disk implies that the already high projected rotational velocity of the star corresponds to an actual rotational velocity that exceeds the critical velocity of the star. This result shows that stars can obtain such high rotation rates at birth. We discuss the impact of this result in terms of the formation of high-mass stars and the main-sequence evolution of classical Be stars. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program IDs 077.D-0071(B-C), 077.D-0095(C-F), 079.C-0012(A-H) and 079.C-0207(A).

  6. SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month

    NASA Astrophysics Data System (ADS)

    Eisenhauer, F.; Genzel, R.; Alexander, T.; Abuter, R.; Paumard, T.; Ott, T.; Gilbert, A.; Gillessen, S.; Horrobin, M.; Trippe, S.; Bonnet, H.; Dumas, C.; Hubin, N.; Kaufer, A.; Kissler-Patig, M.; Monnet, G.; Ströbele, S.; Szeifert, T.; Eckart, A.; Schödel, R.; Zucker, S.

    2005-07-01

    We report on 75 mas resolution, near-IR imaging spectroscopy within the central 30 lt-days of the Galactic center, taken with the new adaptive optics-assisted integral-field spectrometer SINFONI on the ESO VLT. To a limiting magnitude of K~16, 9 of 10 stars in the central 0.4", and 13 of 17 stars out to 0.7" from the central black hole have spectral properties of B0-B9 main-sequence stars. Based on the 2.1127 μm He I line width, all brighter early-type stars have normal rotation velocities, similar to solar neighborhood stars. We combine the new radial velocities with SHARP/NACO astrometry to derive improved three-dimensional stellar orbits for six of these ``S stars'' in the central 0.5". Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1"-10" from Sgr A*. We can thus exclude the hypothesis that the S stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks and then migrated inward within their planes. From the combination of their normal rotation and random orbital orientations, we conclude that the S stars were most likely brought into the central light-month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is R0=7.62+/-0.32 kpc, resulting in a central mass value of (3.61+/-0.32)×106 Msolar. We happened to catch two smaller flaring events from Sgr A* during our spectral observations. The 1.7-2.45 μm spectral energy distributions of these flares are fit by a featureless, ``red'' power law of spectral index α'=-4+/-1 (Sν~να'). The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from accelerated, nonthermal, high-energy electrons in a radiatively inefficient accretion flow in the central R~10RS region. Based on observations obtained at the Very Large Telescope of the European Southern Observatory, Chile.

  7. The INfrared Survey of Young Nebulous Clusters (IN-SYNC): Surveying the Dynamics and Star Formation Histories of Young Clusters with APOGEE

    NASA Astrophysics Data System (ADS)

    Covey, Kevin R.; Cottaar, Michiel; Foster, Jonathan B.; Da Rio, Nicola; Tan, Jonathan; Meyer, Michael; Nidever, David L.; Flaherty, Kevin M.; Arce, Hector G.; Rebull, Luisa M.; Chojnowski, S. Drew; Frinchaboy, Peter M.; Hearty, Fred R.; Majewski, Steven R.; Skrutskie, Michael F.; Stassun, Keivan; Wilson, John C.; Zasowski, Gail

    2015-01-01

    Young clusters are the most prolific sites of star formation in the Milky Way, but demographic studies indicate that relatively few of the Milky Way's stellar clusters persist as bound structures for 100 Myrs or longer. Uniform & precise measurements of the stellar populations and internal dynamics of these regions are difficult to obtain, however, particularly for extremely young clusters whose optical visibility is greatly hampered by their parental molecular cloud. The INfrared Survey of Young Nebulous Clusters (IN-SYNC), an SDSS-III ancillary science program, leverages the stability and multiplex capability of the APOGEE spectrograph to obtain high resolution spectra at near-infrared wavelengths, where photospheric emission is better able to penetrate the dusty shrouds that surround sites of active star formation. We summarize our recent measurements of the kinematics and stellar populations of IC 348 and NGC 1333, two young clusters in the Perseus Molecular Cloud, and of the members of the Orion Nebula Cluster (ONC) and L1641 filament in the Orion molecular complex. These measurements highlight the dynamically 'warm' environment within these young clusters, and suggest a range of stellar radii within these quasi-single-age populations. We close with a preview of plans for continuing this work as part of the APOGEE-2 science portfolio: self-consistent measurements of the kinematics and star formation histories for clusters spanning a range of initial conditions and ages will provide a opportunity to disentangle the mechanisms that drive the formation and dissolution of sites of active star formation.

  8. Tracing Supernova Enrichment of the Nearest Young Star Forming Complex with High Resolution Stellar Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bubar, Eric Joseph; Mamajek, Eric E.; Pecaut, Mark

    2010-02-01

    The chemical evolution of the galaxy can be examined on a small scale locally by searching for evidence of enrichment by core collapse (type II) supernova explosions among stars belonging to the same star- forming complex. We propose to obtain high resolution spectroscopy of a sample of slowly rotating members of nearby, young stellar groups associated with the nearest star-forming complex: Scorpius-Centaurus. These spectra will be used to perform a precise spectroscopic abundance analysis to test for enrichment of the ~5 Myr-old Upper Scorpius region and neighboring regions by supernova explosions in the neighboring ~ 15 Myr-old Upper Centaurus Lupus and Lower Centaurus Crux subgroups. Enrichment by core-collapse supernovae can be traced by enhancements in oxygen and other alpha- element abundances compared to Fe-peak elements. These abundances can also be used for constraining the chemical homogeneity of members of Upper-Sco. This study will allow us to explore the processes of Galactic chemical evolution and SN enrichment on a small scale (< 0.1 kpc, <10-20 SN) in a complex with a relatively well constrained star formation history and high mass stellar membership.

  9. NuSTAR Observations of Bright X-ray Flares from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Vievering, Juliana; Glesener, Lindsay; Grefenstette, Brian; Smith, David

    2016-05-01

    Bright x-ray flares are observed to occur on young stellar objects (YSOs) and are presumed to be driven by similar processes as those seen on our sun. Observations of the flaring activity of YSOs can add to our understanding of the early lives of stars and the development of planetary systems. In particular, x-ray observations of these stellar flares are essential for probing the youngest stars, as these stars are most obscured by dense molecular clouds. One such cloud complex of YSOs, rho Ophiuchi, has been a past target for soft x-ray (SXR) missions, including Chandra and XMM-Newton. However, the energy ranges covered by these missions drop off prior to the hard x-ray (HXR) regime, where the crossover to a dominant nonthermal component could be observed. Whether or not this nonthermal emission is strong enough to be observed could then be an indicator of how large an influence these flares have on the surrounding protoplanetary disk. To begin investigating this HXR emission, two 50ks observations of rho Ophiuchi have been taken with the Nuclear Spectroscopic Telescope Array (NuSTAR), which is optimized over the energy range of 3-79 keV. Multiple stellar flares have been identified in the observations; here we present the preliminary analysis, including light curves and spectra, of the brightest of these flaring events. We explore the implications of the data for flaring activity of YSOs and compare the results to typical flaring activity of the sun.

  10. NEW BROWN DWARF COMPANIONS TO YOUNG STARS IN SCORPIUS-CENTAURUS

    SciTech Connect

    Janson, Markus; Jayawardhana, Ray; Bonavita, Mariangela; Girard, Julien H.; Lafreniere, David; Gizis, John; Brandeker, Alexis

    2012-10-10

    We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of {approx}40-100 M{sub jup} complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of {approx}10-30 M{sub jup}. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.

  11. Substantial reservoirs of molecular hydrogen in the debris disks around young stars

    NASA Technical Reports Server (NTRS)

    Thi, W. F.; Blake, G. A.; van Dishoeck, E. F.; van Zadelhoff, G. J.; Horn, J. M.; Becklin, E. E.; Mannings, V.; Sargent, A. I.; van Den Ancker, M. E.; Natta, A.

    2001-01-01

    Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5 Gyr ago. But the 'debris' disks that encircle more than 15% of nearby main-sequence stars appear to have very small amounts of gas, based on observations of the tracer molecule carbon monoxide: these observations have yielded gas/dust ratios much less than 0.1, whereas the interstellar value is about 100 (ref. 9). Here we report observations of the lowest rotational transitions of molecular hydrogen (H2) that reveal large quantities of gas in the debris disks around the stars beta Pictoris, 49 Ceti and HD135344. The gas masses calculated from the data are several hundreds to a thousand times greater than those estimated from the CO observations, and yield gas/dust ratios of the same order as the interstellar value.

  12. Disks, Young Stars, and Radio Waves: The Quest for Forming Planetary Systems

    NASA Astrophysics Data System (ADS)

    Chandler, C. J.; Shepherd, D. S.

    2008-08-01

    Kant and Laplace suggested the Solar System formed from a rotating gaseous disk in the 18th century, but convincing evidence that young stars are indeed surrounded by such disks was not presented for another 200 years. As we move into the 21st century the emphasis is now on disk formation, the role of disks in star formation, and on how planets form in those disks. Radio wavelengths play a key role in these studies, currently providing some of the highest-spatial-resolution images of disks, along with evidence of the growth of dust grains into planetesimals. The future capabilities of EVLA and ALMA provide extremely exciting prospects for resolving disk structure and kinematics, studying disk chemistry, directly detecting protoplanets, and imaging disks in formation.

  13. A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

    NASA Technical Reports Server (NTRS)

    Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

    1993-01-01

    We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

  14. Economic Development Activities at the Young - Rainey Science, Technology, & Research (STAR) Center

    SciTech Connect

    Paul S. Sacco; Carl Smeigh; John Caponiti, Jr.

    2008-06-30

    Project mission was to mitigate the adverse economic effects of closing the U.S. Department of Energy's Pinellas Plant in Largo, Florida. This project was to facilitate the physical renovation of the plant and to help maintain and create jobs for the employees that worked at the plant when DOE terminated its operations. It also included finding and attracting high technology, industrial manufacturing and related firms to utilize the space and high tech equipment to remain at the plant. Stakeholders included the affected plant employees, local government and related public organizations, and businesses and universities in the Tampa Bay Florida area. The $17.6 million funded for this project helped produce 2,780 jobs at the Young - Rainey STAR Center at an average cost of $6,328. Rental income from STAR Center tenants and third party cash input amounted to approximately $66 million over the project period of 13.3 years.

  15. Gas expulsion in massive star clusters?. Constraints from observations of young and gas-free objects

    NASA Astrophysics Data System (ADS)

    Krause, Martin G. H.; Charbonnel, Corinne; Bastian, Nate; Diehl, Roland

    2016-03-01

    Context. Gas expulsion is a central concept in some of the models for multiple populations and the light-element anti-correlations in globular clusters. If the star formation efficiency was around 30 per cent and the gas expulsion happened on the crossing timescale, this process could preferentially expel stars born with the chemical composition of the proto-cluster gas, while stars with special composition born in the centre would remain bound. Recently, a sample of extragalactic, gas-free, young massive clusters has been identified that has the potential to test the conditions for gas expulsion. Aims: We investigate the conditions required for residual gas expulsion on the crossing timescale. We consider a standard initial mass function and different models for the energy production in the cluster: metallicity-dependent stellar winds, radiation, supernovae and more energetic events, such as hypernovae, which are related to gamma ray bursts. The latter may be more energetic than supernovae by up to two orders of magnitude. Methods: We computed a large number of thin-shell models for the gas dynamics, and calculated whether the Rayleigh-Taylor instability is able to disrupt the shell before it reaches the escape speed. Results: We show that the success of gas expulsion depends on the compactness index of a star cluster C5 ≡ (M∗/ 105 M⊙)/(rh/ pc), with initial stellar mass M∗ and half-mass radius rh. For given C5, a certain critical, local star formation efficiency is required to remove the rest of the gas. Common stellar feedback processes may not lead to gas expulsion with significant loss of stars above C5 ≈ 1. Considering pulsar winds and hypernovae, the limit increases to C5 ≈ 30. If successful, gas expulsion generally takes place on the crossing timescale. Some observed young massive clusters have 1 star clusters with and without multiple populations is achieved by a stellar winds-based gas expulsion model, where gas expulsion would occur exclusively in star clusters without multiple populations. Single and multiple population clusters also have little overlap in metallicity and age. Conclusions: Globular clusters should initially have C5 ≲ 100, if the gas expulsion paradigm was correct. Early gas expulsion, which is suggested by the young massive cluster observations, hence would require special circumstances, and is excluded for several objects. Most likely, the stellar masses did not change significantly at the removal of the primordial gas. Instead, the predictive power of the C5 index for the expression of multiple populations is consistent with the idea that gas expulsion may prevent the expression of multiple populations. On this basis, compact young massive clusters should also have multiple populations.

  16. Are Young Massive Star Clusters in the Local Universe Analogous to Globular Clusters Progenitors?

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne

    2015-08-01

    Several models do compete to reproduce the present-day characteristics of globular clusters (GC) and to explain the origin of the multiple stellar populations these systems are hosting.In parallel, independent clues on GC early evolution may be derived from observations of young massive clusters (YMC) in the Local Group.But are these two populations of clusters related? In this talk, we discuss how and if GC and YMC data can be reconciled.We revisit in particular the impact of massive stars on the early evolution of massive star clusters, as well as the question of early gas expulsion.We propose several tests to probe whether the YMC we are observing today can be considered as the analogues of GC progenitors.

  17. Zeeman-Doppler imaging of active young solar-type stars

    NASA Astrophysics Data System (ADS)

    Hackman, T.; Lehtinen, J.; Rosén, L.; Kochukhov, O.; Käpylä, M. J.

    2016-03-01

    Context. By studying young magnetically active late-type stars, i.e. analogues to the young Sun, we can draw conclusions on the evolution of the solar dynamo. Aims: We determine the topology of the surface magnetic field and study the relation between the magnetic field and cool photospheric spots in three young late-type stars. Methods: High-resolution spectropolarimetry of the targets was obtained with the HARPSpol instrument mounted at the ESO 3.6 m telescope. The signal-to-noise ratios of the Stokes IV measurements were boosted by combining the signal from a large number of spectroscopic absorption lines through the least squares deconvolution technique. Surface brightness and magnetic field maps were calculated using the Zeeman-Doppler imaging technique. Results: All three targets show clear signs of magnetic fields and cool spots. Only one of the targets, V1358 Ori, shows evidence of the dominance of non-axisymmetric modes. In two of the targets, the poloidal field is significantly stronger than the toroidal one, indicative of an α2-type dynamo, in which convective turbulence effects dominate over the weak differential rotation. In two of the cases there is a slight anti-correlation between the cool spots and the strength of the radial magnetic field. However, even in these cases the correlation is much weaker than in the case of sunspots. Conclusions: The weak correlation between the measured radial magnetic field and cool spots may indicate a more complex magnetic field structure in the spots or spot groups involving mixed magnetic polarities. Comparison with a previously published magnetic field map shows that on one of the stars, HD 29615, the underlying magnetic field changed its polarity between 2009 and 2013. Based on observations made with the HARPSpol instrument on the ESO 3.6 m telescope at La Silla (Chile), under the program ID 091.D-0836.

  18. Hokupa'a-Gemini Discovery of Two Ultracool Companions to the Young Star HD 130948

    NASA Astrophysics Data System (ADS)

    Potter, D.; Martín, E. L.; Cushing, M. C.; Baudoz, P.; Brandner, W.; Guyon, O.; Neuhäuser, R.

    2002-03-01

    We report the discovery of two faint ultracool companions to the nearby (d~17.9 pc) young G2 V star HD 130948 (HR 5534, HIP 72567) using the Hokupa'a adaptive optics (AO) instrument mounted on the Gemini North 8 m telescope. Both objects have the same common proper motion as the primary star as seen over a 7 month baseline and have near-IR photometric colors that are consistent with an early L classification. Near-IR spectra taken with the NIRSPEC AO instrument on the Keck II telescope reveal K I lines, FeH, and H2O band heads. Based on these spectra, we determine that both objects have a spectral type of dL2 with an uncertainty of two spectral subclasses. The position of the new companions on the H-R diagram in comparison with theoretical models is consistent with the young age of the primary star (<0.8 Gyr) estimated on the basis of X-ray activity, lithium abundance, and fast rotation. HD 130948B and C likely constitute a pair of young contracting brown dwarfs with an orbital period of about 10 yr and will yield dynamical masses for L dwarfs in the near future. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

  19. CSI 2264: characterizing accretion-burst dominated light curves for young stars in NGC 2264

    SciTech Connect

    Stauffer, John; Cody, Ann Marie; Rebull, Luisa; Carey, Sean; Baglin, Annie; Alencar, Silvia; Hillenbrand, Lynne A.; Carpenter, John; Findeisen, Krzysztof; Venuti, Laura; Bouvier, Jerome; Plavchan, Peter; Terebey, Susan; Morales-Caldern, Mara; Micela, Giusi; Flaccomio, Ettore; Song, Inseok; Gutermuth, Rob; Hartmann, Lee; and others

    2014-04-01

    Based on more than four weeks of continuous high-cadence photometric monitoring of several hundred members of the young cluster NGC 2264 with two space telescopes, NASA's Spitzer and the CNES CoRoT (Convection, Rotation, and planetary Transits), we provide high-quality, multi-wavelength light curves for young stellar objects whose optical variability is dominated by short-duration flux bursts, which we infer are due to enhanced mass accretion rates. These light curves show many briefseveral hours to one daybrightenings at optical and near-infrared wavelengths with amplitudes generally in the range of 5%-50% of the quiescent value. Typically, a dozen or more of these bursts occur in a 30 day period. We demonstrate that stars exhibiting this type of variability have large ultraviolet (UV) excesses and dominate the portion of the u g versus g r color-color diagram with the largest UV excesses. These stars also have large H? equivalent widths, and either centrally peaked, lumpy H? emission profiles or profiles with blueshifted absorption dips associated with disk or stellar winds. Light curves of this type have been predicted for stars whose accretion is dominated by Rayleigh-Taylor instabilities at the boundary between their magnetosphere and inner circumstellar disk, or where magneto-rotational instabilities modulate the accretion rate from the inner disk. Among the stars with the largest UV excesses or largest H? equivalent widths, light curves with this type of variability greatly outnumber light curves with relatively smooth sinusoidal variations associated with long-lived hot spots. We provide quantitative statistics for the average duration and strength of the accretion bursts and for the fraction of the accretion luminosity associated with these bursts.

  20. The relevance of the IUE results on young stars for Earth's paleoatmosphere

    NASA Astrophysics Data System (ADS)

    Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff, C. L.; Giampapa, M. S.

    Using the latest IUE results for seven T Tauri stars, which are believed to represent the young Sun and a detailed photochemical chemical model of the paleoatmosphere, the vertical distribution of Oxygen and Ozone in the early atmosphere was calculated. The calculations indicate that the surface Oxygen mixing ratio is as much as six orders of magnitude larger than previously estimated, but appears low enough for the formation of amino acids via the Urey-Miller type of experiments. It is believed that the quantification of the oxygen level in the Earth's paleoatmosphere presented can reconcile the demands of both biological and geological considerations.

  1. The relevance of the IUE results on young stars for Earth's paleoatmosphere

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff, C. L.; Giampap, M. S.

    1982-01-01

    Using the latest IUE results for seven T Tauri stars, which are believed to represent the young Sun and a detailed photochemical chemical model of the paleoatmosphere, the vertical distribution of Oxygen and Ozone in the early atmosphere was calculated. The calculations indicate that the surface Oxygen mixing ratio is as much as six orders of magnitude larger than previously estimated, but appears low enough for the formation of amino acids via the Urey-Miller type of experiments. It is believed that the quantification of the oxygen level in the Earth's paleoatmosphere presented can reconcile the demands of both biological and geological considerations.

  2. Periodic modulation in pulse arrival times from young pulsars: a renewed case for neutron star precession

    NASA Astrophysics Data System (ADS)

    Kerr, M.; Hobbs, G.; Johnston, S.; Shannon, R. M.

    2016-01-01

    In a search for periodic variation in the arrival times of pulses from 151 young, energetic pulsars, we have identified seven cases of modulation consistent with one or two harmonics of a single fundamental with time-scale 0.5-1.5 yr. We use simulations to show that these modulations are statistically significant and of high quality (sinusoidal) even when contaminated by the strong stochastic timing noise common to young pulsars. Although planetary companions could induce such modulation, the large implied masses and 2:1 mean motion resonances challenge such an explanation. Instead, the modulation is likely to be intrinsic to the pulsar, arising from quasi-periodic switching between stable magnetospheric states, and we propose that precession of the neutron star may regulate this switching.

  3. Episodic formation of cometary material in the outburst of a young Sun-like star.

    PubMed

    Abrahám, P; Juhász, A; Dullemond, C P; Kóspál, A; van Boekel, R; Bouwman, J; Henning, Th; Moór, A; Mosoni, L; Sicilia-Aguilar, A; Sipos, N

    2009-05-14

    The Solar System originated in a cloud of interstellar gas and dust. The dust is in the form of amorphous silicate particles and carbonaceous dust. The composition of cometary material, however, shows that a significant fraction of the amorphous silicate dust was transformed into crystalline form during the early evolution of the protosolar nebula. How and when this transformation happened has been a question of debate, with the main options being heating by the young Sun and shock heating. Here we report mid-infrared features in the outburst spectrum of the young Sun-like star EX Lupi that were not present in quiescence. We attribute them to crystalline forsterite. We conclude that the crystals were produced through thermal annealing in the surface layer of the inner disk by heat from the outburst, a process that has hitherto not been considered. The observed lack of cold crystals excludes shock heating at larger radii. PMID:19444209

  4. A COMPREHENSIVE GALEX ULTRAVIOLET CATALOG OF STAR CLUSTERS IN M31 AND A STUDY OF THE YOUNG CLUSTERS

    SciTech Connect

    Kang, Yongbeom; Rey, Soo-Chang; Lee, Kyungsook; Kim, YoungKwang; Bianchi, Luciana; Sohn, Sangmo Tony E-mail: screy@cnu.ac.kr

    2012-04-01

    We present a comprehensive catalog of 700 confirmed star clusters in the field of M31 compiled from three major existing catalogs. We detect 418 and 257 star clusters in Galaxy Evolution Explorer near-ultraviolet and far-ultraviolet (FUV) imaging, respectively. Our final catalog includes photometry of star clusters in up to 16 passbands ranging from FUV to NIR as well as ancillary information such as reddening, metallicity, and radial velocities. In particular, this is the most extensive and updated catalog of UV-integrated photometry for M31 star clusters. Ages and masses of star clusters are derived by fitting the multi-band photometry with model spectral energy distribution (SED); UV photometry enables more accurate age estimation of young clusters. Our catalog includes 182 young clusters with ages less than 1 Gyr. Our estimated ages and masses of young clusters are in good agreement with previously determined values in the literature. The mean age and mass of young clusters are about 300 Myr and 10{sup 4} M{sub Sun }, respectively. We found that the compiled [Fe/H] values of young clusters included in our catalog are systematically lower (by more than 1 dex) than those from recent high-quality spectroscopic data and our SED-fitting result. We confirm that most of the young clusters' kinematics shows systematic rotation around the minor axis and association with the thin disk of M31. The young cluster distribution exhibits a distinct peak in the M31 disk around 10-12 kpc from the center and follows a spatial distributions similar to other tracers of disk structure such as OB stars, UV star-forming regions, and dust. Some young clusters also show concentration around the ring splitting regions found in the southern part of the M31 disk and most of them have systematically younger (<100 Myr) ages. Considering the kinematical properties and spatial distribution of young clusters, they might be associated with the well-known 10 kpc star formation ring structure in the M31 disk. Consequently, we suggest that various properties of young clusters in M31 might be in line with the scenarios that a satellite galaxy had passed through the disk of M31 less than few hundred million years ago.

  5. Young stars in old galaxies - surprising discovery with the world's leading telescopes

    NASA Astrophysics Data System (ADS)

    2002-06-01

    Do elliptical galaxies only contain old stars? One of the challenges of modern astronomy is to understand how galaxies - large systems of stars, gas and dust - form and evolve. When did most of the stars in the Universe form? Did this happen at a very early stage, within a few billion years of the Big Bang? Have a significant number of the stars we now observe formed much more recently? Spectacular collisions between galaxies take place all the time, triggering the formation of thousands or even millions of stars. However, when looking at the Universe as a whole, most of its stars are found in elliptical galaxies whose overall appearance has so far led us to believe that they, and their stars and as well, are old. These elliptical galaxies do shine with the diffuse, reddish glow normally associated with stars that are many thousand million years old. However, what is the underlying mix of stars that produces this elderly appearance? Could a significant number of much younger stars be 'hiding' among the older ones? Detailed observations with the world's premier telescopes have now cast new light on this central question about the behaviour of some of the major building blocks of the Universe. Cosmic paleonthology To break the stellar 'cocktail' in elliptical galaxies down into its different constituents, a team of European and American astronomers observed massive stellar clusters in and around nearby galaxies. These "globular" clusters, so called because of their shape, exist in large numbers around all observed galaxies and form a kind of 'skeleton' within their host galaxies. These 'bones' receive an imprint for every episode of star formation they undergo. By reading the ages of the globular clusters in a galaxy, it is possible to identify the past epoch(s) of active star formation in a galaxy. Reading the imprints and deducing the distribution of ages of the globular clusters, astronomers can reveal when many of the stars in elliptical galaxies formed. This is similar to the way a palaeontologist uses the skeletons of dinosaurs to deduce information about the era in which they lived. A surprising discovery The team combined images of a number of galaxies from Hubble's Wide Field and Planetary Camera 2 with infrared images obtained from the multi-mode ISAAC instrument on the 8.2m VLT Antu telescope at the ESO Paranal Observatory (Chile). To their great surprise, they discovered that many of the globular clusters in one of these galaxies, NGC 4365, a member of the large Virgo cluster of galaxies, were only a few thousand million years old, much younger than most of the other stars in this galaxy (roughly 12 thousand million years old). The astronomers were able to identify three major groups of stellar clusters. There is an old population of clusters of metal-poor stars, some clusters of old but metal-rich stars and now, seen for the first time, a population of clusters with young and metal-rich stars. These results have been fully confirmed by spectroscopic observations made with another of the world's giant telescopes, the 10-metre Keck on Hawaii. "It is a great pleasure to see two projects wholly or partly funded by Europe - VLT and Hubble - work in concert to produce such an important scientific result", says Piero Benvenuti, ESA Hubble Project Scientist. "The synergy between the most advanced ground and space telescopes continues to prove its effectiveness, paving the way to impressive new discoveries that would not otherwise be possible." The discovery of young globular clusters within old galaxies is surprising since the stars in the giant elliptical galaxies were until now believed to have formed during a single period early in the history of the Universe. It is now clear that some of the galaxies may be hiding their true nature and have indeed experienced much more recent periods of major star formation. Notes for editors This press release is issued in coordination between ESA and ESO. The Hubble Space Telescope project is an international cooperation between ESA and NASA. The team working on these HST/VLT observations is presenting the results at the New Horizons in Globular Cluster Astronomy conference in Padua, Italy, 24-28 June 2002. The team consists of Markus Kissler-Patig (European Southern Observatory, Germany), Thomas H. Puzia (University of Munich, Germany), Stephen E. Zepf (Yale University and Michigan State University, United States), Michael Hilker (Sternwarte University, Bonn, Germany), Dante Minitti (Catholic University, Santiago, Chile), Paul Goudfrooij (STScI, Baltimore, United States) and Maren Hempel (European Southern Observatory, Munich, Germany).

  6. TRIGGERED STAR FORMATION AND YOUNG STELLAR POPULATION IN BRIGHT-RIMMED CLOUD SFO 38

    SciTech Connect

    Choudhury, Rumpa; Bhatt, H. C.; Mookerjea, Bhaswati E-mail: hcbhatt@iiap.res.i

    2010-07-10

    We have investigated the young stellar population in and around SFO 38, one of the massive globules located in the northern part of the Galactic H II region IC 1396, using the Spitzer IRAC and MIPS observations (3.6-24 {mu}m), and followed up with ground-based optical photometric and spectroscopic observations. Based on the IRAC and MIPS colors and H{alpha} emission, we identify {approx}45 young stellar objects (Classes 0/I/II) and 13 probable pre-main-sequence candidates. We derive the spectral types (mostly K- and M-type stars), effective temperatures, and individual extinction of the relatively bright and optically visible Class II objects. Most of the Class II objects show variable H{alpha} emission as well as optical and near-infrared photometric variability, which confirm their 'youth'. Based on optical photometry and theoretical isochrones, we estimate the spread in stellar ages to be between 1 and 8 Myr with a median age of 3 Myr and a mass distribution of 0.3-2.2 M{sub sun} with a median value around 0.5 M{sub sun}. Using the width of the H{alpha} emission line measured at 10% peak intensity, we derive the mass accretion rates of individual objects to be between 10{sup -10} and 10{sup -8} M{sub sun} yr{sup -1}. From the continuum-subtracted H{alpha} line image, we find that the H{alpha} emission of the globule is not spatially symmetric with respect to the O-type ionizing star HD 206267, and the interstellar extinction toward the globule is also anomalous. We clearly detect an enhanced concentration of YSOs closer to the southern rim of SFO 38 and identify an evolutionary sequence of YSOs from the rim to the dense core of the cloud, with most of the Class II objects located at the bright rim. The YSOs appear to be aligned along two different directions toward the O6.5V type star HD 206267 and the B0V type star HD 206773. This is consistent with the Radiation Driven Implosion (RDI) model for triggered star formation. Further, the apparent speed of sequential star formation is consistent with the speed of propagation of shocks in dense globules as derived from numerical simulations of RDI.

  7. Supersaturation and activity-rotation relation in PMS stars: the young cluster h Persei

    NASA Astrophysics Data System (ADS)

    Argiroffi, C.; Caramazza, M.; Micela, G.; Sciortino, S.; Moraux, E.; Bouvier, J.; Flaccomio, E.

    2016-04-01

    Context. Several studies showed that the magnetic activity of late-type main-sequence (MS) stars is characterized by different regimes and that their activity levels are well described by the Rossby number, Ro, defined as the ratio between the rotational period Prot and the convective turnover time. Very young pre-main-sequence (PMS) stars show, similarly to MS stars, intense magnetic activity. However, they do not show clear activity-rotation trends, and it still debated which stellar parameters determine their magnetic activity levels. Aims: To bridge the gap between MS and PMS stars, we studied the activity-rotation relation in the young cluster h Persei, a ~13 Myr old cluster, that contains both fast and slow rotators. The cluster members have ended their accretion phase and have developed a radiative core. It therefore offers us the opportunity of studying the activity level of intermediate-age PMS stars with different rotational velocities, excluding any interactions with the circumstellar environment. Methods: We constrained the magnetic activity levels of h Per members by measuring their X-ray emission from a Chandra observation, while rotational periods were obtained previously in the framework of the MONITOR project. By cross-correlating these data, we collected a final catalog of 414 h Per members with known rotational period, effective temperature, and mass. In 169 of these, X-ray emission has also been detected. Results: We found that h Per members with 1.0 M⊙stars, indicating that at this age, magnetic field production is most likely regulated by the αΩ type dynamo. Moreover, we observed that supersaturation is better described by Prot than Ro, and that the observed patterns are compatible with the hypothesis of centrifugal stripping. In this scenario we inferred that coronae can produce structures as large as ~2 R⋆ above the stellar surface. Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A113

  8. CSI 2264: Accretion process in classical T Tauri stars in the young cluster NGC 2264

    NASA Astrophysics Data System (ADS)

    Sousa, A. P.; Alencar, S. H. P.; Bouvier, J.; Stauffer, J.; Venuti, L.; Hillenbrand, L.; Cody, A. M.; Teixeira, P. S.; Guimarães, M. M.; McGinnis, P. T.; Rebull, L.; Flaccomio, E.; Fürész, G.; Micela, G.; Gameiro, J. F.

    2016-02-01

    Context. NGC 2264 is a young stellar cluster (~3 Myr) with hundreds of low-mass accreting stars that allow a detailed analysis of the accretion process taking place in the pre-main sequence. Aims: Our goal is to relate the photometric and spectroscopic variability of classical T Tauri stars to the physical processes acting in the stellar and circumstellar environment, within a few stellar radii from the star. Methods: NGC 2264 was the target of a multiwavelength observational campaign with CoRoT, MOST, Spitzer, and Chandra satellites and photometric and spectroscopic observations from the ground. We classified the CoRoT light curves of accreting systems according to their morphology and compared our classification to several accretion diagnostics and disk parameters. Results: The morphology of the CoRoT light curve reflects the evolution of the accretion process and of the inner disk region. Accretion burst stars present high mass-accretion rates and optically thick inner disks. AA Tau-like systems, whose light curves are dominated by circumstellar dust obscuration, show intermediate mass-accretion rates and are located in the transition of thick to anemic disks. Classical T Tauri stars with spot-like light curves correspond mostly to systems with a low mass-accretion rate and low mid-IR excess. About 30% of the classical T Tauri stars observed in the 2008 and 2011 CoRoT runs changed their light-curve morphology. Transitions from AA Tau-like and spot-like to aperiodic light curves and vice versa were common. The analysis of the Hα emission line variability of 58 accreting stars showed that 8 presented a periodicity that in a few cases was coincident with the photometric period. The blue and red wings of the Hα line profiles often do not correlate with each other, indicating that they are strongly influenced by different physical processes. Classical T Tauri stars have a dynamic stellar and circumstellar environment that can be explained by magnetospheric accretion and outflow models, including variations from stable to unstable accretion regimes on timescales of a few years. Full Tables 2 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A47

  9. Young stars in nearby early-type galaxies: SED fitting based on ultraviolet (UV) and optical imaging

    NASA Astrophysics Data System (ADS)

    Jeong, Hyunjin; Yi, Sukyoung K.; Bureau, Martin; Davies, Roger L.

    2012-08-01

    Recent studies from the Galaxy Evolution Explore (GALEX) ultraviolet (UV) data have demonstrated that the recent star formation is more common in early-type galaxies (ETGs) than we used to believe. The UV is one order of magnitude more sensitive than the optical to the presence of young stellar populations. The near-ultraviolet (NUV) lights of ETGs, especially, are used to reveal their residual star formation history. Here we used the GALEX UV data of 34 nearby early-type galaxies from the SAURON sample, all of which have optical data from MDM Observatory. At least 15% of the galaxies in this sample show blue UV-optical colours suggesting recent star formation (Jeong et al. 2009). These NUV blue galaxies are generally low velocity dispersion systems and change the slopes of scaling relations (colour-magnitude relations and fundamental planes) and increase the scatters. To quantify the amount of recent star formation in our sample, we assume two bursts of star formation, allowing us to constrain the age and mass fraction of the young component pixel by pixel (Jeong et al. 2007). The pixel-by-pixel SED fitting based on UV and optical imaging reveals that the mass fraction of young (< 1 Gyr old) stars in ETGs varies between 1 and 3% in the nearby universe (Jeong et al. in prep.). We will compare our results with the prediction from the hierarchical merger paradigm to understand the mechanism of low-level recent star formation observed in early-type galaxies.

  10. Star formation rates from young-star counts and the structure of the ISM across the NGC 346/N66 complex in the SMC

    NASA Astrophysics Data System (ADS)

    Hony, S.; Gouliermis, D. A.; Galliano, F.; Galametz, M.; Cormier, D.; Chen, C.-H. R.; Dib, S.; Hughes, A.; Klessen, R. S.; Roman-Duval, J.; Smith, L.; Bernard, J.-P.; Bot, C.; Carlson, L.; Gordon, K.; Indebetouw, R.; Lebouteiller, V.; Lee, M.-Y.; Madden, S. C.; Meixner, M.; Oliveira, J.; Rubio, M.; Sauvage, M.; Wu, R.

    2015-04-01

    The rate at which interstellar gas is converted into stars, and its dependence on environment, is one of the pillars on which our understanding of the visible Universe is build. We present a comparison of the surface density of young stars (Σ⋆) and dust surface density (Σdust) across NGC 346 (N66) in 115 independent pixels of 6 × 6 pc2. We find a correlation between Σ⋆ and Σdust with a considerable scatter. A power-law fit to the data yields a steep relation with an exponent of 2.6 ± 0.2. We convert Σdust to gas surface density (Σgas) and Σ⋆ to star formation rate (SFR) surface densities (ΣSFR), using simple assumptions for the gas-to-dust mass ratio and the duration of star formation. The derived total SFR (4 ± 1×10-3 M⊙ yr-1) is consistent with SFR estimated from the Hα emission integrated over the Hα nebula. On small scales the ΣSFR derived using Hα systematically underestimates the count-based ΣSFR, by up to a factor of 10. This is due to ionizing photons escaping the area, where the stars are counted. We find that individual 36 pc2 pixels fall systematically above integrated disc galaxies in the Schmidt-Kennicutt diagram by on average a factor of ˜7. The NGC 346 average SFR over a larger area (90 pc radius) lies closer to the relation but remains high by a factor of ˜3. The fraction of the total mass (gas plus young stars) locked in young stars is systematically high (˜10 per cent) within the central 15 pc and systematically lower outside (2 per cent), which we interpret as variations in star formation efficiency. The inner 15 pc is dominated by young stars belonging to a centrally condensed cluster, while the outer parts are dominated by a dispersed population. Therefore, the observed trend could reflect a change of star formation efficiency between clustered and non-clustered star formation.

  11. Young stars in ɛ Chamaleontis and their disks: disk evolution in sparse associations

    NASA Astrophysics Data System (ADS)

    Fang, M.; van Boekel, R.; Bouwman, J.; Henning, Th.; Lawson, W. A.; Sicilia-Aguilar, A.

    2013-01-01

    Context. The nearby young stellar association ɛ Cha has an estimated age of 3-5 Myr, making it an ideal laboratory to study the disk dissipation process and provide empirical constraints on the timescale of planet formation. Aims: We wish to complement existing optical and near-infrared data of the ɛ Cha association, which provide the stellar properties of its members, with mid-infrared data that probe the presence, geometry, and mineralogical composition of protoplanetary disks around individual stars. Methods: We combine the available literature data with our Spitzer/IRS spectroscopy and VLT/VISIR imaging data. We use proper motions to refine the membership of ɛ Cha. Masses and ages of individual stars are estimated by fitting model atmospheres to the optical and near-infrared photometry, followed by placement in the Hertzsprung-Russell diagram. The Spitzer/IRS spectra are analyzed using the two-layer temperature distribution spectral decomposition method. Results: Two stars previously identified as members, CXOU J120152.8 and 2MASS J12074597, have proper motions that are very different from those of the other stars. But other observations suggest that the two stars are still young and thus might still be related to ɛ Cha. HD 104237C is the lowest mass member of ɛ Cha with an estimated mass of ~13-15 Jupiter masses. The very low mass stars USNO-B120144.7 and 2MASS J12005517 show globally depleted spectral energy distributions, pointing at strong dust settling. 2MASS J12014343 may have a disk with a very specific inclination, where the central star is effectively screened by the cold outer parts of a flared disk, but the 10 μm radiation of the warm inner disk can still reach us. We find that the disks in sparse stellar associations are dissipated more slowly than those in denser (cluster) environments. We detect C2H2 rovibrational band around 13.7 μm on the IRS spectrum of USNO-B120144.7. We find strong signatures of grain growth and crystallization in all ɛ Cha members with 10 μm features detected in their IRS spectra. We combine the dust properties derived in the ɛ Cha sample with those found using identical or similar methods in the MBM 12, Coronet, η Cha associations, and in the cores-to-disks legacy program. We find that disks around low-mass young stars show a negative radial gradient in the mass-averaged grain size and mass fraction of crystalline silicates. A positive correlation exists between the mass-averaged grain sizes of amorphous silicates and the accretion rates if the latter is above ~10-9 M⊙ yr-1, possibly indicating that those disks are sufficiently turbulent to prevent grains of several microns in size to sink into the disk interior. Based on observations performed at ESO's La Silla-Paranal observatory under programme 076.C-0470.

  12. A wide-field near- and mid-infrared Census of young stars in NGC 6334

    SciTech Connect

    Willis, S.; Marengo, M.; Allen, L.; Fazio, G. G.; Smith, H. A.; Carey, S.

    2013-12-01

    This paper presents a study of the rate and efficiency of star formation in the NGC 6334 star-forming region. We obtained observations at J, H, and K{sub s} taken with the NOAO Extremely Wide-Field Infrared Imager and combined them with observations taken with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope at wavelengths = 3.6, 4.5, 5.8, and 8.0 μm. We also analyzed previous observations taken at 24 μm using the Spitzer MIPS camera as part of the MIPSGAL survey. We have produced a point source catalog with >700, 000 entries. We have identified 2283 young stellar object (YSO) candidates, 375 Class I YSOs, and 1908 Class II YSOs using a combination of existing IRAC-based color classification schemes that we have extended and validated to the near-IR for use with warm Spitzer data. We have identified multiple new sites of ongoing star formation activity along filamentary structures extending tens of parsecs beyond the central molecular ridge of NGC 6334. By mapping the extinction, we derived an estimate for the gas mass, 2.2 × 10{sup 5} M {sub ☉}. The heavy concentration of protostars along the dense filamentary structures indicates that NGC 6334 may be undergoing a 'mini-starburst' event with Σ{sub SFR} > 8.2 M {sub ☉} Myr{sup –1} pc{sup –2} and SFE > 0.10. We have used these estimates to place NGC 6334 in the Kennicutt-Schmidt diagram to help bridge the gap between observations of local low-mass star-forming regions and star formation in other galaxies.

  13. Signatures of Young Star Formation Activity within Two Parsecs of Sgr A*

    NASA Astrophysics Data System (ADS)

    Yusef-Zadeh, F.; Wardle, M.; Sewilo, M.; Roberts, D. A.; Smith, I.; Arendt, R.; Cotton, W.; Lacy, J.; Martin, S.; Pound, M. W.; Rickert, M.; Royster, M.

    2015-07-01

    We present radio and infrared observations indicating ongoing star formation activity inside the ˜2-5 pc circumnuclear ring at the Galactic center. Collectively these measurements suggest a continued disk-based mode of ongoing star formation has taken place near Sgr A* over the last few million years. First, Very Large Array observations with spatial resolution 2.″17 × 0.″81 reveal 13 water masers, several of which have multiple velocity components. The presence of interstellar water masers suggests gas densities that are sufficient for self-gravity to overcome the tidal shear of the 4× {10}6 {M}⊙ black hole. Second, spectral energy distribution modeling of stellar sources indicates massive young stellar object (YSO) candidates interior to the molecular ring, supporting in situ star formation near Sgr A* and appear to show a distribution similar to that of the counter-rotating disks of ˜100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS 5) have bow shock structures, suggesting that they have gaseous disks that are phototoevaporated and photoionized by the strong radiation field. Third, we detect clumps of SiO (2-1) and (5-4) line emission in the ring based on Combined Array for Research in Millimeter-wave Astronomy and Sub-Millimeter Array observations. The FWHM and luminosity of the SiO emission is consistent with shocked protostellar outflows. Fourth, two linear ionized features with an extent of ˜0.8 pc show blue and redshifted velocities between +50 and -40 km s-1, suggesting protostellar jet driven outflows with mass-loss rates of ˜ 5× {10}-5 {M}⊙ yr-1. Finally, we present the imprint of radio dark clouds at 44 GHz, representing a reservoir of molecular gas that feeds star formation activity close to Sgr A*.

  14. The masses of young stars: CN as a probe of dynamical masses

    NASA Astrophysics Data System (ADS)

    Guilloteau, S.; Simon, M.; Piétu, V.; Di Folco, E.; Dutrey, A.; Prato, L.; Chapillon, E.

    2014-07-01

    Aims: We attempt to determine the masses of single or multiple young T Tauri and HAeBe stars from the rotation of their Keplerian disks. Methods: We used the IRAM PdBI interferometer to perform arcsecond resolution images of the CN N = 2-1 transition with good spectral resolution. Integrated spectra from the 30 m radiotelescope show that CN is relatively unaffected by contamination from the molecular clouds. Our sample includes 12 sources, among which isolated stars like DM Tau and MWC 480 are used to demonstrate the method and its accuracy. We derive the dynamical mass by fitting a disk model to the emission, a process giving M/D, the mass-to-distance ratio. We also compare the CN results with higher resolution CO data, that are however affected by contamination. Results: All disks are found in nearly perfect Keplerian rotation. We determine accurate masses for 11 stars, in the mass range 0.5 to 1.9 M⊙. The remaining one, DG Tau B, is a deeply embedded object for which CN emission partially arises from the outflow. With previous determinations, this leads to 14 (single) stars with dynamical masses. Comparison with evolutionary tracks, in a distance independent modified HR diagram, show good overall agreement (with one exception, CW Tau), and indicate that measurement of effective temperatures are the limiting factor. The lack of low mass stars in the sample does not allow to distinguish between alternate tracks. Based on observations carried out with the IRAM Plateau de Bure interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Appendices are available in electronic form at http://www.aanda.org

  15. Protoplanetary Disk Shadowing by Gas Infalling onto the Young Star AK Sco

    NASA Astrophysics Data System (ADS)

    Gómez de Castro, Ana I.; Loyd, Robert O. P.; France, Kevin; Sytov, Alexey; Bisikalo, Dmitry

    2016-02-01

    Young solar-type stars grow through the accretion of material from the circumstellar disk during pre-main-sequence (PMS) evolution. The ultraviolet radiation generated in this process plays a key role in the chemistry and evolution of young planetary disks. In particular, the hydrogen Lyα line (Lyα) etches the disk surface by driving photoevaporative flows that control disk evolution. Using the Hubble Space Telescope, we have monitored the PMS binary star AK Sco during the periastron passage and have detected a drop of the H2 flux by up to 10% lasting 5.9 hr. We show that the decrease of the H2 flux can be produced by the occultation of the stellar Lyα photons by a gas stream in free fall from 3 R{}*. Given the high optical depth of the Lyα line, a very low gas column of {N}{{H}}\\gt 5× {10}17 cm-2 suffices to block the Lyα radiation without producing noticeable effects in the rest of the stellar spectral tracers.

  16. YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD STAR-FORMING REGION N206

    SciTech Connect

    Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B.; Carlson, Lynn Redding; Whitney, B.; Babler, B.; Meade, M.; Indebetouw, R.; Hora, J. L. E-mail: carlson@stsci.ed E-mail: brian@sal.wisc.ed E-mail: jhora@cfa.harvard.ed

    2010-09-20

    We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 {mu}m and MIPS 24 {mu}m), Infrared Survey Facility near-infrared survey (J, H, K{sub s}), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 {mu}m. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of {approx}14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is {approx}520 M{sub sun}. We calculate a current star formation rate of 0.27 x 10{sup -1} M{sub sun} yr{sup -1} kpc{sup -2}. The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

  17. Discovery of a wide planetary-mass companion to the young M3 star GU PSC

    SciTech Connect

    Naud, Marie-Eve; Artigau, Étienne; Malo, Lison; Albert, Loïc; Doyon, René; Lafrenière, David; Gagné, Jonathan; Boucher, Anne; Saumon, Didier; Morley, Caroline V.; Allard, France; Homeier, Derek; Beichman, Charles A.; Gelino, Christopher R.

    2014-05-20

    We present the discovery of a comoving planetary-mass companion ∼42'' (∼2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T {sub eff} = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M {sub Jup} for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE 9.

  18. Mid-infrared [NeII] Imaging of Young Massive Star Clusters Near Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Yeh, Sherry C. C.; Tsai, Chao-Wei; Geballe, Thomas R.; Herrera, Cinthya N.

    2015-08-01

    We present a straightforward approach to study young and highly obscured massive star clusters in ground-based MIR observations. The Kennicutt-Schmitt Law does not necessarily operate near galactic nuclei, and the universality of the cluster formation efficiency (CFE) and mass function is yet to be validated. Ground-based, mid-infrared imaging of [NeII] at 12.8 μm does not suffer from severe extinction, and it simultaneously delivers sub-arcsecond angular resolution and recovers extended emission. We mapped the nuclei of NGC 6946, IC 342, Maffei 2, and NGC 7714 in [NeII] using Subaru Telescope. We identified ~20 compact thermal sources which are likely to be young massive clusters, as well as very extended emission which is presumably associated with non-compact, field star formation. The masses of the clusters are estimated to be 104 to 105 M⊙. By comparing [NeII] fluxes of the compact sources and extended emission, we estimated the CFE to be ~ 5% to 13% in the target galaxies, while a CFE of 10% is found in other galactic environments. We will discuss the cluster physical properties, cluster formation efficiency, cluster mass function, their implications, and the followup spectroscopic work.

  19. IS THE YOUNG STAR CLUSTER NGC 376 DISSOLVING IN THE FIELD OF THE SMALL MAGELLANIC CLOUD?

    SciTech Connect

    Sabbi, E.; Nota, A.; Smith, L. J.; Tosi, M.; Cignoni, M.; Gallagher, J.

    2011-09-20

    We use deep images acquired with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud. Using isochrone fitting we derive for NGC 376 an age of 28 {+-} 7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theoretical model, suggesting that the cluster is not in virial equilibrium. Considering the young age of the cluster, we speculate that the distortion of the radial profiles may be the result of the rapid gas dispersal that follows the initial phase of star formation (SF). The cluster shows clear evidence of dynamical mass segregation. From the properties of the radial profiles and the present-day mass function we conclude that NGC 376 appears to have already lost nearly 90% of its initial stellar mass, probably as a consequence of the sudden gas dispersal that follows the early phase of SF.

  20. The Spatial Distribution of the Young Stellar Clusters in the Star-forming Galaxy NGC 628

    NASA Astrophysics Data System (ADS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Aloisi, A.; Bright, S. N.; Christian, C.; Cignoni, M.; Dale, D. A.; Dobbs, C.; Elmegreen, D. M.; Fumagalli, M.; Gallagher, J. S., III; Grebel, E. K.; Johnson, K. E.; Lee, J. C.; Messa, M.; Smith, L. J.; Ryon, J. E.; Thilker, D.; Ubeda, L.; Wofford, A.

    2015-12-01

    We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (≲ 100 Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of α ˜ -0.8 for all spatial scales below the break at 3.″3 (158 pc at a distance of 9.9 Mpc) and an index of α ˜ -0.18 above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium.

  1. High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

    SciTech Connect

    greenhill, l

    2004-06-25

    The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 {micro}m to 22 {micro}m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L{sub {center_dot}}. Although source I is believed to be more luminous, they do not detect an infrared counterpart even at the longest wavelengths. However, they resolve the closeby infrared source, IRc2, into an arc of knots {approx} 10{sup 3} AU long at all wavelengths. Although the physical relation of source I to IRc2 remains ambiguous, they suggest these sources mark a high density core (10{sup 7}-10{sup 8} pc{sup -3} over {approx} 10{sup 3} AU) within the larger BN/KL star forming cluster. The high density may be a consequence of the core being young and heavily embedded. The authors suggest the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources.

  2. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    SciTech Connect

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; De Koter, A.; Sana, H.; Gvaramadze, V. V.; Liermann, A.

    2014-01-10

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M {sub ☉}.

  3. Orion in a New Light - VISTA exposes high-speed antics of young stars

    NASA Astrophysics Data System (ADS)

    2010-02-01

    The Orion Nebula reveals many of its hidden secrets in a dramatic image taken by ESO's new VISTA survey telescope. The telescope's huge field of view can show the full splendour of the whole nebula and VISTA's infrared vision also allows it to peer deeply into dusty regions that are normally hidden and expose the curious behaviour of the very active young stars buried there. VISTA - the Visible and Infrared Survey Telescope for Astronomy - is the latest addition to ESO's Paranal Observatory (eso0949). It is the largest survey telescope in the world and is dedicated to mapping the sky at infrared wavelengths. The large (4.1-metre) mirror, wide field of view and very sensitive detectors make VISTA a unique instrument. This dramatic new image of the Orion Nebula illustrates VISTA's remarkable powers. The Orion Nebula [1] is a vast stellar nursery lying about 1350 light-years from Earth. Although the nebula is spectacular when seen through an ordinary telescope, what can be seen using visible light is only a small part of a cloud of gas in which stars are forming. Most of the action is deeply embedded in dust clouds and to see what is really happening astronomers need to use telescopes with detectors sensitive to the longer wavelength radiation that can penetrate the dust. VISTA has imaged the Orion Nebula at wavelengths about twice as long as can be detected by the human eye. As in the many visible light pictures of this object, the new wide field VISTA image shows the familiar bat-like form of the nebula in the centre of the picture as well as the fascinating surrounding area. At the very heart of this region lie the four bright stars forming the Trapezium, a group of very hot young stars pumping out fierce ultraviolet radiation that is clearing the surrounding region and making the gas glow. However, observing in the infrared allows VISTA to reveal many other young stars in this central region that cannot be seen in visible light. Looking to the region above the centre of the picture, curious red features appear that are completely invisible except in the infrared. Many of these are very young stars that are still growing and are seen through the dusty clouds from which they form. These youthful stars eject streams of gas with typical speeds of 700 000 km/hour and many of the red features highlight the places where these gas streams collide with the surrounding gas, causing emission from excited molecules and atoms in the gas. There are also a few faint, red features below the Orion Nebula in the image, showing that stars form there too, but with much less vigour. These strange features are of great interest to astronomers studying the birth and youth of stars. This new image shows the power of the VISTA telescope to image wide areas of sky quickly and deeply in the near-infrared part of the spectrum. The telescope is just starting to survey the sky and astronomers are anticipating a rich harvest of science from this unique ESO facility. Notes [1] The Orion Nebula lies in the sword of the famous celestial hunter and is a favourite target both for casual sky watchers and astrophysicists alike. It is faintly visible to the unaided eye and appeared to early telescopic observers as a small cluster of blue-white stars surrounded by a mysterious grey-green mist. The object was first described in the early seventeenth century although the identity of the discoverer is uncertain. The French comet-hunter Messier made an accurate sketch of its main features in the mid-eighteenth century and gave it the number 42 in his famous catalogue. He also allocated the number 43 to the smaller detached region just above the main part of the nebula. Later William Herschel speculated that the nebula might be "the chaotic material of future suns" and astronomers have since discovered that the mist is indeed gas glowing under the fierce ultraviolet light from young hot stars that have recently formed there. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

  4. Young Stars in Old Galaxies - a Cosmic Hide and Seek Game

    NASA Astrophysics Data System (ADS)

    2002-05-01

    Surprise Discovery with World's Leading Telescopes [1] Summary Combining data from the NASA/ESA Hubble Space Telescope (HST) and the ESO Very Large Telescope (VLT) , a group of European and American astronomers [2] have made an unexpected, major discovery. They have identified a huge number of "young" stellar clusters , only a few billion years old [3], inside an "old" elliptical galaxy (NGC 4365), probably aged some 12 billion years. For the first time, it has been possible to identify several distinct periods of star-formation in a galaxy as old as this one . Elliptical galaxies like NGC 4365 have until now been considered to have undergone one early star-forming period and thereafter to be devoid of any star formation. However, the combination of the best and largest telescopes in space and on the ground has now clearly shown that there is more than meets the eye. This important new information will help to understand the early history of galaxies and the general theory of star formation in the Universe . PR Photo 15a/02 : Combined HST+VLT image of elliptical galaxy NGC 4365 PR Photo 15b/02 : Same image, with "old" and "young" stellar clusters indicated PR Photo 15c/02 : Animated GIF image, showing the three cluster populations observed in NGC 4365 Do elliptical galaxies only contain old stars? One of the challenges of modern astronomy is to understand how galaxies, those large systems of stars, gas and dust, form and evolve. In this connection, a central question has always been to learn when most of the stars in the Universe formed. Did this happen at a very early stage, within a few billion years after the Big Bang? Or were a significant number of the stars we now observe formed much more recently? Spectacular collisions between galaxies take place all the time, triggering the formation of thousands or even millions of stars, cf. ESO PR Photo 29b/99 of the dramatic encounter between NGC 6872 and IC 4970. However, when looking at the Universe as a whole, most of its stars are found in large elliptical galaxies (this refers to their form) whose overall appearance has so far led us to believe that they, and their stars as well, are very old, indeed among the oldest objects in the Universe. These elliptical galaxies do shine with the diffuse, reddish glow normally associated with stars that are many billions of years old. However, what is really the underlying mix of stars that produces this elderly appearance? Could perhaps a significant number of much younger stars be "hiding" among the older ones? Whatever the case, this question must obviously be looked into, before it is possible to claim understanding of the evolution of these old galaxies. It is a very challenging investigation and it is only now that new and more detailed observations with the world's premier telescopes have been obtained that cast more light on this central question and thus on the true behaviour of some of the major building blocks of the Universe. Cosmic archaeology In order to identify the constitutents of the stellar "cocktail" in elliptical galaxies, a team of European and American astronomers [2] observed massive stellar clusters in and around several nearby galaxies. These clusters, referred to as "globular" because of their shape, are present in large numbers around most galaxies and together they form a kind of "skeleton" within their host galaxies. These "bones" receive an imprint for every episode of star formation they undergo. Thus, by reading the ages of the globular clusters in a galaxy, it is possible to identify the past epoch(s) of active star formation in that galaxy. This is like digging into the ruins of an ancient archaeological city site and to find those layers and establish those times when the city underwent bursts of building activity. In this way, by the study of the distribution and ages of the globular clusters in an elliptical galaxy, astronomers can reveal when many of its stars were formed. A surprise discovery ESO PR Photo 15a/02 ESO PR Photo 15a/02 [Preview - JPEG: 400 x 484 pix - 120k [Normal - JPEG: 800 x 967 pix - 408k] [HiRes - JPEG: 1854 x 2241 pix - 1.5M] ESO PR Photo 15b/02 ESO PR Photo 15b/02 [Preview - JPEG: 400 x 484 pix - 160k] [Normal - JPEG: 800 x 967 pix - 480k] ESO PR Photo 15c/02 ESO PR Photo 15c/02 [Animated GIF: 400 x 414 pix - 264k] Caption : PR Photo 15a/02 shows a colour composite of the elliptical galaxy NGC 4365, prepared from two exposures with the HST and one from the VLT. Many of the objects seen are stellar clusters in this galaxy. There are also a large number of background galaxies in the field. In PR Photo 15b/02 , the distribution of "old" (red circles) and "young" (blue circles) stellar clusters in NGC 4365 are shown, as they were identified during the present investigation. PR Photo 15c/02 shows the distribution of three populations of stellar clusters mentioned in the text (a: old and metal-poor; b: old and metal-rich; c: young and metal-rich). Technical information about these photos is available below. The team combined images in visual light of a number of galaxies from Hubble's Wide Field and Planetary Camera 2 (WFPC2) with infrared images obtained with the multi-mode ISAAC instrument on the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory (Chile). When measuring very accurately the colours of the globular clusters in one of these galaxies, NGC 4365 that is a member of the large Virgo Cluster of galaxies, they discovered to their great surprise that many of these clusters are only a few billion years old, i.e. much younger than the age of most other stars in that galaxy, roughly 12 billion years. In fact, the astronomers were able to identify three major groups of globular clusters in NGC 4365 . First, there is an old population of clusters of metal-poor stars, then there are some clusters of old, but metal-rich stars and now, seen for the first time, a third population of clusters with young and metal-rich stars . "We needed the combination of the Hubble and the VLT with the latest space- and ground-based astronomical technology to break this new ground", says group leader Markus Kissler-Patig from the European Southern Observatory Headquarters in Garching (Germany). "Once we had found those young clusters, we then went on to observe them spectroscopically with another of the world's giant telescopes, the 10-m Keck on Hawaii - and this fully confirmed our results." A new important clue to the evolution of the Universe This is a surprising discovery since the stars in giant elliptical galaxies were until now believed to have formed exclusively early on in the history of the Universe. However, it is now clear that some of the old galaxies may have been hiding their true nature and have indeed experienced much more recent periods of major star formation. This is priceless new information for the current attempts to understand the early history of galaxies and the general theory of star formation in the Universe. More information The information presented in this Press Release is based on a research article that has been accepted for publication in the European journal "Astronomy & Astrophysics" ("Extragalactic Globular Clusters in the Near-Infrared: II. The Globular Cluster Systems of NGC 3115 and NGC 4365" by Thomas H. Puzia, Stephen E. Zepf, Markus Kissler-Patig, Michael Hilker, Dante Minniti and Paul Goudfrooij; astro-ph/0206147 ). Notes [1]: This press release is issued in coordination between ESA and ESO. The Hubble Space Telescope is an international cooperation between ESA and NASA. The team is presenting these results at the New Horizons in Globular Cluster Astronomy conference in Padova, Italy 24-28 June, 2002. [2]: The team consists of Thomas H. Puzia (Sternwarte Müenchen, Germany), Stephen E. Zepf (Yale University and Michigan State University, USA), Markus Kissler-Patig and Maren Hempel (ESO, Garching, Germany), Michael Hilker (Sternwarte Bonn, Germany), Dante Minniti (Universidad Catolica, Santiago de Chile) and Paul Goudfrooij (Space Telescope Science Institute, Baltimore, USA). [3]: 1 billion = 1,000 million = 1,000,000,000

  5. HUBBLE SPACE TELESCOPE/NICMOS Imaging of Disks and Envelopes around Very Young Stars

    NASA Astrophysics Data System (ADS)

    Padgett, Deborah L.; Brandner, Wolfgang; Stapelfeldt, Karl R.; Strom, Stephen E.; Terebey, Susan; Koerner, David

    1999-03-01

    We present HST/NICMOS observations with ~0.1"~15 AU resolution of six young stellar objects in the Taurus star formation region. The targets of our survey are three Class I IRAS sources (IRAS 04016+2610, IRAS 04248+2612, and IRAS 04302+2247) and three low-luminosity stars (DG Tau B, Haro 6-5B, and CoKu Tau/1) associated with Herbig-Haro jets. The broadband images show that the near-infrared radiation from these sources is dominated by light scattered from dusty circumstellar material distributed in a region 10-15 times the size of our solar system. Although the detailed morphologies of the individual objects are unique, the observed young stellar objects share common features. All of the circumstellar reflection nebulae are crossed by dark lanes from 500 to 900 AU in extent and from less than 50 to 350 AU in apparent thickness. The absorption lanes extend perpendicular to known optical and millimeter outflows in these sources. We interpret the dark lanes as optically thick circumstellar disks seen in silhouette against bright reflection nebulosity. The bipolar reflection nebulae extending perpendicular to the dust lanes appear to be produced by scattering from the upper and lower surfaces of the disks and from dusty material within or on the walls of the outflow cavities. Of five objects in which the central source is directly detected, two are found to be subarcsecond binaries. This minisurvey is the highest resolution near-infrared study to date of circumstellar environments around solar-type stars with age<=1 Myr.

  6. He I λ10830 as a Probe of Winds in Accreting Young Stars

    NASA Astrophysics Data System (ADS)

    Edwards, Suzan; Fischer, William; Kwan, John; Hillenbrand, Lynne; Dupree, A. K.

    2003-12-01

    He I λ10830 profiles acquired with Keck's NIRSPEC for six young low-mass stars with high disk accretion rates (AS 353A, DG Tau, DL Tau, DR Tau, HL Tau, and SVS 13) provide new insight into accretion-driven winds. In four of the stars, the profiles have the signature of resonance scattering, and they possess a deep and broad blueshifted absorption that penetrates more than 50% into the 1 μm continuum over a continuous range of velocities from near the stellar rest velocity to the terminal velocity of the wind, unlike inner wind signatures seen in other spectral features. This deep and broad absorption provides the first observational tracer of the acceleration region of the inner wind and suggests that this acceleration region is situated such that it occults a significant portion of the stellar disk. The remaining two stars also have blue absorption extending below the continuum, although here the profiles are dominated by emission, requiring an additional source of helium excitation beyond resonant scattering. This is likely the same process that produces the emission profiles seen at He I 5876 Å.

  7. Exploring Bias and Uncertainty in Gaussian Mixture Models of Young, Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Elrod, Aunna; Clarkson, William I.

    2016-06-01

    Mixture models are important for studies of star clusters observed against a foreground or background field population. By directly estimating both the distribution parameters of the components and the component fractions (and thus the formal membership probabilities), the populations of interest can be fit directly without recourse to binning. Gaussian Mixtures are a highly popular choice when modeling star clusters, and their determination using the Expectation Maximization algorithm, or its extension to cases with strongly varying measurement uncertainty (e.g. Bovy et al.’s Extreme Deconvolution) now appears in some statistics textbooks.Here we describe our Monte Carlo study to estimate the effect of the choice of instrumental setup, particularly different field of views, on parameter recovery for simulated star clusters under a variety of situations. We simulate observations of a Young, Massive Cluster like those near the Galactic Center, focusing mainly on scenarios where the same cluster is observed from ground and from space. We characterize the bias and uncertainty that might be introduced when using this fairly recent yet increasingly popular technique across heterogenous instrumental setups.

  8. VizieR Online Data Catalog: Stellar physical parameters for young stars (Monguio+, 2014)

    NASA Astrophysics Data System (ADS)

    Monguio, M.; Figueras, F.; Grosbol, P.

    2014-08-01

    A uvbyHβ Stromgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. Physical parameters like stellar distances and extinctions for the young stars of our survey are presented here. We developed a new method for deriving physical parameters from Stromgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m1], [c1] and Hβ. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for around 12000 OBA-type stars in our Stromgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data. (1 data file).

  9. A new method for measuring metallicities of young super star clusters

    SciTech Connect

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio; Davies, Ben; Bastian, Nate; Bergemann, Maria; Plez, Bertrand; Evans, Chris; Patrick, Lee; Schinnerer, Eva

    2014-06-01

    We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ∼6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ∼ 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ∼ 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper.

  10. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    SciTech Connect

    Craig, Jonathan; Krumholz, Mark R.

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  11. THE GALACTIC CENTER CLOUD G2-A YOUNG LOW-MASS STAR WITH A STELLAR WIND

    SciTech Connect

    Scoville, N.; Burkert, A.

    2013-05-10

    We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s{sup -1}, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} and wind velocity 100 km s{sup -1}, the bow shock will have an emission measure (EM = n {sup 2} vol) at a distance {approx}10{sup 16} cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ({approx}3 AU for a stellar mass of 2 M{sub Sun }). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.

  12. NGC 2782: A Merger Remnant with Young Stars in its Gaseous Tidal Tail

    NASA Technical Reports Server (NTRS)

    Torres-Flores, S.; de Oliveira, C. Mendes; de Mello, D. F.; Scarano, S. Jr.; Urrutia-Viscarra, R.

    2012-01-01

    We have searched for young star-forming regions around the merger remnant NGC 2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources, located at distances greater than 26 kpc from the center of NGG 2782, and coinciding with its western HI tidal tail. These regions were resolved in several smaller systems when Gemini/GMOS r-band images were used. We compared the observed colors to stellar population synthesis models and we found that these objects have ages of l to ll11yr and masses ranging from 10(exp 3.9) to l0(exp 4.6) Solar Mass. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H)=8.74+/-0.20, 8.81+/-0.20 and 8.78+/-0.20). These metallicities are similar to the value presented by the nuclear region of NGG 2782 and also similar to the value presented for an object located close to the main body of NGG 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGG 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the center of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.

  13. GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC3

    NASA Astrophysics Data System (ADS)

    Origlia, L.; Oliva, E.; Sanna, N.; Mucciarelli, A.; Dalessandro, E.; Scuderi, S.; Baffa, C.; Biliotti, V.; Carbonaro, L.; Falcini, G.; Giani, E.; Iuzzolino, M.; Massi, F.; Sozzi, M.; Tozzi, A.; Ghedina, A.; Ghinassi, F.; Lodi, M.; Harutyunyan, A.; Pedani, M.

    2016-01-01

    Aims: The Scutum complex in the inner disk of the Galaxy has a number of young star clusters dominated by red supergiants that are heavily obscured by dust extinction and observable only at infrared wavelengths. These clusters are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. Methods: During the technical commissioning and as a first science verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we secured high-resolution (R ≃ 50 000) near-infrared spectra of five red supergiants in the young Scutum cluster RSGC3. Results: Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to measure several tens of atomic and molecular lines that were suitable for determining chemical abundances. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and iron-peak elements such as Ni, Cr, and Cu, alpha (O, Mg, Si, Ca, Ti), other light elements (C, N, F, Na, Al, and Sc), and some s-process elements (Y, Sr). We found average half-solar iron abundances and solar-scaled [X/Fe] abundance patterns for most of the elements, consistent with a thin-disk chemistry. We found depletion of [C/Fe] and enhancement of [N/Fe], consistent with standard CN burning, and low 12C /13C abundance ratios (between 9 and 11), which require extra-mixing processes in the stellar interiors during the post-main sequence evolution. We also found local standard of rest VLSR = 106 km s-1 and heliocentric Vhel = 90 km s-1 radial velocities with a dispersion of 2.3 km s-1. Conclusions: The inferred radial velocities, abundances, and abundance patterns of RSGC3 are very similar to those previously measured in the other two young clusters of the Scutum complex, RSGC1 and RSGC2, suggesting a common kinematics and chemistry within the Scutum complex.

  14. GMRT detections of low mass young stars at 323 and 608 MHz

    NASA Astrophysics Data System (ADS)

    Ainsworth, Rachael E.; Scaife, Anna M. M.; Green, David A.; Coughlan, Colm P.; Ray, Tom P.

    2016-03-01

    We present the results of a pathfinder project conducted with the Giant Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low radio frequencies. The goal of these investigations is to locate the break in the free-free spectrum where the optical depth equals unity in order to constrain physical parameters of these systems, such as the mass of the ionised gas surrounding these young stars. We detect all three target sources, L1551 IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz (wavelengths 90 and 50 cm, respectively). These are the first detections of low mass young stellar objects (YSOs) at such low frequencies. We combine these new GMRT data with archival information to construct the spectral energy distributions for each system and find a continuation of the optically thin free-free spectra extrapolated from higher radio frequencies to 323 MHz for each target. We use these results to place limits on the masses of the ionised gas and average electron densities associated with these young systems on scales of ˜1000 au. Future observations with higher angular resolution at lower frequencies are required to constrain these physical parameters further.

  15. GMRT detections of low-mass young stars at 323 and 608 MHz

    NASA Astrophysics Data System (ADS)

    Ainsworth, Rachael E.; Scaife, Anna M. M.; Green, David A.; Coughlan, Colm P.; Ray, Tom P.

    2016-06-01

    We present the results of a pathfinder project conducted with the Giant Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low radio frequencies. The goal of these investigations is to locate the break in the free-free spectrum where the optical depth equals unity in order to constrain physical parameters of these systems, such as the mass of the ionized gas surrounding these young stars. We detect all three target sources, L1551 IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz (wavelengths 90 and 50 cm, respectively). These are the first detections of low-mass young stellar objects at such low frequencies. We combine these new GMRT data with archival information to construct the spectral energy distributions for each system and find a continuation of the optically thin free-free spectra extrapolated from higher radio frequencies to 323 MHz for each target. We use these results to place limits on the masses of the ionized gas and average electron densities associated with these young systems on scales of ˜1000 au. Future observations with higher angular resolution at lower frequencies are required to constrain these physical parameters further.

  16. Young ``Dipper" Stars in Upper Sco and Oph Observed by K2

    NASA Astrophysics Data System (ADS)

    Ansdell, M.; Gaidos, E.; Rappaport, S. A.; Jacobs, T. L.; LaCourse, D. M.; Jek, K. J.; Mann, A. W.; Wyatt, M. C.; Kennedy, G.; Williams, J. P.; Boyajian, T. S.

    2016-01-01

    We present ten young (≲10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show ˜10-20 dips in flux over the 80-day observing campaign with durations of ˜0.5-2 days and depths of up to ˜40%. These stars are all members of the ρ Ophiuchus (˜1 Myr) or Upper Scorpius (˜10 Myr) star-forming regions. To investigate the nature of these “dippers” we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. The spectra reveal Li i absorption and Hα emission consistent with stellar youth (<50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within ˜10 stellar radii in most cases; however, the sub-millimeter observations imply disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 (Wide-field Infrared Survey Explorer-2) excess, which we interpret as evidence that the dipper phenomenon is related to occulting structures in the inner disk, although this is difficult to reconcile with the weakly accreting aperiodic dippers. We consider three mechanisms to explain the dipper phenomenon: inner disk warps near the co-rotation radius related to accretion; vortices at the inner disk edge produced by the Rossby Wave Instability; and clumps of circumstellar material related to planetesimal formation.

  17. The Starchive: An open access, open source archive of nearby and young stars and their planets

    NASA Astrophysics Data System (ADS)

    Tanner, Angelle; Gelino, Chris; Elfeki, Mario

    2015-12-01

    Historically, astronomers have utilized a piecemeal set of archives such as SIMBAD, the Washington Double Star Catalog, various exoplanet encyclopedias and electronic tables from the literature to cobble together stellar and exo-planetary parameters in the absence of corresponding images and spectra. As the search for planets around young stars through direct imaging, transits and infrared/optical radial velocity surveys blossoms, there is a void in the available set of to create comprehensive lists of the stellar parameters of nearby stars especially for important parameters such as metallicity and stellar activity indicators. For direct imaging surveys, we need better resources for downloading existing high contrast images to help confirm new discoveries and find ideal target stars. Once we have discovered new planets, we need a uniform database of stellar and planetary parameters from which to look for correlations to better understand the formation and evolution of these systems. As a solution to these issues, we are developing the Starchive - an open access stellar archive in the spirit of the open exoplanet catalog, the Kepler Community Follow-up Program and many others. The archive will allow users to download various datasets, upload new images, spectra and metadata and will contain multiple plotting tools to use in presentations and data interpretations. While we will highly regulate and constantly validate the data being placed into our archive the open nature of its design is intended to allow the database to be expanded efficiently and have a level of versatility which is necessary in today's fast moving, big data community. Finally, the front-end scripts will be placed on github and users will be encouraged to contribute new plotting tools. Here, I will introduce the community to the content and expected capabilities of the archive and query the audience for community feedback.

  18. Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. III. The Antennae

    NASA Astrophysics Data System (ADS)

    Bastian, Nate; Trancho, Gelys; Konstantopoulos, Iraklis S.; Miller, Bryan W.

    2009-08-01

    We present optical spectroscopy of 16 star clusters in the merging galaxies NGC 4038/39 ("the Antennae") and supplement this data set with Hubble Space Telescope imaging. The age and metallicity of each cluster is derived through a comparison between the observed Balmer and metal line strengths with simple stellar population models. We then estimate extinctions and masses using the photometry. We find that all but three clusters have ages between ~3 and 200 Myr, consistent with the expected increase in the star formation rate (SFR) due to the merger. Most of the clusters have velocities in agreement with nearby molecular and H I gas that has been previously shown to be rotating within the progenitor galaxies, hence star/cluster formation is still taking place within the galactic disks. However, three clusters have radial velocities that are inconsistent with being part of the rotating gas disks, which is surprising given their young (200-500 Myr) ages. Interestingly, we find a stellar association with the same colors (V - I) near one of these three clusters, suggesting that the cluster and association were formed concurrently and have remained spatially correlated. We find evidence for spatially distributed cluster formation throughout the duration of the merger. The impact of various assumptions about the SFR/cluster formation rate on the interpretation of the cluster age distribution is explored, and we do not find evidence for long-term "infant mortality" as has been previously suggested. Models of galaxy mergers that include a prescription for star formation can provide an overall good fit to the observed cluster age distribution.

  19. GEMINI SPECTROSCOPIC SURVEY OF YOUNG STAR CLUSTERS IN MERGING/INTERACTING GALAXIES. III. THE ANTENNAE

    SciTech Connect

    Bastian, Nate; Trancho, Gelys; Konstantopoulos, Iraklis S.; Miller, Bryan W. E-mail: gtrancho@gemini.edu

    2009-08-10

    We present optical spectroscopy of 16 star clusters in the merging galaxies NGC 4038/39 ('the Antennae') and supplement this data set with Hubble Space Telescope imaging. The age and metallicity of each cluster is derived through a comparison between the observed Balmer and metal line strengths with simple stellar population models. We then estimate extinctions and masses using the photometry. We find that all but three clusters have ages between {approx}3 and 200 Myr, consistent with the expected increase in the star formation rate (SFR) due to the merger. Most of the clusters have velocities in agreement with nearby molecular and H I gas that has been previously shown to be rotating within the progenitor galaxies, hence star/cluster formation is still taking place within the galactic disks. However, three clusters have radial velocities that are inconsistent with being part of the rotating gas disks, which is surprising given their young (200-500 Myr) ages. Interestingly, we find a stellar association with the same colors (V - I) near one of these three clusters, suggesting that the cluster and association were formed concurrently and have remained spatially correlated. We find evidence for spatially distributed cluster formation throughout the duration of the merger. The impact of various assumptions about the SFR/cluster formation rate on the interpretation of the cluster age distribution is explored, and we do not find evidence for long-term 'infant mortality' as has been previously suggested. Models of galaxy mergers that include a prescription for star formation can provide an overall good fit to the observed cluster age distribution.

  20. Disk Braking in young Stars: Probing Rotation in Chamaeleon i and Taurus-Auriga

    NASA Astrophysics Data System (ADS)

    Nguyen, Duy Cuong; Jayawardhana, Ray; van Kerkwijk, Marten H.; Brandeker, Alexis; Scholz, Alexander; Damjanov, Ivana

    2009-04-01

    We present a comprehensive study of rotation, disk, and accretion signatures for 144 T Tauri stars in the young (~2 Myr old) Chamaeleon I and Taurus-Auriga star-forming regions based on multi-epoch high-resolution optical spectra from the Magellan Clay 6.5 m telescope supplemented by mid-infrared photometry from the Spitzer Space Telescope. In contrast to previous studies in the Orion Nebula Cluster and NGC 2264, we do not see a clear signature of disk braking in Tau-Aur and Cha I. We find that both accretors and non-accretors have similar distributions of vsin i. This result could be due to different initial conditions, insufficient time for disk braking, or a significant age spread within the regions. The rotational velocities in both regions show a clear mass dependence, with F-K stars rotating on average about twice as fast as M stars, consistent with results reported for other clusters of similar age. Similarly, we find the upper envelope of the observed values of specific angular momentum j varies as M 0.5 for our sample which spans a mass range of ~0.16-3 M sun. This power law complements previous studies in Orion which estimated j vprop M 0.25 for lsim2 Myr stars in the same mass regime, and a sharp decline in j with decreasing mass for older stars (~10 Myr) with M < 2 M sun. Furthermore, the overall specific angular momentum of this ~10 Myr population is five times lower than that of non-accretors in our sample, and implies a stellar braking mechanism other than disk braking could be at work. For a subsample of 67 objects with mid-infrared photometry, we examine the connection between accretion signatures and dusty disks: in the vast majority of cases (63/67), the two properties correlate well, which suggests that the timescale of gas accretion is similar to the lifetime of inner disks.

  1. Observed Luminosity Spread in Young Clusters and FU Ori Stars: A Unified Picture

    NASA Astrophysics Data System (ADS)

    Baraffe, I.; Vorobyov, E.; Chabrier, G.

    2012-09-01

    The idea that non-steady accretion during the embedded phase of protostar evolution can produce the observed luminosity spread in the Herzsprung-Russell diagram (HRD) of young clusters has recently been called into question. Observations of FU Ori, for instance, suggest an expansion of the star during strong accretion events, whereas the luminosity spread implies a contraction of the accreting objects, decreasing their radiating surface. In this paper, we present a global scenario based on calculations coupling episodic accretion histories derived from numerical simulations of collapsing cloud prestellar cores of various masses and subsequent protostar evolution. Our calculations show that, assuming an initial protostar mass Mi ~ 1 M Jup, typical of the second Larson's core, both the luminosity spread in the HRD and the inferred properties of FU Ori events (mass, radius, accretion rate) can be explained by this scenario, providing two conditions. First, there must be some variation within the fraction of accretion energy absorbed by the protostar during the accretion process. Second, the range of this variation should increase with increasing accretion burst intensity and thus with the initial core mass and final star mass. The numerical hydrodynamics simulations of collapsing cloud prestellar cores indeed show that the intensity of the accretion bursts correlates with the mass and initial angular momentum of the prestellar core. Massive prestellar cores with high initial angular momentum are found to produce intense bursts characteristic of FU Ori-like events. Our results thus suggest a link between the burst intensities and the fraction of accretion energy absorbed by the protostar, with some threshold in the accretion rate, of the order of 10-5 M ⊙ yr-1, delimitating the transition from "cold" to "hot" accretion. Such a transition might reflect a change in the accretion geometry with increasing accretion rate, i.e., a transition from magnetospheric or thin-disk to thick-disk accretion, or in the magnetospheric interaction between the star and the disk. Conversely, the luminosity spread can also be explained by a variation of the initial protostar mass within the ~1-5 M Jup range, although it is unclear for now whether such a spread among the second Larson's core can be produced during the prestellar core second collapse. This unified picture confirms the idea that early accretion during protostar and proto-brown dwarf formation/evolution can explain the observed luminosity spread in young clusters without invoking any significant age spread, and that the concept of a well-defined birthline does not apply for low-mass objects. Finally, we examine the impact of accretion on the determination of the initial mass function in young clusters.

  2. Elemental abundances of low-mass stars in nearby young associations: AB Doradus, Carina Near and Ursa Major

    NASA Astrophysics Data System (ADS)

    Biazzo, K.; D'Orazi, V.; Desidera, S.; Covino, E.; Alcal, J. M.; Zusi, M.

    2012-12-01

    We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near and Ursa Major. The exoplanet-host star ? Horologii is also analysed. The three young associations have lithium abundance consistent with their age. All other elements show solar abundances. The three groups are characterized by a small scatter in all abundances, with mean [Fe/H] values of 0.10 (? = 0.03), 0.08 (? = 0.05) and 0.01 (? = 0.03) dex for AB Doradus, Carina Near and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocity surveys. The young planet-host star ? Horologii shows a lithium abundance lower than that found for the young association members. It is found to have a slightly super-solar iron abundance ([Fe/H] = 0.16 0.09), while all [X/Fe] ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seems to reinforce the idea of a possible common origin with the primordial cluster. Based on observations performed with European Southern Observatory (ESO) telescopes [programme IDs: 70.D-0081(A), 082.A-9007(A), 083.A-9011(B), 084.A-9011(B)].

  3. Fundamental Parameters of a Large, Unbiased Sample of Massive, Young, Embedded Star Clusters in the Milky Way

    NASA Astrophysics Data System (ADS)

    Dallilar, Yigit; Barnes, Peter; Lada, Elizabeth; Ryder, Stuart

    2015-08-01

    Massive star cluster formation in our Galaxy is still a mystery. Unlike studies on nearby star formation regions (Pleiades, Orion Nebula), there is no unbiased sample of massive young star clusters except the CHaMP survey, which is focused on the Carina Arm (Barnes et al. 2011, ApJS, 196, 12). In this project, we examine properties of young clusters identified in the CHaMP survey through infrared photometry. Near infrared (J,H,K) imaging was obtained with the Australian Astronomical Telescope and deep mid infrared (IRAC bands 1,2) imaging was obtained with the Spitzer Space Telescope during the warm mission. Photometric analysis was performed with a combination of Sextrac- tor and Psfex software. Photometric calibration for NIR data was handled exploiting 2Mass coverage for our fields. For MIR data, photometric calibration was obtained using GLIMPSE coverage for a small number of our images, then bootstrapping this to calibrate other images, since all images are obtained with the same pipeline. To identify cluster members, we provide constraints on the source classification using field AGB stars and faint background galaxies, which have similar characteristics as reddened young stellar objects. Predicted locations of these objects on color-magnitude and color-color diagrams are used as a guide, as are the stellar classification parameter from Sextractor and faint galaxy catalogs covering our fields. We also examine extinction properties towards these young clusters, exploiting well known properties of AGB star population in our fields. Combining the IR data with existing mm-wave specroscopy, we compute values for the gas to dust ratio of these young clusters using extinction properties plus differential H-K color maps and NH column density measurements, all obtained as a part of the CHaMP survey. These results help us to identify evolutionary stages of these young clusters. Eventually, we will constrain cluster properties like age, distance and metallicity with isochrone fitting routines.

  4. Direct imaging search for planets around low-mass stars and spectroscopic characterization of young exoplanets

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan Peter

    Low--mass stars between 0.1--0.6 M⊙ are the most abundant members our galaxy and may be the most common sites of planet formation, but little is known about the outer architecture of their planetary systems. We have carried out a high-contrast adaptive imaging search for gas giant planets between 1--13 MJup around 122 newly identified young M dwarfs in the solar neighborhood ( ≲ 35 pc). Half of our targets are younger than 145 Myr, and 90% are younger than 580 Myr. After removing 39 resolved stellar binaries, our homogeneous sample of 83 single young M dwarfs makes it the largest imaging search for planets around low--mass stars to date. Our H- and K- band coronagraphic observations with Subaru/HiCIAO and Keck/NIRC2 achieve typical contrasts of 9--13 mag and 12--14 mag at 100, respectively, which corresponds to limiting masses of ˜1--10 M Jup at 10--30 AU for most of our sample. We discovered four brown dwarfs with masses between 25--60 MJup at projected separations of 4--190 AU. Over 100 candidate planets were discovered, nearly all of which were found to be background stars from follow-up second epoch imaging. Our null detection of planets nevertheless provides strong statistical constraints on the occurrence rate of giant planets around M dwarfs. Assuming circular orbits and a logarithmically-flat power law distribution in planet mass and semi--major axis of the form d 2N=(dloga dlogm) infinity m0 a0, we measure an upper limit (at the 95% confidence level) of 8.8% and 12.6% for 1--13 MJup companions between 10--100 AU for hot start and cold start evolutionary models, respectively. For massive gas giant planets in the 5--13 M Jup range like those orbiting HR 8799, GJ 504, and beta Pictoris, we find that fewer than 5.3% (7.8%) of M dwarfs harbor these planets between 10--100 AU for a hot start (cold start) formation scenario. Our best constraints are for brown dwarf companions; the frequency of 13--75 MJup companions between (de--projected) physical separations of 10--100 AU is 2.1+2.1-1.2 %. Altogether, our results show that gas giant planets, especially massive ones, are rare in the outskirts of M dwarf planetary systems. If disk instability is a viable way to form planets, our constraints for the most common type of star imply that overall it is an inefficient mechanism.

  5. Young Stars in Orion May Solve Mystery of Our Solar System

    NASA Astrophysics Data System (ADS)

    2001-09-01

    Scientists may have to give the Sun a little more credit. Exotic isotopes present in the early Solar System--which scientists have long-assumed were sprinkled there by a powerful, nearby star explosion--may have instead been forged locally by our Sun during the colossal solar-flare tantrums of its baby years. The isotopes--special forms of atomic nuclei, such as aluminum-26, calcium-41, and beryllium-10--can form in the X-ray solar flares of young stars in the Orion Nebula, which behave just like our Sun would have at such an early age. The finding, based on observations by the Chandra X-ray Observatory, has broad implications for the formation of our own Solar System. Eric Feigelson, professor of astronomy and astrophysics at Penn State, led a team of scientists on this Chandra observation and presents these results in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra". "The Chandra study of Orion gives us the first chance to study the flaring properties of stars resembling the Sun when our solar system was forming," said Feigelson. "We found a much higher rate of flares than expected, sufficient to explain the production of many unusual isotopes locked away in ancient meteorites. If the young stars in Orion can do it, then our Sun should have been able to do it too." Scientists who study how our Solar System formed from a collapsed cloud of dust and gas have been hard pressed to explain the presence of these extremely unusual chemical isotopes. The isotopes are short-lived and had to have been formed no earlier than the creation of the Solar System, some five billion years ago. Yet these elements cannot be produced by a star as massive as our Sun under normal circumstances. (Other elements, such as silver and gold, were created long before the creation of the solar system.) The perplexing presence of these isotopic anomalies, found in ancient meteoroids orbiting the Earth, led to the theory that a supernova explosion occurred very close to the Solar System's progenitor gas cloud, simultaneously triggering its collapse and seeding it with short-lived isotopes. Solar flares could produce such isotopes, but the flares would have to be hundreds of thousands of times more powerful and hundreds of times more frequent than those our Sun generates. Enter the stars in the Orion Nebula. This star-forming region has several dozen new stars nearly identical to our Sun, only much younger. Feigelson's team used Chandra to study the flaring in these analogs of the early Sun and found that nearly all exhibit extremely high levels of X-ray flaring--powerful and frequent enough to forge many of the kinds of isotopes found in the ancient meteorites from the early solar system. "This is a very exciting result for space X-ray astronomy," said Donald Clayton, Centennial Professor of Physics and Astronomy at Clemson University. "The Chandra Penn State team has shown that stellar-flare acceleration produces radioactive nuclei whether we want them or not. Now the science debate can concentrate on whether such irradiation made some or even all of the extinct radioactivities that were present when our solar system was formed, or whether some contamination of our birth molecular cloud by external material is also needed." "This is an excellent example of how apparently distant scientific fields, like X-ray astronomy and the origins of solar systems, can in fact be closely linked," said Feigelson. The Orion observation was made with Chandra's Advanced CCD Imaging Spectrometer, which was conceived and developed for NASA by Penn State and Massachusetts Institute of Technology under the leadership of Gordon Garmire, the Evan Pugh Professor of Astronomy and Astrophysics at Penn State. The Penn State observation team includes Pat Broos, James Gaffney, Gordon Garmire, Leisa Townsley and Yohko Tsuboi. Collaborators also include Lynne Hillenbrand of CalTech and Steven Pravdo of the NASA Jet Propulsion Laboratory. Background: Isotopes are atoms whose nuclei have different numbers of neutrons. Many isotopes are unstable, or radioactive, and decay into other elements. A famous example is carbon-14 whose decay gives scientists the opportunity to date organic materials over thousands of years. A rare type of ancient meteorite called carbonaceous chondrites, which are rocks from the Asteroid Belt whose orbits are perturbed and fall to the Earth, date back to the formation of our Solar System 4.55 billion years ago. Studying carbonaceous chondrites gives us a unique window on conditions in the solar nebula when the Sun and Solar System were forming. Certain portions of carbonaceous chondrites, small melted pebbles called Calcium-Aluminum-rich Inclusions or CAIs, have unusually high abundances of decay products of rare, short-lived isotopes. These include beryllium-10, calcium-41, 26-aluminum and 53-manganese, among others. Explaining the presence of these short-lived isotopes, which do not appear anywhere else in solar system material, has been one of the toughest challenges of solar system science. The favored explanation has been that a star exploded in a supernova and triggered a nearby cloud of dust and gas to collapse to form our Sun and planetary system. But conditions have to be carefully adjusted for this model, and it cannot be widely applied to all stars. The principal alternative model is that energetic particles from violent flares hit particles in the solar nebula and transformed some of their atoms to radioactive isotopes. A drawback to this model has been that the level of flaring needed, around 100,000 times the flaring level of the Sun today, was thought to be impossibly high. However, the X-ray observations reported here give direct evidence for just this high level of flaring. In addition, this model readily applied to all young stars and solar systems, not just a few.

  6. Deep Near-Infrared Surveys and Young Brown Dwarf Populations in Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Tamura, M.; Naoi, T.; Oasa, Y.; Nakajima, Y.; Nagashima, C.; Nagayama, T.; Baba, D.; Nagata, T.; Sato, S.; Kato, D.; Kurita, M.; Sugitani, K.; Itoh, Y.; Nakaya, H.; Pickles, A.

    2003-06-01

    We are currently conducting three kinds of IR surveys of star forming regions (SFRs) in order to seek for very low-mass young stellar populations. First is a deep JHKs-bands (simultaneous) survey with the SIRIUS camera on the IRSF 1.4m or the UH 2.2m telescopes. Second is a very deep JHKs survey with the CISCO IR camera on the Subaru 8.2m telescope. Third is a high resolution companion search around nearby YSOs with the CIAO adaptive optics coronagraph IR camera on the Subaru. In this contribution, we describe our SIRIUS camera and present preliminary results of the ongoing surveys with this new instrument.

  7. COMPARISON OF CONVECTIVE OVERSHOOTING MODELS AND THEIR IMPACT ON ABUNDANCES FROM INTEGRATED LIGHT SPECTROSCOPY OF YOUNG (<3 Gyr) STAR CLUSTERS

    SciTech Connect

    Colucci, Janet E.; Bernstein, Rebecca A. E-mail: rab@ucolick.org

    2012-04-20

    As part of an ongoing program to measure detailed chemical abundances in nearby galaxies, we use a sample of young- to intermediate-age clusters in the Large Magellanic Cloud with ages of 10 Myr-2 Gyr to evaluate the effect of isochrone parameters, specifically core convective overshooting, on Fe abundance results from high-resolution, integrated light spectroscopy. In this work we also obtain fiducial Fe abundances from high-resolution spectroscopy of the cluster individual member stars. We compare the Fe abundance results for the individual stars to the results from isochrones and integrated light spectroscopy to determine whether isochrones with convective overshooting should be used in our integrated light analysis of young- to intermediate-age (10 Myr-3 Gyr) star clusters. We find that when using the isochrones from the Teramo group, we obtain more accurate results for young- and intermediate-age clusters over the entire age range when using isochrones without convective overshooting. While convective overshooting is not the only uncertain aspect of stellar evolution, it is one of the most readily parameterized ingredients in stellar evolution models, and thus important to evaluate for the specific models used in our integrated light analysis. This work demonstrates that our method for integrated light spectroscopy of star clusters can provide unique tests for future constraints on stellar evolution models of young- and intermediate-age clusters.

  8. A kinematically unbiased search for nearby young stars in the Northern hemisphere selected using SuperWASP rotation periods

    NASA Astrophysics Data System (ADS)

    Binks, A. S.; Jeffries, R. D.; Maxted, P. F. L.

    2015-09-01

    We present a kinematically-unbiased search to identify young, nearby low-mass members of kinematic moving groups (MGs). Objects with both rotation periods shorter than 5 d in the SuperWASP All-Sky Survey and X-ray counterparts in the ROSAT All-Sky Survey were chosen to create a catalogue of several thousand rapidly rotating, X-ray active FGK stars. These objects are expected to be either young single stars or tidally locked spectroscopic binaries. We obtained optical spectra for a sub-sample of 146 stars to determine their ages and kinematics, and in some cases repeat radial velocity measurements were used to identify binarity. 26 stars are found to have lithium abundances consistent with an age of ≤200 Myr, and show no evidence for binarity and in most cases measurements of H α and v sin i support their youthful status. Based on their youth, their radial velocities and estimates of their three-dimensional kinematics, we find 11 objects that may be members of known MGs, eight that do not appear associated with any young MG and a further seven that are close to the kinematics of the recently proposed `Octans-Near' MG, and which may be the first members of this MG found in the Northern hemisphere. The initial search mechanism was ˜18 per cent efficient at identifying likely-single stars younger than 200 Myr, of which 80 per cent were early-K spectral types.

  9. Revealing the full young stellar population in the Carina Nebula, the nearest laboratory of massive star feedback, with VISTA

    NASA Astrophysics Data System (ADS)

    Zeidler, Peter; Preibisch, Thomas; Ratzka, Thorsten; Gaczkowski, Benjamin; Roccatagliata, Veronica

    2013-07-01

    The Carina Nebula (NGC 3372) represents one of the most massive star forming regions in our Galaxy. With a distance of 2.3 kpc, it has the most extreme stellar population within a few kpc of the sun (at least 65 O-type stars). It is our best connection between the nearby star forming regions like the Orion Nebula and the even larger and extremer, but more distant regions like 30 Doradus in the Large Magellanic Cloud. Therefore it is a unique target and our richest nearby laboratory for detailed studies of violent massive star formation and its resulting feedback effects of cloud dispersal and triggered star formation. Our recent Herschel far-infrared survey of the Carina Nebula showed that the cloud complex extends over some 2 × 2.5 deg on the sky. Most of the recent investigations of the Carina Nebula had, however, been focused on the central, ≤ 1 square-degree area of the region, leaving the periphery of the cloud complex poorly studied. In order to solve this problem and to allow a characterization of the young stars throughout the entire extent of the complex, we have used the ESO Visible and Infrared Survey Telescope for Astronomy (VISTA) to map a ˜2 × 3 deg area around the Carina Nebula in the near-infrared J-, H-, Ks bands. Our NIR survey is large enough to cover the full spatial extent of the Carina Nebula complex and is deep enough to detect all young stars down to masses of 0.1 Msun through extinctions of at least Av = 10 mag. We detected in more than ˜ 4 million individual point sources. The data has a typical completeness limit of J ≃ 18, H ≃ 18, and Ks ≃ 17. In combination with a recent Chandra X-ray survey, Spitzer-IRAC, and Herschel observations we have now a sample of data, which reaches from X-ray to the FIR. It will allow us to distinguish between young stars and background contaminating objects and it will allow the identification and characterization of all X-ray selected young stars and the embedded young stellar objects revealed by Herschel.

  10. Successful Field-Scale In Situ Thermal NAPL Remediation at the Young-Rainey Star Center

    SciTech Connect

    Juhlin, Randall; Butherus, Michael; Joseph Daniel; Ingle, David S.; Heron, Gorm; McGee, Bruce

    2004-05-04

    The U.S. Department of Energy (DOE) successfully completed a fieldscale remediation to remove non-aqueous phase liquids (NAPLs) from the subsurface at a site on the Young-Rainey Science, Technology, and Research (STAR) Center, Largo, Florida. The STAR Center is a former DOE facility. The remediation project covered an area of 930 m2 (10,000 ft2) and depths extending to 10.5 m (35 ft) below ground surface. In July 2001, DOE’s contractor awarded a subcontract to SteamTech Environmental Services for removal of NAPLs from a portion of the Northeast Site. The technologies used for remediation were steam-enhanced extraction and Electro-Thermal Dynamic Stripping Process, an electrical resistive heating technology. McMillan-McGee Corporation implemented the process. Construction of the remediation system was completed in September 2002. Operations began immediately after construction, and active heating ended in February 2003. After operations were completed, confirmatory sampling was conducted over a 6-month period to verify the level of cleanup achieved. Results of the sampling showed that NAPL concentrations were reduced significantly below the required cleanup goals and, in most cases, below the regulatory maximum contaminant levels. Lessons learned relative to the design, construction, operation, confirmatory sampling approach, and subcontracting could benefit managers of similar remediation projects

  11. Young Galaxy Surrounded by Material Needed to Make Stars, VLA Reveals

    NASA Astrophysics Data System (ADS)

    2001-01-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered a massive reservoir of cold gas from which a primeval galaxy formed its first stars. Looking more than 12 billion years into the past, the scientists found that the young galaxy experiencing a "burst" of star formation was surrounded by enough cold molecular gas to make 100 billion suns. Optical and Radio Images of APM 08279+5255 at About the Same Scale "This is the first time anyone has seen the massive reservoir of cold gas required for these incredible 'starbursts' to produce a galaxy," said Chris Carilli, an astronomer at the NSF's National Radio Astronomy Observatory (NRAO) in Socorro, NM. "There is much more gas here than we anticipated," Carilli added. The research team was led by Padeli Papadoupoulos of Leiden Observatory in the Netherlands and also included Rob Ivison of University College London and Geraint Lewis of the Anglo-Australian Observatory in Australia. The scientists reported their findings in the January 4 edition of the journal Nature. The astronomers found the gas when studying a quasar called APM 08279+5255, discovered in 1998. Observations with optical and infrared telescopes revealed that the quasar, a young galaxy with a voracious black hole at its center, was forming new stars rapidly in a starburst. At a distance of more than 12 billion light-years, the quasar is seen as it was more than 12 billion years ago, just a billion or so years after the Big Bang. "This thing is at the edge of the dark ages," before the first stars in the universe were born, said Carilli. The year after its discovery, APM 08279+5255 was found to have warm carbon monoxide (CO) gas near its center, heated by the energy released as the galaxy's black hole devours material. The VLA observations revealed cold CO gas much more widely distributed than its warmer counterpart. Based on observations of closer objects, the astronomers presume the CO gas is accompanied by large amounts of molecular hydrogen gas (H2). Cold CO gas never has been detected before in such a distant object. Though APM 08279+5255 is a young galaxy undergoing its first massive burst of star formation, the CO gas indicates that very massive stars formed quickly, lived through their short lifetimes, and exploded as supernovae. Carbon and Oxygen, the component elements of CO, are formed in the cores of stars, so their presence in the cold gas tells the astronomers that massive, short-lived stars had to have exploded already, spreading these elements throughout the galaxy's interstellar gas. "The original discovery of this quasar was quite a surprise, as observations revealed it is among the most luminous objects known in the universe. The discovery of this massive reservoir of cold gas is equally surprising. It provides vital clues to the birth of galaxies, such as our own Milky Way," Lewis said. Discovery of the gas was made possible by the galaxy's great distance. The expansion of the universe "stretches" light and radio waves to longer wavelengths -- the more distant the object, the more stretching is seen. Radio waves emitted by the cold CO gas originally had wavelengths of about 1.3 and 2.6 millimeters, but were "redshifted" to wavelengths of 7 and 13 millimeters -- wavelengths the VLA can receive. "It took eight years to refine this technique, but the effort has been worthwhile. This is the golden age of cosmology. We are learning more and more about our universe, from the smallest planets to the largest galaxy clusters. This new result is a crucial piece in the jigsaw and may help resolve many misconceptions about how galaxies form and evolve" Ivison said. "Because of its sensitivity and its ability to make detailed images, the VLA is the only telescope able to unveil these large reservoirs of cold molecular gas in the distant universe," Carilli said. "In addition, as we expand the technical capabilities of the VLA in the coming years, making it even more sensitive and able to show more detail, it will become the world's premier tool for studying this vital aspect of the young universe." The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

  12. Periodic Disk Eclipsing Stars: A New Class of Variable Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Plavchan, Peter; Laohakunakorn, N.; Seifahrt, A.; Staplefeldt, K.; Gee, A. H.

    2010-01-01

    We present the discovery of 92.6 day periodic near-infrared flu variability for the Class I T Tauri star YLW 16A. Our data are from the 2MASS Calibration Point Source Working Database and constitute 1582 observations in J, H and Ks of a field in Rho Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve that brightens from a quiescent faint state by 0.4 mag for only 20% of the period. The long period cannot be explained by stellar rotation. We propose that YLW 16A is a triple YSO system, with an inner binary orbital period of 92.6 days. We postulate that we are observing a component of the binary being eclipsed by a circumbinary disk with respect to our line of site. YLW 16A joins WL 4 and KH-15D as a third member of a new class of disk-eclipsing young stars. Both YLW 16A and WL 4 have been identified to have tertiary companions with projected separations of 20--50 AU. We propose that the tertiary companion can warp the inner circumbinary disk to produce the disk eclipses. We present NIRSPEC observations of WL 4 that suggest three distinct radial velocity components, and present a model SED for YLW 16A. These systems will be useful in investigating terrestrial-zone YSO disk properties and dynamics at 1 Myr.

  13. Discovery of young, isolated planetary mass objects in the final sigma Orionis star cluster.

    PubMed

    Zapatero Osorio, M R; Béjar, V J; Martín, E L; Rebolo, R; Barrado y Navascués, D; Bailer-Jones, C A; Mundt, R

    2000-10-01

    We present the discovery by optical and near-infrared imaging of an extremely red, low-luminosity population of isolated objects in the young, nearby stellar cluster around the multiple, massive star final sigma Orionis. The proximity (352 parsecs), youth (1 million to 5 million years), and low internal extinction make this cluster an ideal site to explore the substellar domain from the hydrogen mass limit down to a few Jupiter masses. Optical and near-infrared low-resolution spectroscopy of three of these objects confirms the very cool spectral energy distribution (atmospheric effective temperatures of 1700 to 2200 kelvin) expected for cluster members with masses in the range 5 to 15 times that of Jupiter. Like the planets of the solar system, these objects are unable to sustain stable nuclear burning in their interiors, but in contrast they are not bound to stars. This new kind of isolated giant planet, which apparently forms on time scales of less than a few million years, offers a challenge to our understanding of the formation processes of planetary mass objects. PMID:11021788

  14. Exocomets in the disk of two young A-type stars

    NASA Astrophysics Data System (ADS)

    Kiefer, F.; Lecavelier des Etangs, A.; Vidal-Madjar, A.

    2014-12-01

    Optical spectra of the 20 Myrs old A-type stars β Pictoris and HD172555 have been collected between 2003 and 2011 with the HARPS instrument installed at the La Silla 3.6m telescope. In the two stellar absorption lines composing the Ca II doublet at 3950 Å, we observed for these two targets narrow and doppler-shifted variable absorption features, which in the case of β Pictoris were known to occur since 1987. These transient signals are interpreted by the passage of orbiting evaporating bodies in front of the stellar disk, or transits of exocomets. We collected 493 individual detections of independent exocomets around β Pictoris allowing us to perform an unprecedented statistical studies of their physical properties (Kiefer et al. 2014a). Moreover, we report the detection of 4 transits of exocomets in front of the young A-type star HD172555; thus promoting this system as the second with simultaneous detection of exocomet transits in both lines of the Ca II doublet (Kiefer et al. 2014b).

  15. NuSTAR Observations of the Young, Energetic Radio Pulsar PSR B1509-58

    NASA Astrophysics Data System (ADS)

    Chen, Ge; An, Hongjun; Kaspi, Victoria M.; Harrison, Fiona A.; Madsen, Kristin K.; Stern, Daniel

    2016-02-01

    We report on Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of the young rotation-powered radio pulsar PSR B1509-59 in the supernova remnant MSH 15-52. We confirm the previously reported curvature in the hard X-ray spectrum, showing that a log parabolic model provides a statistically superior fit to the spectrum compared with the standard power law. The log parabolic model describes the NuSTAR data, as well as previously published γ-ray data obtained with COMPTEL and AGILE, all together spanning 3 keV through 500 MeV. Our spectral modeling allows us to constrain the peak of the broadband high energy spectrum to be at 2.6 ± 0.8 MeV, an improvement of nearly an order of magnitude in precision over previous measurements. In addition, we calculate NuSTAR spectra in 26 pulse phase bins and confirm previously reported variations of photon indices with phase. Finally, we measure the pulsed fraction of PSR B1509-58 in the hard X-ray energy band for the first time. Using the energy resolved pulsed fraction results, we estimate that the pulsar’s off-pulse emission has a photon index value between 1.26 and 1.96. Our results support a model in which the pulsar’s lack of GeV emission is due to viewing geometry, with the X-rays originating from synchrotron emission from secondary pairs in the magnetosphere.

  16. Spitzer Space Telescope Research Program for Teachers and Students: Young Stars in IC2118

    NASA Astrophysics Data System (ADS)

    Weehler, C. R.; Herrera, J. M.; Maranto, A. R.; Greer, M. T.; Preis, J. V.; Weston, P. D.; Rebull, L. M.; Roelofsen, T. E.; Sepulveda, B.; Hughes, A. S.; Sharma, N. D.; Spuck, T. S.; Bowser, D. H., II; Ehrhart, B. R.

    2005-12-01

    The Spitzer Space Telescope Teacher Program is a collaboration between the Spitzer Science Center and National Optical Astronomy Observatory. Through the program, twelve teachers were selected to submit observing proposals for time on the Spitzer Space Telescope. The Young Stars in IC 2118 Project was one of those selected and awarded 62 minutes of Director's discretionary observing time to study a small region of IC 2118 (the Witch Head Nebula), a star forming region of small-mass stars embedded in their natal cloud. The five teachers involved in this project met at the Spitzer Science Center in August and September 2005 to analyze the data received from IRAC and MIPS observations. Six high school students were included in these visits, and several more are working on data analysis at their home schools. We are making tri-color images to identify structure in the ISM, Spectral Energy Distributions to identify cluster members and color plots to determine their stage of development, thereby estimating their ages. We are working toward adapting lessons that can use software that is readily available in public schools to do the data analysis. As teachers develop lesson plans for these activities, they will apply them in their science classes and provide professional development on infrared astronomy and the use of astronomical data to other teachers through in-service training around the country. The team is being mentored by Dr. Luisa Rebull from the Spitzer Science Center. Please see our companion poster, Spuck et al., on our science results using these data.

  17. YOUNG STELLAR OBJECTS IN LYNDS 1641: DISKS, ACCRETION, AND STAR FORMATION HISTORY

    SciTech Connect

    Fang Min; Kim, Jinyoung Serena; Flaherty, Kevin; Van Boekel, Roy; Henning, Thomas; Sicilia-Aguilar, Aurora

    2013-07-01

    We investigate the young stellar objects (YSOs) in the Lynds 1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, the Two Micron All Sky Survey, and XMM covering {approx}1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use these data, along with archival photometric data, to derive spectral types, extinction values, masses, ages, and accretion rates. We obtain a disk fraction of {approx}50% in L1641. The disk frequency is almost constant as a function of stellar mass with a slight peak at log (M{sub *}/M{sub Sun }) Almost-Equal-To -0.25. The analysis of multi-epoch spectroscopic data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses. Forty-six new transition disk (TD) objects are confirmed in this work, and we find that the fraction of accreting TDs is lower than for optically thick disks (40%-45% versus 77%-79%, respectively). We confirm our previous result that the accreting TDs have a median accretion rate similar to normal optically thick disks. We confirm that two star formation modes (isolated versus clustered) exist in L1641. We find that the diskless YSOs are statistically older than the YSOs with optically thick disks and the TD objects have a median age that is intermediate between those of the other two populations. We tentatively study the star formation history in L1641 based on the age distribution and find that star formation started to be active 2-3 Myr ago.

  18. On the time dependence of differential rotation in young late-type stars

    NASA Astrophysics Data System (ADS)

    Lanza, Antonino F.

    2006-12-01

    A model for the angular momentum transfer within the convection zone of a rapidly rotating star is introduced and applied to the analysis of recent observations of temporal fluctuations of the differential rotation on the young late-type stars AB Doradus (AB Dor) and LQ Hydrae (LQ Hya). Under the hypothesis that the mean magnetic field produced by the stellar dynamo rules the angular momentum exchanges and that the angular velocity depends only on the distance s from the rotation axis and the time, the minimum azimuthal Maxwell stress |BsBϕ|, averaged over the convection zone, is found to range from ~0.04 to ~0.14T2. If the poloidal mean magnetic field Bs is of the order of 0.01T, as indicated by the Zeeman-Doppler imaging maps of those stars, then the azimuthal mean field Bϕ can reach an intensity of several teslas, which significantly exceeds equipartition with the turbulent kinetic energy. Such strong fields can account also for the orbital period modulation observed in cataclysmic variables and RS Canum Venaticorum systems with a main-sequence secondary component. Moreover, the model allows us to compute the kinetic energy dissipation rate during the maintenance of the differential rotation. Only in the case of the largest surface shear observed on LQ Hya may the dissipated power exceed the stellar luminosity, but the lack of a sufficient statistic on the occurrence of such episodes of large shear does not allow us to estimate their impact on the energy budget of the convection zone.

  19. Direct Exoplanet/Disk Search Around Young & Nearby Early-Type Stars; The International Deep Planet Survey (IDPS)

    NASA Astrophysics Data System (ADS)

    Marois, Christian; Macintosh, Bruce; Patience, Jennifer; Doyon, Rene; Zuckerman, Benjamin; Song, Inseok; Lafreniere, David; Barman, Travis

    2008-02-01

    We propose to continue a deep AO survey for exoplanets around young and close A- and F-type stars using a refined version of the very successful Angular Differential Imaging technique, which distinguishes true companions/disks from artifacts through sidereal rotation. Stars as massive as A- and early F-type stars have been neglected in AO searches, including the Gemini Deep Planet Survey, while radial velocity surveys have reduced sensitivity for such stars. Thus planet/BD formation around more massive stars remains unconstrained. For each target, a two-hour sequence of images will achieve a contrast limit 3-4 magnitudes better than previous surveys made with HST or conventional AO. We will be capable of detecting exoplanets of 5 Jupiter mass at separations of 1.5 arcsec, corresponding to 60 AU for a typical proposed target star. After combining this new A- and F-type star survey with our previous GKM star GDPS survey, we will have, for the first time, a broader picture of the population of massive planets at large semi-major axes around a wide range of spectral type.

  20. Sizes and shapes of young star cluster light profiles in M83

    NASA Astrophysics Data System (ADS)

    Ryon, J. E.; Bastian, N.; Adamo, A.; Konstantopoulos, I. S.; Gallagher, J. S.; Larsen, S.; Hollyhead, K.; Silva-Villa, E.; Smith, L. J.

    2015-09-01

    We measure the radii and two-dimensional light profiles of a large sample of young, massive star clusters in M83 using archival HST/Wide Field Camera 3 (WFC3) imaging of seven adjacent fields. We use GALFIT to fit the two-dimensional light profiles of the clusters, from which we find effective (half-light) radii, core radii, and slopes of the power-law (EFF) profile (η). We find lognormal distributions of effective radius and core radius, with medians of ≈2.5 and ≈1.3 pc, respectively. Our results provide strong evidence for a characteristic size of young, massive clusters. The average effective radius and core radius increase somewhat with cluster age. Little to no change in effective radius is observed with increasing galactocentric distance, except perhaps for clusters younger than 100 Myr. We find a shallow correlation between effective radius and mass for the full cluster sample, but a stronger correlation is present for clusters 200-300 Myr in age. Finally, the majority of the clusters are best fit by an EFF model with index η ≲ 3.0. There is no strong evidence for change in η with cluster age, mass, or galactocentric distance. Our results suggest that clusters emerge from early evolution with similar radii and are not strongly affected by the tidal field of M83. Mass-loss due to stellar evolution and/or giant molecular cloud interactions appear to dominate cluster expansion in the age range we study.

  1. A pulsation search among young brown dwarfs and very-low-mass stars

    SciTech Connect

    Cody, Ann Marie; Hillenbrand, Lynne A.

    2014-12-01

    In 2005, Palla and Baraffe proposed that brown dwarfs (BDs) and very-low-mass stars (VLMSs; < 0.1 solar masses) may be unstable to radial oscillations during the pre-main-sequence deuterium burning phase. With associated periods of one to four hours, this potentially new class of pulsation offers unprecedented opportunities to probe the interiors and evolution of low-mass objects in the 1-15 million year age range. Following up on reports of short-period variability in young clusters, we designed a high-cadence photometric monitoring campaign to search for deuterium-burning pulsation among a sample of 348 BDs and VLMSs in the four young clusters σ Orionis, Chamaeleon I, IC 348, and Upper Scorpius. In the resulting light curves we achieved sensitivity to periodic signals of amplitude several millimagnitudes, on timescales from 15 minutes to two weeks. Despite the exquisite data quality, we failed to detect any periodicities below seven hours. We conclude that D-burning pulsations are not able to grow to observable amplitudes in the early pre-main sequence. In spite of the nondetection, we did uncover a rich set of variability behavior—both periodic and aperiodic—on day to week timescales. We present new compilations of variable sources from our sample, as well as three new candidate cluster members in Chamaeleon I.

  2. How Do Astronomers Know That? Educating Teachers, Students & the Public on HOW You Discover Young Stars

    NASA Astrophysics Data System (ADS)

    Bonadurer, Robert; Piper, M.; French, D.; Barge, J.; Novatne, L. J.; Rebull, L. M.; Ali, B.; Laher, R.; Armstrong, J.

    2013-01-01

    Every day amazing astronomical facts are taught to thousands of curious people. Students learn them in the classroom. Museum visitors hear them in a Planetarium show or lecture. When it’s time for questions, many intuitively ask, “how do you know that?” NITARP helps close this gap in astronomy education. NITARP stands for NASA/IPAC Teacher Archive Research Program. NITARP brings together an astronomer with a small group of teachers and students to do real astronomical research. After the year long program is completed, the education and experiences gained the teachers are brought back to their classrooms and museums across America. Our NITARP group researched apparent infrared (IR) excesses to identify Young Stellar Objects (YSOs). Our science results are presented in a companion paper, Novatne et al, at this AAS conference. We concentrated our search in the Bright Rimmed Cloud (BRC) 27, located in the constellation Canis Major. Our main focus was to use data from the Wide-field Infrared Survey Explorer (WISE), along with other archived infrared data such as Spitzer and 2MASS. Thus, our NITARP group was called C-WAYS—standing for Cool, WISE and Young Stars. In this poster, we present our educational plan to connect real science by astronomers to educators, students, and ultimately our communities.

  3. X-shooter spectroscopy of young stellar objects. V. Slow winds in T Tauri stars

    NASA Astrophysics Data System (ADS)

    Natta, A.; Testi, L.; Alcalá, J. M.; Rigliaco, E.; Covino, E.; Stelzer, B.; D'Elia, V.

    2014-09-01

    Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been identified, one characterized by velocity shifts of tens to hundreds of km s-1 (HVC) and one with a much lower velocity of a few km s-1 (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly low-mass young stars in Lupus and σ Ori observed with the X-shooter ESO spectrometer. We detect forbidden line emission of O i, O ii, S ii, N i, and N ii, and characterize the line profiles as LVC, blueshifted HVC, and redshifted HVC. We focus our study on the LVC. We show that there is a good correlation between line luminosity and both Lstar and the accretion luminosity (or the mass accretion rate) over a large interval of values (Lstar~ 10-2-1 L⊙; Lacc~ 10-5-10-1 L⊙; Ṁacc~ 10-11 - 10-7 M⊙/yr). The lines show the presence of a slow wind (Vpeak< 20 km s-1) that is dense (nH> 108 cm-3), warm (T ~ 5000-10 000 K), mostly neutral. We estimate the mass of the emitting gas and provide a value for the maximum volume it occupies. Both quantities increase steeply with the stellar mass, from ~ 10-12 M⊙ and ~0.01 AU3 for Mstar~ 0.1 M⊙, to ~ 3 × 10-10 M⊙ and ~1 AU3 for Mstar~ 1 M⊙, respectively. These results provide quite stringent constraints to wind models in low-mass young stars, that need to be explored further. Based on observations collected at the European Souther Observatory at Paranal, under programs 084.C-0269(A), 085.C-0238(A), 086.C-0173(A), 087.C-0244(A) and 089.C-0143(A).Appendices are available in electronic form at http://www.aanda.org

  4. GEMINI SPECTROSCOPIC SURVEY OF YOUNG STAR CLUSTERS IN MERGING/INTERACTING GALAXIES. IV. STEPHAN's QUINTET

    SciTech Connect

    Trancho, Gelys; Konstantopoulos, Iraklis S.; Mullan, Brendan; Charlton, Jane C.; Bastian, Nate; Fedotov, Konstantin; Gallagher, Sarah

    2012-04-01

    We present a spectroscopic survey of 21 young massive clusters and complexes and one tidal dwarf galaxy (TDG) candidate in Stephan's Quintet, an interacting compact group of galaxies. All of the selected targets lie outside the main galaxies of the system and are associated with tidal debris. We find clusters with ages between a few and 125 Myr and confirm the ages estimated through Hubble Space Telescope photometry by Fedotov et al., as well as their modeled interaction history of the Quintet. Many of the clusters are found to be relatively long-lived, given their spectrosopically derived ages, while their high masses suggest that they will likely evolve to eventually become intergalactic clusters. One cluster, T118, is particularly interesting, given its age ({approx}125 Myr), high mass ({approx}2 Multiplication-Sign 10{sup 6} M{sub Sun }), and position in the extreme outer end of the young tidal tail. This cluster appears to be quite extended (R{sub eff} {approx} 12-15 pc) compared to clusters observed in galaxy disks (R{sub eff} {approx} 3-4 pc), which confirms an effect we previously found in the tidal tails of NGC 3256, where clusters are similarly extended. We find that star and cluster formation can proceed at a continuous pace for at least {approx}150 Myr within the tidal debris of interacting galaxies. The spectrum of the TDG candidate is dominated by a young population ({approx}7 Myr), and, assuming a single age for the entire region, has a mass of at least 10{sup 6} M{sub Sun }.

  5. A UKIDSS-based search for low-mass stars and small stellar clumps in off-cloud parts of young star-forming regions *

    NASA Astrophysics Data System (ADS)

    Perger, M.; Lodieu, N.; Martín, E. L.; Barrado Y Navascués, D.

    2011-07-01

    The form and universality of the mass function of young and nearby star-forming regions is still under debate. Its relation to the stellar density, its mass peak and the dependency on most recent models shows significant differencies for the various regions and remains unclear up to date. We aim to get a more complete census of two of such regions. We investigate yet unexplored areas of Orion and Taurus-Auriga, observed by the UKIDSS survey. In the latter, we search for low-mass stars via photometric and proper motion criteria and signs for variability. In Orion, we search for small stellar clumps via nearest-neighbor methods. Highlights in Taurus would be the finding of the missing low-mass stars and the detection of a young cluster T dwarf. In Orion, we discovered small stellar associations of its OB1b and OB1c populations. Combined with what is known in literature, we will provide by this investigations a general picture of the results of the star-forming processes in large areas of Taurus and Orion and probe the most recent models. Based on data of the UKIRT (operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the U.K.) Infrared Deep Sky Survey (UKIDSS).Supported by the Marie Curie Research Training Network `CONSTELLATION' under grant no. MRTN-CT-2006-035890.

  6. X-ray sources associated with young stellar objects in the star formation region CMa R1

    NASA Astrophysics Data System (ADS)

    Santos-Silva, Thais; Gregorio-Hetem, Jane; Montmerle, Thierry

    2013-07-01

    In previous works we studied the star formation scenario in the molecular cloud Canis Major R1 (CMa R1), derived from the existence of young stellar population groups near the Be stars Z CMa and GU CMa. Using data from the ROSAT X-ray satellite, having a field-of-view of ~ 1° in diameter, Gregorio-Hetem et al. (2009) discovered in this region young stellar objects mainly grouped in two clusters of different ages, with others located in between. In order to investigate the nature of these objects and to test a possible scenario of sequential star formation in this region, four fields (each 30 arcmin diameter, with some overlap) have been observed with the XMM-Newton satellite, with a sensitivity about 10 times better than ROSAT. The XMM-Newton data are currently under analysis. Preliminary results indicate the presence of about 324 sources, most of them apparently having one or more near-infrared counterparts showing typical colors of young stars. The youth of the X-ray sources was also confirmed by X-ray hardness ratio diagrams (XHRD), in different energy bands, giving an estimate of their Lx/Lbol ratios. In addition to these results, we present a detailed study of the XMM field covering the cluster near Z CMa. Several of these sources were classified as T Tauri and Herbig Ae/Be stars, using optical spectroscopy obtained with Gemini telescopes, in order to validate the use of XHRD applied to the entire sample. This classification is also used to confirm the relation between the luminosities in the near-infrared and X-ray bands expected for the T Tauri stars in CMa R1. In the present work we show the results of the study based on the spectra of about 90 sources found nearby Z CMa. We checked that the X-ray spectra (0.3 to 10 keV) of young objects is different from that observed in field stars and extragalactic objects. Some of the candidates also have light curve showing flares that are typical of T Tauri stars, which confirms the young nature of these X-ray sources.

  7. Using young massive star clusters to understand star formation and feedback in high-redshift-like environments

    NASA Astrophysics Data System (ADS)

    Longmore, S.; Barnes, A.; Battersby, C.; Bally, J.; Kruijssen, J. M. Diederik; Dale, J.; Henshaw, J.; Walker, D.; Rathborne, J.; Testi, L.; Ott, J.; Ginsburg, A.

    2016-05-01

    The formation environment of stars in massive stellar clusters is similar to the environment of stars forming in galaxies at a redshift of 1 - 3, at the peak star formation rate density of the Universe. As massive clusters are still forming at the present day at a fraction of the distance to high-redshift galaxies they offer an opportunity to understand the processes controlling star formation and feedback in conditions similar to those in which most stars in the Universe formed. Here we describe a system of massive clusters and their progenitor gas clouds in the centre of the Milky Way, and outline how detailed observations of this system may be able to: (i) help answer some of the fundamental open questions in star formation and (ii) quantify how stellar feedback couples to the surrounding interstellar medium in this high-pressure, high-redshift analogue environment.

  8. Absolute parameters of young stars: GG Lup and μ1 Sco

    NASA Astrophysics Data System (ADS)

    Budding, E.; Butland, R.; Blackford, M.

    2015-04-01

    New high-resolution spectroscopy and BVR photometry, together with literature data, on the Gould's Belt close binary systems GG Lup and μ1 Sco are presented and analysed. In the case of GG Lup, light and radial velocity curve fittings confirm a near-main-sequence picture of a pair of close stars. Absolute parameters are found, to within a few per cent, thus: M1 = 4.16 ± 0.12, M2 = 2.64 ± 0.12 (M⊙); R1 = 2.42 ± 0.05, R2 = 1.79 ± 0.04 (R⊙); T1 ˜ 13 000, T2 ˜ 10 600 (K); photometric distance ˜160 (pc). The high eccentricity and relatively short period (105 yr) of apsidal revolution may be related to an apparent `slow B-type pulsator' oscillation. Disturbances of the outer envelope of at least one of the components then compromise comparisons to standard evolutionary models, at least regarding the age of the system. A rate of apsidal advance is derived, which allows a check on the mean internal structure constant overline{k_2} = 0.0058 ± 0.0004. This is in agreement with values recently derived for young stars of solar composition and mass ˜3 M⊙. For μ1 Sco, we agree with previous authors that the secondary component is considerably oversized for its mass, implying binary (interactive) stellar evolution, probably of the `Case A' type. The primary appears relatively little affected by this evolution, however. Its parameters show consistency with a star of its derived mass at age about 13 Myr, consistent with the star's membership of the Sco-Cen OB2 Association. The absolute parameters are as follows: M1 = 8.3 ± 1.0, M2 = 4.6 ± 1.0 (M⊙); R1 = 3.9 ± 0.3, R2 = 4.6 ± 0.4 (R⊙); T1 ˜ 24 000, T2 ˜ 17 000 (K); photometric distance ˜135 (pc).

  9. Evolution of dynamo-generated magnetic fields in accretion disks around compact and young stars

    NASA Technical Reports Server (NTRS)

    Stepinski, Tomasz F.

    1994-01-01

    Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized objects because the accreted matter, whether it comes from the companion star (binaries) or from a collapsing molecular cloud core (single young stars), carries an embedded magnetic field. In addition, most accretion disks are hot and turbulent, thus meeting the condition for the MHD turbulent dynamo to maintain and amplify any seed field magnetic field. In fact, for a disk's magnetic field to persist long enough in comparison with the disk viscous time it must be contemporaneously regenerated because the characteristic diffusion time of a magnetic field is typically much shorter than a disk's viscous time. This is true for most thin accretion disks. Consequently, studying magentic fields in thin disks is usually synonymous with studying magnetic dynamos, a fact that is not commonly recognized in the literature. Progress in studying the structure of many accretion disks was achieved mainly because most disks can be regarded as two-dimensional flows in which vertical and radial structures are largely decoupled. By analogy, in a thin disk, one may expect that vertical and radial structures of the magnetic field are decoupled because the magnetic field diffuses more rapidly to the vertical boundary of the disk than along the radius. Thus, an asymptotic method, called an adiabatic approximation, can be applied to accretion disk dynamo. We can represent the solution to the dynamo equation in the form B = Q(r)b(r,z), where Q(r) describes the field distribution along the radius, while the field distribution across the disk is included in the vector function b, which parametrically depends on r and is normalized by the condition max (b(z)) = 1. The field distribution across the disk is established rapidly, while the radial distribution Q(r) evolves on a considerably longer timescale. It is this evolution that is the subject of this paper.

  10. Stellar and Gas Phase Metallicity of Low Surface Brighness Galaxies: Implication on Star Formation Process within Young Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Ji Hoon

    2015-08-01

    Low surface brightness (LSB) galaxies, whose central surface brightness, μB, is fainter than 23 mag/arcsec2 in the B-band, have been one of the most intriguing galaxy populations. Their unique characteristics, such as blue colors in optical and near-infrared light, low metallicity, low stellar and gas surface densities, low dust content, and high gas mass fraction (up to 90%), resemble physical conditions of young galaxies of the early Universe whose interstellar medium (ISM) has not been enriched before major star formation activities initiated and should provide a testbed for star formation process at the exremly low surface density regime. Given that their star formation histories are still poorly constrained, LSB galaxies are known to have large specific star formation rates (sSFRs) with large gas fractions. There is also a correlation between their sSFRs and gas fractions. One of plausible scenarios is that the star formation efficiency may be an increasing funtion of time, perhaps due in part to the slow build up of metals and dust. Moreover, it is suspected that, being located in low number density area in terms of galaxy environment, LSB galaxies may receive additional gas to fuel their star formation activity via sporadic cold gas accretion, especially toward their outskirt regions analogous to extended ultraviolet disks. Due to their relatively isolated nature without having endured much interactions, LSB galaxies can mimic star formation processes of disk galaxies of the early Universe within their interstellar media (ISM). We present preliminary results based on stellar and gas phase metallicity of LSB galaxies along with their environment parameters to show how star-forming ISM of young disk galaxies before metal enrichment.

  11. Star Formation in W3—AFGL 333: Young Stellar Content, Properties, and Roles of External Feedback

    NASA Astrophysics Data System (ADS)

    Jose, Jessy; Kim, Jinyoung S.; Herczeg, Gregory J.; Samal, Manash R.; Bieging, John H.; Meyer, Michael R.; Sherry, William H.

    2016-05-01

    One of the key questions in the field of star formation is the role of stellar feedback on the subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the massive stars in W4. This paper presents a study of the star formation activity within AFGL 333, a ˜104 M ⊙ cloud within W3, using deep JHK s photometry obtained from the NOAO Extremely Wide Field Infrared Imager combined with Spitzer IRAC and MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects (YSOs) in the complex, of which 99 are Class I and 713 are Class II sources. The stellar density analysis of YSOs reveals three major stellar aggregates within AFGL 333, namely AFGL 333 Main, AFGL 333 NW1 and AFGL 333 NW2. The disk fraction within AFGL 333 is estimated to be ˜50%-60%. We use the extinction map made from the H-{K}s colors of the background stars and CO data to understand the cloud structure and to estimate the cloud mass. From the stellar and cloud mass associated with AFGL 333, we infer that the region is currently forming stars with an efficiency of ˜4.5% and at a rate of ˜2-3 M ⊙ Myr-1 pc-2. In general, the star formation activity within AFGL 333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL 333 region.

  12. TENTATIVE EVIDENCE FOR RELATIVISTIC ELECTRONS GENERATED BY THE JET OF THE YOUNG SUN-LIKE STAR DG Tau

    SciTech Connect

    Ainsworth, Rachael E.; Ray, Tom P.; Taylor, Andrew M.; Scaife, Anna M. M.; Green, David A.; Buckle, Jane V.

    2014-09-01

    Synchrotron emission has recently been detected in the jet of a massive protostar, providing further evidence that certain jet formation characteristics for young stars are similar to those found for highly relativistic jets from active galactic nuclei. We present data at 325 and 610 MHz taken with the Giant Metrewave Radio Telescope of the young, low-mass star DG Tau, an analog of the Sun soon after its birth. This is the first investigation of a low-mass young stellar object at such low frequencies. We detect emission with a synchrotron spectral index in the proximity of the DG Tau jet and interpret this emission as a prominent bow shock associated with this outflow. This result provides tentative evidence for the acceleration of particles to relativistic energies due to the shock impact of this otherwise very low-power jet against the ambient medium. We calculate the equipartition magnetic field strength B {sub min} ≈ 0.11 mG and particle energy E {sub min} ≈ 4 × 10{sup 40} erg, which are the minimum requirements to account for the synchrotron emission of the DG Tau bow shock. These results suggest the possibility of low energy cosmic rays being generated by young Sun-like stars.

  13. The evolution of surface magnetic fields in young solar-type stars - I. The first 250 Myr

    NASA Astrophysics Data System (ADS)

    Folsom, C. P.; Petit, P.; Bouvier, J.; Lèbre, A.; Amard, L.; Palacios, A.; Morin, J.; Donati, J.-F.; Jeffers, S. V.; Marsden, S. C.; Vidotto, A. A.

    2016-03-01

    The surface rotation rates of young solar-type stars vary rapidly with age from the end of the pre-main sequence through the early main sequence. Important changes in the dynamos operating in these stars may result from this evolution, which should be observable in their surface magnetic fields. Here we present a study aimed at observing the evolution of these magnetic fields through this critical time period. We observed stars in open clusters and stellar associations of known ages, and used Zeeman Doppler imaging to characterize their complex magnetic large-scale fields. Presented here are results for 15 stars, from five associations, with ages from 20 to 250 Myr, masses from 0.7 to 1.2 M⊙, and rotation periods from 0.4 to 6 d. We find complex large-scale magnetic field geometries, with global average strengths from 14 to 140 G. There is a clear trend towards decreasing average large-scale magnetic field strength with age, and a tight correlation between magnetic field strength and Rossby number. Comparing the magnetic properties of our zero-age main-sequence sample to those of both younger and older stars, it appears that the magnetic evolution of solar-type stars during the pre-main sequence is primarily driven by structural changes, while it closely follows the stars' rotational evolution on the main sequence.

  14. Core-Halo Age Gradients and Star Formation in the Orion Nebula and NGC 2024 Young Stellar Clusters

    NASA Astrophysics Data System (ADS)

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

    2014-06-01

    We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on AgeJX estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  15. Core-halo age gradients and star formation in the Orion Nebula and NGS 2024 young stellar clusters

    SciTech Connect

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

    2014-06-01

    We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age{sub JX} , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age{sub JX} estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  16. DYNAMICAL EVOLUTION OF THE YOUNG STARS IN THE GALACTIC CENTER: N-BODY SIMULATIONS OF THE S-STARS

    SciTech Connect

    Perets, Hagai B.; Kupi, Gabor; Alexander, Tal; Gualandris, Alessia; Merritt, David

    2009-09-10

    We use Newtonian N-body simulations to study the evolution of the orbital eccentricities of stars deposited near ({approx}<0.05 pc) the Milky Way massive black hole (MBH), starting from initial conditions motivated by two competing models for their origin: formation in a disk followed by inward migration and exchange interactions involving a binary star. The first model predicts modest eccentricities, lower than those observed in the S-star cluster, while the second model predicts higher eccentricities than observed. The Newtonian N-body simulations include a dense cluster of 10 M{sub sun} stellar-mass black holes (SBHs), expected to accumulate near the MBH by mass segregation. Perturbations from the SBHs tend to randomize the stellar orbits, partially erasing the dynamical signatures of their origin. The eccentricities of the initially highly eccentric stars evolve, in 20 Myr (the S-star lifespan), to a distribution that is consistent with the observed eccentricity distribution. In contrast, the eccentricities of the initially more circular orbits fail to evolve to the observed values in 20 Myr, arguing against the disk migration scenario. We find that 20%-30% of the S-stars are tidally disrupted by the MBH over their lifetimes, and that the S-stars are not likely to be ejected as hypervelocity stars outside the central 0.05 pc by close encounters with SBHs.

  17. Mass and period limits on the ringed companion transiting the young star J1407

    NASA Astrophysics Data System (ADS)

    Kenworthy, M. A.; Lacour, S.; Kraus, A.; Triaud, A. H. M. J.; Mamajek, E. E.; Scott, E. L.; Ségransan, D.; Ireland, M.; Hambsch, F.-J.; Reichart, D. E.; Haislip, J. B.; LaCluyze, A. P.; Moore, J. P.; Frank, N. R.

    2015-01-01

    The young (˜16 Myr) pre-main-sequence star in Sco-Cen 1SWASP J140747.93-394542.6, hereafter referred to as J1407, underwent a deep eclipse in 2007 April, bracketed by several shallower eclipses in the surrounding 54 d. This has been interpreted as the first detection of an eclipsing ring system circling a substellar object (dubbed J1407b). We report on a search for this companion with Sparse Aperture Mask imaging and direct imaging with both the UT4 VLT and Keck telescopes. Radial velocity measurements of J1407 provide additional constraints on J1407b and on short period companions to the central star. Follow-up photometric monitoring using the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT)-4 and ROAD observatories during 2012-2014 has not yielded any additional eclipses. Large regions of mass-period space are ruled out for the companion. For circular orbits the companion period is constrained to the range 3.5-13.8 yr (a ≃ 2.2-5.6 au), and stellar masses (>80MJup) are ruled out at 3σ significance over these periods. The complex ring system appears to occupy more than 0.15 of its Hill radius, much larger than its Roche radius and suggesting a ring structure in transition. Further, we demonstrate that the radial velocity of J1407 is consistent with membership in the Upper Cen-Lup subgroup of the Sco-Cen association, and constraints on the rotation period and projected rotational velocity of J1407 are consistent with a stellar inclination of i⋆ ≃ 68° ± 10°.

  18. A direct imaging search for close stellar and sub-stellar companions to young nearby stars

    NASA Astrophysics Data System (ADS)

    Vogt, N.; Mugrauer, M.; Neuhäuser, R.; Schmidt, T. O. B.; Contreras-Quijada, A.; Schmidt, J. G.

    2015-01-01

    A total of 28 young nearby stars (ages {≤ 60} Myr) have been observed in the K_s-band with the adaptive optics imager Naos-Conica of the Very Large Telescope at the Paranal Observatory in Chile. Among the targets are ten visual binaries and one triple system at distances between 10 and 130 pc, all previously known. During a first observing epoch a total of 20 faint stellar or sub-stellar companion-candidates were detected around seven of the targets. These fields, as well as most of the stellar binaries, were re-observed with the same instrument during a second epoch, about one year later. We present the astrometric observations of all binaries. Their analysis revealed that all stellar binaries are co-moving. In two cases (HD 119022 AB and FG Aqr B/C) indications for significant orbital motions were found. However, all sub-stellar companion candidates turned out to be non-moving background objects except PZ Tel which is part of this project but whose results were published elsewhere. Detection limits were determined for all targets, and limiting masses were derived adopting three different age values; they turn out to be less than 10 Jupiter masses in most cases, well below the brown dwarf mass range. The fraction of stellar multiplicity and of the sub-stellar companion occurrence in the star forming regions in Chamaeleon are compared to the statistics of our search, and possible reasons for the observed differences are discussed. Based on observations made with ESO telescopes at Paranal Observatory under programme IDs 083.C-0150(B), 084.C-0364(A), 084.C-0364(B), 084.C-0364(C), 086.C-0600(A) and 086.C-0600(B).

  19. Chemistry and Kinematics of Red Supergiant Stars in the Young Massive Cluster NGC 2100

    NASA Astrophysics Data System (ADS)

    Patrick, L. R.; Evans, C. J.; Davies, B.; Kudritzki, R.-P.; Hénault-Brunet, V.; Bastian, N.; Lapenna, E.; Bergemann, M.

    2016-03-01

    We have obtained K-band Multi-Object Spectrograph (KMOS) near-IR spectroscopy for 14 red supergiant stars (RSGs) in the young massive star cluster NGC 2100 in the Large Magellanic Cloud (LMC). Stellar parameters including metallicity are estimated using the J-band analysis technique, which has been rigorously tested in the Local Universe. We find an average metallicity for NGC 2100 of [Z] = -0.43 ± 0.10 dex, in good agreement with estimates from the literature for the LMC. Comparing our results in NGC 2100 with those for a Galactic cluster (at Solar-like metallicity) with a similar mass and age we find no significant difference in the location of RSGs in the Hertzsprung-Russell diagram. We combine the observed KMOS spectra to form a simulated integrated-light cluster spectrum and show that, by analysing this spectrum as a single RSG, the results are consistent with the average properties of the cluster. Radial velocities are estimated for the targets and the dynamical properties are estimated for the first time within this cluster. The data are consistent with a flat velocity dispersion profile, and with an upper limit of 3.9 kms-1, at the 95% confidence level, for the velocity dispersion of the cluster. However, the intrinsic velocity dispersion is unresolved and could, therefore, be significantly smaller than the upper limit reported here. An upper limit on the dynamical mass of the cluster is derived as Mdyn ≤ 15.2 × 104M⊙ assuming virial equilibrium.

  20. THE FIRST X-SHOOTER OBSERVATIONS OF JETS FROM YOUNG STARS

    SciTech Connect

    Bacciotti, F.; Randich, S.; Whelan, E. T.; Alcala, J. M.; Nisini, B.; Podio, L.; Stelzer, B.; Cupani, G.

    2011-08-20

    We present the first pilot study of jets from young stars conducted with X-shooter, on the ESO/Very Large Telescope. As it offers simultaneous, high-quality spectra in the range 300-2500 nm, X-shooter is uniquely important for spectral diagnostics in jet studies. We chose to probe the accretion/ejection mechanisms at low stellar masses examining two targets with well-resolved continuous jets lying on the plane of the sky: ESO-HA 574 in Chameleon I and Par-Lup3-4 in Lupus III. The mass of the latter is close to the sub-stellar boundary (M{sub *} = 0.13 M{sub sun}). A large number of emission lines probing regions of different excitation are identified, position-velocity diagrams are presented, and mass outflow/accretion rates are estimated. Comparison between the two objects is striking. ESO-HA 574 is a weakly accreting star for which we estimate a mass accretion rate of log ( M-dot{sub acc}) = -10.8{+-}0.5 (in M{sub sun} yr{sup -1}), yet it drives a powerful jet with M-dot{sub out} {approx} 1.5-2.7 x 10{sup -9} M{sub sun} yr{sup -1}. These values can be reconciled with a magneto-centrifugal jet acceleration mechanism assuming that the presence of the edge-on disk severely depresses the luminosity of the accretion tracers. In comparison, Par-Lup3-4, with stronger mass accretion ( log ( M-dot{sub acc}) = -9.1{+-}0.4 M{sub sun} yr{sup -1}), drives a low-excitation jet with about M-dot{sub out} {approx} 3.2 x 10{sup -10} M{sub sun} yr{sup -1} in both lobes. Despite the low stellar mass, M-dot{sub out}/ M-dot{sub acc} for Par-Lup3-4 is at the upper limit of the range usually measured for young objects, but still compatible with a steady magneto-centrifugal wind scenario if all uncertainties are considered.

  1. Effects of turbulence on cosmic ray propagation in protostars and young star/disk systems

    SciTech Connect

    Fatuzzo, Marco; Adams, Fred C. E-mail: fca@umich.edu

    2014-05-20

    The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when δB/B {sub 0} > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.

  2. Magnetic activity and differential rotation in the very young star KIC 8429280

    NASA Astrophysics Data System (ADS)

    Frasca, A.; Fröhlich, H.-E.; Bonanno, A.; Catanzaro, G.; Biazzo, K.; Molenda-Żakowicz, J.

    2011-08-01

    Aims: We present a spectroscopic and photometric analysis of the rapid rotator KIC 8429280, discovered by ourselves as a very young star and observed by the NASA Kepler mission, designed to determine its activity level, spot distribution, and differential rotation. Methods: We use ground-based data, such as high-resolution spectroscopy and multicolor broad-band photometry, to derive stellar parameters (vsini, spectral type, Teff, log g, and [Fe/H]), and we adopt a spectral subtraction technique to highlight the strong chromospheric emission in the cores of hydrogen Hα and Ca ii H&K and infrared triplet (IRT) lines. We then fit a robust spot model to the high-precision Kepler photometry spanning 138 days. Model selection and parameter estimation is performed in a Bayesian manner using a Markov chain Monte Carlo method. Results: We find that KIC 8429280 is a cool (K2 V) star with an age of about 50 Myr, based on its lithium content, that has passed its T Tau phase and is spinning up approaching the ZAMS on its radiative track. Its high level of chromospheric activity is clearly indicated by the strong radiative losses in Ca ii H&K and IRT, Hα, and Hβ lines. Furthermore, its Balmer decrement and the flux ratio of Ca ii IRT lines imply that these lines are mainly formed in optically-thick regions similar to solar plages. The analysis of the Kepler data uncovers evidence of at least seven enduring spots. Since the star's inclination is rather high - nearly 70° - the assignment of the spots to either the northern or southern hemisphere is not unambiguous. We find at least three solutions with nearly the same level of residuals. Even in the case of seven spots, the fit is far from being perfect. Owing to the exceptional precision of the Kepler photometry, it is not possible to reach the noise floor without strongly enhancing the degrees of freedom and, consequently, the non-uniqueness of the solution. The distribution of the active regions is such that the spots are located around three latitude belts, i.e. around the star's equator and around ± (50°-60°), with the high-latitude spots rotating slower than the low-latitude ones. The equator-to-pole differential rotation dΩ ≃ 0.27 rad d-1 is at variance with some recent mean-field models of differential rotation in rapidly rotating main-sequence stars, which predict a much smaller latitudinal shear. Our results are consistent with the scenario of a higher differential rotation, which changes along the magnetic cycle, as proposed by other models. Based on public Kepler data, on observations made with the Italian Telescopio Nazionale Galileo operated on the island of La Palma by the Fundación Galileo Galilei of INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque del los Muchachos of the Instituto de Astrofisica de Canarias, and on observations collected at the Catania Astrophysical Observatory (Italy).

  3. The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Reines, Amy E.; Nidever, David L.; Whelan, David G.; Johnson, Kelsey E.

    2010-01-01

    In this spectroscopic study of infant massive star clusters, we find that continuum emission from ionized gas rivals the stellar luminosity at optical wavelengths. In addition, we find that nebular line emission is significant in many commonly used broadband Hubble Space Telescope (HST) filters including the F814W I-band, the F555W V-band, and the F435W B-band. Two young massive clusters (YMCs) in the nearby starburst galaxy NGC 4449 were targeted for follow-up spectroscopic observations after Reines et al. discovered an F814W I-band excess in their photometric study of radio-detected clusters in the galaxy. The spectra were obtained with the Dual Imaging Spectrograph (DIS) on the 3.5 m Apache Point Observatory (APO) telescope and have a spectral range of ~3800-9800 Å. We supplement these data with HST and Sloan Digital Sky Survey photometry of the clusters. By comparing our data to the Starburst99 and GALEV evolutionary synthesis models, we find that nebular continuum emission competes with the stellar light in our observations and that the relative contribution from the nebular continuum is largest in the U- and I-bands, where the Balmer (3646 Å) and Paschen jumps (8207 Å) are located. The spectra also exhibit strong line emission including the [S III] λλ9069, 9532 lines in the HST F814W I-band. We find that the combination of nebular continuum and line emission can account for the F814W I-band excess previously found by Reines et al. In an effort to provide a benchmark for estimating the impact of ionized gas emission on photometric observations of young massive stellar populations, we compute the relative contributions of the stellar continuum, nebular continuum, and emission lines to the total observed flux of a 3 Myr old cluster through various HST filter/instrument combinations, including filters in the Wide Field Camera 3. We urge caution when comparing observations of YMCs to evolutionary synthesis models since nebular continuum and line emission can have a large impact on magnitudes and colors of young (lsim5 Myr) clusters, significantly affecting inferred properties such as ages, masses and extinctions.

  4. CLOSE COMPANIONS TO YOUNG STARS. I. A LARGE SPECTROSCOPIC SURVEY IN CHAMAELEON I AND TAURUS-AURIGA

    SciTech Connect

    Nguyen, Duy Cuong; Brandeker, Alexis; Van Kerkwijk, Marten H.; Jayawardhana, Ray E-mail: mhvk@astro.utoronto.ca E-mail: dcnguyen@pas.rochester.edu E-mail: alexis@astro.su.se

    2012-02-01

    We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m telescope. From these data, we achieved a typical radial velocity (RV) precision of {approx}80 m s{sup -1} with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on RV variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Chamaeleon I (7%) and Taurus-Auriga (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient RV precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.

  5. Accretion shocks in young stars: the role of local absorption on the X-ray emission

    NASA Astrophysics Data System (ADS)

    Bonito, R.; Argiroffi, C.; Orlando, S.; Miceli, M.

    2014-07-01

    We analyze the X-ray emission from accretion shocks formed where the infalling material impact the surface of young stars. Several aspects in observations and in models of accretion are still debated: the density vs temperature structure of the shocked plasma is opposite of what expected from simple accretion shock models and the X-ray luminosity detected from post-shock plasma is below the predicted value. To address these open issues we performed numerical simulations describing the impact of an accretion stream onto the stellar surface (exploring different configurations of the magnetic field) and taken into account the local absorption due to the surrounding medium. We investigated the effects of absorption for different viewing angles and wavelengths. From the model results we synthesize the X-ray emission from the accretion shock and perform density and temperature diagnostics on the synthetic spectra. By comparing our results with the observations, we find that the X-ray fluxes detected are lower than expected because of the local absorption. The emerging spectra suggest higher density for higher temperature as derived from the observations, proving that a detailed model accounting for a realistic treatment of the local absorption is needed to interpret the observations of X-ray emitting accretion shocks.

  6. Do circumstellar disks regulate rotation in young very low mass stars and brown dwarfs?

    NASA Astrophysics Data System (ADS)

    Rodriguez-Ledesma, M. V.; Mundt, R.; Eislöffel, J.

    Rotational studies at a variety of ages and masses are important for con- straining the angular momentum evolution of young stellar objects. Of particular interest are the very low mass (VLM) stars and brown dwarfs (BDs), because of the significant lack of known rotational periods in that mass range. We present results of an extensive rotational study in the Orion Nebula Clus- ter from where 487 new rotational periods were measured. In order to inves- tigate a rotation-disk correlation, we derived near infrared (NIR) excesses (from IJHK photometry) for a sample of 732 very low mass periodic vari- ables. We found a highly significant rotation-disk correlation for objects with masses between 0.4-0.075 M , in which objects with NIR excess tend to rotate slower than objects without NIR excess. Interestingly we found no corre- lation in the substellar regime. We discuss possible scenarios which may explain the lack of rotation-disk connection in the substellar mass regime.

  7. Multiwavelength Study of the Starburst Galaxy NGC 7714. II. The Balance between Young, Intermediate-Age, and Old Stars

    NASA Astrophysics Data System (ADS)

    Lançon, Ariane; Goldader, Jeffrey D.; Leitherer, Claus; González Delgado, Rosa M.

    2001-05-01

    We combine existing multiwavelength data (including an HST/GHRS UV spectrum and a ground-based optical spectrum) with unpublished HST/WFPC2 images, near-IR photometry, and K-band spectroscopy. We use these data to constrain the young, the intermediate-age, and the old stellar populations in the central regions of the starburst galaxy NGC 7714. In a previous paper the stellar features in the HST/GHRS ultraviolet (UV) spectrum and the optical emission lines were used to identify an ~5 Myr old, very little reddened stellar population as the main source of UV light in the central ~330 pc. The optical data indicated the existence of an older population. The nature of the latter is investigated here. Stellar absorption features in the optical and the near-IR are used to break partly the strong degeneracy between the effects of aging and those of the inhomogeneous dust distribution on the UV-optical-IR colors. Consistency with far-IR, X-ray, and radio data is also addressed. The successful models have essential features in common. We find that the young burst responsible for the UV light represents only a small part of an extended episode of enhanced star formation, initiated a few times 108 yr ago. The star formation rate is likely to have varied on this timescale, averaging about 1 Msolar yr-1. The mass of young and intermediate-age stars thus formed equals at least 10% of the mass locked in preexisting stars of the underlying spiral galaxy nucleus, and fractions around 25% are favored. The spectrophotometric star formation timescale is long compared to the ~110 Myr elapsed since closest contact with the neighboring NGC 7715, according to the 1992 dynamical models of Smith & Wallin. The initial trigger of the starburst thus remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight toward young stars. Our results based on the integrated spectrophotometry of the central ~330 pc are supported by high-resolution images of this area. The different extinction values obtained when different spectral indicators are used result naturally from the coexistence of populations with various ages and obscurations. The near-IR continuum image looks smoothest, as a consequence of lower sensitivity to extinction and of a larger contribution of old stars. We compare the nuclear properties of NGC 7714 with results from studies in larger apertures. We emphasize that the global properties of starburst galaxies are the result of the averaging over many lines of sight with very diverse properties in terms of obscuration and stellar ages. The overall picture is strongly reminiscent of the other nearby ``prototypical'' starburst, M82.

  8. Star formation in the outer Galaxy: membership and fundamental parameters of the young open cluster NGC 1893

    NASA Astrophysics Data System (ADS)

    Prisinzano, L.; Sanz-Forcada, J.; Micela, G.; Caramazza, M.; Guarcello, M. G.; Sciortino, S.; Testi, L.

    2011-03-01

    Context. Different environmental conditions can play a crucial role in determining final products of the star formation process, and in this context, less favorable activities of star formation are expected in the external regions of our Galaxy. Aims: We studied the properties of the young open cluster NGC 1893 located about 12 Kpc from the galactic center, to investigate how different physical conditions can affect the process of star formation. Methods: By adopting a multiwavelength approach, we compiled a catalog extending from X-rays to NIR data to derive the cluster membership. In addition, optical and NIR photometric properties are used to evaluate the cluster parameters. Results: We find 415 diskless candidate members and 1061 young stellar objects with a circumstellar disk or class II candidate members, 125 of which are also Hα emitters. Considering the diskless candidate members, we find that the cluster distance is 3.6 ± 0.2 kpc and the mean interstellar reddening is E(B - V) = 0.6 ± 0.1 with evidence of differential reddening in the whole surveyed region. Conclusions: NGC 1893 contains a conspicuous population of pre-main sequence stars, together with the well-studied main sequence cluster population. We found a disk fraction of about 70% similar to the one found in clusters of similar age in the solar neighbor and then, despite expected unfavorable conditions for star formation, we conclude that very rich young clusters can also form in the outer regions of our Galaxy. Full Tables 5-8 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A77

  9. THE GEMINI NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF GIANT PLANETS AROUND YOUNG B AND A STARS

    SciTech Connect

    Nielsen, Eric L.; Liu, Michael C.; Chun, Mark; Ftaclas, Christ; Wahhaj, Zahed; Biller, Beth A.; Hayward, Thomas L.; Hartung, Markus; Alencar, Silvia H. P.; Artymowicz, Pawel; Boss, Alan; Clarke, Fraser; De Gouveia Dal Pino, Elisabete; Gregorio-Hetem, Jane; Kuchner, Marc; Lin, Douglas N. C.; and others

    2013-10-10

    We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5-2.5 M{sub ☉}) conducted to date and includes the planet hosts β Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58{sup +21}{sub -20} M{sub Jup} and 55{sup +20}{sub -19} M{sub Jup}, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M{sub ☉} stars can have giant planets greater than 4 M{sub Jup} between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M{sub Jup} between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M{sub Jup}, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.

  10. The embedded young stars in the Taurus-Auriga molecular cloud. I - Models for spectral energy distributions

    NASA Technical Reports Server (NTRS)

    Kenyon, Scott J.; Calvet, Nuria; Hartmann, Lee

    1993-01-01

    We describe radiative transfer calculations of infalling, dusty envelopes surrounding pre-main-sequence stars and use these models to derive physical properties for a sample of 21 heavily reddened young stars in the Taurus-Auriga molecular cloud. The density distributions needed to match the FIR peaks in the spectral energy distributions of these embedded sources suggest mass infall rates similar to those predicted for simple thermally supported clouds with temperatures about 10 K. Unless the dust opacities are badly in error, our models require substantial departures from spherical symmetry in the envelopes of all sources. These flattened envelopes may be produced by a combination of rotation and cavities excavated by bipolar flows. The rotating infall models of Terebey et al. (1984) models indicate a centrifugal radius of about 70 AU for many objects if rotation is the only important physical effect, and this radius is reasonably consistent with typical estimates for the sizes of circumstellar disks around T Tauri stars.

  11. KEPLER-63b: A GIANT PLANET IN A POLAR ORBIT AROUND A YOUNG SUN-LIKE STAR

    SciTech Connect

    Sanchis-Ojeda, Roberto; Winn, Joshua N.; Albrecht, Simon; Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.; Johnson, John Asher; Torres, Guillermo; Carter, Joshua A.; Dawson, Rebekah I.; Geary, John C.; Campante, Tiago L.; Chaplin, William J.; Davies, Guy R.; Lund, Mikkel N.; Buchhave, Lars A.; Everett, Mark E.; Fischer, Debra A.; Gilliland, Ronald L.; Horch, Elliott P.; and others

    2013-09-20

    We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, m{sub Kp} = 11.6, T{sub eff} = 5576 K, M{sub *} = 0.98 M{sub ☉}). The planet transits every 9.43 days, with apparent depth variations and brightening anomalies caused by large starspots. The planet's radius is 6.1 ± 0.2 R{sub ⊕}, based on the transit light curve and the estimated stellar parameters. The planet's mass could not be measured with the existing radial-velocity data, due to the high level of stellar activity, but if we assume a circular orbit, then we can place a rough upper bound of 120 M{sub ⊕} (3σ). The host star has a high obliquity (ψ = 104°), based on the Rossiter-McLaughlin effect and an analysis of starspot-crossing events. This result is valuable because almost all previous obliquity measurements are for stars with more massive planets and shorter-period orbits. In addition, the polar orbit of the planet combined with an analysis of spot-crossing events reveals a large and persistent polar starspot. Such spots have previously been inferred using Doppler tomography, and predicted in simulations of magnetic activity of young Sun-like stars.

  12. Kepler-63b: A Giant Planet in a Polar Orbit around a Young Sun-like Star

    NASA Astrophysics Data System (ADS)

    Sanchis-Ojeda, Roberto; Winn, Joshua N.; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard; Johnson, John Asher; Torres, Guillermo; Albrecht, Simon; Campante, Tiago L.; Chaplin, William J.; Davies, Guy R.; Lund, Mikkel N.; Carter, Joshua A.; Dawson, Rebekah I.; Buchhave, Lars A.; Everett, Mark E.; Fischer, Debra A.; Geary, John C.; Gilliland, Ronald L.; Horch, Elliott P.; Howell, Steve B.; Latham, David W.

    2013-09-01

    We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, m Kp = 11.6, T eff = 5576 K, M sstarf = 0.98 M ?). The planet transits every 9.43 days, with apparent depth variations and brightening anomalies caused by large starspots. The planet's radius is 6.1 0.2 R ?, based on the transit light curve and the estimated stellar parameters. The planet's mass could not be measured with the existing radial-velocity data, due to the high level of stellar activity, but if we assume a circular orbit, then we can place a rough upper bound of 120 M ? (3?). The host star has a high obliquity (? = 104), based on the Rossiter-McLaughlin effect and an analysis of starspot-crossing events. This result is valuable because almost all previous obliquity measurements are for stars with more massive planets and shorter-period orbits. In addition, the polar orbit of the planet combined with an analysis of spot-crossing events reveals a large and persistent polar starspot. Such spots have previously been inferred using Doppler tomography, and predicted in simulations of magnetic activity of young Sun-like stars.

  13. Optical Spectroscopy of X-Ray-selected Young Stars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Vaidya, Kaushar; Chen, Wen-Ping; Lee, Hsu-Tai

    2015-12-01

    We present low-resolution optical spectra for 29 X-ray sources identified as either massive star candidates or low-mass pre-main-sequence (PMS) star candidates in the clusters Trumpler 16 and Trumpler 14 of the Carina Nebula. Spectra of two more objects (one with an X-ray counterpart, and one with no X-ray counterpart), not originally our targets, but found close (˜3″) to two of our targets, are presented as well. Twenty early-type stars, including an O8 star, seven B1-B2 stars, two B3 stars, a B5 star, and nine emission-line stars, are identified. Eleven T Tauri stars, including eight classical T Tauri stars (CTTSs) and three weak-lined T Tauri stars, are identified. The early-type stars in our sample are more reddened compared to the previously known OB stars of the region. The Chandra hardness ratios of our T Tauri stars are found to be consistent with the Chandra hardness ratios of T Tauri stars of the Orion Nebula Cluster. Most early-type stars are found to be nonvariable in X-ray emission, except the B2 star J104518.81-594217.9, the B3 star J104507.84-594134.0, and the Ae star J104424.76-594555.0, which are possible X-ray variables. J104452.20-594155.1, a CTTS, is among the brightest and the hardest X-ray sources in our sample, appears to be a variable, and shows a strong X-ray flare. The mean optical and near-infrared photometric variability in the V and Ks bands, of all sources, is found to be ˜0.04 and 0.05 mag, respectively. The T Tauri stars show significantly larger mean variation, ˜0.1 mag, in the Ks band. The addition of one O star and seven B1-B2 stars reported here contributes to an 11% increase of the known OB population in the observed field. The 11 T Tauri stars are the first ever confirmed low-mass PMS stars in the Carina Nebula region.

  14. The massive disk around the young B-star AFGL 490

    NASA Astrophysics Data System (ADS)

    Schreyer, Katharina; Semenov, Dmitry; Henning, Thomas; Pavlyuchenkov, Yaroslav; Dullemond, Cornelius

    The AFGL 490 is a key target in the class of deeply embedded young stellar objects with masses of 8x10 Msol being in a transition stage to the pre-main-sequence Herbig Be stars. We observe this system at sub-arcsecond resolution with the Plateau de Bure Interferometer (PdBI) in the C17O(2-1) transition in order to confirm the presence of a rotating disk. The C17O(2-1) data show clear evidence for a rotating ~ 1 500 AU disk centered at the the 1 mm continuum point source. We model these data iteratively. First, the physical structure of the disk is obtained using a two-dimensional radiative transfer code. Second, with this model in hand, we calculate time-dependent abundances in the disk using a gas-grain chemical network. Finally, the beam-convolved C17O(2-1) interferometric map is synthesized by a 2D line transfer code, and these results are compared with the observations in the step-by-step way (Semenov et al. 2005). We estimate that (1) the disk inclination angle is 30 ± 5◦, (2) its positional angle is 150 ± 10◦, (3) the disk is in Keplerian rotation, (4) it has a radius of about 1 400 AU, and (5) the disk mass is about 0.2-0.4 Msol (depending on the assumed surface density gradient p ~ -1). This is in contrast to the value of 4 ± 2 Msol estimated from the intensity of the PdBI 1 mm continuum emission within 1000 AU around the star, and ~ 8 Msol for the mass of the gas located within about 4 000 AU around the star, as it has been found using our CS(2-1) PdBI data (Schreyer et al. 2002). It is interesting that the geometry of the detected C17O emission map speaks in favor of a larger inclination angle, > 60◦. Thus, the C17O interferometric map traces the densest part of a more extended and likely asymmetric disklike structure. Moreover, we find clear indication for on-going accretion in this object, since the detected PdBI CH3OH J=2(0,2)-1(0,1) A+ emission lines show characteristic inverse P Cygni profiles. Given the large mass of the circumstellar gas, comparable to the mass of the central star, we suggest that accretion in AFGL 490 is globally regulated by gravitational instabilities, inevitably leading to the formation of several spiral arms (as predicted by Fromang et al. 2004), while the detected C17O emission arises in a small inner region that is already fully relaxed to the Keplerian state.

  15. Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy

    NASA Astrophysics Data System (ADS)

    Zwintz, K.; Ryabchikova, T.; Lenz, P.; Pamyatnykh, A. A.; Fossati, L.; Sitnova, T.; Breger, M.; Poretti, E.; Rainer, M.; Hareter, M.; Mantegazza, L.

    2014-07-01

    Context. HD 144277 was previously discovered by Microvariability and Oscillations of Stars (MOST) space photometry to be a young and hot δ Scuti star showing regular groups of pulsation frequencies. The first asteroseismic models required lower than solar metallicity to fit the observed frequency range based on a purely photometric analysis. Aims: The aim of the present paper is to determine, by means of high-resolution spectroscopy, fundamental stellar parameters required for the asteroseismic model of HD 144277, and subsequently, to refine it. Methods: High-resolution, high signal-to-noise spectroscopic data obtained with the HARPS spectrograph were used to determine the fundamental parameters and chemical abundances of HD 144277. These values were put into context alongside the results from asteroseismic models. Results: The effective temperature, Teff, of HD 144277 was determined as 8640 +300-100 K, log g is 4.14 ± 0.15 and the projected rotational velocity, υsini, is 62.0 ± 2.0 km s-1. As the υsini value is significantly larger than previously assumed, we refined the first asteroseimic model accordingly. The overall metallicity Z was determined to be 0.011 where the light elements He, C, O, Na, and S show solar chemical composition, but the heavier elements are significantly underabundant. In addition, the radius of HD 144277 was determined to be 1.55 ± 0.65 R⊙ from spectral energy distribution fitting, based on photometric data taken from the literature. Conclusions: From the spectroscopic observations, we could confirm our previous assumption from asteroseismic models that HD 144277 has less than solar metallicity. The fundamental parameters derived from asteroseismology, Teff, log g, L/L⊙ and R/R⊙ agree within one sigma to the values found from spectroscopic analysis. As the υsini value is significantly higher than assumed in the first analysis, near-degeneracies and rotational mode coupling were taken into account in the new models. These suggest that HD 144277 has an equatorial rotational velocity of about 80 km s-1 and is seen equator-on. The observed frequencies are identified as prograde modes. This work is based on ground-based observations made with the 3.6 m telescope at La Silla Observatory under the ESO Large Programme LP185.D-0056.

  16. An Extraordinary Cluster of Massive Young Stars in the Milky Way's Nucleus

    NASA Technical Reports Server (NTRS)

    Serabyn, E.; Shupe, D.; Figer, D. F.

    1998-01-01

    The mass distribution of newborn stars is key to the evolution of galaxies, as it determines whether a galaxy's interstellar medium is funneled predominantly into dim, long-lived, low-mass stars, as is the case in normal galactic disks, or into bright, short-lived, massive stars, as is perhaps the case in starburst nuclei.

  17. The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Reines, Amy E.; Nidever, D. L.; Whelan, D. G.; Johnson, K. E.

    2010-01-01

    In this spectroscopic study of infant massive star clusters, we find that continuum emission from ionized gas rivals the stellar luminosity at optical wavelengths. We also find that nebular line emission is significant in many commonly used broad-band HST filters including the F814W I-band, the F555W V-band and the F435W B-band. Two young massive clusters (YMCs) in the galaxy NGC 4449 were targeted for follow-up spectroscopic observations after Reines et al. (2008) discovered an F814W I-band excess in their photometric study of radio-detected clusters in the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the 3.5 m APO telescope and we supplement this data with HST and SDSS photometry. By comparing our data to the Starburst99 and GALEV evolutionary synthesis models, we find that nebular continuum emission competes with the stellar light in our observations and that the relative contribution from the nebular continuum is largest in the U- and I-bands, where the Balmer and Paschen jumps are located. The spectra also exhibit strong line emission including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the combination of nebular continuum and line emission can account for the F814W I-band excess previously found by Reines et al. (2008). In an effort to provide a benchmark for estimating the impact of ionized gas emission on photometric observations of YMCs, we compute the relative contributions of stellar continuum, nebular continuum, and emission lines to the total observed flux of a 3 Myr-old cluster through various HST filter/instrument combinations, including filters in WFC3. We urge caution when comparing observations of YMCs to evolutionary synthesis models since nebular continuum and line emission can have a large impact on magnitudes and colors of young (< 6 Myr) clusters, significantly affecting inferred properties such as ages, masses and extinctions.

  18. Identifying the Young Low-mass Stars within 25 pc. I. Spectroscopic Observations

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya; Liu, Michael C.; Reid, I. Neill

    2009-07-01

    We have completed a high-resolution (R ≈ 60,000) optical spectroscopic survey of 185 nearby M dwarfs identified using ROSAT data to select active, young objects with fractional X-ray luminosities comparable to or greater than Pleiades members. Our targets are drawn from the NStars 20 pc census and the Moving-M sample with distances determined from parallaxes or spectrophotometric relations. We limited our sample to 25 pc from the Sun, prior to correcting for pre-main-sequence overluminosity or binarity. Nearly half of the resulting M dwarfs are not present in the Gliese catalog and have no previously published spectral types. We identified 30 spectroscopic binaries (SBs) from the sample, which have strong X-ray emission due to tidal spin-up rather than youth. This is equivalent to a 16% SB fraction, with at most a handful of undiscovered SBs. We estimate upper limits on the age of the remaining M dwarfs using spectroscopic youth indicators such as surface gravity-sensitive indices (CaH and K I). We find that for a sample of field stars with no metallicity measurements, a single CaH gravity index may not be sufficient, as higher metallicities mimic lower gravity. This is demonstrated in a subsample of metal-rich radial velocity (RV) standards, which appear to have low surface gravity as measured by the CaH index, yet show no other evidence of youth. We also use additional youth diagnostics such as lithium absorption and strong Hα emission to set more stringent age limits. Eleven M dwarfs with no Hα emission or absorption are likely old (>400 Myr) and were caught during an X-ray flare. We estimate that our final sample of the 144 youngest and nearest low-mass objects in the field is less than 300 Myr old, with 30% of them being younger than 150 Myr and four very young (lap10 Myr), representing a generally untapped and well-characterized resource of M dwarfs for intensive planet and disk searches. Based on observations collected at the W. M. Keck Observatory and the Canada-France-Hawaii Telescope. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. The CFHT is operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

  19. An M Dwarf Companion to an F-type Star in a Young Main-sequence Binary

    NASA Astrophysics Data System (ADS)

    Eigmüller, Ph.; Eislöffel, J.; Csizmadia, Sz.; Lehmann, H.; Erikson, A.; Fridlund, M.; Hartmann, M.; Hatzes, A.; Pasternacki, Th.; Rauer, H.; Tkachenko, A.; Voss, H.

    2016-03-01

    Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung-Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M⊙ and a radius of (1.474 ± 0.040) R⊙. The companion is an M dwarf with a mass of (0.188 ± 0.014) M⊙ and a radius of (0.234 ± 0.009) R⊙. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin-orbit synchronization. This indicates a young main-sequence binary with an age below ˜250 Myr. The mass-radius relation of both components are in agreement with this finding.

  20. Star formation in the LMC: Comparative CCD observations of young stellar populations in two giant molecular clouds

    NASA Astrophysics Data System (ADS)

    Ruppert, J.; Zinnecker, H.

    2009-08-01

    This work deals with a CCD imaging study at optical and near-infrared wavelength of two giant molecular clouds (plus a control field) in the southern region of the Large Magellanic Cloud, one of which shows multiple signs of star formation, whereas the other does not. The observational data from VLT FORS2 (R band) and NTT SOFI (K s band) have been analyzed to derive luminosity functions and color-magnitude diagrams. The young stellar content of these two giant molecular clouds is compared and confirmed to be different, in the sense that the apparently `` starless" cloud has so far formed only low-luminosity, low-mass stars (fainter than {mK s˜ 16.5} mag, not seen by 2MASS), while the other cloud has formed both faint low-mass and luminous high-mass stars. The surface density excess of low-luminosity stars (˜ 2 per square arcmin) in the `` starless" cloud with respect to the control field is about 20% whereas the excess is about a factor of 3 in the known star-forming cloud. The difference may be explained theoretically by the gravo-turbulent evolution of giant molecular clouds, one being younger and less centrally concentrated than the other.

  1. Star Formation in the LMC: Comparative CCD Observations of Young Stellar Populations in two Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Ruppert, Jan; Zinnecker, Hans

    2010-04-01

    This work deals with a CCD imaging study at optical and near-infrared wavelength of two giant molecular clouds (plus a control field) in the southern region of the Large Magellanic Cloud, one of which shows multiple signs of star formation, whereas the other does not. The observational data from VLT FORS2 (R-band) and NTT SOFI (Ks-band) have been analyzed to derive luminosity functions and color-magnitude diagrams. The young stellar content of these two giant molecular clouds is compared and confirmed to be different, in the sense that the apparently “starless” cloud has so far formed only low-luminosity, low-mass stars (fainter than mKs = 16.5 mag, not seen by 2MASS), while the other cloud has formed both faint low-mass and luminous high-mass stars. The surface density excess of low-luminosity stars (~ 2 per square arcmin) in the “starless” cloud with respect to the control field is about 20% whereas the excess is about a factor of 3 in the known star-forming cloud. The difference may be explained theoretically by the gravo-turbulent evolution of giant molecular clouds, one being younger and less centrally concentrated than the other.

  2. NEAR-INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN THE STAR FORMATION REGION CYGNUS OB7

    SciTech Connect

    Wolk, Scott J.; Rice, Thomas S.; Aspin, Colin

    2013-08-20

    We present an analysis of near-infrared time-series photometry in J, H, and K bands for about 100 epochs of a 1 Degree-Sign Multiplication-Sign 1 Degree-Sign region of the Lynds 1003/1004 dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field Infrared Survey Explorer, we identify 96 candidate disk bearing young stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or earlier. Using the Wide-Field Imaging Camera on the United Kingdom Infrared Telescope, we were able to obtain photometry over three observing seasons, with photometric uncertainty better than 0.05 mag down to J Almost-Equal-To 17. We study detailed light curves and color trajectories of {approx}50 of the YSOs in the monitored field. We investigate the variability and periodicity of the YSOs and find the data are consistent with all YSOs being variable in these wavelengths on timescales of a few years. We divide the variability into four observational classes: (1) stars with periodic variability stable over long timescales, (2) variables which exhibit short-lived cyclic behavior, (3) long-duration variables, and (4) stochastic variables. Some YSO variability defies simple classification. We can explain much of the observed variability as being due to dynamic and rotational changes in the disk, including an asymmetric or changing blocking fraction, changes to the inner disk hole size, as well as changes to the accretion rate. Overall, we find that the Class I:Class II ratio of the cluster is consistent with an age of <1 Myr, with at least one individual, wildly varying source {approx}100, 000 yr old. We have also discovered a Class II eclipsing binary system with a period of 17.87 days.

  3. Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars

    NASA Astrophysics Data System (ADS)

    van der Tak, Floris F. S.; van Dishoeck, Ewine F.; Evans, Neal J., II; Blake, Geoffrey A.

    2000-07-01

    The physical structure of the envelopes around a sample of 14 massive young stars is investigated using maps and spectra in submillimeter continuum and lines of C17O, CS, C34S, and H2CO. Nine of the sources are highly embedded luminous (103-105 Lsolar) young stellar objects that are bright near-infrared sources but weak in radio continuum; the other objects are similar but not bright in the near-infrared and contain ``hot-core''-type objects and/or ultracompact H II regions. The data are used to constrain the temperature and density structure of the circumstellar envelopes on 102-105 AU scales, to investigate the relation between the different objects, and to search for evolutionary effects. The total column densities and the temperature profiles are obtained by fitting self-consistent dust models to submillimeter photometry. The calculated temperatures range from 300 to 1000 K at ~102 AU and from 10 to 30 K at ~105 AU from the star. Visual extinctions are a few hundred to a few thousand magnitudes, assuming a grain opacity at 1300 μm of ~1 cm-2 g-1 of dust, as derived earlier for one of our sources. The mid-infrared data are consistent with a 30% decrease of the opacity at higher temperatures, caused by the evaporation of the ice mantles. The CS, C34S, and H2CO data as well as the submillimeter dust emission maps indicate density gradients n~r-α. Assuming a constant CS abundance throughout the envelope, values of α=1.0-1.5 are found, which is significantly flatter than the α=2.0+/-0.3 generally found for low-mass objects. This flattening may indicate that in massive young stellar objects, nonthermal pressure is more important for the support against gravitational collapse, while thermal pressure dominates for low-mass sources. We find α=2 for two hot-core-type sources but regard this as an upper limit since, in these objects, the CS abundance may be enhanced in the warm gas close to the star. The assumption of spherical symmetry is tested by modeling infrared absorption line data of 13CO, CS emission-line profiles and near-infrared continuum. There is a distinct, but small deviation from spherical symmetry: the data are consistent with a decrease of the optical depth by a factor of ~3 in the central <~10". The homogeneity of the envelopes is verified by the good agreement of the total masses in the power-law models with the virial masses. Modeling of C17O emission shows that ~40%-90% of the CO is frozen out onto the dust. The CO abundances show a clear correlation with temperature, as expected if the abundance is controlled by freeze-out and thermal desorption. The CS abundance is 3×10-9 on average, ranging from (4-8)×10-10 in the cold source GL 7009S to (1-2)×10-8 in the two hot-core-type sources. Dense outflowing gas is seen in the CS and H2CO line wings; the predominance of blueshifted emission suggests the presence of dense, optically thick material within 10" of the center. Interferometric continuum observations at 1300-3500 μm show compact emission, probably from a 0.3" diameter, optically thick dust component, such as a dense shell or a disk. The emission is a factor of 10-100 stronger than expected for the envelopes seen in the single-dish data, so that this component may be opaque enough to explain the asymmetric CS and H2CO line profiles. The evolution of the sources is traced by the overall temperature (measured by the far-infrared color), which increases systematically with the decreasing ratio of envelope mass to stellar mass. The observed anticorrelation of near-infrared and radio continuum emission suggests that the erosion of the envelope proceeds from the inside out. Conventional tracers of the evolution of low-mass objects do not change much over this narrow age range.

  4. The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters

    NASA Astrophysics Data System (ADS)

    Luhman, K. L.; Rieke, G. H.; Young, Erick T.; Cotera, Angela S.; Chen, H.; Rieke, Marcia J.; Schneider, Glenn; Thompson, Rodger I.

    2000-09-01

    We have obtained images of the Trapezium Cluster (140''×140'' 0.3 pc×0.3 pc) with the Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). Combining these data with new ground-based K-band spectra (R=800) and existing spectral types and photometry, we have constructed an H-R diagram and used it and other arguments to infer masses and ages. To allow comparison with the results of our previous studies of IC 348 and ρ Oph, we first use the models of D'Antona & Mazzitelli. With these models, the distributions of ages of comparable samples of stars in the Trapezium, ρ Oph, and IC 348 indicate median ages of ~0.4 Myr for the first two regions and ~1-2 Myr for the latter. The low-mass initial mass functions (IMFs) in these sites of clustered star formation are similar over a wide range of stellar densities (ρ Oph, n=0.2-1×103 pc-3 IC 348, n=1×103 pc-3 Trapezium, n=1-5×104 pc-3) and other environmental conditions (e.g., presence or absence of OB stars). With current data, we cannot rule out modest variations in the substellar mass functions among these clusters. We then make the best estimate of the true form of the IMF in the Trapezium by using the evolutionary models of Baraffe et al. and an empirically adjusted temperature scale and compare this mass function to recent results for the Pleiades and the field. All of these data are consistent with an IMF that is flat or rises slowly from the substellar regime to about 0.6 Msolar and then rolls over into a power law that continues from about 1 Msolar to higher masses with a slope similar to or somewhat larger than the Salpeter value of 1.35. For the Trapezium, this behavior holds from our completeness limit of ~0.02 Msolar and probably, after a modest completeness correction, even from 0.01-0.02 Msolar. These data include ~50 likely brown dwarfs. We test the predictions of theories of the IMF against (1) the shape of the IMF, which is not log-normal, in clusters and the field, (2) the similarity of the IMFs among young clusters, (3) the lowest mass observed for brown dwarfs, and (4) the suggested connection between the stellar IMF and the mass function of prestellar clumps. In particular, most models do not predict the formation of the moderately large numbers of isolated objects down to 0.01 Msolar that we find in the Trapezium. Based on observations made with the Multiple Mirror Telescope operated by the Smithsonian Astrophysical Observatory and the University of Arizona. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal ID 7217.

  5. Stars

    NASA Astrophysics Data System (ADS)

    Capelato, Hugo Vicente

    1999-01-01

    We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.

  6. THE GEMINI NICI PLANET-FINDING CAMPAIGN: DISCOVERY OF A MULTIPLE SYSTEM ORBITING THE YOUNG A STAR HD 1160

    SciTech Connect

    Nielsen, Eric L.; Liu, Michael C.; Wahhaj, Zahed; Bowler, Brendan; Kraus, Adam; Chun, Mark; Ftaclas, Christ; Biller, Beth A.; Hayward, Thomas L.; Shkolnik, Evgenya L.; Tecza, Matthias; Clarke, Fraser; Close, Laird M.; Hartung, Markus; Males, Jared R.; Skemer, Andrew J.; Reid, I. Neill; Alencar, Silvia H. P.; Burrows, Adam; and others

    2012-05-01

    We report the discovery of two low-mass companions to the young A0V star HD 1160 at projected separations of 81 {+-} 5 AU (HD 1160 B) and 533 {+-} 25 AU (HD 1160 C) by the Gemini NICI Planet-Finding Campaign. Very Large Telescope images of the system taken over a decade for the purpose of using HD 1160 A as a photometric calibrator confirm that both companions are physically associated. By comparing the system to members of young moving groups and open clusters with well-established ages, we estimate an age of 50{sup +50}{sub -40} Myr for HD 1160 ABC. While the UVW motion of the system does not match any known moving group, the small magnitude of the space velocity is consistent with youth. Near-IR spectroscopy shows HD 1160 C to be an M3.5 {+-} 0.5 star with an estimated mass of 0.22{sup +0.03}{sub -0.04} M{sub Sun }, while NIR photometry of HD 1160 B suggests a brown dwarf with a mass of 33{sup +12}{sub -9} M{sub Jup}. The very small mass ratio (0.014) between the A and B components of the system is rare for A star binaries, and would represent a planetary-mass companion were HD 1160 A to be slightly less massive than the Sun.

  7. ON THE DYNAMICAL FORMATION OF VERY YOUNG, X-RAY EMITTING BLACK HOLE BINARIES IN DENSE STAR CLUSTERS

    SciTech Connect

    Garofali, Kristen; Converse, Joseph M.; Chandar, Rupali; Rangelov, Blagoy

    2012-08-10

    We recently discovered a population of very young ({tau} {approx}< 6-8 Myr), X-ray emitting black hole binaries (BHBs) in the nearby starburst galaxy NGC 4449. These BHBs are located within or near to very young star clusters, indicating that they form within the clusters, but that some fraction are dynamically ejected. Here we present results from a suite of N-body simulations of N = 16,384 ({approx}6000 M{sub Sun }) star clusters, similar to the masses of BHB hosts in NGC 4449, through the first 10 Myr of their lives. Our goal is to determine whether dynamical interactions are responsible for the observed population of BHBs in NGC 4449. Our simulations span a wide range of initial size and density profiles, both with and without primordial mass segregation, testing both realistic initial conditions and extreme ones. We find that clusters without primordial mass segregation only dynamically produce BHBs within 10 Myr when they are extremely compact and centrally concentrated. Preliminary results that include primordial binaries support this conclusion. The introduction of strong primordial mass segregation, however, greatly increases the rapidity with which the binaries form, although these are still not tight enough that they will emit X-rays. We conclude that X-ray emitting BHBs are unlikely to form dynamically in clusters of this mass under realistic conditions. Instead, they probably originate from binaries that contain two massive stars with small orbital separations, which are present from the cluster's birth.

  8. The contribution of disks and envelopes to the millimeter continuum emission from very young low-mass stars

    NASA Technical Reports Server (NTRS)

    Terebey, S.; Chandler, C. J.; Andre, P.

    1993-01-01

    We investigate the question of disk formation during the protostar phase. We model the dust continuum emission from the dense cloud core using the cloud-collapse models of Terebey et al. (1984) and show that dust emission from the dense core is important when measured with large single-dish telescopes at 1.3 mm, but nearly negligible with interferometers at 2.7 mm. From published and new data, we conclude that massive disks are also seen toward a number of other sources including L1448 IRS 3, whose disk mass is estimated to be 0.5 solar mass. However, 1.3 mm data show that massive disks are relatively rare, occurring around perhaps 5 percent of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. The median 1.3 mm flux density of IRAS-Dense cores in our sample is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass is not significantly higher during the embedded phase than during the later T Tauri phase.

  9. How and Why Do Geysers Erupt?

    NASA Astrophysics Data System (ADS)

    Manga, M.

    2014-12-01

    Geysers are features that produce episodic eruptions of water, steam and sometimes non-condensable gases. Natural geysers are rare, with fewer than 1,000 worldwide. They are more than curiosities and popular tourist attractions: they offer a direct window into geothermal processes, and may serve as a natural small-scale laboratory to study larger-scale eruptive process such as those at volcanoes, and other self-organized, intermittent processes that result from phase separation and localized input of energy and mass. Despite > 200 years of scientific study, basic questions remain: Do eruptions begin from the bottom or top of the geyser? What controls eruption duration? Why do eruptions end? What are the required special subsurface geometries? Why are some geysers periodic, and others irregular? How and why do they respond to external influences such as weather, tides, and earthquakes? This presentation will review new insights from field studies at Lone Star geyser, Yellowstone National Park, geysers in the El Tatio geyser field, Chile, and laboratory models. At Lone Star we infer that dynamics are controlled by thermal and mechanical coupling between the conduit and a deeper, laterally-offset reservoir (called a "bubble trap" in previous studies). At El Tatio, we measured pressure and temperature within geysers over multiple eruption cycles: this data document the heating of liquid water by steam delivered from below. The laboratory experiments reveal how episodic release of steam from a bubble trap prepares a conduit for eruption and can generate a range of eruption intensities. In all cases, the eruption initiation, duration and termination are controlled by the interaction between the accumulation and transport of steam and liquid, and modulated by the geometry of the geyser's plumbing. Time series of thousands of eruptions confirm that internal processes control eruptions, with only pool geysers showing a sensitivity to air temperature; only very large stress changes influence eruptions.

  10. Solar Activity and Solar Eruptions

    NASA Technical Reports Server (NTRS)

    Sterling, Alphonse C.

    2006-01-01

    Our Sun is a dynamic, ever-changing star. In general, its atmosphere displays major variation on an 11-year cycle. Throughout the cycle, the atmosphere occasionally exhibits large, sudden outbursts of energy. These "solar eruptions" manifest themselves in the form of solar flares, filament eruptions, coronal mass ejections (CMEs), and energetic particle releases. They are of high interest to scientists both because they represent fundamental processes that occur in various astrophysical context, and because, if directed toward Earth, they can disrupt Earth-based systems and satellites. Research over the last few decades has shown that the source of the eruptions is localized regions of energy-storing magnetic field on the Sun that become destabilized, leading to a release of the stored energy. Solar scientists have (probably) unraveled the basic outline of what happens in these eruptions, but many details are still not understood. In recent years we have been studying what triggers these magnetic eruptions, using ground-based and satellite-based solar observations in combination with predictions from various theoretical models. We will present an overview of solar activity and solar eruptions, give results from some of our own research, and discuss questions that remain to be explored.

  11. YOUNG STARS NEAR EARTH: THE OCTANS-NEAR ASSOCIATION AND CASTOR MOVING GROUP

    SciTech Connect

    Zuckerman, B.; Vican, Laura; Song, Inseok; Schneider, Adam E-mail: lvican@ucla.edu E-mail: Adam.Schneider@Utoledo.edu

    2013-11-20

    All cataloged stellar moving groups and associations with ages ≤100 Myr and within 100 pc of Earth have Galactic space motions (UVW) situated in a 'good box' with dimensions ∼20 km s{sup –1} on a side. Torres et al. defined the Octans Association as a group of 15 stars with age '20 Myr?' and located ∼140 pc from Earth, but with average V space velocity –3.6 km s{sup –1} that is well outside of the good box. We present a list of 14 Hipparcos star systems within 100 pc of Earth that we call {sup O}ctans-Near{sup ;} these systems have UVW similar to those of the much more distant Octans Association. The Octans-Near stars have apparent ages between about 30 and 100 Myr and their relationship to the Octans Association stars is unclear. Six additional star systems have UVW similar to those of Octans-Near stars and likely ages ≤200 Myr. These six systems include the late-type binary star EQ Peg—6.2 pc from Earth with likely age ≤100 Myr and thus likely to be the nearest known pre-main sequence star system. The UVW of stars in a previously proposed ∼200 Myr old Castor moving group are not too dissimilar from the UVW of Octans-Near stars. However, stars in the Castor group—if it exists at all—are mostly substantially older than 200 Myr and thus generally can readily be distinguished from the much younger Octans-Near stars.

  12. Do All Stars Form in Clusters?: Masses and Ages of Young Supergiants in Andromeda

    NASA Astrophysics Data System (ADS)

    Choudhury, Zareen; Debs, C.; Kirby, E. N.; Guhathakurta, P.

    2013-01-01

    Currently it is not understood whether seemingly isolated stars formed in situ or were ejected from star clusters as runaway stars. Previous studies determined the origins of isolated stars by measuring their velocities, but past research was limited to OB stars in the Milky Way and Magellanic Clouds due to the difficulty of computing velocities of distant objects. This study proposed an innovative velocity test to statistically determine whether six seemingly isolated BA-type supergiants in Andromeda are runaways. We calculated the minimum relative transverse velocity needed for each supergiant to travel to its current location from the nearest open cluster. By comparing the minimum velocity with Andromedas known velocity dispersion, a statistical measure of the stars actual velocities, we determined whether the star had the necessary velocity to be a runaway. Minimum velocity was computed from the age of the star, which was calculated from its effective temperature and surface gravity. To compute effective temperature and surface gravity, we applied three new techniques based on Balmer absorption features. The results suggest that all six supergiants had the necessary velocities to be runaways. Although the proposed velocity test is a statistical assessment, it offers a valuable new tool for future investigation of isolated stars beyond the Milky Way and its satellites. This research was supported by the Science Internship Program (SIP) at UCSC, the National Science Foundation, NASA, and Palomar Observatory.

  13. High Mass Star Formation in the Vicinity of a Young Massive Protocluster IRAS 04073+5102 (SH 209)

    NASA Astrophysics Data System (ADS)

    Chibueze, J. O.; Pillai, T.; Kauffmann, J.; Baobab, H.-L.

    2015-12-01

    IRAS 04073 is a massive high mass star forming regions hosting massive protoclusters. Star formation in the vicinity of expanding HII region could toll different path from those of pristine environment. IRAS 04073+5102 (SH 209) provides an ideal region to study the influence of expanding region on the star formation activities in a region. We observed the region at 230 GHz with SMA and detected 12CO, 13CO, C18O and SO. We used SMA dust continuum and CO data to identify and characterize the major filaments and cores in the complex. The brightest mm clump of 4000 M⊙ observed at low resolution fragments into just three cores and the prominent core is an excellent candidate for a massive protocluster. Comparing of SMA images with Spitzer images, we could isolate very young filaments containing pre-protoclusters that would likely form clusters. The expanding HII region may have contributed to the formation of the observed filamentary structures and in triggering star formation in the region.

  14. Limits of detection in debris disks around young stars with NaCo/Sparse Aperture Masking observations

    NASA Astrophysics Data System (ADS)

    Gauchet, L.; Lacour, S.

    2014-09-01

    To understand the formation and evolution of solar systems and planets formations in the stars neighbourhood, we need to obtain information of their state at different time of their evolution. Here, we focus on debris disks around young stars aged of ten to few tens of Myr, we analyze NaCo/Sparse Aperture Masking (SAM) observations in the L' band (3.8 μm) of eight objects (beta Pictoris, AU Mic, 49 Ceti, eta Tel, Fomalhaut, G Lupi, HD182327 and HR8799). The aim is to get limits of detection about the mass of the debris orbiting around their stars. The SAM technique consists in transforming a sing