Sample records for young eruptive star

  1. DDT_akospal_2: Rapid inner disk re-arrangements in a young eruptive star

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.

    2011-09-01

    We propose a 4-epoch PACS photometric monitoring, in coordination with Spitzer and ground-based telescopes, of the newly discovered young eruptive star V2492 Cyg, to verify our hypothesis on rapid re-arrangement of its circumstellar disk structure.

  2. The outburst and nature of two young eruptive stars in the North America\\/Pelican Nebula Complex

    Microsoft Academic Search

    Á. Kóspál; P. Ábrahám; J. A. Acosta-Pulido; M. J. Arévalo Morales; M. I. Carnerero; E. Elek; J. Kelemen; M. Kun; A. Pál; R. Szakáts; K. Vida

    2010-01-01

    Context. In August 2010, the sudden optical brightening of two young stellar\\u000aobjects, located in the North America\\/Pelican Nebula Complex, was announced.\\u000aEarly observations indicated that these objects may belong to the FUor or EXor\\u000aclass of young eruptive stars. The eruptions of FUors and EXors are often\\u000aexplained by enhanced accretion of material from the circumstellar disk to the

  3. The outburst and nature of two young eruptive stars in the North America\\/Pelican Nebula Complex

    Microsoft Academic Search

    Á. Kóspál; P. Ábrahám; J. A. Acosta-Pulido; M. J. Arévalo Morales; M. I. Carnerero; E. Elek; J. Kelemen; M. Kun; A. Pál; R. Szakáts; K. Vida

    2011-01-01

    Context. The sudden optical brightening of two young stellar objects, HBC 722 and VSX J205126.1+440523, located in the North America\\/Pelican Nebula Complex, was announced in August 2010. Early photometric and spectroscopic observations of these objects indicated that they may belong to the FUor or EXor class of young eruptive stars. The eruptions of FUors and EXors are often explained by

  4. 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 H? 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

  5. The outburst of the eruptive young star OO Serpentis between 1995 and 2006

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Ábrahám, P.; Prusti, T.; Acosta-Pulido, J.; Hony, S.; Moór, A.; Siebenmorgen, R.

    2007-07-01

    Aims:OO Serpentis is a deeply embedded pre-main sequence star in the Serpens NW star-forming region. The star went into outburst in 1995 and gradually faded afterwards. In many respects its eruption resembled the well-known FU Orionis-type (FUor) or EX Lupi-type (EXor) outbursts. Since very few such events have ever been documented at infrared wavelengths, our aim is to study the temporal evolution of OO Ser in the infrared. Methods: OO Ser was monitored with the Infrared Space Observatory in the 3.6-100 ?m wavelength range, starting 4 months after peak brightness and covering a period of 20 months. Eight years later, in 2004-2006 we again observed OO Ser at 2.2 and 12 ?m from the ground and complemented this dataset with archival Spitzer observations also from 2004. We analysed these data with special attention to source confusion and constructed light curves at 10 different wavelengths as well as spectral energy distributions. Results: The outburst caused brightening in the whole infrared regime. According to the infrared light curves, OO Ser started a wavelength-independent fading after the peak brightness. Later the flux decay became slower but stayed practically wavelength-independent. The fading is still ongoing, and current fading rates indicate that OO Ser will not return to quiescent state before 2011. The outburst timescale of OO Ser seems to be shorter than that of FUors, but longer than that of EXors. Conclusions: The outburst timescale and the moderate luminosity suggest that OO Ser is different from both FUors and EXors, and shows some similarities to the recently erupted young star V1647 Ori. Based on its SED and bolometric temperature, OO Ser seems to be an early class I object, with an age of <105 yr. As proposed by outburst models, the object is probably surrounded by an accretion disc and a dense envelope. This picture is also supported by the wavelength-independence of the fading. Due to the shorter outburst timescales, models developed for FUors can only work for OO Ser if the viscosity parameter in the circumstellar disc, ?, is set to an order of magnitude higher value than usual for FUors. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries France, Germany, the Netherlands and the UK) with participation of ISAS and NASA. Tables 1 and 2 are only available in electronic form at http://www.aanda.org

  6. The outburst and nature of two young eruptive stars in the North America/Pelican Nebula Complex

    E-print Network

    Kóspál, Á; Acosta-Pulido, J A; Morales, M J Arévalo; Carnerero, M I; Elek, E; Kun, M; Pál, A; Szakáts, R

    2010-01-01

    Context. In August 2010, the sudden optical brightening of two young stellar objects, located in the North America/Pelican Nebula Complex, was announced. Early photometric and spectroscopic observations of these objects indicated that they may belong to the FUor or EXor class of young eruptive stars. The eruptions of FUors and EXors are often explained by enhanced accretion of material from the circumstellar disk to the protostar. Aims. In order to determine the true nature of these two objects, we started an optical and near-infrared monitoring program, and complemented our data with archival observations and data from the literature. Methods. We plot and analyze pre-outburst and outburst spectral energy distributions (SEDs), multi-filter light curves, and color-color diagrams. Results. While the quiescent SED of HBC 722 is consistent with that of a slightly reddened normal T Tauri-type star, the quiescent SED of VSX J205126.1+440523 is highly extincted, either due to an envelope, or an edge-on disk geometry...

  7. Ages of young stars

    E-print Network

    Soderblom, David R; Jeffries, Rob D; Mamajek, Eric E; Naylor, Tim

    2013-01-01

    Determining the sequence of events in the formation of stars and planetary systems and their time-scales is essential for understanding those processes, yet establishing ages is fundamentally difficult because we lack direct indicators. In this review we discuss the age challenge for young stars, specifically those less than ~100 Myr old. Most age determination methods that we discuss are primarily applicable to groups of stars but can be used to estimate the age of individual objects. A reliable age scale is established above 20 Myr from measurement of the Lithium Depletion Boundary (LDB) in young clusters, and consistency is shown between these ages and those from the upper main sequence and the main sequence turn-off -- if modest core convection and rotation is included in the models of higher-mass stars. Other available methods for age estimation include the kinematics of young groups, placing stars in Hertzsprung-Russell diagrams, pulsations and seismology, surface gravity measurement, rotation and activ...

  8. Planets of young stars

    E-print Network

    E. W. Guenther; E. Esposito

    2007-01-10

    Since the first massive planet in a short period orbit was discovered, the question arised how such an object could have formed. There are basically two formation scenarios: migration due to planet-disk or planet-planet interaction. Which of the two scenarios is more realistic can be found out by observing short-period planets of stars with an age between 10E7 and 10E8 yrs. The second aim of the survey is to find out how many planets originally formed, and how many of these are destroyed in the first Gyrs: Do most young, close-in planets evaporate, or spiral into the host stars? In here we report on the first results of a radial-velocity search program for planets of young stars which we began in 2004. Using HARPS, we currently monitor 85 stars with ages between 10E7 and 10E8 yrs. We show that the detection of planets of young stars is possible. Up to now, we have identified 3 planet-candidates. Taking this result together with the results of other surveys, we conclude that the frequency of massive-short period planets of young stars is not dramatically higher than that of old stars.

  9. Instability considerations for massive star eruptions

    SciTech Connect

    Guzik, J. A. (Joyce Ann)

    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.

  10. A Young Stellar Cluster Surrounding the Peculiar Eruptive Variable V838 Monocerotis

    E-print Network

    Melike Af?ar; Howard E. Bond

    2006-10-26

    The unusual variable star V838 Monocerotis underwent an eruption in 2002. It continues to illuminate a spectacular series of light echoes, as the outburst light is scattered from circumstellar dust. V838 Mon has an unresolved B3 V companion star. We serendipitously discovered that a neighboring 16th-mag star is also of type B. We then carried out a survey of other stars in the vicinity, revealing two more B-type stars within 45" of V838 Mon. We have determined the distance to this sparse, young cluster, based on spectral classification and photometric main-sequence fitting of the three B stars. The cluster distance is found to be 6.2+-1.2 kpc, in excellent agreement with the geometric distance to V838 Mon of 5.9 kpc obtained from Hubble Space Telescope polarimetry of the light echoes. Using our distance determination, we show that the B3 V companion of V838 Mon is sufficient to account for the entire luminosity of the star measured on survey photographs before its outburst. The B3 star is currently, however, about 1 mag fainter than before the eruption, suggesting that it is now suffering extinction due to dust ejected from V838 Mon. Considerations of the pre-outburst luminosity and cluster age appear to leave stellar-collision or -merger scenarios as one of the remaining viable explanations for the outburst of V838 Mon.

  11. 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

  12. 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.

  13. Eruptive Mass Loss in Very Massive Stars and Population III Stars

    E-print Network

    Nathan Smith

    2006-07-24

    I discuss the role played by short-duration eruptive mass loss in the evolution of very massive stars. Giant eruptions of Luminous Blue Variables (LBVs) like the 19th century event of eta Carinae can remove large quantities of mass almost instantaneously, making them significant in stellar evolution. They can potentially remove much more mass from the star than line-driven winds, especially if stellar winds are highly clumped such that previous estimates of O star mass-loss rates need to be revised downward. When seen in other galaxies as ``supernova impostors'', these LBV eruptions typically last for less than a decade, and they can remove of order 10 Msun as indicated by massive nebulae around LBVs. Such extreme mass-loss rates cannot be driven by radiation pressure on spectral lines, because the lines will completely saturate during the events. Instead, these outbursts must either be continuum-driven super-Eddington winds or outright hydrodynamic explosions, both of which are insensitive to metallicity. As such, this eruptive mode of mass loss could also play a pivotal role in the evolution and ultimate fate of massive metal-poor stars in the early universe. If they occur in these Population III stars, such eruptions would also profoundly affect the chemical yield and types of remnants from early supernovae and hypernovae thought to be the origin of long gamma ray bursts.

  14. Interstellar Extinction Toward Young Stars

    NASA Astrophysics Data System (ADS)

    McJunkin, Matthew; France, Kevin

    2015-01-01

    We present work on a molecular hydrogen (H2) fluorescence model to characterize the ultraviolet (UV) extinction curve along the line of sight towards young stars with circumstellar disks. Stellar UV radiation plays a strong role in heating the disk gas and driving chemical reactions, so it is important to measure the UV extinction curve in order to reconstruct the intrinsic stellar UV flux impacting the disk. To measure the extinction, we compare modeled H2 fluorescence spectra to observed H2 lines. Lyman-alpha radiation from the stars pumps electronic transitions of H2 in the disk, and we model the flux that is re-emitted through the subsequent fluorescent cascade. We then extract the extinction along the line-of-sight over the 1100-1700 Angstrom wavelength region from the difference between the modeled H2 fluorescence and the HST-COS data. The shape of the extinction curve allows us to characterize the dust grain distribution in the intervening material as well as to recover the intrinsic spectral energy distribution of the stars over a wide wavelength range.

  15. The GALEX Nearby Young-Star Survey

    NASA Astrophysics Data System (ADS)

    Rodriguez, David; Zuckerman, B. M.; Kastner, J. H.; Vican, L.; Bessell, M. S.; Faherty, J. K.; Murphy, S.

    2014-01-01

    Over the last few decades, many young stars (ages ~10-100 Myr) have been discovered in moving groups within 100 parsecs of Earth. These stars represent excellent targets for direct imaging searches of extrasolar planets during the coming decades as new imaging systems and larger telescopes are commissioned. However, if the mass functions of nearby young moving groups resembles that of the field or young, rich clusters, then the presently known membership of these nearby groups is significantly lacking in low-mass stars. We have initiated a program, the GALEX Nearby Young-Star Survey, or GALNYSS, to search for these missing M-stars. GALNYSS has combined ultraviolet data from GALEX with near-IR surveys (WISE and 2MASS), as well as kinematic information, in order to identify over 2000 candidate young low-mass stars near Earth. Spectroscopic followup is ongoing, and results thus far confirm the youthful nature of many stars among the GALNYSS sample. This suggests that our technique is capable of revealing the populations of low-mass stars that are presently missing from the nearby young moving groups. We present an overview of our survey to date, including the characteristics of the GALNYSS sample and a summary of GALNYSS's latest contributions to our knowledge of the number and membership of nearby, young stellar associations. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile.

  16. 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.

  17. Variability of Young Stars: the Importance of Keeping an Eye on Children

    NASA Astrophysics Data System (ADS)

    Herbst, W.

    2013-06-01

    (Abstract only) I will review the state of our understanding of young stars with an emphasis on how and why they vary in brightness. The main causes of the variations will be reviewed, including the rotation of spotted weak-lined T Tauri stars, accretion onto classical T Tauri stars, the eruptive behavior of FUors, and the enigmatic variations of the UXors. The important role that amateurs have and will continue to play in these studies is highlighted. I will also discuss the latest results on two unusual young binaries, BM Orionis in the Trapezium asterism and KH 15D in NGC 2264.

  18. Triggered star formation in the environment of young massive stars

    Microsoft Academic Search

    Matthias Gritschneder; T. Naab; F. Heitsch; A. Burkert

    2007-01-01

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to

  19. THE GALEX NEARBY YOUNG-STAR SURVEY

    SciTech Connect

    Rodriguez, David R.; Faherty, Jacqueline K. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Zuckerman, B. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Kastner, Joel H. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Bessell, M. S.; Murphy, Simon J., E-mail: drodrigu@das.uchile.cl [Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)

    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.

  20. Spatial Distributions of Young Stars

    NASA Astrophysics Data System (ADS)

    Kraus, Adam L.; Hillenbrand, Lynne A.

    2008-10-01

    We analyze the spatial distribution of young stars in Taurus-Auriga and Upper Sco, as determined from the two-point correlation function (i.e., the mean surface density of neighbors). The corresponding power-law fits allow us to determine the fractal dimensions of each association's spatial distribution, measure the stellar velocity dispersions, and distinguish between the bound binary population and chance alignments of members. We find that the fractal dimension of Taurus is D~1.05, consistent with its filamentary structure. The fractal dimension of Upper Sco may be even shallower (D~0.7), but this fit is uncertain due to the limited area and possible spatially variable incompleteness. We also find that random stellar motions have erased all primordial structure on scales of <~0.07° in Taurus and <~1.7° in Upper Sco; given ages of ~1 and ~5 Myr, the corresponding internal velocity dispersions are ~0.2 and ~1.0 km s-1, respectively. Finally, we find that binaries can be distinguished from chance alignments at separations of <~120" (17,000 AU) in Taurus and <~75" (11,000 AU) in Upper Sco. The binary populations in these associations that we previously studied, spanning separations of 3"-30", is dominated by binary systems. However, the few lowest mass pairs (Mprim <~ 0.3 Msolar) might be chance alignments.

  1. Numerical Simulations of Giant Eruptions from Massive Stars and their Recoveries

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    We use a 3D hydro code to model the response of a massive star to a high mass loss episode. Starting with a modified version of the 1D stellar evolution code MESA, we obtain a model of an evolved massive star, with properties similar to those of Eta Carinae, known for its giant eruption in the 19th century.We simulate a giant eruption using two approaches:1.Removing a layer from the star using energy from inner layers.2.Extracting energy from the core to outer layers that spontaneously causes mass loss.We then follow the evolution of the star using the FLASH code. Our hydrodynamical simulation includes radiation transfer with realistic opacities and convection.We find that the star develops a strong wind, powered by pulsation in the inner parts of the star. The strong eruptive mass loss phase lasts for a few years, followed by centuries of continually weakening mass loss.

  2. 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).

  3. The GALEX Nearby Young-Star Survey

    NASA Astrophysics Data System (ADS)

    Rodriguez, David; Zuckerman, Ben; Kastner, Joel; Bessell, Mike; Faherty, Jacqueline; Murphy, Simon; Vican, Laura

    2013-07-01

    Over the last few decades, many ~10-100 Myr-old stars have been identified in moving groups located closer than 100 parsecs to Earth. For direct imaging searches of extrasolar planets these stars represent the best targets and they will be continuously observed during the coming decades as new imaging systems and larger telescopes are commissioned. Recent work has shown that near-IR surveys, like 2MASS, combined with ultraviolet data from GALEX can be used to identify additional members in these moving groups. In particular, this methodology is well suited to searching for low-mass stars, which are generally lacking in moving group member statistics. Initial searches for young stars relied on optical identification (such as with Tycho and Hipparcos) and X-ray detection with ROSAT. The recent release of the all-sky WISE catalog has opened up a new frontier in the search for nearby, young, low-mass stars. We have carried out an all-sky cross correlation between the GALEX, WISE, and 2MASS databases and identified many candidate young, low-mass stars. Early spectroscopic results confirm the youthful nature of our candidates. This suggests that our technique is capable of identifying the many low-mass stars that remain to be found among the nearby young moving groups. This work is supported by a NASA Astrophysics Data Analysis Program award to RIT and UCLA and a FONDECYT grant at Universidad de Chile.

  4. Multiplicity among the young stars in Taurus

    NASA Technical Reports Server (NTRS)

    Simon, M.; Chen, W. P.; Howell, R. R.; Benson, J. A.; Slowik, D.

    1992-01-01

    Twenty-eight young stars systems in the northern Taurus star-forming region are surveyed for multiplicity. These observations, made by infrared lunar occultation and imaging techniques, can identify binaries in the angular separation range 0.005-10 arcsec. Of the 28 systems, 11 are binaries and two are triples, giving an observed multiplicity of 1.5 stars per system. The binary frequency and distribution of separations are similar to those of the main-sequence F and G spectral-type stars. Stars that have detected companions and those without are indistinguishable in H-alpha equivalent width, indicating that stars with active inner disks are represented in both groups. The multiple systems are in general weaker 1.3 mm continuum emitters than the single stars, indicating that the large-scale disks in these systems are less massive. However, there are important exceptions so the evolution of disks in multiple systems is not clear.

  5. ERUPTIVE VARIABLE STARS AND OUTFLOWS IN SERPENS NW

    SciTech Connect

    Hodapp, Klaus W. [Institute for Astronomy, University of Hawaii, 640 N. Aohoku Place, Hilo, HI 96720 (United States); Chini, Rolf; Watermann, Ramon; Lemke, Roland, E-mail: hodapp@ifa.hawaii.edu [Ruhr Universitaet Bochum, Astronomisches Institut, Universitaetsstrasse 150, D-44801 Bochum (Germany)

    2012-01-01

    We study the outflow activity, photometric variability, and morphology of three very young stellar objects in the Serpens NW star-forming region: OO Serpentis, EC 37 (V370 Ser), and EC 53 (V371 Ser). High spatial resolution Keck/NIRC2 laser guide star adaptive optics images obtained in 2007 and 2009 in broadband K and in a narrowband filter centered on the 1-0 S(1) emission line of H{sub 2} allow us to identify the outflows from all three objects. We also present new, seeing-limited data on the photometric evolution of the OO Ser reflection nebula and re-analyze previously published data. We find that OO Ser declined in brightness from its outburst peak in 1995 to about 2003, but that this decline has recently stopped and actually reversed itself in some areas of the reflection nebula. The morphology and proper motions of the shock fronts MHO 2218 near EC 37 suggest that they all originate in EC 37 and that this is an outflow seen nearly along its axis. We identify an H{sub 2} jet emerging from the cometary nebula EC 53. The star illuminating EC 53 is periodically variable with a period of 543 days and has a close-by, non-variable companion at a projected distance of 92 AU. We argue that the periodic variability is the result of accretion instabilities triggered by another very close, not directly observable, binary companion and that EC 53 can be understood in the model of a multiple system developing into a hierarchical configuration.

  6. 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.

  7. Young stars and clouds in Camelopardalis

    E-print Network

    V. Straizys; V. Laugalys

    2008-11-18

    Star formation in the Local spiral arm in the direction of the Galactic longitudes 132--158 deg is reviewed. Recent star-forming activity in this Milky Way direction is evidenced by the presence here of the Cam OB1 association and dense dust and molecular clouds containing H$\\alpha$ emission stars, young irregular variables and infrared stellar objects. The clouds of the Local arm concentrate in two layers at 150-300 pc and at about 900 pc from the Sun. The Perseus arm objects in this direction are at a distance of about 2 kpc.

  8. The accretion disk paradigm for young stars

    NASA Astrophysics Data System (ADS)

    Bertout, Claude

    2007-05-01

    Accretion and magnetic fields play major roles in several of the many models put forward to explain the properties of T Tauri stars since their discovery by Alfred Joy in the 1940s. Early investigators already recognized in the 1950s that a source of energy external to the star was needed to account for the emission properties of these stars in the optical range. The opening of new spectral windows from the infrared to the ultraviolet in the 1970s and 1980s showed that the excess emission of T Tauri stars and related objects extends into all wavelength domains, while evidence of outflow and/or infall in their circumstellar medium was accumulating. Although the disk hypothesis had been put forward by Merle Walker as early as 1972 to explain properties of YY Orionis stars and although Lynden-Bell and Pringle worked out the accretion disk model and applied it specifically to T Tauri stars in 1974, the prevailing model for young stellar objects until the mid-1980s assumed that they experienced extreme solar-type activity. It then took until the late 1980s before the indirect evidence of disks presented by several teams of researchers became so compelling that a paradigm shift occurred, leading to the current consensual picture. I briefly review the various models proposed for explaining the properties of young stellar objects, from their discovery to the direct observations of circumstellar disks that have so elegantly confirmed the nature of young stars. I will go on to discuss more modern issues concerning their accretion disk properties and conclude with some results obtained in a recent attempt to better understand the evolution of Taurus-Auriga young stellar objects.

  9. Young Massive Star Clusters. II. (Larsen, 1999)

    Microsoft Academic Search

    S. S. Larsen

    1999-01-01

    Table 4 lists photometric data for Young Massive Star Clusters identified in a sample of 21 nearby galaxies. The photometric data have been corrected for Galactic foreground extinction. Each cluster is identified by the abbreviated NGC number of its host galaxy and an object number: nxxx-yyy is object number yyy in the galaxy NGC xxx. Effective cluster radii have been

  10. 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

  11. Episodic Accretion in Young Stars

    E-print Network

    Audard, Marc; Dunham, Michael M; Green, Joel D; Grosso, Nicolas; Hamaguchi, Kenji; Kastner, Joel H; Kóspál, Ágnes; Lodato, Giuseppe; Romanova, Marina; Skinner, Stephen L; Vorobyov, Eduard I; Zhu, Zhaohuan

    2014-01-01

    In the last twenty years, the topic of episodic accretion has gained significant interest in the star formation community. It is now viewed as a common, though still poorly understood, phenomenon in low-mass star formation. The FU Orionis objects (FUors) are long-studied examples of this phenomenon. FUors are believed to undergo accretion outbursts during which the accretion rate rapidly increases from typically $10^{-7}$ to a few $10^{-4}$ $M_\\odot$ yr$^{-1}$, and remains elevated over several decades or more. EXors, a loosely defined class of pre-main sequence stars, exhibit shorter and repetitive outbursts, associated with lower accretion rates. The relationship between the two classes, and their connection to the standard pre-main sequence evolutionary sequence, is an open question: do they represent two distinct classes, are they triggered by the same physical mechanism, and do they occur in the same evolutionary phases? Over the past couple of decades, many theoretical and numerical models have been dev...

  12. 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.

  13. Triggered star formation in the environment of young massive stars

    NASA Astrophysics Data System (ADS)

    Gritschneder, Matthias; Naab, T.; Heitsch, F.; Burkert, A.

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (VINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

  14. Triggered Star Formation in the Environment of Young Massive Stars

    E-print Network

    M. Gritschneder; T. Naab; F. Heitsch; A. Burkert

    2006-09-26

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (called IVINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

  15. Periodic flow instabilities during Lone Star Geyser (YNP) eruptions, as deduced from acoustic measurements

    NASA Astrophysics Data System (ADS)

    Vandemeulebrouck, J.; Hurwitz, S.; Johnston, M. J.; Rudolph, M. L.; Karlstrom, L.; Sohn, R. A.; Murphy, F.; McPhee, D. K.; Glen, J. M.; Soule, S. A.; Meertens, C. M.

    2011-12-01

    We performed continuous acoustic measurements during four days at Lone Star Geyser, Yellowstone National Park, USA. The microphone was located at 10 meters from the geyser's cone, and the acoustic signal was sampled at 1000 Hz. The 3-hour-long eruptive cycle at Lone Star Geyser contains several water fountaining episodes followed by the main eruption, which generally lasts 25 minutes. During the 30 main eruptions that we studied, the acoustic signal patterns are very similar, and indicate the flow is unstable and clearly follows a pulsating regime. The period of the acoustic pulses drastically increases during the liquid to steam transition in the flow. This abrupt change in the flow regime corresponds to the start of the ground deflation recorded by tiltmeters, and could be due to a transition from hydro-static to vapor-static conditions in the vent.

  16. Diabetic lipemia with eruptive xanthomatosis in a lean young female with apolipoprotein E4/4.

    PubMed

    Shinozaki, Satoshi; Itabashi, Naoki; Rokkaku, Kumiko; Ichiki, Kenji; Nagasaka, Shoichiro; Okada, Koji; Fujimoto, Mitsuo; Ohtsuki, Mamitaro; Ishibashi, Shun

    2005-11-01

    Eruptive xanthomas in adults are usually indicative of chylomicronemia. Although diabetes mellitus is the most common secondary cause of chylomicronemia, which is designated as diabetic lipemia, the clinical characteristics of diabetes with regard to development of xanthomas are not well defined. In this paper, we describe a young female who displayed eruptive xanthomas as an initial manifestation of diabetic lipemia. The patient was a 20-year-old female with a body mass index of 18.9 kg/m2 and Marfanoid appearance. Her past history was unremarkable, except for patent ductus arteriosus and mild mental retardation. She was admitted to our division for eruptive xanthomas on the extremities and marked hyperglycemia (random glucose, 520 mg/dl) and hypertriglyceridemia (6880 mg/dl). She was diagnosed with Type 2 diabetes based on the positive family history of diabetes, residual secretory capacity of insulin, and absence of autoantibodies related to Type 1 diabetes. Based on the increase in the concentrations of both chylomicrons and very low density lipoproteins, type V hyperlipoproteinemia was diagnosed. After the initiation of insulin therapy, both hypertriglyceridemia and eruptive xanthomas subsided, without administering any hypolipidemic agents. Minimal model analysis of a frequently sampled intravenous glucose tolerance test revealed severe insulin resistance, despite the absence of obesity. Post-heparin lipoprotein lipase (LPL) activity was moderately decreased, and common mutations in the LPL gene were not demonstrated by genetic screening. The apolipoprotein E phenotype was E4/4, which is known to be associated with type V hyperlipoproteinemia. Hypoadiponectinemia of 1.7 microg/ml was also revealed, which may, in part, account for the insulin resistance and decreased LPL activity. In conclusion, the clustering of apolipoprotein E4/4 and hypoadiponectinemia, in addition to insulin resistance and poor glycemic control, might have resulted in hypertriglyceridemia with eruptive xanthomatosis in this subject. PMID:16188578

  17. Chromospheric Activity in Young Galactic Cluster Stars

    Microsoft Academic Search

    K. Soto; C. A. Pilachowski

    2003-01-01

    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

  18. Stellar ejecta from falling comet-like bodies: young stars

    NASA Astrophysics Data System (ADS)

    Ibodov, Firuz S.; Ibadov, Subhon

    2014-01-01

    High-resolution spectral observations of young stars with dense protoplanetary discs like Beta Pictoris led to the discovery of variable emission lines of metal atoms, Na, Fe etc., that indicate the presence of fluxes of comet-like evaporating bodies falling onto the stars, FEBs. Assuming the presence of stellar atmospheres similar to the solar one, we show that passages of the FEBs through the stellar chromosphere and photosphere with velocities around 600 km/s will be accompanied by aerodynamic crushing of the nuclei, transverse expansion of the crushed matter, ``explosion'' of the flattened nuclei in a relatively very thin sub-photosphere layer due to sharp deceleration, and impulse production of a hot plasma. The impulsive rise of the layer's temperature and density lead to the generation of a strong ``blast'' shock wave and shock wave-induced ejection/eruption of hot plasma into space above the chromosphere. Observations of such impact-induced high-temperature phenomena are of interest for the physics/prognosis of stellar/solar flares as well as physics of comets.

  19. Triggered Star Formation in the Environment of Young Massive Stars

    Microsoft Academic Search

    M. Gritschneder; T. Naab; F. Heitsch; A. Burkert

    2006-01-01

    Recent observations with the Spitzer Space Telescope show clear evidence that\\u000astar formation takes place in the surrounding of young massive O-type stars,\\u000awhich are shaping their environment due to their powerful radiation and stellar\\u000awinds. In this work we investigate the effect of ionising radiation of massive\\u000astars on the ambient interstellar medium (ISM): In particular we want to

  20. NEW YOUNG STAR CANDIDATES IN CG4 AND Sa101

    SciTech Connect

    Rebull, L. M.; Laine, S.; Laher, R.; Legassie, M. [Spitzer Science Center/Caltech, M/S 220-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Johnson, C. H. [Breck School Science Department, 123 Ottawa Ave., N., Golden Valley, MN 55422 (United States); Hoette, V. [The University of Chicago Department of Astronomy and Astrophysics, Yerkes Observatory Education and Outreach, 373 W. Geneva St., Williams Bay, WI 53191 (United States); Kim, J. S.; Foster, M. [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Mallory, C. R. [Department of Astronomy, Pierce College, 6201 Winnetka Ave., Woodland Hills, CA 91371 (United States); McCarron, K. [Science Division, Oak Park and River Forest High School, 201 N. Scoville Ave., Oak Park, IL 60302 (United States); Sherry, W. H., E-mail: luisa.rebull@jpl.nasa.gov [NOAO/NSO, 950 N. Cherry Ave., Tucson, AZ 85719 (United States)

    2011-07-15

    The CG4 and Sa101 regions together cover a region of {approx}0.5 deg{sup 2} in the vicinity of a 'cometary globule' that is part of the Gum Nebula. There are seven previously identified young stars in this region; we have searched for new young stars using mid- and far-infrared data (3.6-70 {mu}m) from the Spitzer Space Telescope, combined with ground-based optical data and near-infrared data from the Two Micron All Sky Survey. We find infrared excesses in all six of the previously identified young stars in our maps and identify 16 more candidate young stars based on apparent infrared excesses. Most (73%) of the new young stars are Class II objects. There is a tighter grouping of young stars and young star candidates in the Sa101 region, in contrast to the CG4 region, where there are fewer young stars and young star candidates, and they are more dispersed. Few likely young objects are found in the 'fingers' of the dust being disturbed by the ionization front from the heart of the Gum Nebula.

  1. 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.

  2. Shock Waves in Out ows from Young Stars Patrick Hartigan

    E-print Network

    Hartigan, Patrick

    Shock Waves in Out ows from Young Stars Patrick Hartigan Dept. of Physics and Astronomy, Rice 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

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

    SciTech Connect

    Kochanek, C. S. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

    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.

  4. Young, massive star clusters in the antennae

    NASA Astrophysics Data System (ADS)

    Christopher, Micol Huw

    2008-12-01

    While massive star clusters have been detected in almost every galaxy with appreciable star formation, they are most prevalent in interacting and merging galaxies. As many as 95% of these clusters will ultimately be disrupted, often in the first 10 Myr, but those clusters that do survive may be the progenitors of globular clusters. Many questions exist regarding these massive clusters and the processes that lead to their formation and disruption, including the uniformity of these processes within a galaxy and between galaxies with different degrees of cluster formation (e.g., quiescent spirals, starbursts, and merging systems). To address these questions, we present a detailed spectroscopic survey of young, massive star clusters in the Antennae, one of the best examples of cluster formation in a merging galaxy. Using near-infrared imaging, we selected a sample of 117 clusters to observe with a combination of near-infrared and optical spectroscopy at the W.M. Keck Observatory. These clusters were chosen to sample the major star-forming regions within the Antennae. This is the largest spectroscopic survey of young massive star clusters in any merging galaxy. Comparing the equivalent widths of hydrogen recombination lines and CO absorption bandheads to the population synthesis models of Starburst99, we measure the age of each cluster. More than half of the clusters show the simultaneous presence of hydrogen recombination lines and CO bandheads, which is not predicted by an instantaneous burst model of cluster formation. We determine that cluster formation is better modeled by a 5 Myr duration constant rate burst of star formation, which we apply to our cluster measurements. We find the vast majority of clusters have ages between 7 and 12 Myr, with a few younger clusters. Comparing cluster ages with predictions of the temporal evolution of cluster luminosity, we find the lack of older (>12 Myr) clusters (and to a lesser extent younger (<7 Myr) clusters) is not a selection effect but a true deficit. Variation in cluster ages exists with location in the Antennae, with the youngest clusters found in the overlap region where the disks of the two galaxies coincide. We interpret these age variations as an indication that cluster disruption rates differ by location within the Antennae. Cluster masses are measured by comparing the extinction-corrected K-band luminosity with model luminosity predictions. We find most cluster masses are between 10^5 and 10^6 Msun with a median cluster mass around 3.5 x 10^5 Msun. Substantial variation exists in masses between different regions, with the overlap region having the most massive clusters on average. These mass differences can be interpreted as size-of-sample effects and our results are consistent with a uniform cluster initial mass function throughout the Antennae. Improved spatial resolution CO (1-0) observations of the Antennae show that younger clusters coincide with areas of enhanced molecular gas concentration and, not surprisingly, also have on average higher extinctions. From two metallicity tracers, we find cluster metallicities consistent with solar values. Based on CO bandhead and SiI equivalent widths in the near-infrared spectra, we uncover strong evidence of a substantial population of M2--M4 supergiants in many of the older clusters.

  5. Recent outburst of the young star V1180 Cassiopeiae

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Aims: We report on the ongoing outburst of the young variable V1180 Cas, which is known to display characteristics in common with EXor eruptive variables. We present results that support the scenario of an accretion-driven nature of the brightness variations of the object and provide the first evidence of jet structures around the source. Methods: We monitored the recent flux variations of the target in the RC, J, H, and K bands. New optical and near-IR spectra taken during the current high state of V1180 Cas are presented, in conjunction with H2 narrow-band imaging of the source. Results: Observed near-IR colour variations are analogous to those observed in EXors and consistent with excess emission originating from an accretion event. The spectra show numerous emission lines, which indicates accretion, ejection of matter, and an active disc. Using optical and near-IR emission features we derive a mass accretion rate of ~ 3 × 10-8M? yr-1, which is an order of magnitude lower than previous estimates. In addition, a mass loss rate of ~ 4 × 10-9 and ~ 4 × 10-10M? yr-1 are estimated from atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright knots of emission around the source and the nearby optically invisible star V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution observations of the detected jet will help to clarify whether V1180 Cas is the driving source and to determine the relation between the observed knots. Optical and NIR spectra (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/565/L7

  6. JOURNAL OF GEOPHYSICAL RESEARCH: SOLID EARTH, VOL. 118, 115, doi:10.1002/jgrb.50251, 2013 Eruptions at Lone Star Geyser, Yellowstone National Park, USA

    E-print Network

    Manga, Michael

    Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics Leif processes. We present results from a 4 day experiment at Lone Star Geyser in Yellowstone National Park, USA Yellowstone Caldera. Citation: Karlstrom, L., S. Hurwitz, R. Sohn, J. Vandemeulebrouck, F. Murphy, M. L

  7. K-band spectroscopy of deeply embedded, young OB stars

    E-print Network

    A. Bik; L. Kaper; M. M. Hanson; L. B. F. M. Waters

    2006-08-31

    We have obtained high resolution (R = 10,000) K-band spectra of candidate young massive stars deeply embedded in high-mass star-forming regions. These objects were selected from a near-infrared survey of 44 regions of high-mass star-formation (Kaper et al, 2006). In these clusters, 38 OB stars are identified whose K-band spectra are dominated by photospheric emission. In almost all those stars, the K-band spectra are indistinguishable from field stars. However, in some stars the profile of the Bracket gamma line is different (less deep, or absent) from those of the O field stars. One of the explanations of these profiles might be an enhanced mass-loss.

  8. Search for associations containing young stars (SACY). II. Chemical abundances of stars in 11 young associations in the solar neighborhood

    Microsoft Academic Search

    P. Viana Almeida; N. C. Santos; C. Melo; M. Ammler-von Eiff; C. A. O. Torres; G. R. Quast; J. F. Gameiro; M. Sterzik

    2009-01-01

    The recently discovered coeval, moving groups of young stellar objects in the solar neighborhood represent invaluable laboratories for studying recent star formation and searching for high metallicity stars that can be included in future exo-planet surveys. In this study, we derived through an uniform and homogeneous method stellar atmospheric parameters and abundances for iron, silicium, and nickel in 63 post-T

  9. THE FORMATION OF YOUNG DENSE STAR CLUSTERS THROUGH MERGERS

    SciTech Connect

    Fujii, M. S.; Portegies Zwart, S. F. [Leiden Observatory, Leiden University, NL-2300RA Leiden (Netherlands); Saitoh, T. R. [Interactive Research Center of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551 (Japan)

    2012-07-01

    Young star clusters such as NGC 3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.

  10. 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.

  11. 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

  12. THE ORIGIN OF S-STARS AND A YOUNG STELLAR DISK: DISTRIBUTION OF DEBRIS STARS OF A SINKING STAR CLUSTER

    SciTech Connect

    Fujii, M. [Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan); Iwasawa, M.; Makino, J. [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Funato, Y., E-mail: fujii@cfca.j, E-mail: makino@cfca.j, E-mail: iwasawa@cfca.ac.j, E-mail: funato@artcompsci.or [Department of General System Studies, College of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan)

    2010-06-10

    Within the distance of 1 pc from the Galactic center (GC), more than 100 young massive stars have been found. The massive stars at 0.1-1 pc from the GC are located in one or two disks, while those within 0.1 pc from the GC, S-stars, have an isotropic distribution. How these stars are formed is not well understood, especially for S-stars. Here, we propose that a young star cluster with an intermediate-mass black hole (IMBH) can form both the disks and S-stars. We performed a fully self-consistent N-body simulation of a star cluster near the GC. Stars that escaped from the tidally disrupted star cluster were carried to the GC due to a 1:1 mean motion resonance with the IMBH formed in the cluster. In the final phase of the evolution, the eccentricity of the IMBH becomes very high. In this phase, stars carried by the 1:1 resonance with the IMBH were dropped from the resonance and their orbits are randomized by a chaotic Kozai mechanism. The mass function of these carried stars is extremely top-heavy within 10''. The surface density distribution of young massive stars has a slope of -1.5 within 10'' from the GC. The distribution of stars in the most central region is isotropic. These characteristics agree well with those of stars observed within 10'' from the GC.

  13. Young stars in the CO Cepheus void and its surrounding

    NASA Astrophysics Data System (ADS)

    Klutsch, A.; Montes, D.; Guillout, P.; Frasca, A.; Pineau, F.-X.; Grosso, N.; Marilli, E.; López-Santiago, J.

    2013-05-01

    After mixing in the Galactic plane, young stars are barely discernible from old ones. In the RasTyc sample we have identified several stars whose lithium content is higher than that of the Pleiades cluster members. Furthermore, four of them are concentrated, within a few degrees, inside the CO Cepheus void. They likely constitute a new young association. To discover further additional members, we used multivariate analysis methods for selecting optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources cross-identified with late-type stars. From our spectroscopic observations, we distinguished two populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster are mostly projected towards the Galactic plane, the youngest stars are mainly located in the sky area surrounding the CO Cepheus void and have an age of about 5 - 15 Myr. The latter stars have properties (age, proper motions, radial velocity, dots) rather similar to those derived for the four comoving T Tauri stars already found in this region. Thus, they form the first young association of the northern sky. The discovery of young field stars is of great importance to give new insight into the process of stellar formation outside standard star-forming regions. Further data, such as those from the future Gaia mission, will certainly shed light on this issue and on the origin of this group that could be related to the Cepheus-Cassiopeia complex, which is the closest active star-forming region.

  14. M33's Variable A -- A Hypergiant Star More Than 35 Years in Eruption

    E-print Network

    Humphreys, R M; Gordon, K; Helton, A; Hinz, J; Jones, T J; Koppelman, M; McQuinn, K; Polomski, E; Wagner, R M; Willner, S P; Woodward, C E; Gehrz, Robert D.; Gordon, Karl; Helton, Andrew; Hinz, Joannah; Humphreys, Roberta M.; Jones, Terry J.; Koppelman, Michael; Polomski, Elisha; Quinn, Kristen Mc

    2006-01-01

    Variable A in M33 is a member of a rare class of highly luminous, evolved stars near the upper luminosity boundary that show sudden and dramatic shifts in apparent temperature due to the formation of optically thick winds in high mass loss episodes. Recent optical and infrared spectroscopy and imaging reveal that its ``eruption'' begun in $\\sim$1950 has ended, {\\it lasting $\\approx$ 45 yrs}. Our current observations show major changes in its wind from a cool, dense envelope to a much warmer state surrounded by low density gas with rare emission lines of Ca II, [Ca II] and K I. Its spectral energy distribution has unexpectedly changed, especially at the long wavelengths, with a significant decrease in its apparent flux, while the star remains optically obscured. We conclude that much of its radiation is now escaping out of our line of sight. We attribute this to the changing structure and distribution of its circumstellar ejecta corresponding to the altered state of its wind as the star recovers from a high ma...

  15. M33's Variable A -- A Hypergiant Star More Than 35 Years in Eruption

    E-print Network

    Roberta M. Humphreys; Terry J. Jones; Elisha Polomski; Michael Koppelman; Andrew Helton; Kristen McQuinn; Robert D. Gehrz; C. E. Woodward; R. Mark Wagner; Karl Gordon; Joannah Hinz; S. P. Willner

    2006-01-05

    Variable A in M33 is a member of a rare class of highly luminous, evolved stars near the upper luminosity boundary that show sudden and dramatic shifts in apparent temperature due to the formation of optically thick winds in high mass loss episodes. Recent optical and infrared spectroscopy and imaging reveal that its ``eruption'' begun in $\\sim$1950 has ended, {\\it lasting $\\approx$ 45 yrs}. Our current observations show major changes in its wind from a cool, dense envelope to a much warmer state surrounded by low density gas with rare emission lines of Ca II, [Ca II] and K I. Its spectral energy distribution has unexpectedly changed, especially at the long wavelengths, with a significant decrease in its apparent flux, while the star remains optically obscured. We conclude that much of its radiation is now escaping out of our line of sight. We attribute this to the changing structure and distribution of its circumstellar ejecta corresponding to the altered state of its wind as the star recovers from a high mass loss event.

  16. M33's Variable A: A Hypergiant Star More Than 35 YEARS in Eruption

    NASA Astrophysics Data System (ADS)

    Humphreys, Roberta M.; Jones, Terry J.; Polomski, Elisha; Koppelman, Michael; Helton, Andrew; McQuinn, Kristen; Gehrz, Robert D.; Woodward, C. E.; Wagner, R. Mark; Gordon, Karl; Hinz, Joannah; Willner, S. P.

    2006-04-01

    Variable A in M33 is a member of a rare class of highly luminous, evolved stars near the upper luminosity boundary that show sudden and dramatic shifts in apparent temperature due to the formation of optically thick winds in high mass loss episodes. Recent optical and infrared spectroscopy and imaging reveal that its ``eruption,'' begun in ~1950, has ended, having lasted ~45 yr. Our current observations show major changes in its wind from a cool, dense envelope to a much warmer state surrounded by low-density gas with rare emission lines of Ca II, [Ca II], and K I. Its spectral energy distribution has unexpectedly changed, especially at the long wavelengths, with a significant decrease in its apparent flux, while the star remains optically obscured. We conclude that much of its radiation is now escaping out of our line of sight. We attribute this to the changing structure and distribution of its circumstellar ejecta, corresponding to the altered state of its wind as the star recovers from a high mass loss event.

  17. SACY - a Search for Associations Containing Young stars

    E-print Network

    Carlos A. O. Torres; Germano R. Quast; Ramiro de la Reza; Licio da Silva; Claudio H. F. Melo; Michael Sterzik

    2003-06-12

    The scientific goal of the SACY (Search for Associations Containing Young-stars) was to identify possible associations of stars younger than the Pleiades Association among optical counterparts of the ROSAT X-ray bright sources. High-resolution spectra for possible optical counterparts later than G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. The newly identified young stars present a patchy distribution in UVW and XYZ, revealing the existence of huge nearby young associations. Here we present the associations identified in this survey.

  18. 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 ?m 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

  19. HST Observations of Young Star Clusters in Interacting Galaxies

    E-print Network

    K. D. Borne; W. C. Keel; P. N. Appleton; C. Struck; R. A. Lucas; A. Schultz

    2001-05-10

    We present early results from the analysis of HST imaging observations for several pairs of interacting galaxies. We include two cases that were specifically chosen to represent a strong early (young) encounter (Arp 81 = NGC 6621/6622) and a weak late (old) encounter (Arp 297 = NGC 5752/5754). The goals of the project include a determination of the timing, frequency, strength, and characteristics of the young star clusters formed in these two limiting cases of tidal encounters.

  20. Young stars and protostellar cores near NGC 2023

    Microsoft Academic Search

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

    2010-01-01

    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

  1. Multiobject Spectroscopy of Young Star Clusters in NGC 4676

    NASA Astrophysics Data System (ADS)

    Chien, Li-Hsin; Barnes, Joshua E.; Kewley, Lisa J.; Chambers, Kenneth C.

    2007-05-01

    Galaxy interactions are known to trigger starbursts. The young star clusters formed in mergers may be young globular clusters. The ages of these young star clusters yield the timing of interaction-triggered star formation and provide an important way to reconstruct the history of merging galaxies. Here we present the first results from our investigation into age and metallicity of 12 young clusters in the merging galaxy pair NGC 4676, using spectra from the multiobject Low Resolution Imaging Spectrometer (LRIS) on Keck. For 10 clusters, comparison of the Balmer emission lines with model equivalent widths (EWs) yields ages less than 10 Myr. Two spectra display Balmer absorption lines typical of star clusters dominated by A-type stars, with estimated ages of about 170 Myr. These ages are comparable to the dynamical age of the tidal tails and are consistent with star formation triggered during the first passage of the pair. The locations of these two clusters in the tidal tails are generally consistent with predictions of shock-induced star formation models. One of these older objects appears unresolved on the image and is luminous enough to qualify as a young globular cluster. Using EWs of the diagnostic lines [O II] and [O III], we obtain oxygen abundances in the range 7.3<12+log(O/H)<9.0. These values show a nearly flat distribution along the northern tail, suggesting efficient gas mixing in the tail. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, University of California, and National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  2. Tenuous Disks around Young G Stars: Temperature & Chemistry

    Microsoft Academic Search

    Inga Kamp; Fatima Sammar

    2003-01-01

    The chemistry of circumstellar disks around young (~10 Myr) solar-type stars is mainly driven by the strong UV radiation field of the central star. Stationary non-flaring disk models are used to derive self-consistently the chemical composition and gas\\/dust temperatures. Such models and high resolution observations are needed for a better understanding of the transition phase from gaseous protoplanetary disks to

  3. Winds and Accretion in Young Stars

    E-print Network

    Suzan Edwards

    2008-09-21

    Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new diagnostic to probe the magnetically controlled star-disk interaction and wind-launching region. The high opacity and resonance scattering properties of this line offer a powerful probe of the geometry of both the funnel flow and the inner wind that, together with other atomic and molecular spectral lines covering a wide range of excitation and ionization states, suggests that the magnetic interaction between the star and disk, and the subsequent launching of the inner high velocity wind, is sensitive to the disk accretion rate.

  4. A Photometric Study of Young Stars in the (lambda) Orionis Star-Forming Region

    NASA Astrophysics Data System (ADS)

    Dolan, Christopher J.; Mathieu, Robert D.

    1999-08-01

    With 11 OB stars centered in an unobscured ring of clouds littered with low-mass pre-main sequence stars, the (lambda) Orionis star- forming region is an excellent laboratory for studying the effects of massive stars on low-mass star formation. We propose a BVRI photometric survey of the entire star-forming region with the wide-field 0.9m/Mosaic imager. The goals of the photometry will be (1) to identify young stellar candidates throughout the region via pre-main sequence loci in the color-magnitude diagram and (2) to derive ages and masses by comparison with pre-main-sequence evolutionary tracks. The ages will allow us to deduce the sequence of star formation in the region, while the masses will reveal the spatial dependence of the initial mass function. Together, these results allow us to determine the influence of the OB stars on the formation of low- mass stars.

  5. The Circumstellar Environments of Young Stars at AU Scales

    E-print Network

    Rafael Millan-Gabet; Fabien Malbet; Rachel Akeson; Christoph Leinert; John Monnier; Rens Waters

    2006-03-21

    We review recent advances in our understanding of the innermost regions of the circumstellar environment around young stars, made possible by the technique of long baseline interferometry at infrared wavelengths. Near-infrared observations directly probe the location of the hottest dust. The characteristic sizes found are much larger than previously thought, and strongly correlate with the luminosity of the central young stars. This relation has motivated in part a new class of models of the inner disk structure. The first mid-infrared observations have probed disk emission over a larger range of scales, and spectrally resolved interferometry has for the first time revealed mineralogy gradients in the disk. These new measurements provide crucial information on the structure and physical properties of young circumstellar disks, as initial conditions for planet formation.

  6. Instabilities in Very Young Neutron Stars: Temperature

    NSDL National Science Digital Library

    Pamela ONeil

    1994-02-12

    This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the temperature structure for 20 milliseconds after the shock stalls. The minimum temperature is approximately 1.35 MeV. The maximum temperature varies from 6 MeV at the beginning of the calculation to 10 MeV at the later times.

  7. Instabilities in Very Young Neutron Stars: Density

    NSDL National Science Digital Library

    Pamela ONeil

    1994-02-12

    This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the density evolution for 20 milliseconds after the shock stalls. The density is plotted on a log scale. Values range from 10^9 gm-cm^3 at the outer boundary to 1.4 x 10^12 gm-cm^3 at the inner boundary.

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

    E-print Network

    Herczeg, Gregory J

    2015-01-01

    Absolute ages of young stars are important for many issues in pre-main sequence stellar and circumstellar evolution but are long recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in HR diagrams for low-mass stars and brown dwarfs in the eta Cha, epsilon Cha, and TW Hya Associations and the beta 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 models lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncert...

  9. X-ray Investigations of Young Stars Near Earth

    NASA Astrophysics Data System (ADS)

    Kastner, Joel

    2014-11-01

    The rapidly growing number of known young (age ˜8--100 Myr) stars within ˜100 pc of Earth offer unparalleled opportunities to investigate the early evolution of low-to intermediate-mass stars and the dispersal of planet-forming disks. I will present results from our ongoing XMM and Chandra studies of known and candidate members of nearby, young moving groups (NYMGs). Targeted and serendipitous X-ray observations of M-type NYMG members reveal the magnetic activity levels of very low-mass stars during their post-T Tauri evolutionary stages. Simultaneous X-ray and near-infrared spectroscopy campaigns targeting T Cha and TWA 30A, both of which are viewed through inclined, dusty accretion disks, provide insight into the compositions and clumpiness of these highly evolved disks.

  10. 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

  11. Photoevaporation of Circumstellar Disks around Young Stars

    Microsoft Academic Search

    Ian G. McCarthy; Doug Johnstone; David R. Ballantyne

    2004-01-01

    We examine the ability of photoevaporative disk winds to explain the\\u000alow-velocity components observed in the forbidden line spectra of low-mass T\\u000aTauri stars. Using the analytic model of Shu, Johnstone, & Hollenbach (1993)\\u000aand Hollenbach et al. (1994) as a basis, we examine the characteristics of\\u000aphotoevaporative outflows with hydrodynamic simulations. General results from\\u000athe simulations agree well with

  12. Evolution of the central stars of young planetary nebulae

    NASA Astrophysics Data System (ADS)

    Hajduk, M.; van Hoof, P. A. M.; Zijlstra, A. A.

    2015-01-01

    Aims: The evolution of central stars of planetary nebulae was so far documented in just a few cases. However, spectra collected a few decades ago may provide a good reference for studying the evolution of central stars using the emission line fluxes of their nebulae. We investigated evolutionary changes of the [O iii] 5007 Å line flux in the spectra of planetary nebulae. Methods: We compared nebular fluxes collected during a decade or longer. We used literature data and newly obtained spectra. A grid of cloudy models was computed using existing evolutionary models, and the models were compared with the observations. Results: An increase of the [O iii] 5007 Å line flux is frequently observed in young planetary nebulae hosting H-rich central stars. The increasing nebular excitation is the response to the increasing temperature and hardening radiation of the central stars. We did not observe any changes in the nebular fluxes in the planetary nebulae hosting late-type Wolf-Rayet (WR) central stars. This may indicate a slower temperature evolution (which may stem from a different evolutionary status) of late-[WR] stars. Conclusions: In young planetary nebulae with H-rich central stars, the evolution can be followed using optical spectra collected during a decade or longer. The observed evolution of H-rich central stars is consistent with the predictions of the evolutionary models provided in the literature. Late-[WR] stars possibly follow a different evolutionary path. Reduced spectra from the Torun and SAAO observatories 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/573/A65

  13. 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.

  14. Thermal Evolution and Light Curves of Young Bare Strange Stars

    NASA Astrophysics Data System (ADS)

    Page, Dany; Usov, Vladimir V.

    2002-09-01

    We study numerically the cooling of a young bare strange star and show that its thermal luminosity, mostly due to e(sup +)e(sup -) pair production from the quark surface, may be much higher than the Eddington limit. The mean energy of photons far from the strange star is [approx]10(sup 2) keV or even more. This differs both qualitatively and quantitatively from the thermal emission from neutron stars and provides a definite observational signature for bare strange stars. It is shown that the energy gap of superconducting quark matter may be estimated from the light curves if it is in the range from [approx]0.5 MeV to a few MeV.

  15. AN INTERMEDIATE LUMINOSITY TRANSIENT IN NGC 300: THE ERUPTION OF A DUST-ENSHROUDED MASSIVE STAR

    SciTech Connect

    Berger, E.; Soderberg, A. M.; Foley, R. J.; Dupree, A. K. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Chevalier, R. A. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Fransson, C. [Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm (Sweden); Leonard, D. C. [Department of Astronomy, San Diego State University, PA-210, 5500 Campanile Drive, San Diego, CA 92182-1221 (United States); Debes, J. H. [Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road, Washington, DC 20015 (United States); Diamond-Stanic, A. M.; Tremonti, C. A. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Ivans, I. I.; Thompson, I. B. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Simmerer, J. [Lund Observatory, Box 43, SE-221 00 Lund (Sweden)

    2009-07-10

    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{sub bol} {approx} -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 ({approx}200-1000 km s{sup -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 and K absorption with a broad red wing extending to {approx}10{sup 3} km s{sup -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 x 10{sup 4} L{sub sun}, indicative of a {approx}10-20 M{sub 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.

  16. 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.

  17. Dependency of Dynamical Ejections of O Stars on the Masses of Very Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Oh, Seungkyung; Kroupa, Pavel; Pflamm-Altenburg, Jan

    2015-06-01

    Massive stars can be efficiently ejected from their birth star clusters through encounters with other massive stars. We study how the dynamical ejection fraction of O star systems varies with the masses of very young star clusters, {{M}ecl}, by means of direct N-body calculations. We include diverse initial conditions by varying the half-mass radius, initial mass segregation, initial binary fraction, and orbital parameters of the massive binaries. The results show robustly that the ejection fraction of O star systems exhibits a maximum at a cluster mass of {{10}3.5} {{M}? } for all models, even though the number of ejected systems increases with cluster mass. We show that lower mass clusters ({{M}ecl}? 400 {{M}? }) are the dominant sources for populating the Galactic field with O stars by dynamical ejections, considering the mass function of embedded clusters. About 15% (up to ?38%, depending on the cluster models) of O stars of which a significant fraction are binaries, and which would have formed in a ?10 Myr epoch of star formation in a distribution of embedded clusters, will be dynamically ejected to the field. Individual clusters may eject 100% of their original O star content. A large fraction of such O stars have velocities up to only 10 km s?1. Synthesising a young star cluster mass function, it follows, given the stellar-dynamical results presented here, that the observed fractions of field and runaway O stars, and the binary fractions among them, can be well understood theoretically if all O stars form in embedded clusters.

  18. 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 3? 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.

  19. Circumbinary molecular rings around young stars in Orion

    NASA Astrophysics Data System (ADS)

    Zapata, L. A.; Ho, P. T. P.; Rodríguez, L. F.; Schilke, P.; Kurtz, S.

    2007-09-01

    We present high angular resolution 1.3 mm continuum, methyl cyanide molecular line, and 7 mm continuum observations made with the Submillimeter Array and the Very Large Array, toward the most highly obscured and southern part of the massive star forming region OMC1S located behind the Orion Nebula. We find two flattened and rotating molecular structures with sizes of a few hundred astronomical units suggestive of circumbinary molecular rings produced by the presence of two stars with very compact circumstellar disks with sizes and separations of about 50 AU, associated with the young stellar objects 139-409 and 134-411. Furthermore, these two circumbinary rotating rings are related to two compact and bright hot molecular cores. The dynamic mass of the binary systems obtained from our data are ?4 M_? for 139-409 and ?0.5 M_? for 134-411. This result supports the idea that intermediate-mass stars will form through circumstellar disks and jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass stars are in multiple systems they seem to form a circumbinary ring similar to those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).

  20. Spherical episodic ejection of material from a young star.

    PubMed

    Torrelles, J M; Patel, N A; Gómez, J F; Ho, P T; Rodríguez, L F; Anglada, G; Garay, G; Greenhill, L; Curiel, S; Cantó, J

    2001-05-17

    The exact processes by which interstellar matter condenses to form young stars are of great interest, in part because they bear on the formation of planets like our own from the material that fails to become part of the star. Theoretical models suggest that ejection of gas during early phases of stellar evolution is a key mechanism for removing excess angular momentum, thereby allowing material to drift inwards towards the star through an accretion disk. Such ejections also limit the mass that can be accumulated by the stellar core. To date, these ejections have been observed to be bipolar and highly collimated, in agreement with theory. Here we report observations at very high angular resolution of the proper motions of an arc of water-vapour masers near a very young, massive star in Cepheus. We find that the arc of masers can be fitted to a circle with an accuracy of one part in a thousand, and that the structure is expanding. Only a sphere will always produce a circle in projection, so our observations strongly suggest that the perfectly spherical ejection of material from this star took place about 33 years earlier. The spherical symmetry of the ejecta and its episodic nature are very surprising in the light of present theories. PMID:11357123

  1. Young Stars at the Center of the Milky Way?

    NASA Astrophysics Data System (ADS)

    Eckart, A.; Moultaka, J.; Viehmann, T.; Straubmeier, C.; Mouawad, N.

    2004-02-01

    We present results from the first diffraction-limited images of the Galactic center (GC) at 1.6, 2.1, and 3.8 ?m with the new adaptive optics (AO) camera NAOS/CONICA at the ESO Very Large Telescope, as well as 3-4 ?m low-resolution spectroscopy. We have discovered a small (0.13 lt-yr diameter) cluster of compact sources about 0.5" north of IRS 13 with strong IR excesses due to T>500 K dust. The nature of the sources is unclear. They may be a cluster of highly extincted stars that heat the local environment of the minispiral. We also consider an explanation that involves the presence of young stars at evolutionary stages between young stellar objects and Herbig Ae/Be objects with ages of about 0.1 to 1 million yr. This scenario would imply more recent star formation in the GC than previously suspected. The AO observations also resolve the central IRS 13 complex. In addition to the previously known bright stars E1 and E2, the K- and L'-band images for the first time resolve object E3 into two components, E3N and E3c. The latter one is closest to the 7 mm Very Large Array radio continuum source found at the location of the IRS 13 complex. E3c may be associated with a strong stellar wind or a dusty Wolf-Rayet-like star at that location.

  2. Accretion Shocks on Young Stars: A Laboratory-Astrophysics Investigation

    NASA Astrophysics Data System (ADS)

    Young, R. P.

    2014-10-01

    We intend to present results of a laboratory-astrophysics investigation of accretion shocks at the surface of young stars. We have scaled a stellar accretion shock to an OMEGA experiment by creating a plasma jet (representing the accreting material) and colliding it with a solid block (representing the surface of the young star). Magnetic fields are thought to play crucial role in this phenomenon, and therefore we conducted our experiments with imposed magnetic fields of 0 T, 3 T and 7 T. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0001840, and the National Laser User Facility Program, Grant Number DE-NA0000850, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-FC52-08NA28302.

  3. Shock-heating of stellar envelopes: a possible common mechanism at the origin of explosions and eruptions in massive stars

    NASA Astrophysics Data System (ADS)

    Dessart, Luc; Livne, Eli; Waldman, Roni

    2010-07-01

    Observations of transient phenomena in the Universe reveal a spectrum of mass-ejection properties associated with massive stars, covering from Type II/Ib/Ic core-collapse supernovae (SNe) to giant eruptions of luminous blue variables (LBV) and optical transients. In this work, we hypothesize that a large fraction of these phenomena may have an explosive origin, the distinguishing ingredient being the ratio of the prompt energy release Edep to the envelope binding energy Ebinding. Using one-dimensional one-group radiation hydrodynamics and a set of 10 -25 Msolar massive-star models, we explore the dynamical response of a stellar envelope subject to a strong, sudden and deeply rooted energy release. Following energy deposition, a shock systematically forms, crosses the progenitor envelope on a time-scale of a day and breaks out with a signal of a duration of hours to days and a 105 -1011 Lsolar luminosity. We identify three different regimes, corresponding to a transition from dynamic to quasi-static diffusion transport. For Edep > Ebinding, full envelope ejection results with an SN-like bolometric luminosity and kinetic energy, modulations being commensurate to the energy deposited and echoing the diversity of Type II-Plateau SNe. For Edep ~ Ebinding, partial envelope ejection results with a small expansion speed and a more modest but year-long luminosity plateau, reminiscent of LBV eruptions or so-called SN impostors. For Edep < Ebinding, we obtain a `puffed-up' star, secularly relaxing back to thermal equilibrium. In parallel with gravitational collapse and Type II SNe, we argue that thermonuclear combustion, for example of as little as a few 0.01 Msolar of C/O, could power a wide range of explosions/eruptions. Besides massive stars close to the Eddington limit and/or critical rotation, 8 -12 Msolar red supergiants, which are amongst the least bound of all stars, represent attractive candidates for transient phenomena.

  4. 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.

  5. Wolf-Rayet Stars in Very Young Starburst Galaxies

    E-print Network

    Thierry Contini

    1996-10-10

    Preliminary results from spectrophotometric observations of galaxies with very young starbursts are presented. Starburst galaxies with an age of the burst in the range between 3 and 6 Myr have been observed and new detections of Wolf-Rayet galaxies are reported. We discuss the origin of high excitation nebular lines observed in these galaxies and their possible link with the population of Wolf-Rayet stars.

  6. Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

    2011-11-01

    Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ? several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular shells typical of luminous blue variable and late WN-type Wolf-Rayet stars.

  7. 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.

  8. 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.

  9. 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 ?m 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.

  10. Young alpha-enriched giant stars in the solar neighbourhood

    E-print Network

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

    2014-01-01

    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 [{\\alpha}/Fe] values from APOGEE DR12 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 [{\\alpha}/Fe], at least 14 out of 241 stars with [{\\alpha}/Fe]>0.13 are younger than 6 Gyr. Five stars with [{\\alpha}/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 a...

  11. Twinkle, Twinkle: Characterizing Variable Stars in Young Open Clusters

    NASA Astrophysics Data System (ADS)

    Nava, Chantanelle; Stetson, P. B.; Walker, G. E.; West, M.

    2014-01-01

    The usefulness of identifying and characterizing variable stars has proven timeless since the first variable discovery in the sixteenth century. From distance calculations to binary star discoveries to development of stellar evolution theories, variable star observations have made, and continue to make, significant contributions to astronomy. Here we present the results of an ongoing investigation of four young open star clusters: ASCC 105, ASCC 109, Collinder 359, and IC 4665. Observations of the four clusters were collected with the Maria Mitchell Observatory’s 17-inch reflecting telescope. The data collected were used primarily to characterize known variable stars and to identify new variables. Images of each of the four fields were also used to characterize non-variable members in order to refine estimates of the cluster’s membership, distance, reddening, age, and chemical abundance. The main goals of the project were to determine these characteristics of the cluster fields to higher precision than previously measured, and to provide a foundational list of variable stars for future spectroscopic data collection.

  12. A Method to Search for Associations of Young Stars

    E-print Network

    Germano R. Quast; Carlos A. O. Torres; Claudio H. F. Melo; Michael Sterzik; Ramiro de la Reza; Licio da Silva

    2003-06-12

    In the SACY (Search for Associations Containing Young-stars) project we try to identify associations of stars younger than the Local Association among HIPPARCOS and/or TYCHO-2 stars later than G0 which are counterparts of the ROSAT X-ray bright sources. High-resolution spectra for the possible optical counterparts were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. Associations are characterized mainly by the similarity in UVW velocity space of their proposed member, but other parameters, as evolutionary age, Li abundance and distribution in space must also be taken into account. We proposed a method to identify associations when proper motions and radial velocities are available, but no parallaxes. Using the method we found eleven associations in the SACY data.

  13. Probing the Evolution of Stellar Activity in Young A Stars with FUSE

    Microsoft Academic Search

    M. Grady

    2004-01-01

    Spatially resolved spectroscopy of several Herbig Ae stars at Lyman alpha has demonstrated that these stars drive collimated, bipolar outflows through much of their pre-main sequence evolution, and therefore closely resemble young solar-mass T Tauri stars. For those objects, the stellar magnetic field is important in channelling material accreting onto the star and in collimating the outflow. Older A stars,

  14. Observation of light echoes around very young stars

    NASA Astrophysics Data System (ADS)

    Ortiz, J. L.; Sugerman, B. E. K.; de La Cueva, I.; Santos-Sanz, P.; Duffard, R.; Gil-Hutton, R.; Melita, M.; Morales, N.

    2010-09-01

    Aims: The goal of the paper is to present new results on light echoes from young stellar objects. Methods: Broad band CCD images were obtained over three months at one-to-two week intervals for the field of NGC 6726, using the large field-of-view remotely-operated telescope on top of Cerro Burek. Results: We detected scattered light echoes around two young, low-amplitude, irregular variable stars. Observations revealed not just one, but multiple light echoes from brightness pulses of the T Tauri star S CrA and the Herbig Ae/Be star R CrA. Analysis of S CrA's recurring echoes suggests that the star is located 138 ± 16 pc from Earth, making these the closest echoes ever detected. The environment that scatters the stellar light from S CrA is compatible with an incomplete dust shell or an inclined torus some 10 000 AU in radius and containing ~2 × 10-3 M? of dust. The cause of such concentration at ~10 000 AU from the star is unknown. It could be the remnant of the envelope from which the star formed, but the distance of the cloud is remarkably similar to the nominal distance of the Oort cloud to the Sun, leading us to also speculate that the dust (or ice) seen around S CrA might have the same origin as the Solar System Oort cloud. Movies are available in electronic form at http://www.aanda.org, http://www.iaa.es/~ortiz/animacion1.avi, and http://www.iaa.es/~ortiz/S-animation.gif

  15. Outflows from young stars : The Rosetta stone of astrophysical Jets?

    NASA Astrophysics Data System (ADS)

    Ray, T.

    2012-02-01

    It can be argued that all astrophysical jets, from lowly sub-stellar objects such as young brown dwarfs to massive black holes at the centre of AGN, are generated by the same basic physical mechanism. While the nature of that mechanism is still debated, jets from young stars may represent our best chance of deciphering it. There are several reasons for this statement. First of all they are nearby, thus affording us not only high spatial resolution studies of the "central engine" but also time-resolved analysis of their kinematics. Moreover as they radiate emission lines, spectroscopy can reveal radial velocities, temperature, density, ion fraction, etc., along their flow. This wealth of data is a challenge to the theorist/computational simulator but also a highly effective means of discriminating between models. In addition, the observations tightly constrain laboratory experiments. Here, I briefly review what is known about conditions in jets from young stars as a guide to experiments, their generation including their link with accretion disks, and their evolution from the earliest proto-stellar to pre-main sequence phase.

  16. 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.

  17. 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.

  18. The Evolution of X-Ray Emission in Young Stars

    NASA Astrophysics Data System (ADS)

    Preibisch, Thomas; Feigelson, Eric D.

    2005-10-01

    The evolution of magnetic activity in late-type stars is part of the intertwined rotation-age-activity relation, which provides an empirical foundation to the theory of magnetic dynamos. We study the age-activity relation in the pre-main-sequence (PMS) regime, for the first time using mass-stratified subsamples. The effort is based on the Chandra Orion Ultradeep Project (COUP), which provides very sensitive and homogenous X-ray data on a uniquely large sample of 481 optically well-characterized low-extinction low-mass members of the Orion Nebula Cluster, for which individual stellar masses and ages could be determined. More than 98% of the stars in this sample are detected as X-ray sources. Within the PMS phase for stellar ages in the range ~0.1-10 Myr, we establish a mild decay in activity with stellar age ? roughly as LX~?-1/3. On longer timescales, when the Orion stars are compared to main-sequence stars, the X-ray luminosity decay law for stars in the 0.5 Msolarstars. The magnetic activity history for M stars with masses 0.1 Msolarstars, we find that the activity-age decay is strong across the entire history of solar-type stars but is not attributable to rotational deceleration during the early epochs. A combination of tachocline and distributed convective dynamos may be operative in young solar-type stars. The results for the lowest mass stars are most easily understood by the dominance of convective dynamos during both the PMS and main-sequence phases.

  19. UV Radiation Fields Produced by Young Embedded Star Clusters

    E-print Network

    M. Fatuzzo; F. C. Adams

    2007-12-20

    A large fraction of stars form within young embedded clusters, and these environments produce a substantial ultraviolet (UV) background radiation field, which can provide feedback on the star formation process. To assess the possible effects of young stellar clusters on the formation of their constituent stars and planets, this paper constructs the expected radiation fields produced by these clusters. We include both the observed distribution of cluster sizes $N$ in the solar neighborhood and an extended distribution that includes clusters with larger $N$. The paper presents distributions of the FUV and EUV luminosities for clusters with given stellar membership $N$, distributions of FUV and EUV luminosity convolved over the expected distribution of cluster sizes $N$, and the corresponding distributions of FUV and EUV fluxes. These flux distributions are calculated both with and without the effects of extinction. Finally, we consider the effects of variations in the stellar initial mass function on these radiation fields. Taken together, these results specify the distributions of radiation environments that forming solar systems are expected to experience.

  20. Disk-related Bursts and Fades in Young Stars

    NASA Astrophysics Data System (ADS)

    Findeisen, Krzysztof; Hillenbrand, Lynne; Ofek, Eran; Levitan, David; Sesar, Branimir; Laher, Russ; Surace, Jason

    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 PTF ? 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.

  1. DISK-RELATED BURSTS AND FADES IN YOUNG STARS

    SciTech Connect

    Findeisen, Krzysztof; Hillenbrand, Lynne; Levitan, David; Sesar, Branimir [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Ofek, Eran [Benoziyo Center for Astrophysics, Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Laher, Russ; Surace, Jason, E-mail: krzys@astro.caltech.edu, E-mail: lah@astro.caltech.edu [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States)

    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.

  2. Cooling of young neutron stars in GRB associated to supernovae

    NASA Astrophysics Data System (ADS)

    Negreiros, R.; Ruffini, R.; Bianco, C. L.; Rueda, J. A.

    2012-04-01

    Context. The traditional study of neutron star cooling has been generally applied to quite old objects such as the Crab Pulsar (957 years) or the central compact object in Cassiopeia A (330 years) with an observed surface temperature ~106 K. However, recent observations of the late (t = 108-109 s) emission of the supernovae (SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures ~107-108 K. Similar features have been also observed in two Type Ic SNe SN 2002ap and SN 1994I that are not associated to GRBs. Aims: We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star just formed in the SN event, here defined as a neo-neutron star. Methods: We discuss the thermal evolution of neo-neutron stars in the age regime that spans from ~1 min (just after the proto-neutron star phase) all the way up to ages <10-100 yr. We examine critically the key factor governing the neo-neutron star cooling with special emphasis on the neutrino emission. We introduce a phenomenological heating source, as well as new boundary conditions, in order to mimic the high temperature of the atmosphere for young neutron stars. In this way we match the neo-neutron star luminosity to the observed late X-ray emission of the GRB-SN events: URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. Results: We identify the major role played by the neutrino emissivity in the thermal evolution of neo-neutron stars. By calibrating our additional heating source at early times to ~1012-1015 erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of a neo-neutron stars with the prolonged (t = 108-109 s) X-ray emission observed in GRB associated with SN. It is therefore appropriate a revision of the boundary conditions usually used in the thermal cooling theory of neutron stars, to match the proper conditions of the atmosphere at young ages. The traditional thermal processes taking place in the crust might be enhanced by the extreme high-temperature conditions of a neo-neutron star. Additional heating processes that are still not studied within this context, such as e+e- pair creation by overcritical fields, nuclear fusion, and fission energy release, might also take place under such conditions and deserve further analysis. Conclusions: Observation of GRB-SN has shown the possibility of witnessing the thermal evolution of neo-neutron stars. A new campaign of dedicated observations is recommended both of GRB-SN and of isolated Type Ic SN.

  3. 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.

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

    SciTech Connect

    Rebull, L. M.; Laher, R.; Legassie, M. [Spitzer Science Center/Caltech, M/S 220-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Johnson, C. H.; Carlson, S.; Clark, M.; Killingstad, N.; Koop, S. [Breck School, 123 Ottawa Avenue N., Golden Valley, MN 55422 (United States); Gibbs, J. C.; Aryal, S.; Canakapalli, T. S. [Glencoe High School, 2700 NW Glencoe Rd., Hillsboro, OR 97124 (United States); Linahan, M.; Ezyk, N.; Fagan, J. [Carmel Catholic High School, One Carmel Parkway, Mundelein, IL 60060 (United States); Sartore, D.; Badura, K. S. [Pine Ridge High School, 926 Howland Blvd., Deltona, FL 32738 (United States); Armstrong, J. D. [Las Cumbres Observatory Global Telescope (LCOGT) Network, Inc., 6740 Cortona Dr. Suite 102, Goleta, CA 93117 (United States); Allen, L. E. [National Optical Astronomy Observatory (NOAO), Tucson, AZ 85719 (United States); McGehee, P. [Infrared Processing and Analysis Center (IPAC), M/S 220-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Padgett, D. L., E-mail: rebull@ipac.caltech.edu [NASA's Goddard Space Flight Center (GSFC), 8800 Greenbelt Rd., Greenbelt, MD 20771 (United States); 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.

  5. Multiple jets from the young star IRAS 21334 + 5039

    NASA Technical Reports Server (NTRS)

    Smith, Howard A.; Fischer, Jacqueline

    1992-01-01

    The source IRAS 21334 + 5039, a young stellar object (YSO) with broad CO outflow velocity profiles, was imaged in the 1-2 micron region with broad-band J, H, and K filters, and with a Fabry-Perot set to the molecular hydorgen v = 1-0 S(1) line, the hydrogen Br-gamma recombination line, and the neighboring continua. At 2 microns the source has an elongated continuum emission structure centered on the star. The structure has very blue tips, with a weak VLA 6 cm continuum source coincident with one of them. Strong molecular hydrogen emission appears as bow-shaped arcs oriented along an axis perpendicular to the continuum emission, and as a weaker structure aligned with it. Both the continuum and the molecular hydrogen emission are most likely produced by jets, possibly emanating in multiple directions from the central source at large angles to each other. While jets are a common feature of young stars, this source provides solid evidence for multiple jet structures.

  6. Dependency of dynamical ejections of O stars on the masses of very young star clusters

    E-print Network

    Oh, Seungkyung; Pflamm-Altenburg, Jan

    2015-01-01

    Massive stars can be efficiently ejected from their birth clusters through encounters with other massive stars. We study how the dynamical ejection fraction of O star systems varies with the masses of very young star clusters, Mecl, by means of direct N -body calculations. We include diverse initial conditions by varying the half-mass radius, initial mass-segregation, initial binary fraction and orbital parameters of the massive binaries. The results show robustly that the ejection fraction of O star systems exhibits a maximum at a cluster mass of $10^{3.5}$ Msun for all models, even though the number of the ejected systems increases with cluster mass. We show that lower mass clusters (Mecl ~ 400 Msun ) are the dominant sources for populating the Galactic field with O stars by dynamical ejections, considering the mass function of embedded clusters. About 15 per cent (up to 38 per cent, depending on the cluster models) of O stars of which a significant fraction are binaries, and which would have formed in a 10...

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

    SciTech Connect

    Vaidya, Bhargav; Porth, Oliver [Member of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD) and the Heidelberg Graduate School of Fundamental Physics (HGSFP). (Germany); Fendt, Christian; Beuther, Henrik, E-mail: vaidya@mpia.de, E-mail: fendt@mpia.de [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    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.

  8. 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.

  9. 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.

  10. Late-Type Stars in Young Open Clusters Duncan C. Foster

    E-print Network

    -type stars, this thesis presents a study of two young open clusters, IC2602 and Stock 2. This thesis attempts that IC 2602 is a very sparsely populated cluster. In Stock 2 the search for members was more successfulLate-Type Stars in Young Open Clusters by Duncan C. Foster Armagh Observatory B.A. (TCD) 1994

  11. Disk Accretion and Mass Loss From Young Stars Patrick Hartigan 1

    E-print Network

    Hartigan, Patrick

    Foundation. #12; -- 2 -- ABSTRACT In this paper we investigate how mass outflows from young stars relateDisk Accretion and Mass Loss From Young Stars Patrick Hartigan 1 Department of Space Physics Received ; accepted Accepted by the Astrophysical Journal 5/1/95 1 Visiting Astronomer, Kitt Peak National

  12. 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.

  13. 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., E-mail: vansaders@astronomy.ohio-state.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

    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.

  14. Analysis of star-disk interaction in young stellar systems

    NASA Astrophysics Data System (ADS)

    Fonseca, Nathalia N. J.; Alencar, Silvia H. P.; Bouvier, Jérôme

    2014-08-01

    We present preliminary results of the study of star-disk interaction in the classical T Tauri star V354 Mon, a member of the young stellar cluster NGC 2264. As part of an international campaign of observations of NGC 2264 organized from December 2011 to February 2012, high resolution photometric and spectroscopic data of this object were obtained simultaneously with the Chandra, CoRoT and Spitzer satellites, and ground-based telescopes, such as CFHT and ESO/VLT. The optical and infrared light curves of V354 Mon show periodic brightness minima that vary in depth and width every 5.21 days rotational cycle. We found evidence that the H? emission line profile changes according to the period of photometric variations, indicating that the same phenomenon causes both modulations. Such correlation was also identified in a previous observational campaign on the same object, where we concluded that material non-uniformly distributed in the inner part of the disk is the main cause of the photometric modulation. This assumption is supported by the fact that the system is seen at high inclination. It is believed that this distortion of the inner part of the disk results from the dynamical interaction between the stellar magnetosphere, inclined with respect to the rotation axis, and the circumstellar disk, as also observed in the classical T Tauri star AA Tau, and predicted by magnetohydrodynamic numerical simulations. A model of occultation by circumstellar material was applied to the photometric data in order to determine the parameters of the obscuring material during both observational campaigns, thus providing an investigation of its stability on a timescale of a few years. We also studied V422 Mon, a classical T Tauri star with photometric variations similar to those of V354 Mon at optical wavelengths, but with a distinct behavior in the infrared. The mechanism that produces such a difference is investigated, testing the predictions of magnetospheric accretion models.

  15. Absolute parameters of young stars: GG Lup and ?1 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 ?1 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 ?1 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).

  16. Young Cool Stars Divided on the Issue of Rotation

    E-print Network

    Søren Meibom

    2008-11-09

    We present the results of a combination of new stellar rotation periods and extensive information about membership in the young open clusters M35 and M34. The observations show that late-type members of both clusters divide into two distinct groups, each with a different dependence of rotation on mass (color). We discuss these new results in the context of existing rotation data for cool stars in older clusters, with a focus on the dependence of rotation on mass and age. We mention briefly tests of rotation as an "astronomical clock" (gyrochronology), and our plans to use the Kepler space mission to push observations of stellar rotation periods beyond the age of the Hyades and the Sun.

  17. Infrared observations of young stars. VIII - Spectra in the ten-micron region

    Microsoft Academic Search

    M. Cohen

    1980-01-01

    Filter-wheel spectrophotometry is presented of 14 young stars. Very similar broad emission features are seen in five stars which qualitatively compare very favorably with the 'silicate' emission of the Orion Trapezium region. HL Tau has a silicate absorption feature, and three other stars show weak 10 micron absorptions. The amount of silicate material observed in HL Tau is determined. It

  18. Discovery of a luminous white dwarf in a young star cluster in the Large Magellanic Cloud

    E-print Network

    Rebecca A. W. Elson; Steinn Sigurdsson; Jarrod Hurley; Melvyn B. Davies; Gerard F. Gilmore

    1998-03-19

    We have identified a candidate 1-2 x 10^5 year old luminous white dwarf in NGC 1818, a young star cluster in the Large Magellanic Cloud. This discovery strongly constrains the boundary mass M_c at which stars stop forming neutron stars and start forming white dwarfs, to M_c > 7.6 Msun.

  19. 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).

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

    SciTech Connect

    Matt, Sean P.; Greene, Thomas P. [NASA Ames Research Center, M.S. 245-6, Moffett Field, CA 94035-1000 (United States); Pinzon, Giovanni [Observatorio Astronomico Nacional, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota (Colombia); De la Reza, Ramiro, E-mail: sean.p.matt@nasa.go, E-mail: thomas.p.greene@nasa.go, E-mail: gapinzone@unal.edu.c, E-mail: delareza@on.b [Observatorio Nacional, Rio de Janeiro (Brazil)

    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.

  1. Analysis of star-disk interaction in young stellar systems

    NASA Astrophysics Data System (ADS)

    Fonseca, N. N. J.; Alencar, S. H. P.; Bouvier, J.

    2014-01-01

    We present preliminary results of the study of star-disk interaction in the classical T Tauri star V354 Mon, a member of the young stellar cluster NGC 2264. As part of an international campaign of observation of NGC 2264 organized from December 2011 to February 2012, high resolution photometric and spectroscopic data of this object were obtained simultaneously with the Chandra, CoRoT and Spitzer satellites, and ground-based telescopes, as CFHT and VLT at ESO. The optical and infrared light curves of V354 Mon show periodic brightness minima that vary in depth and width every rotational cycle. We found evidence that the H? emission line profile changes according to the period of photometric variations, indicating that the same phenomenon causes both modulations. Such a correlation between emission line variability and light curve modulation was also identified in a previous observational campaign on the same object, where we concluded that material non-uniformly distributed in the inner part of the disk is the main cause of the photometric modulation. This assumption is supported by the fact that the system is seen at high inclination. It is believed that this distortion of the inner part of the disk results from the dynamical interaction between the stellar magnetosphere, inclined with respect to the rotation axis, and the circumstellar disk, as also observed in the classical T Tauri star AA Tau, and predicted by magnetohydrodynamic numerical simulations. A model of occultation by circumstellar material was applied to the photometric data in order to determine the parameters of the obscuring material during both observational campaigns, thus providing an investigation of its stability on a timescale of a few years.

  2. Variable Stars in the Field of Young Open Cluster NGC 581

    E-print Network

    L. Wyrzykowski; G. Pietrzynski; O. Szewczyk

    2002-04-16

    We present results of the search for variable stars in the field of young open cluster NGC 581. Based on 19 nights of observations, 6 new variable stars were discovered. Two of them turned out to be eclipsing binary systems. Another two detected variable stars are most probably of gamma Dor type. During our observations one of the known Be stars located in our field of view showed irregular variations of brightness, typical for this class of stars. The sixth variable star is a pulsating red giant.

  3. A global jet/circulation model for young stars

    NASA Astrophysics Data System (ADS)

    Lery, T.; Henriksen, R. N.; Fiege, J. D.; Ray, T. P.; Frank, A.; Bacciotti, F.

    2002-05-01

    Powerful, highly collimated jets, surrounded by bipolar molecular outflows, are commonly observed near Young Stellar Objects (YSOs). In the usual theoretical picture of star formation, a jet is ejected from a magnetized accretion disk, with a molecular outflow being driven either by the jet or by a wider wind coming from the disk. Here, we propose an alternative global model for the flows surrounding YSOs. In addition to a central accretion-ejection engine driving the jet, the molecular outflow is powered by the infalling matter and follows a circulation pattern around the central object without necessarily being entrained by a jet. It is shown that the model produces a heated pressure-driven outflow with magneto-centrifugal acceleration and collimation. We report solutions for the three different parts of this self-similar model, i.e. the jet, the infalling envelope and the circulating matter that eventually forms the molecular outflow. This new picture of the accretion/outflow phase provides a possible explanation for several observed properties of YSO outflows. The most relevant ones are the presence of high mass molecular outflows around massive protostars, and a realistic fraction (typically 0.1) of the accretion flow that goes into the jet.

  4. The nature of FS CMa stars as revealed by host young clusters

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F.

    2015-05-01

    The nature and evolutionary state of the diverse objects displaying the B[e] phenomenon are reasonably known, except for a rare subtype named FS CMa stars. These are surrounded by compact disks of warm dust whose origin is unclear. Although the luminosity of these objects corresponds to main-sequence stars, mass loss rates derived from emission lines are 2 orders of magnitude larger than predicted by wind theory. Hitherto, FS CMa stars have been only found in isolation, which hinders the study of their nature. In this contribution, we present the discovery of FS CMa stars in two young Galactic clusters, which host Wolf-Rayet stars and OB supergiants. Membership to these coeval populations allows us to constrain the luminosity, circumstellar extinction and age of FS CMa stars in an unprecedented way. Due to their relatively low brightness when compared with coeval evolved massive stars, a high number of these objects may remain unnoticed in young clusters.

  5. Precision Photometric Monitoring of Young Low-mass Stars and Brown Dwarfs: Shedding Light on Rotation, Pulsation, and the Star-disk Connection

    Microsoft Academic Search

    Ann Marie Cody; L. A. Hillenbrand

    2010-01-01

    Young star-forming regions are host to a variety of optically variable sources, from accreting and flaring stars to those whose light is modulated by surface spots. In addition, recent theory has suggested that a new type of variability-- pulsation powered by deuterium burning-- may be at work on hour timescales in young brown dwarfs and very low mass stars. Photometric

  6. Angular Momentum Evolution of Young Stars: Toward a Synthesis of Observations, Theory, and Modeling

    E-print Network

    Keivan G. Stassun; Donald Terndrup

    2003-03-17

    The aim of this AAS Topical Session was to update the community on the current state of knowledge about the angular momentum evolution of young stars. For newcomers to the subject, the session was intended to provide an introduction and general overview and to highlight emerging issues. For experienced workers in this field, the session provided an opportunity for synthesizing recent developments in observations, theory, and modeling of rotation of young stars and for identifying promising new research directions.

  7. `Tail-end' Bondi-Hoyle accretion in young star clusters: Implications for disks, planets, and stars

    E-print Network

    Henry B. Throop; John Bally

    2008-04-03

    Young stars orbiting in the gravitational potential well of forming star clusters pass through the cluster's dense molecular gas and can experience Bondi-Hoyle accretion from reservoirs outside their individual protostellar cloud cores. Accretion can occur for several million years after the stars form, but before the cluster disperses. This accretion is predominantly onto the disk and not the star. N-body simulations of stars orbiting in three young model clusters containing 30, 300, and 3000 stars are presented. The simulations include the gravitational potential of the molecular gas which smoothly disperses over time. The clusters have a star formation efficiency of 33% and a radius of 0.22 pc. We find that the disks surrounding solar-mass stars in the N=30 cluster accretes ~0.01 M_sol (~1 minimum-mass solar nebula, MMSN) per Myr. The accretion rate scales as M^2.1 for stars of mass M. The accretion rate is ~5 times lower for N=3000 cluster, due to its higher stellar velocities and higher temperature. The Bondi-Hoyle accretion rates onto the disks are several times lower than accretion rates observed directly onto young stars (e.g., Muzerolle et al 2005): these two accretion rates follow the same M^2 behavior and may be related. The accreted disk mass is large enough that it may have a substantial and unappreciated effect on disk structure and the formation of planetary systems. We discuss a variety of implications of this process, including its effect on metallicity differences between cluster stars, compositional differences between a star and its disk, the formation of terrestrial and gas-giant planets, and isotopic anomalies observed in our Solar System.

  8. Search for associations containing young stars (SACY):II. Chemical abundances of stars in 11 young Associations in the Solar neighborhood

    Microsoft Academic Search

    P. Viana Almeida; N. C. Santos; C. Melo; M. Ammler-von Eiff; C. A. O. Torres; G. R. Quast; J. F. Gameiro; M. Sterzik

    2009-01-01

    The recently discovered coeval, moving groups of young stellar objects in the\\u000asolar neighborhood represent invaluable laboratories to study recent star\\u000aformation and to search for high metallicity stars which can be included in\\u000afuture exo-planet surveys. In this study we derived through an uniform and\\u000ahomogeneous method stellar atmospheric parameters and abundances for iron,\\u000asilicium and nickel in 63

  9. 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.

  10. AGE AND MASS STUDIES FOR YOUNG STAR CLUSTERS IN M31 FROM SEDS-FIT

    SciTech Connect

    Wang Song; Ma Jun; Fan Zhou; Wu Zhenyu; Zhang Tianmeng; Zou Hu; Zhou Xu, E-mail: majun@nao.cas.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2012-12-01

    In this paper, we present photometry for young star clusters in M31, which are selected from Caldwell et al. These star clusters have been observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March. The BATC images including these star clusters are taken with 15 intermediate-band filters covering 3000-10000 A. Combined with photometry in the GALEX far- and near-ultraviolet, broadband UBV RI, SDSS ugriz, and infrared JHK{sub s} of Two Micron All Sky Survey, we obtain their accurate spectral energy distributions (SEDs) from 1538 to 20000 A. We derive these star clusters' ages and masses by comparing their SEDs with stellar population synthesis models. Our results are in good agreement with previous determinations. The mean value of age and mass of young clusters (<2 Gyr) is about 385 Myr and 2 Multiplication-Sign 10{sup 4} M{sub Sun }, respectively. There are two distinct peaks in the age distribution, a highest peak at age {approx}60 Myr and a secondary peak around 250 Myr, while the mass distribution shows a single peak around 10{sup 4} M{sub Sun }. A few young star clusters have two-body relaxation times greater than their ages, indicating that those clusters have not been well dynamically relaxed and therefore have not established the thermal equilibrium. There are several regions showing aggregations of young star clusters around the 10 kpc ring and the outer ring, indicating that the distribution of the young star clusters is well correlated with M31's star-forming regions. The young massive star clusters (age {<=}100 Myr and mass {>=}10{sup 4} M{sub Sun }) show apparent concentration around the ring splitting region, suggesting a recent passage of a satellite galaxy (M32) through M31 disk.

  11. 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 ?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.

  12. Extreme Star Formation in the Massive Young Cluster Westerlund 1

    NASA Astrophysics Data System (ADS)

    Hora, Joseph; Kraemer, Kathleen; Megeath, Tom; Gutermuth, Rob; Smith, Howard; Martinez Galarza, Juan Rafael; Guzman Fernandez, Andres; Carey, Sean; Koenig, Xavier; Schneider, Nicola; Motte, Frederique; Bontemps, Sylvain; Adams, Joseph; Simon, Robert; Nguyen-Luong, Quang; Schilke, Peter; Keto, Eric; Fazio, Giovanni; Allen, Lori

    2012-12-01

    We propose to extend Spitzer's study of massive star formation to the massive cluster Westerlund 1, which at ~4 kpc is the closest and most massive 'Super Star Cluster' known in the Galaxy. Star formation may have proceeded differently in this region, having created a higher overall density of coeval massive stars. The proposed observations will allow us to compare star formation in this region to that seen near the Sun, in the massive Cygnus-X complex, and in the outer Galaxy (coming from the studies of W5, the Cycle-5 SMOG project, and GLIMPSE360), and therefore to complete a more representative view of star formation in the Galaxy.

  13. The Stellar Composition of the Star Formation Region CMa R1. II. Spectroscopic and Photometric Observations of 9 Young Stars

    E-print Network

    H. R. E. Tjin A Djie; M. E. van den Ancker; P. F. C. Blondel; V. S. Shevchenko; O. V. Ezhkova; D. de Winter; K. N. Grankin

    2001-03-21

    We present new high and low resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circumstellar dust at some distance as could be expected from their association with reflection nebulosity. Four stars (HD 52721, HD 53367, LkHalpha 220 and LkHalpha 218) show Halpha emission and we argue that they are Herbig Be stars with discs. Our photometric and spectroscopic observations on these stars reveal new characteristics of their variability. We present first interpretations of the variability of HD 52721, HD 53367 and the two LkHalpha stars in terms of a partially eclipsing binary, a magnetic activity cycle and circumstellar dust variations, respectively. The remaining five stars show no clear indications of Halpha emission in their spectra, although their spectral types and ages are comparable with those of HD 52721 and HD 53367. This indicates that the presence of a disc around a star in CMa R1 may depend on the environment of the star. In particular we find that all Halpha emission stars are located at or outside the arc-shaped border of the H II region, which suggests that the stars inside the arc have lost their discs through evaporation by UV photons from nearby O stars, or from the nearby (< 25 pc) supernova, about 1 Myr ago.

  14. A Coronagraphic Search for Substellar Companions to Young Stars

    E-print Network

    Schneider, Glenn

    Searches for sub­stellar companions to main sequence stars and white dwarfs be­ gan over a decade ago to the white dwarf GD 165 (Becklin& Zuckerman 1988, Zucker­ man & Becklin 1992). Until recently it had the coolest temperature (ß1800K) of any dwarf star, but it remained unclear if it was a very low­mass star

  15. SPITZER INFRARED SPECTROGRAPH SURVEY OF YOUNG STARS IN THE CHAMAELEON I STAR-FORMING REGION

    SciTech Connect

    Manoj, P.; Kim, K. H.; Watson, Dan M.; Forrest, W. J.; Bohac, C.; Arnold, L. A. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Furlan, E. [JPL, Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); McClure, M. K.; Calvet, N. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Espaillat, C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78 Cambridge, MA 02138 (United States); Najita, J. R. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); D'Alessio, P.; Adame, L. [Instituto de AstronomIa, UNAM, Apartado Postal 70-264, Ciudad Universitaria, 04510, Mexico DF (Mexico); Sargent, B. A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Green, J. D., E-mail: manoj@pas.rochester.edu [Department of Astronomy, University of Texas at Austin, Austin, TX 78712-0259 (United States)

    2011-03-15

    We present 5-36 {mu}m mid-infrared spectra of 82 young stars in the {approx}2 Myr old Chamaeleon I star-forming region, obtained with the Spitzer Infrared Spectrograph (IRS). We have classified these objects into various evolutionary classes based on their spectral energy distributions and the spectral features seen in the IRS spectra. We have analyzed the mid-IR spectra of Class II objects in Chamaeleon I in detail, in order to study the vertical and radial structure of the protoplanetary disks surrounding these stars. We find evidence for substantial dust settling in most protoplanetary disks in Chamaeleon I. We have identified several disks with altered radial structures in Chamaeleon I, among them transitional disk candidates which have holes or gaps in their disks. Analysis of the silicate emission features in the IRS spectra of Class II objects in Cha I shows that the dust grains in these disks have undergone significant processing (grain growth and crystallization). However, disks with radial holes/gaps appear to have relatively unprocessed grains. We further find the crystalline dust content in the inner ({approx}<1-2 AU) and the intermediate ({approx}<10 AU) regions of the protoplanetary disks to be tightly correlated. We also investigate the effects of accretion and stellar multiplicity on the disk structure and dust properties. Finally, we compare the observed properties of protoplanetary disks in Cha I with those in slightly younger Taurus and Ophiuchus regions and discuss the effects of disk evolution in the first 1-2 Myr.

  16. Life and Death of Young Dense Star Clusters near the Galactic Center

    E-print Network

    Simon Portegies Zwart; Stephen McMillan; Holger Baumgardt

    2004-03-05

    We discuss the structural change and degree of mass segregation of young dense star clusters within about 100pc of the Galactic center. In our calculations, which are performed with GRAPE-6, the equations of motion of all stars and binaries are calculated accurately but the external potential of the Galaxy is solved (semi)analytically. The simulations are preformed to model the Arches star cluster. We find that star clusters with are less strongly perturbed by the tidal field and dynamical friction are much stronger affected by mass segregation; resulting in a significant pile-up of massive stars in the cluster center. At an age of about 3.5Myr more than 90 per cent of the stars more massive than ~10Msun are concentrated within the half-mass radius of the surviving cluster. Star clusters which are strongly perturbed by the tidal field of the parent Galaxy are much less affected by mass segregation.

  17. 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: gallardo@das.uchile.cl, E-mail: ldelvall@das.uchile.cl, E-mail: mtruiz@das.uchile.cl [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile)

    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.

  18. Identification and Analysis of Young Star Cluster Candidates in M31

    E-print Network

    Benjamin F. Williams; Paul W. Hodge

    2001-05-29

    We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ~60 arcmin^2, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (~<5 pc) young (~10-200 Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximations of their reddenings and ages. We also look for patterns of cluster formation with galactocentric distance, but our rough estimates are not precise enough to reveal any clear patterns.

  19. Optical Spectroscopic Classification and Membership of Young M Dwarfs in Star-Forming Regions

    E-print Network

    F. C. Riddick; P. F. Roche; P. W. Lucas

    2007-08-09

    The spectral type is a key parameter in calibrating the temperature which is required to estimate the mass of young stars and brown dwarfs. We describe an approach developed to classify low-mass stars and brown dwarfs in the Trapezium Cluster using red optical spectra, which can be applied to other star-forming regions. The classification uses two methods for greater accuracy: the use of narrowband spectral indices which rely on the variation of the strength of molecular lines with spectral type and a comparison with other previously classified young, low-mass objects in the Chamaeleon I star-forming region. We have investigated and compared many different molecular indices and have identified a small number of indices which work well for classifying M-type objects in nebular regions. The indices are calibrated for young, pre-main sequence objects whose spectra are affected by their lower surface gravities compared with those on the main sequence. Spectral types obtained are essentially independent of both reddening and nebular emission lines. Confirmation of candidate young stars and brown dwarfs as bona fide cluster members may be accomplished with moderate resolution spectra in the optical region by an analysis of the strength of the gravity-sensitive Na doublet. It has been established that this feature is much weaker in these very young objects than in field dwarfs. A sodium spectral index is used to estimate the surface gravity and to demonstrate quantitatively the difference between young (1-2Myr) objects, and dwarf and giant field stars.

  20. Spectral Characteristics of Young Stars Associated with the Sh2-296 Nebula

    NASA Astrophysics Data System (ADS)

    Fernandes, Beatriz; Gregorio-Hetem, Jane

    Aiming to contribute to the understanding of star formation and evolution in the Canis Major (CMa R1) Molecular Clouds Complex, we analyze the spectral characteristics of a population of young stars associated with the arc-shaped nebula Sh2-296. Our XMM/Newton observations detected 109 X-ray sources in the region and optical spectroscopy was performed with Gemini telescope for 85 optical counterparts. We identified and characterized 51 objects that present features typically found in young objects, such as H? emission and strong absorption on the Li I line.

  1. A NEW METHOD TO IDENTIFY NEARBY, YOUNG, LOW-MASS STARS

    SciTech Connect

    Rodriguez, David R.; Zuckerman, B. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Bessell, M. S. [Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Kastner, Joel H., E-mail: drodrigu@astro.ucla.edu [Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2011-02-01

    We describe a new method to identify young, late-type stars within {approx}150 pc of the Earth that employs visual or near-infrared (NIR) data and the GALEX GR4/5 database. For spectral types later than K5, we demonstrate that the ratio of GALEX near-ultraviolet to visual and NIR emission is larger for stars with ages between 10 and 100 Myr than for older, main-sequence stars. A search in regions of the sky encompassing the TW Hya and Scorpius-Centaurus Associations has returned 54 high-quality candidates for follow up. Spectroscopic observations of 24 of these M1-M5 objects reveal Li 6708 A absorption in at least 17 systems. Because GALEX surveys have covered a significant fraction of the sky, this methodology should prove valuable for future young star studies.

  2. A Parameter Study of the Dust and Gas Temperature in a Field of Young Stars

    E-print Network

    Andrea Urban; Neal J. Evans II; Steven D. Doty

    2007-10-21

    We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using Dusty, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with Dusty, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.

  3. Characterization of young field stars in the vicinity of the CO Cepheus void

    NASA Astrophysics Data System (ADS)

    Klutsch, A.; Montes, D.; Guillout, P.; Frasca, A.; Pineau, F.-X.; Grosso, N.; Marilli, E.; López-Santiago, J.

    2012-12-01

    After mixing in the Galactic plane, young stars are barely discernible from old ones. Nonetheless, the characterization of stars in the RasTyc} sample has ledto the discovery of several sources whose lithium content is higher than that of the Pleiades cluster members. In the locus of the CO Cepheus void, we identified four comoving T Tauri stars within a few degrees. They likely form a new young association. Looking for the presence of further members, we performed selections through multivariate analysis. We focused on the late-type stars in the field, which are identified as the optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources and are in a 30^circ-wide region encompassing this new moving group. Based on our spectroscopic observations of this dataset, we identified two distinct populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster are mostly projected in front of the Galactic plane, the youngest stars are mainly located towards the sky area surrounding the CO Cepheus void. The latter stars have an age of about 5-15 Myr, which is rather similar to that derived for the four comoving T Tauri stars previously found in this region. The discovery and characterization of all the young stars in the field are of great importance to have new insights into the process of stellar formation outside the typical star-forming regions. The Gaia mission will certainly shed light on this issue and on the origin of this group that could be related to the Cepheus-Cassiopeia complex.

  4. Dense cores in dark clouds - Young embedded stars at 2 micrometers

    NASA Technical Reports Server (NTRS)

    Benson, P. J.; Myers, P. C.; Wright, E. L.

    1984-01-01

    Twenty-five visually opaque regions which contain strong sources of NH3 (1,1) line emission (dense cores) have been surveyed for evidence of associated stars at two microns. Five such stars have been found, of which three - in B5, L1489, and L1582 - are optically invisible and probably embedded in their associated cores. The stars in B5 and L1489 have 2-100 micron spectra and luminosity similar to those of HL Tau, a very young T Tauri star. These stars probably formed in the cores where they are now seen. These results tend to confirm earlier suggestions that low-mass stars form in dense cores.

  5. IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 pc. II. DISTANCES, KINEMATICS, AND GROUP MEMBERSHIP

    SciTech Connect

    Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Anglada-Escude, Guillem [Institut fuer Astrophysik, Universitaet Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Liu, Michael C.; Bowler, Brendan P. [Institute for Astronomy, University of Hawaii at Manoa 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Weinberger, Alycia J.; Boss, Alan P. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Reid, I. Neill [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Tamura, Motohide, E-mail: shkolnik@lowell.edu [National Astronomical Observatory of Japan, Tokyo (Japan)

    2012-10-10

    We have conducted a kinematic study of 165 young M dwarfs with ages of {approx}<300 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 {approx}<25 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 ({approx}<3 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 {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages {approx}<150 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.

  6. Evolution of the Central Stars of Young Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Hajduk, M.; van Hoof, P. A. M.; Zijlstra, A. A.

    2015-06-01

    The evolution of central stars of planetary nebulae was hitherto documented in just a few cases. We look for evolutionary changes of the [O iii] 5007 Å line flux in the spectra of planetary nebulae. We compared nebular fluxes collected over a time interval of a decade or more. We used literature data and newly obtained spectra. A grid of Cloudy models was computed using existing evolutionary models and compared with the observations. The observed evolution of the [O iii] 5007 Å/rmH? line flux ratio is consistent with the evolutionary model calculations for H-rich central stars. Low-excitation planetary nebulae with [WR]-type and wels central stars show slower evolution than their coutnerparts containing H-rich central stars.

  7. The Role of Environment in Star Formation: Young Clusters Forming in Isolation

    NASA Astrophysics Data System (ADS)

    Peterson, D.; Gutermuth, R.; Bourke, T.

    2011-05-01

    We present preliminary results from a study of a large sample of Bok globules that have been observed with the NASA Spitzer Space Telescope. We identify and classify young stellar objects using Spitzer and near-infrared 2MASS photometry, and will present the ratio of Class I to Class II YSOs in each of the regions. In addition, near-infrared extinction maps will be presented. The stellar populations will be used, along with the known gas masses of these clouds to estimate the fraction of the gas from a molecular cloud that typically ends up as stars. The initial conditions for the formation of a single star, binary or cluster of stars can be constrained, and with an estimate of the age from theoretical models, the time it takes a star (or a cluster of stars) to form can also be constrained, as well as the timescales for the various evolutionary states. Bok globules are unique because they are simple environments, free from the confusing effects of winds and external turbulence that are often seen in young clusters embedded within larger, star-forming complexes. As part of our study, we will compare these simple structures, which span a wide range of evolutionary states, with more complex bright-rimmed clouds, which are strongly influenced by nearby O and B stars, ultimately studying the role of environment in star formation.

  8. The Role of Environment in Star Formation: Young Clusters forming in Isolation

    NASA Astrophysics Data System (ADS)

    Peterson, D.; Allen, L.; Gutermuth, R.; Bourke, T.

    We present preliminary results from a study of a large sample of Bok globules that have been observed with the NASA Spitzer Space Telescope. We identify and classify young stellar objects using Spitzer and near-infrared 2MASS photometry, and will present the ratio of Class I to Class II YSOs in each of the regions. In addition, near-infrared extinction maps will be presented. The stellar populations will be used, along with the known gas masses of these clouds to estimate the fraction of the gas from a molecular cloud that typically ends up as stars. The initial conditions for the formation of a single star, binary or cluster of stars can be constrained, and with an estimate of the age from theoretical models, the time it takes a star (or a cluster of stars) to form can also be constrained,as well as the timescales for the various evolutionary states. Bok globules are unique because they are simple environments, free from the confusing effects of winds and external turbulence that are often seen in young clusters embedded within larger, star-forming complexes. As part of our study, we will compare these simple structures, which span a wide range of evolutionary states, with more complex bright-rimmed clouds, which are strongly influenced by nearby O and B stars, ultimately studying the role of environment in star formation.

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

    Microsoft Academic Search

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

    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

  10. Analysis of MOST light curves of five young stars in Taurus-Auriga and Lupus~3 Star Forming Regions

    E-print Network

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

    2011-01-01

    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 Tau stars, V410 Tau, V987 Tau and Lupus 3-14; for another spotted WTTS, Lupus 3-48, the data are consistent with a rigidly rotating surface (k=0). Three flares of similar rise (4 min 30 sec) and decay (1 h 45 min) times were detected in the light curve of Lupus 3-14. The brightness of the classical T Tau star RY Tau continuously decreased over 3 weeks of its observations with a variable modulation not showing any obvious periodic signal.

  11. X-Ray Plasma Diagnostics of Stellar Winds in Young Massive Stars

    E-print Network

    N. S. Schulz; C. R. Canizares; D. P. Huenemoerder; J. Lee; K. Tibetts

    2001-10-01

    High resolution X-ray spectra of very young massive stars opened a new chapter in the diagnostics and understanding of the properties of stellar wind plasmas. Observations of several very young early type stars in the Orion Trapezium demonstrated that the conventional model of shock heated plasmas in stellar winds is not sufficient to explain the observed X-ray spectra. Detailed X-ray line diagnostics revealed extreme temperatures in some of the candidates as well as evidence for high plasma densities. It is also evident from high resolution spectra of more conventional early type stars, that not all show such extreme characteristics. However, the fact that some of the stars show hot and dense components and some do not requires more understanding of the physical processes involved in stellar wind emissions. The Orion Trapezium stars distinguish themselves from all the others by their extreme youth. By comparing the diverse spectral properties of theta Ori A and theta Ori E with those of theta Ori C, we further demonstrate that X-ray spectral properties of very young massive stars are far from understood.

  12. The similar emission-line spectra of the young star LkH-alpha 101 and the hypergiant MWC 300

    NASA Astrophysics Data System (ADS)

    Hamann, Fred; Persson, S. E.

    1989-12-01

    High-resolution spectra from 0.63 to 1.75 microns are presented, showing that the luminous young star LkH-alpha 101 and the post-main-sequence hypergiant MWC 300 have very similar emission-line properties. Tables are given of line measurements and identifications. It is found that, in spite of their different histories, these stars have similar conditions of density, temperature, kinematics, and possibly geometry in their line-emitting envelopes. The results support models of hypergiants and luminous young stars which both invoke dense equatorial disks and suggest that disk structures around some evolved hot young stars are created by dense equatorial winds.

  13. The Collimation and Propagation of Jets from Young Stars

    Microsoft Academic Search

    Thomas Ray

    1994-01-01

    It is over ten years since the discovery of young stellar object (YSO) jets. Although clearly there is an association between these jets and YSO disks, their collimation mechanism is poorly understood. Moreover while radiative shocks are known to be the source of their emission, the origin of these shocks is uncertain. To address these problems, we propose to study

  14. Young stars and protostellar cores near NGC 2023

    Microsoft Academic Search

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

    2009-01-01

    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

  15. M-dwarf Rapid Rotators and the Detection of Relatively Young Multiple M-Star Systems

    NASA Astrophysics Data System (ADS)

    Rappaport, S.; Swift, J.; Levine, A.; Joss, M.; Sanchis-Ojeda, R.; Barclay, T.; Still, M.; Handler, G.; Oláh, K.; Muirhead, P. S.; Huber, D.; Vida, K.

    2014-06-01

    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 rot, of <2 days, and 110 with P 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. 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: sar@mit.edu, E-mail: mattjoss@mit.edu, E-mail: rsanchis86@gmail.com [Department of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); 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.

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

    E-print Network

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

    2015-04-28

    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.

  18. Gravitational Slingshot of Young Massive Stars in Orion

    E-print Network

    Chatterjee, Sourav

    2012-01-01

    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 amongst the ONC's ~1000 members are: \\theta^1 Ori C, the most massive binary in the cluster with stars of masses 38 and 9 msun (Kraus et al. 2009); the Becklin-Neugebauer (BN) object, a 30 km/s runaway star of ~8 msun (Tan 2004); and the Kleinmann-Low (KL) nebula protostar, a highly-obscured, ~15 msun object still accreting gas while also driving a powerful, apparently ``explosive' outflow (Allen & Burton 1993). 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 ~10^7 numerical experiments of gravitational interactions of the \\theta1C 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 ma...

  19. Core dissolution and the dynamics of massive stars in young stellar clusters

    E-print Network

    S. G. Vine; I. A. Bonnell

    2003-02-21

    We investigate the dynamical effects of rapid gas expulsion from the core of a young stellar cluster. The aims of this study are to determine 1) whether a mass-segregated core survives the gas expulsion and 2) the probable location of any massive stars that have escaped from the core. Feedback from massive stars is expected to remove the gas from the core of the cluster first, as that is where most massive stars are located. We find that gas expulsion has little effect on the core for a core star formation efficiency, of greater than 50%. For lower values of star formation efficiency down to 20%, a reduced core survives containing the majority of the massive stars while some of them are dispersed into the rest of the cluster. In fact we find that ejected stars migrate from radial to tangential orbits due to stellar encounters once they leave the core. Thus, the location of massive stars outside of the core does not exclude their forming in the dense cluster core. Few massive stars are expected to remain in the core for a star formation efficiency lower than 20%.

  20. Investigating the rotational evolution of young, low-mass stars using Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Vasconcelos, M. J.; Bouvier, J.

    2015-06-01

    Context. Young stars rotate well below break-up velocity, which is thought to result from the magnetic coupling with their accretion disk. Aims: We investigate the rotational evolution of young stars under the disk-locking hypothesis through Monte Carlo simulations. Methods: Our simulations included 280 000 stars, each of which was initially assigned a mass, a rotational period, and a mass accretion rate. The mass accretion rate depends on both mass and time, following power-law indices of 1.4 and -1.5, respectively. A mass-dependent accretion threshold was defined below which a star was considered as diskless, which resulted in a distribution of disk lifetimes that matches observations. Stars were evolved at constant angular spin rate while accreting and at constant angular momentum when they became diskless. Results: Starting with a bimodal distribution of periods for disk and diskless stars, we recovered the bimodal period distribution seen in several young clusters. The short-period peak mostly consists of diskless stars, and the long-period peak is mainly populated by accreting stars. Both distributions, however, present a long tail toward long periods, and a population of slowly rotating diskless stars is observed at all ages. We reproduced the observed correlations between disk fraction and spin rate, as well as between IR excess and rotational period. The period-mass relation we derived from the simulations only shows the same global trend as observed in young clusters when we released the disk-locking assumption for the lowest mass stars. Finally, we find that the time evolution of median specific angular momentum follows a power-law index of -0.65 for accreting stars, as expected from disk locking, and of -0.53 for diskless stars, a shallower slope that results from a wide distribution of disk lifetimes. At the end of the accretion phase, our simulations reproduce the angular momentum distribution of the low-mass members of the 13 Myr h Per cluster. Conclusions: Using observationally documented distributions of disk lifetimes, mass accretion rates, and initial rotation periods, and evolving an initial population from 1 to 12 Myr, we reproduced the main characteristics of pre-main sequence angular momentum evolution, which supports the disk-locking hypothesis.

  1. 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. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Christopher, Micol H.; Scoville, Nick Z., E-mail: jgreissl@as.arizona.ed [California Institute of Technology, Pasadena, CA 91125 (United States)

    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.

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

    SciTech Connect

    Durré, Mark; Mould, Jeremy, E-mail: mdurre@swin.edu.au [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia)

    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.

  3. MAD Science Demonstration Proposal Young massive star clusters in the Carina Nebula

    E-print Network

    Liske, Jochen

    MAD Science Demonstration Proposal Young massive star clusters in the Carina Nebula Investigators MPIA Heidelberg henning@mpia.de Abstract: The Carina Nebula (NGC 3372) is a very spectacular feature in the central part of the Carina Nebula. The high-mass population of Trumpler 16, the older of the two, includes

  4. Stellar contents and star formation in the young open cluster Stock 8

    Microsoft Academic Search

    Jessy Jose; A. K. Pandey; D. K. Ojha; K. Ogura; W. P. Chen; B. C. Bhatt; S. K. Ghosh; H. Mito; G. Maheswar; Saurabh Sharma

    2008-01-01

    We present UBVIc CCD photometry of the young open cluster Stock 8 with the aim of studying its basic properties such as the amount of interstellar extinction, distance, age, stellar contents and initial mass function (IMF). We also studied the star formation scenario in this region. From optical data, the radius of the cluster is found to be ~6 arcmin

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

    Microsoft Academic Search

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

    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

  6. VizieR Online Data Catalog: Red MSX survey (RMS) massive young stars (Urquhart+, 2011)

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Hoare, M. G.; Lumsden, S. L.; Oudmaijer, R. D.; Rathborne, J. M.; Mottram, J. C.; Davies, B.; Stead, J. J.

    2011-08-01

    Parameters for the GRS cloud and RMS sources including positions, assigned distances, distance from the Galactic mid-plane and the Galactic centre, bolometric luminosity and cloud masses for a sample of young massive stars located in the northern Galactic plane (18

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

    SciTech Connect

    Schlieder, Joshua E.; Simon, Michal [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Lepine, Sebastien, E-mail: michal.simon@stonybrook.edu, E-mail: schlieder@mpia-hd.mpg.de, E-mail: lepine@amnh.org [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

    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.

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

    SciTech Connect

    Matt, Sean P. [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette (France); Pinzon, Giovanni [Observatorio Astronomico Nacional, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota (Colombia); Greene, Thomas P. [NASA Ames Research Center, M.S. 245-6, Moffett Field, CA 94035-1000 (United States); Pudritz, Ralph E., E-mail: sean.matt@cea.fr, E-mail: thomas.p.greene@nasa.gov, E-mail: gapinzone@unal.edu.co, E-mail: pudritz@physics.mcmaster.ca [Physics and Astronomy Department, McMaster University, Hamilton, ON L8S 4M1 (Canada)

    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.

  9. 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

  10. Instabilities in Very Young Neutron Stars: Electron Fraction

    NSDL National Science Digital Library

    Pamela ONeil

    1994-02-12

    This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the mixing of composition which results from the convective motions. The variable plotted is the electron fraction Ye, which ranges from 0.2 to 0.5.

  11. Young Stars and Protostellar Cores near NGC 2023

    Microsoft Academic Search

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

    2009-01-01

    We investigate the young (proto)stellar population in NGC 2023 and the L 1630\\u000amolecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS\\u000aarchive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA\\u000aobservations of one of the Class 0 protostars, NGC 2023 MM1. We have performed\\u000aphotometry of all IRAC and MIPS images, and

  12. A X-ray view of the young star population in CMa R1

    NASA Astrophysics Data System (ADS)

    Santos-Silva, T.; Gregorio-Hetem, J.; Montmerle, T.

    2014-10-01

    In previous works we studied the star formation scenario in the molecular cloud Canis Major R1 (CMa R1), revealing the existence of young stellar groups near the Be stars Z CMa and GU CMa. Using data from the ROSAT X-ray satellite, Gregorio-Hetem et al. (2009) - GH2009 - discovered in this region young stellar objects (YSOs) mainly grouped in two clusters of different ages. 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' diameter, with some overlap - Figure 1) have been observed with the XMM-Newton satellite that has a sensitivity about 10 times better than ROSAT.

  13. Near-IR integral field spectroscopy of ionizing stars and young stellar objects on the borders of H II regions

    Microsoft Academic Search

    F. Martins; M. Pomarès; L. Deharveng; A. Zavagno; J. C. Bouret

    2010-01-01

    Aims: We study three Galactic H ii regions - RCW 79, RCW 82, and RCW 120 - where triggered star formation is taking place. Two stellar populations are observed: the ionizing stars of each H ii region and young stellar objects on their borders. Our goal is to show that they represent two distinct populations, as expected from successive star-forming

  14. 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.

  15. 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 [Departement de physique and Observatoire du Mont-Megantic, Universite de Montreal, Montreal, QC H3C 3J7 (Canada)] [Departement de physique and Observatoire du Mont-Megantic, Universite de Montreal, Montreal, QC H3C 3J7 (Canada); Riedel, Adric, E-mail: malo@astro.umontreal.ca, E-mail: doyon@astro.umontreal.ca, E-mail: david@astro.umontreal.ca, E-mail: artigau@astro.umontreal.ca, E-mail: gagne@astro.umontreal.ca, E-mail: baron@astro.umontreal.ca, E-mail: riedel@phy-astr.gsu.edu [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)] [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

    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.

  16. The Environment Around Young Stars in Molecular Cores

    NASA Astrophysics Data System (ADS)

    Gibb, Andy

    1996-11-01

    It has been established in recent years that molecular clouds exhibit a hierarchichal structure (Goldsmith). This structure can be loosely categorized in the following way: molecular clouds are composed of 'cores', which in turn are composed of 'clumps', within which stars form. The cores have mean molecular hydrogen densities of a few 104/cu cm and radii 0.1-0.5 pc. These structures are often traced by ammonia emission (Benson & Myers). Higher resolution observations in the emission of HCO(+), CS etc. reveal substructure within these cores. The clumps are more compact (r approximately 0.05 pc or less) and somewhat denser (nH2 approximately 106/cu cm). The ultimate signature of the (proto)stars themselves, such as infrared and radio emission, arises from within the clumps.

  17. Near-Infrared Variability in Young Stars with Disks

    Microsoft Academic Search

    Thomas Rice; S. J. Wolk; C. Aspin

    2011-01-01

    We present the results from the analysis of 120 epoch time-series photometry of a 1 square degree region of the Lynds 1003 dark cloud in the Cygnus OB7 association. Using the Wide-Field imaging camera (WFCAM) on UKIRT we were able to obtain almost-nightly J,H,K' photometry over three observing seasons of over 100,000 stars with photometric uncertainty better than 0.02 mag

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

    SciTech Connect

    Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Leitherer, Claus, E-mail: Emily.Levesque@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    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 H?, H?, and Br? 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.

  19. 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.

  20. Lunar Occultations of Young Stars in Southern Taurus

    NASA Astrophysics Data System (ADS)

    Simon, M.; Beck, Tracy L.; Greene, T. P.; Howell, R. R.; Lumsden, S.; Prato, L.

    1999-03-01

    We have obtained lunar occultation observations of NTT 042916+1751, V826 Tau, L1551-55, HN Tau, DQ Tau, and DR Tau by high-speed single-channel photometry in the IR K band. We detect no companions in the angular separation range 0.020"-10" to a magnitude limit typically 2 mag fainter than the target. Additional occultation observations of GG Tau and HL Tau using IR cameras at K reveal no new stars in the GG Tau A binary within ~2 mag of the primary in the range ~0.08"-10" and no companion of HL Tau within 1.5 mag and ~0.09"-10". The binary fraction of the 56 systems in the Taurus star formation region that have been surveyed by lunar occultation and imaging is 61%. Of the 56 systems, 53 have been surveyed for companions in the angular separation range 0.020"-10". Their binary frequency is at least 1.4+/-0.3 times that measured by Duquennoy & Mayor for the nearby F and G stars. These values for the binary frequency are lower bounds because they contain no corrections for incompleteness.

  1. Empirical Limits on Radial Velocity - Planet Detection for Young Stars

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne; Isaacson, Howard; Marcy, Geoffrey; Barenfeld, Scott; Fischer, Debra; Howard, Andrew

    2015-01-01

    We report initial results from our long term search using precision radial velocities for planetary-mass companions located within a few AU of stars younger than the Sun. Based on a sample of >150 stars, we define a floor in the radial velocity scatter, ?_{RV}, as a function of the chromospheric activity level R'_{HK}. This lower bound to the jitter, which increases with increasing stellar activity, sets the minimum planet mass that could be detected. Adopting a median activity-age relationship reveals the astrophysical limits to planet masses discernable via radial velocity monitoring, as a function of stellar age. Considering solar-mass primaries having the mean jitter-activity level, when they are younger than 100 / 300 / 1000 Myr, the stochastic jitter component in radial velocity measurements restricts detectable companion masses to > 0.3 / 0.2 / 0.1 M_{Jupiter}. These numbers require a large number - several tens - of radial velocity observations taken over a time frame longer than the orbital period. Lower companion mass limits can be achieved for stars with less than the mean jitter and/or with an increased number of observations.

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

    SciTech Connect

    Van den Heuvel, E. P. J. [Astronomical Institute Anton Pannekoek, University of Amsterdam, P.O. Box 94249, 1090 GE Amsterdam (Netherlands); Portegies Zwart, S. F. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)

    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.

  3. Massive Young Stellar Objects in high-mass star-forming regions

    E-print Network

    Arjan Bik; Lex Kaper; Wing-Fai Thi; Rens Waters

    2005-06-14

    High-quality K-band spectra of point sources, deeply embedded in massive star-forming regions, have revealed a population of 20 young massive stars showing no photospheric absorption lines, but only emission lines. The K-band spectra exhibit one or more features commonly associated with massive Young Stellar Objects surrounded by circumstellar material: a very red color (J-K) = 2, CO bandhead emission, hydrogen emission lines (sometimes doubly peaked), and FeII and/or MgII emission lines. The CO emission comes from a relatively dense (~10^10 cm^(-3)) and hot (T ~ 2000-5000 K) region, sufficiently shielded from the intense UV radiation field of the young massive star. Modeling of the CO-first overtone emission shows that the CO gas is located within 5 AU of the star. The hydrogen emission is produced in an ionized medium exposed to UV radiation. The best geometrical configuration is a dense and neutral circumstellar disk causing the CO bandhead emission, and an ionized upper layer where the hydrogen lines are produced. We argue that the circumstellar disk is likely a remnant of the accretion via a circumstellar disk.

  4. A Survey of 10-Micron Silicate Emission from Dust around Young Sun-Like Stars

    E-print Network

    Eric Gaidos; Christopher Koresko

    2003-07-22

    We obtained low resolution (R = 100) mid-infrared (8-13 micron wavelengths) spectra of 8 nearby young main sequence stars with the Keck 1 telescope and Long-Wavelength Spectrometer (LWS) to search for 10 micron silicate (Si-O stretch) emission from circumstellar dust. No stars exhibited readily apparent emission: Spectra were then analyzed by least-squares fitting of a template based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to constrain the level of silicate emission to a threshold ten times below what was previously possible from space. We found one star, HD 17925, with a spectrum statistically different from its calibrator and consistent with a silicate emission peak of 7% of the photosphere at a wavelength of 10 microns. Excess emission at 60 microns from this star has already been reported.

  5. Angular momentum evolution of young low-mass stars and brown dwarfs: observations and theory

    E-print Network

    Bouvier, J; Mohanty, S; Scholz, A; Stassun, K G; Zanni, C

    2013-01-01

    This chapter aims at providing the most complete review of both the emerging concepts and the latest observational results regarding the angular momentum evolution of young low-mass stars and brown dwarfs. In the time since Protostars & Planets V, there have been major developments in the availability of rotation period measurements at multiple ages and in different star-forming environments that are essential for testing theory. In parallel, substantial theoretical developments have been carried out in the last few years, including the physics of the star-disk interaction, numerical simulations of stellar winds, and the investigation of angular momentum transport processes in stellar interiors. This chapter reviews both the recent observational and theoretical advances that prompted the development of renewed angular momentum evolution models for cool stars and brown dwarfs. While the main observational trends of the rotational history of low mass objects seem to be accounted for by these new models, a n...

  6. Structure and Evolution of Circumstellar Disks Around Young Stars: New Views from ISO

    E-print Network

    Michael R. Meyer; Steven V. W. Beckwith

    2000-01-31

    A question central to understanding the origin of our solar system is: how do planets form in circumstellar disks around young stars? Because of the complex nature of the physical processes involved, multi-wavelength observations of large samples will be required in order to obtain a complete answer to this question. Surveys undertaken with ISO have helped to solve pieces of this puzzle in addition to uncovering new mysteries. We review a variety of studies aimed at understanding; i) the physical structure and composition of circumstellar disks commonly found surrounding young stellar objects; and ii) the evolution of circumstellar disks from the active accretion phase to post-planet building debris disks.

  7. Eruptive dermal clear cell desmo-plastic mesenchymal tumors with perivascular myoid differentiation in a young boy. A clinical, histopathologic, immunohistochemical and electron microscopy study of 17 lesions.

    PubMed

    Tomasini, Carlo; Metze, Dieter; Osella-Abate, Simona; Novelli, Mauro; Kutzner, Heinz

    2014-02-01

    Clear cell tumors of the skin are observed in a wide variety of benign and malignant conditions with different histogenesis, sharing the presence of cells with abundant clear cytoplasm. Herein, we report the clinicopathologic features of a healthy young patient affected by asymptomatic, eruptive and disseminated, benign clear cell dermal tumors since early infancy. Neither family history nor genetic testing and counseling provided further useful information. The lesions were mostly confined to the face and lower left extremity with pink teleangiectatic papules and small nodules. Over a 4-year period, a total of 16 different cutaneous lesions were biopsied and histopathologic and immunohistochemical studies carried out; an additional lesion was also removed for electron microscopy examination. Histopathology evidenced multiple perivascular growths of spindle to oval and round cells intermingled with clear/granular cells throughout the dermis, with prominent desmoplasia and numerous capillary-like vessels with focal hemangiopericytoma-like features. Immunohistochemical neoplastic cells were uniformly positive for h-caldesmon and focally smooth muscle ?-actin and CD13 indicating myoid differentiation whereas the consistent diffuse cytoplasmic staining for lysosome antigen, such as CD68PG-M1 and NKI/C3 along with the ultrastructural findings supported the view of a lysosome-mediated apoptotic process. The differential diagnosis with other clear cell cutaneous neoplasms is discussed. PMID:24117956

  8. Acneiform eruptions.

    PubMed

    Dessinioti, Clio; Antoniou, Christina; Katsambas, Andreas

    2014-01-01

    Is it acne or is it not? When this question arises, we can presume that we have crossed the boundaries of "acneiform eruptions" of the face. Although acne may be considered a condition fairly easy to diagnose, it is not rare for the practicing dermatologist or the general physician to wonder when faced with an acneiform eruption before establishing a diagnosis. In this review, we address facial acneiform eruptions in children and in adults, including perioral dermatitis, granulomatous periorificial dermatitis, nevus comedonicus, acne cosmetica, rosacea, demodicosis, folliculitis, acneiform presentation of cutaneous lymphomas, and drug-induced [epidermal growth factor receptor (EGFR) inhibitors, steroids, etc.] acneiform eruptions, along with their diagnosis and therapeutic approaches. The major distinguishing factor in acneiform eruptions is that, in contrast to acne, there are no comedones (whiteheads or blackheads). PMID:24314375

  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. Broad Halpha wings in Nebulae around Evolved Stars and in Young Planetary Nebulae

    E-print Network

    A. Arrieta; S. Torres-Peimbert

    2003-02-19

    Eleven objects that have been reported as proto-planetary nebula or as young planetary nebulae that show very extended Halpha wings are presented. The extension of these wings is larger than 800 km/s. Data for two symbiotic stars that show this same characteristic is also presented. Raman scattering is the mechanism that best explains the wings in 10 of the PNe and in the 2 symbiotic stars. In the PN IRAS 20462+3416 the wing profile can be explained by very intense stellar wind.

  11. K-Star rapid rotators and the detection of relatively young multiple K-Star systems

    E-print Network

    Joss, Matthew Albert Henry

    2014-01-01

    In this thesis, I searched through the Kepler light curves of 14,440 K-star targets for evidence of periodicities that indicate rapid stellar rotation. Many Kepler M, K, and G stars show modulations in flux due to rotating ...

  12. C32, A Young Star Cluster in IC 1613

    E-print Network

    Wyder, T K; Cole, A; Wyder, Ted K; Hodge, Paul W; Cole, Andrew

    2000-01-01

    The Local Group irregular galaxy IC 1613 has remained an enigma for manyyears because of its apparent lack of star clusters. We report the successfulsearch for clusters among several of the candidate objects identified manyyears ago on photographic plates. We have used a single HST WFPC2 pointing anda series of images obtained with the WIYN telescope under exceptional seeingconditions, examining a total of 23 of the previously published candidates. Allbut six of these objects were found to be either asterisms or backgroundgalaxies. Five of the six remaining candidates possibly are small, sparseclusters and the sixth, C32, is an obvious cluster. It is a compact, youngobject, with an age of less than 10 million years and a total absolutemagnitude of M_V = -5.78+/-0.16 within a radius of 13 pc.

  13. Statistical fractal analysis of 25 young star clusters

    NASA Astrophysics Data System (ADS)

    Gregorio-Hetem, J.; Hetem, A.; Santos-Silva, T.; Fernandes, B.

    2015-04-01

    A large sample of young stellar groups is analysed to investigate their clustering properties and dynamical evolution. A comparison of the Q statistical parameter, measured for the clusters, with the fractal dimension estimated for the projected clouds, shows that 52 per cent of the sample has substructures and tends to follow the theoretically expected relation between clusters and clouds, according to calculations for the artificial distribution of points. The fractal statistics was also compared to structural parameters, revealing that clusters having a radial density profile show a trend of parameter overline{s} increasing with mean surface stellar density. The core radius of the sample, as a function of age, follows a similar distribution to that observed in stellar groups of the Milky Way and other galaxies. They also have dynamical age, indicated by their crossing time, which is similar to unbound associations. The statistical analysis allowed us to separate the sample into two groups showing different clustering characteristics. However, they have the same dynamical evolution, since the whole sample has been revealed as expanding objects, for which the substructures seem to have not been erased. These results are in agreement with simulations that adopt low surface densities and models under supervirial conditions.

  14. The young open cluster Stock 16 - an example of star formation in an elephant trunk?

    Microsoft Academic Search

    D. G. Turner

    1985-01-01

    UBV photometry is presented for 33 stars in the young open cluster Stock 16 lying in the H II region RCW 75, and these observations are used to obtain new values for the E(B-V) = 0.49 + or - 0.01 reddening, 1.90 + or - 0.08 kpc distance and 3-5 x 10 to the 6th yr age of the cluster.

  15. Jets from young stars - CCD imaging, long-slit spectroscopy, and interpretation of existing data

    Microsoft Academic Search

    Reinhard Mundt; Edward W. Brugel; Thomas Buehrke

    1987-01-01

    High-velocity jets and collimated outflows are now recognized as phenomena commonly associated with young stars. New CCD imaging of five objects, and in particular spatially resolved spectroscopy of eight highly-collimated flows, are discussed. Through the CCD imaging, three new jets have been discovered. It is shown that several previously known Herbig-Haro objects have extended bow-shock-like structures. In most of the

  16. Fundamental properties of pre-main sequence stars in young, southern star forming regions: metallicities

    E-print Network

    David J. James; Claudio Melo; Nuno C. Santos; Jerome Bouvier

    2005-10-20

    Aims: The primary motivation for this project is to search for metal-rich star forming regions, in which, stars of super-solar metallicity will be created, as hopefully, will be extra-solar planets orbiting them ! Results: We find (pre-main sequence) model-dependent isochronal ages of the Lupus, Chamaeleon and CrA targets to be $9.1 \\pm 2.1$ Myr, $4.5 \\pm 1.6$ Myr and $9.0 \\pm 3.9$ Myr respectively. The majority of the stars have Li I 6707.8A equivalent widths similar to, or above those of, their similar mass Pleiades counterparts, confirming their youthfulness. Most stars are kinematic members, either single or binary, of their regions. We find a mean radial velocity for objects in the Lupus cloud to be ${\\bar {RV}}=+2.6 \\pm 1.8$ km s$^{-1}$, for the Chamaeleon I & II clouds, ${\\bar {RV}}=+12.8 \\pm 3.6$ km s$^{-1}$ whereas for the CrA cloud, we find ${\\bar {RV}}=-1.1 \\pm 0.5$ km s$^{-1}$. All stars are coronally and chromospherically active, exhibiting X-ray and H$\\alpha$ emission levels marginally less, approximately equal or superior to that of their older IC 2602/2391 and/or Pleiades counterparts. All bar three of the targets show little or no signature of accretion from a circumstellar environment, according to their positions in a J$-$K/H$-$K$^{'}$ diagram. We have performed a metallicity analysis for 5 stars in Chamaeleon, 4 stars in Lupus and 3 stars in the CrA star forming regions. These results show that all three regions are slightly metal-poor, with marginally sub-solar metallicities, with $ = -0.11 \\pm 0.14$, $-0.10 \\pm 0.04$ & $-0.04 \\pm 0.05$ respectively.

  17. Optical and Near-Infrared Imaging of Young Binary Star Environments

    NASA Astrophysics Data System (ADS)

    Ménard, François; Stapelfeldt, Karl

    We review recent imaging results on the circumstellar matter of young binaries obtained using the Hubble Space Telescope (HST) and by PUEO, a ground-based adaptive optics (AO) system operating at CFHT. In the area of circumbinary disks, new results for GG Tau help form a more complete picture of this prototype system. However, HST images of the UY Aur ring indicate a more complex system than first thought. A new example of a circumstellar disk in a multiple star system has been found in HV Tau, joining HK Tau in this category. Examples of envelopes, outflow cavities, and jets are shown for several young binaries. About half of the nearby young binaries in our survey possess some kind of local nebulosity at optical or near-IR wavelengths.

  18. SPATIALLY EXTENDED BRACKETT GAMMA EMISSION IN THE ENVIRONMENTS OF YOUNG STARS

    SciTech Connect

    Beck, Tracy L. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bary, Jeffery S. [Colgate University, Department of Physics and Astronomy, 13 Oak Drive, Hamilton, NY 13346 (United States); McGregor, Peter J., E-mail: tbeck@stsci.ed, E-mail: jbary@colgate.ed, E-mail: peter@mso.anu.edu.a [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia)

    2010-10-20

    The majority of atomic hydrogen Br{gamma} emission detected in the spectra of young stellar objects is believed to arise from the recombination regions associated with the magnetospheric accretion of circumstellar disk material onto the forming star. In this paper, we present the results of a K-band integral field unit spectroscopic study of Br{gamma} emission in eight young protostars: CW Tau, DG Tau, Haro 6-10, HL Tau, HV Tau C, RW Aur, T Tau, and XZ Tau. We spatially resolve Br{gamma} emission structures in half of these young stars and find that most of the extended emission is consistent with the location and velocities of the known Herbig-Haro flows associated with these systems. At some velocities through the Br{gamma} line profile, the spatially extended emission comprises 20% or more of the integrated flux in that spectral channel. However, the total spatially extended Br{gamma} is typically less than {approx}10% of the flux integrated over the full emission profile. For DG Tau and Haro 6-10 S, we estimate the mass outflow rate using simple assumptions about the hydrogen emission region and compare this to the derived mass accretion rate. We detect extended Br{gamma} in the vicinity of the more obscured targets in our sample and conclude that spatially extended Br{gamma} emission may exist toward other stars, but unattenuated photospheric flux probably limits its detectability.

  19. Evidence for Warped Disks of Young Stars in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Bartko, H.; Martins, F.; Fritz, T. K.; Genzel, R.; Levin, Y.; Perets, H. B.; Paumard, T.; Nayakshin, S.; Gerhard, O.; Alexander, T.; Dodds-Eden, K.; Eisenhauer, F.; Gillessen, S.; Mascetti, L.; Ott, T.; Perrin, G.; Pfuhl, O.; Reid, M. J.; Rouan, D.; Sternberg, A.; Trippe, S.

    2009-06-01

    The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the clockwise system. The mean eccentricity of the clockwise system is 0.36 ± 0.06. The distribution of the counterclockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterclockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterclockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars.

  20. Planets around stars in young nearby associations. Radial velocity searches: a feasibility study and first results

    NASA Astrophysics Data System (ADS)

    Lagrange, A.-M.; Meunier, N.; Chauvin, G.; Sterzik, M.; Galland, F.; Lo Curto, G.; Rameau, J.; Sosnowska, D.

    2013-11-01

    Context. Stars in young nearby associations are the only targets that allow giant planet searches in the near future, at all separations by coupling indirect techniques, such as radial velocity (RV) and deep imaging. These stars are first priority targets for the forthcoming planet imagers on eight- to ten-metre class telescopes. Young stars rotate more rapidly and are more active than their older counterparts. Both effects can limit the ability to detect planets using RV. Aims: We wish to explore the planet detection abilities of a representative sample of stars in close and young associations with RV data and to explore the complementarity between this technique and direct imaging. Methods: We observed 26 such targets with spectral types from A to K and ages from 8 to 300 Myr with HARPS. We computed the detection limits with two methods, in particular, a method we have recently developed that takes the frequency distribution of the RV variations into account. We also attempted to improve the detection limits in a few cases by correcting for the stellar activity. Results: Our A-type stars RV show high-frequency variations due to pulsations, while our F-K stars clearly show activity with more or less complex patterns. For F-K stars, the RV jitter and vsini rapidly decrease with star age. The data allow us to search for planets with periods typically ranging from 1 day to 100 days, and up to more than 500 days in a few cases. Within the present detection limits, no planet was found in our sample. For the bulk of our F-K stars, the detection limits fall to sub-Jupiter masses. We show that these limits can be significantly improved by correcting even partially for stellar activity, down to a few Neptune masses for the least active stars. The detection limits on A-type stars can be significantly improved, down to a few Jupiter-mass planets, provided an appropriate observing strategy. We finally show the tremendous potential of coupling RV and adaptive-optics deep imaging results. Conclusions: The RV technique allows the detection of planets lighter than Jupiter, reaching a few Neptune masses around young stars aged typically 30 Myr or more. Detection limits increase at younger ages, but (sub-)Jupiter mass planets are still detectable. In the next few years, using complementary techniques will allow a full exploration of the Jupiter-mass planets' content of many of these stars. Based on observations made with the ESO3.6m/Harps spectrograph at La Silla.083.C-0794(ABCD); 084.C-1039(A); 084.C-1024(A).Appendices A and B are available in electronic form at http://www.aanda.orgTables of radial velocities 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/559/A83

  1. The structure of protoplanetary discs around evolving young stars

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders; Lambrechts, Michiel; Morbidelli, Alessandro

    2015-03-01

    The formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time scales of several million years. Small dust particles stick to each other to form pebbles, pebbles concentrate in the turbulent flow to form planetesimals and planetary embryos and grow to planets, which undergo substantial radial migration. All these processes are influenced by the underlying structure of the protoplanetary disc, specifically the profiles of temperature, gas scale height, and density. The commonly used disc structure of the minimum mass solar nebula (MMSN) is a simple power law in all these quantities. However, protoplanetary disc models with both viscous and stellar heating show several bumps and dips in temperature, scale height, and density caused by transitions in opacity, which are missing in the MMSN model. These play an important role in the formation of planets, since they can act as sweet spots for forming planetesimals via the streaming instability and affect the direction and magnitude of type-I migration. We present 2D simulations of accretion discs that feature radiative cooling and viscous and stellar heating, and they are linked to the observed evolutionary stages of protoplanetary discs and their host stars. These models allow us to identify preferred planetesimal and planet formation regions in the protoplanetary disc as a function of the disc's metallicity, accretion rate, and lifetime. We derive simple fitting formulae that feature all structural characteristics of protoplanetary discs during the evolution of several Myr. These fits are straightforward for applying to modelling any growth stage of planets where detailed knowledge of the underlying disc structure is required. Appendix A is available in electronic form at http://www.aanda.org

  2. An infrared coronagraphic search for substellar companions to young nearby stars

    NASA Astrophysics Data System (ADS)

    McCarthy, Chris

    2001-08-01

    This dissertation presents a comprehensive infrared coronagraphic search for substellar companions to stars. The research consists of: (1) a 102 star infrared survey using the Keck telescope, capable of detecting extrasolar brown dwarfs and planets typically more massive than 10 MJupiter , orbiting between about 75 and 300 AU, (2) a 178 star infrared survey at Steward and Lick Observatories, with optical followup from Keck Observatory, capable of detecting companions with masses greater than 30 MJupiter, orbiting between about 120 to 1200 AU and (3) a 24 star survey of two very young stellar associations TW Hydrae and MBM 12, capable of detecting companions down to 2 MJupiter, between about 25 and 1000 AU. These searches are the first to place limits on the frequency of massive planets orbiting beyond 75 AU, and the most sensitive to encompass such a large number of stars. This research resulted in the discovery of one brown dwarf companion, zero planets and 23 double stars. The frequency of brown dwarf companions to G, K & M stars orbiting between 75 and 300 AU is measured to be 1 +/- 1%, the most precise measurement of this quantity to date. The frequency of massive (>30MJupiter) brown dwarf companions is found to be 0.6% +/- 0.6%. The frequency of giant planet companions with masses between 5 and 10 MJupiter orbiting between 75 and 300 AU is measured here for the first time to be no more than 3%. Taken together with results of other searches encompassing a wide range of orbital separations, this research implies that objects with masses between 12 and 75 MJupiter form very rarely as companions to stars. Theories of star formation which could explain these data are only now beginning to emerge.

  3. Puzzling wind properties of young massive stars in SMC-N81

    E-print Network

    F. Martins; D. Schaerer; D. J. Hillier; M. Heydari-Malayeri

    2004-03-17

    We present a quantitative study of the stellar and wind properties of massive stars in the compact star forming region SMC-N81. Non-LTE spherically extended atmosphere models including line-blanketing have been computed with the code CMFGEN (Hillier & Miller 1998) and the analysis of UV STIS spectra lead to the following results: 1) The SMC-N81 components are young (~ 0-4 Myrs) O stars with Teff compatible with medium to late subtypes and with luminosities lower than average Galactic O dwarfs, rendering them possible ZAMS candidates; 2) The winds are extremely weak: the mass loss rates (~1e-8/1e-9 Msol/yr) and the modified wind momenta are 1 to 2 orders of magnitude lower than observed so far for Galactic stars, and are lower than the predictions of the most recent hydrodynamical models. The reasons for such weak winds are investigated with special emphasis on the modified wind momenta: 1) There may be a break-down of the wind momentum - luminosity relation (WLR) for dwarf stars at low luminosity (log L/Lsol < 5.5). However, reasons for such a breakdown remain unknown; 2) The slope of the WLR may be steeper at low metallicity. This is predicted by the radiation driven wind theory, but the current hydrodynamical simulations do not show any change of the slope at SMC metallicity. Moreover, there are indications that some Galactic objects have wind momenta similar to those of the SMC stars; 3) Decoupling in the atmosphere may lead to multicomponent winds, but various tests indicate that this is not likely to be the case for the SMC-N81 stars. Hence, the origin of the weakness of the wind observed in these objects remains unknown. We suggest that this weakness may be linked with the youth of these stars and represents possibly the onset of stellar winds in recently formed massive stars.

  4. Discovery of 9 New Companions to Nearby Young M Stars with the Altair AO System

    E-print Network

    Daemgen, S; Reid, I N; Close, L M; Daemgen, Sebastian; Siegler, Nick; Close, Laird M.

    2006-01-01

    We present results of a high-resolution, near-infrared survey of 41 nearby, young (= M6 very low-mass, VLM) populations. We find that the separation distribution of the binaries in this sample peaks at 13+14-9 AU, which is consistent with previous measurements of early-M binaries. Hence, early-M binaries seem to occur in--on average--tighter systems than G binaries. At the same time they are significantly wider than field VLM binary stars. The distribution of mass ratios q of primary and secondary stars was found to show an intermediate distribution between the strongly q-->1 peaked distribution of field VLM systems and the almost flat distribution of earlier-type stars. Consequently, we show evidence for relatively young, early-M binaries representing a transition between the well known earlier star distributions and the recently examined field VLM population characteristics. Despite the fact that this survey was dedicated to the search for faint brown dwarf and planetary mass companions, all planetary mass ...

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

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.; Finzell, Thomas, E-mail: mpeacock@msu.edu [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    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.

  6. Spectroscopic Study of Young Star Clusters in the Outskirts of NGC 1275 (Perseus A)

    NASA Astrophysics Data System (ADS)

    Gallagher, John S., III; Smith, Linda J.; Trancho, Gelys; Westmoquette, Mark; Zweibel, Ellen

    2009-08-01

    NGC 1275, the brightest galaxy in the A426 (Perseus) cluster, offers an extraordinary opportunity to explore feedback processes in a nearby (75 Mpc) system. This galaxy hosts a powerful AGN that feeds a double- lobe radio source in combination with a massive molecular ISM that supports extensive star formation. While the existence of a spider web array of ionized gas filaments extending R=90 kpc to the north is well known, their quiescent kinematics, molecular content, and associated spatially extended star formation only now is becoming clear. Our ongoing research addresses a variety of interrelated issues ranging from understanding what prevents high ICM cooling rates to the origin and evolution of the giant ionized filaments and the population of the halo with massive young star clusters. A major theme is an exploration of the ways in which mechanical luminosity and momentum from the AGN and SNe II operate as a feedback mechanism to halt the cooling flow and build new stellar content in NGC 1275. This proposal requests use of the Gemini-N GMOS IFU system to obtain spectra of young star clusters and their associated ionized gas located at a progression of galactocentric radii in NGC 1275. The resulting measurements of cluster kinematics, conditions in surrounding HII filaments, estimated ages, and chemical abundances will add fundamental new constraints on the evolution of this amazing galaxy.

  7. 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.

  8. VizieR Online Data Catalog: IC 2391 and Argus young stars (de Silva+, 2013)

    NASA Astrophysics Data System (ADS)

    de Silva, G. M.; D'Orazi, V.; Melo, C.; Torres, C. A. O.; Gieles, M.; Quast, G. R.; Sterzik, M.

    2014-01-01

    We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the search for associations containing young stars survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogeneous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba. All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H]=-0.04+/-0.03 for cluster stars and [Fe/H]=-0.06+/-0.05 for Argus stars. Effects of overionization/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support the fact that the Argus association stars originated from the open cluster IC 2391. Simple modelling of this system finds this dissolution to be consistent with two-body interactions. (4 data files).

  9. Cosmologically significant population of galaxies dominated by very young star formation

    SciTech Connect

    Cowie, L.L.; Lilly, S.J.; Gardner, J.; Mclean, I.S.

    1988-09-01

    A population of galaxies whose light is dominated at all wavelengths from B to K by a very young stellar population has been found in an extremely deep optical and IR small-field survey. These galaxies must represent one of the main star-forming epochs in the history of the universe and approximately 10-100 percent of the metals must have formed in them. They must have a redshift less than 3.5 and may constitute either a genuine protogalaxy population or a rejuvenation phase of galaxies that formed earlier. The faint I band star counts in the field eliminate the possibility that the Galactic dark halo may be composed of hydrogen-burning main-sequence stars. 16 references.

  10. Sizes and Shapes of Young, Massive Star Clusters in M83

    NASA Astrophysics Data System (ADS)

    Ryon, Jenna E.; Bastian, Nate; Adamo, Angela; Silva-Villa, Esteban; Gallagher, John S.

    2015-01-01

    Using HST imaging, the surface brightness profiles of individual star clusters in nearby galaxies can be resolved, in that clusters are clearly more extended than the stellar PSF. Previous studies of the sizes and shapes of star clusters find little variation with cluster age, mass, or galaxy environment. We use observations from seven pointings on M83 from HST/WFC3 programs GO/DD-11360 (PI O'Connell) and GO-12513 (PI Blair) to obtain a large sample of young, massive star clusters. We measure the half-light radii and power-law indices of the EFF light profile (Elson, Fall, & Freeman 1987) of these clusters using the galfit software package (Peng et al. 2002). We present our results on the relationships between cluster size, shape, age, mass, and environment in the disk of M83.

  11. Stellar contents and star formation in the young open cluster Stock 8

    E-print Network

    Jessy Jose; A. K. Pandey; D. K. Ojha; K. Ogura; W. P. Chen; B. C. Bhatt; S. K. Ghosh; H. Mito; G. Maheswar; Saurabh Sharma

    2007-12-13

    We present $UBVI_c$ CCD photometry of the young open cluster Stock 8 with the aim to study the basic properties and star formation scenario in this region. The radius of the cluster is found to be $\\sim 6^{\\prime}$ ($\\sim 3.6$ pc) and the reddening within the cluster region varies from $E(B-V)=0.40$ to 0.60 mag. The cluster is located at a distance of $2.05 \\pm 0.10$ kpc. Using H$\\alpha$ slitless spectroscopy and 2MASS NIR data we identified H$\\alpha$ emission and NIR excess young stellar objects (YSOs), respectively. The colour-magnitude diagrams of these YSOs reveal that majority of these objects have ages between 1 to 5 Myr indicating a non-coeval star formation in the cluster. Massive stars in the cluster region reveal an average age of $\\le$ 2 Myr. In the cluster region ($r \\le 6^\\prime$) the slope of the mass function (MF), $\\Gamma$, in the mass range $\\sim 1.0 \\le M/M_\\odot cluster ($r \\le 6^\\prime$) is found to be $0.31\\pm0.02$, which is smaller than the average value ($\\sim$ 0.4) obtained for embedded star clusters. A significant number of YSOs are distributed along a Nebulous Stream towards the east side of the cluster. A small cluster is embedded in the Nebulous Stream. The YSOs lying in the Nebulous Stream and in the embedded cluster are found to be younger than the stars in the cluster Stock 8. It appears that star formation activity in the Nebulous Stream and embedded cluster may be independent from that of Stock 8.

  12. 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.

  13. A Search for Hot Massive Extrasolar Planets around Nearby Young Stars with the Adaptive Optics System NACO

    Microsoft Academic Search

    E. Masciadri; R. Mundt; Th. Henning; C. Alvarez; D. Barrado y Navascués

    2005-01-01

    We report on a survey devoted to the search of exoplanets around young and nearby stars carried out with NACO at the VLT. The detection limit for 28 among the best available targets versus the angular separation from the star is presented. The nondetection of any planetary mass companion in our survey is used to derive, for the first time,

  14. KEPLER-63b: A GIANT PLANET IN A POLAR ORBIT AROUND A YOUNG SUN-LIKE STAR

    E-print Network

    Marcy, Geoffrey W.

    We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, m [subscript Kp] = 11.6, T [subscript eff] = 5576 K, M [star] = 0.98 M [subscript ?]). The planet transits ...

  15. XMM-Newton investigations of the Lambda Orionis star-forming region (XILO). I. The young cluster Collinder 69

    Microsoft Academic Search

    D. Barrado; B. Stelzer; M. Morales-Calderón; A. Bayo; N. Huélamo; J. R. Stauffer; S. Hodgkin; F. Galindo; E. Verdugo

    2011-01-01

    Context. This is the first paper of a series devoted to the Lambda Orionis star-forming region, Orion's Head, from the X-ray perspective. Our final aim is to provide a comprehensive view of this complex region, which includes several distinct associations and dark clouds. Aims: We aim to uncover the population of the central, young star cluster Collinder 69, and in

  16. 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!

  17. Search for associations containing young stars (SACY). V. Is multiplicity universal? Tight multiple systems

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Context. Dynamically undisrupted, young populations of stars are crucial in studying the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close (<150 pc) pre-main sequence (PMS) stars across the very important age range (?5-70 Myr) to conduct such research. Aims: We characterize the short period multiplicity fraction of the search for associations containing young stars (SACY) sample, accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods: Using the cross-correlation technique we identified double-lined and triple-lined spectroscopic systems (SB2/SB3s), in addition to this we computed radial velocity (RV) values for our subsample of SACY targets using several epochs of Fiber-fed Extended Range Optical Spectrograph (FEROS) and Ultraviolet and Visual Echelle Spectrograph (UVES) data. These values were used to revise the membership of each association that was then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results: We identified seven new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction (Fm) of the SACY sample and that of close star-forming regions (?1-2 Myr) and the field (Fm ? 10%). These are seen both as a function of age and as a function of primary mass, M1, in the ranges P [1:200 day] and M2 [0.08 M?-M1], respectively. Conclusions: Our results are consistent with the picture of universal star formation, when compared to the field and close star-forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with the primary mass within the close companion range in relation to star formation. Based on observations obtained using the instruments FEROS at La Silla (ESO 1.5 m and MPG/ESO 2.2 m) UVES at VLT (ESO 8 m).Appendices are available in electronic form at http://www.aanda.orgTables C.1, C.2 and D.1 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/568/A26

  18. Spatially Extended Brackett Gamma Emission in the Environments of Young Stars

    E-print Network

    Beck, Tracy L; McGregor, Peter J

    2010-01-01

    The majority of atomic hydrogen Br{\\gamma} emission detected in the spectra of young stellar objects (YSOs) is believed to arise from the recombination regions associated with the magnetospheric accretion of circumstellar disk material onto the forming star. In this paper, we present the results of a K-band IFU spectroscopic study of Br{\\gamma} emission in eight young protostars: CW Tau, DG Tau, Haro 6-10, HL Tau, HV Tau C, RW Aur, T Tau and XZ Tau. We spatially resolve Br{\\gamma} emission structures in half of these young stars and find that most of the extended emission is consistent with the location and velocities of the known Herbig-Haro flows associated with these systems. At some velocities through the Br{\\gamma} line profile, the spatially extended emission comprises 20% or more of the integrated flux in that spectral channel. However, the total spatially extended Br{\\gamma} is typically less than ~10% of the flux integrated over the full emission profile. For DG Tau and Haro 6-10 S, we estimate the m...

  19. IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

    SciTech Connect

    Schneider, Adam; Song, Inseok [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States); Melis, Carl [Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093 (United States); Zuckerman, B. [Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095 (United States); Bessell, Mike, E-mail: aschneid@physast.uga.edu, E-mail: song@physast.uga.edu, E-mail: cmelis@ucsd.edu, E-mail: ben@astro.ucla.edu, E-mail: bessell@mso.anu.edu.au [Research School of Astronomy and Astrophysics, The Australian National University, Weston Creek, ACT 2611 (Australia)

    2012-10-01

    It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age {approx}<10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ('TWA 33' and 'TWA 34') of the TW Hydrae Association (TWA). Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer catalog and they show proper motion and youthful spectroscopic characteristics-namely, H{alpha} emission, strong lithium absorption, and low surface gravity features consistent with known TWA members. We also detect mid-IR excess-the first unambiguous evidence of a dusty circumstellar disk-around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius-Centaurus Complex.

  20. 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).

  1. ASSESSMENT OF STELLAR STRATIFICATION IN THREE YOUNG STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Rochau, Boyke [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Mackey, Dougal [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Xin Yu, E-mail: dgoulier@mpia-hd.mpg.d, E-mail: rochau@mpia-hd.mpg.d, E-mail: dmy@roe.ac.u, E-mail: yxin@astro.uni-bonn.d [Argelander Institut fuer Astronomie, Rheinische Friedrich-Wilhelms-Universitaet Bonn, Auf dem Huegel 71, 53121 Bonn (Germany)

    2010-01-20

    We present a comprehensive study of stellar stratification in young star clusters in the Large Magellanic Cloud (LMC). We apply our recently developed effective radius method for the assessment of stellar stratification on imaging data obtained with the Advanced Camera for Surveys of three young LMC clusters to characterize the phenomenon and develop a comparative scheme for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC 2002, and NGC 2010, are selected on the basis of their youthfulness, and their variety in appearance, structure, stellar content, and surrounding stellar ambient. Our photometry is complete for magnitudes down to m{sub 814} approx = 23 mag, allowing the calculation of the structural parameters of the clusters, the estimation of their ages, and the determination of their stellar content. Our study shows that each cluster in our sample demonstrates stellar stratification in a quite different manner and at different degree from the others. Specifically, NGC 1983 shows partial segregation, with the effective radius increasing with fainter magnitudes only for the faintest stars of the cluster. Our method on NGC 2002 provides evidence of strong stellar stratification for both bright and faint stars; the cluster demonstrates the phenomenon with the highest degree in the sample. Finally, NGC 2010 is not segregated, as its bright stellar content is not centrally concentrated, the relation of effective radius to magnitude for stars of intermediate brightness is rather flat, and we find no evidence of stratification for its faintest stars. For the parameterization of the phenomenon of stellar stratification and its quantitative comparison among these clusters, we propose the slope derived from the change in the effective radius over the corresponding magnitude range as indicative parameter of the degree of stratification in the clusters. A positive value of this slope indicates mass segregation in the cluster, while a negative or zero value signifies the lack of the phenomenon.

  2. Discovery of 9 New Companions to Nearby Young M Stars with the Altair AO System

    E-print Network

    Sebastian Daemgen; Nick Siegler; I. Neill Reid; Laird M. Close

    2006-12-30

    We present results of a high-resolution, near-infrared survey of 41 nearby, young (Altair natural guide star adaptive optics system at the Gemini North telescope. Twelve of the objects appear to be binaries, 7 of which are reported here for the first time. One triple system was discovered. Statistical properties are studied and compared with earlier (F to K) and later (>= M6 very low-mass, VLM) populations. We find that the separation distribution of the binaries in this sample peaks at 13+14-9 AU, which is consistent with previous measurements of early-M binaries. Hence, early-M binaries seem to occur in--on average--tighter systems than G binaries. At the same time they are significantly wider than field VLM binary stars. The distribution of mass ratios q of primary and secondary stars was found to show an intermediate distribution between the strongly q-->1 peaked distribution of field VLM systems and the almost flat distribution of earlier-type stars. Consequently, we show evidence for relatively young, early-M binaries representing a transition between the well known earlier star distributions and the recently examined field VLM population characteristics. Despite the fact that this survey was dedicated to the search for faint brown dwarf and planetary mass companions, all planetary mass candidates were background objects. We exclude the existence of physical companions with masses greater than 10 Jupiter masses (M_Jup) at separations of >~40 AU and masses greater than 24 M_Jup for separations >~10 AU around 37 of the 41 observed objects.

  3. Stellar contents and star formation in the young open cluster Stock 8

    E-print Network

    Jose, Jessy; Ojha, D K; Ogura, K; Chen, W P; Bhatt, B C; Ghosh, S K; Mito, H; Maheswar, G; Sharma, Saurabh

    2007-01-01

    We present $UBVI_c$ CCD photometry of the young open cluster Stock 8 with the aim to study the basic properties and star formation scenario in this region. The radius of the cluster is found to be $\\sim 6^{\\prime}$ ($\\sim 3.6$ pc) and the reddening within the cluster region varies from $E(B-V)=0.40$ to 0.60 mag. The cluster is located at a distance of $2.05 \\pm 0.10$ kpc. Using H$\\alpha$ slitless spectroscopy and 2MASS NIR data we identified H$\\alpha$ emission and NIR excess young stellar objects (YSOs), respectively. The colour-magnitude diagrams of these YSOs reveal that majority of these objects have ages between 1 to 5 Myr indicating a non-coeval star formation in the cluster. Massive stars in the cluster region reveal an average age of $\\le$ 2 Myr. In the cluster region ($r \\le 6^\\prime$) the slope of the mass function (MF), $\\Gamma$, in the mass range $\\sim 1.0 \\le M/M_\\odot < 13.4$ can be represented by a power law having a slope of $-1.38\\pm0.12$, which agrees well with Salpeter value (-1.35). In t...

  4. Direct measurement of interstellar extinction toward young stars using atomic hydrogen Ly? absorption

    SciTech Connect

    McJunkin, Matthew; France, Kevin; Brown, Alexander [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Schneider, P. C. [Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany); Herczeg, Gregory J. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Hillenbrand, Lynne [California Institute of Technology, Department of Astrophysics, MC105-24, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Schindhelm, Eric [Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302 (United States); Edwards, Suzan, E-mail: matthew.mcjunkin@colorado.edu [Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States)

    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 Ly? 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.

  5. A double-lined spectroscopic orbit for the young star HD 34700

    E-print Network

    Guillermo Torres

    2003-11-07

    We report high-resolution spectroscopic observations of the young star HD 34700, which confirm it to be a double-lined spectroscopic binary. We derive an accurate orbital solution with a period of 23.4877 +/- 0.0013 days and an eccentricity of e = 0.2501 +/- 0.0068. The stars are found to be of similar mass (M2/M1 = 0.987 +/- 0.014) and luminosity. We derive also the effective temperatures (5900 K and 5800 K) and projected rotational velocities (28 km/s and 22 km/s) of the components. These values of v sin i are much higher than expected for main-sequence stars of similar spectral type (G0), and are not due to tidal synchronization. We discuss also the indicators of youth available for the object. Although there is considerable evidence that the system is young --strong infrared excess, X-ray emission, Li I 6708 absorption (0.17 Angstroms equivalent width), H alpha emission (0.6 Angstroms), rapid rotation-- the precise age cannot yet be established because the distance is unknown.

  6. Direct Measurement of Interstellar Extinction toward Young Stars Using Atomic Hydrogen Ly? Absorption

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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 Ly? 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 log10(N(H I)) ?19.6-21.1, with corresponding visual extinctions of AV =0.02-0.72 mag, assuming an RV 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.

  7. Magnetic complexity as an explanation for bimodal rotation populations among young stars

    E-print Network

    Garraffo, Cecilia; Cohen, Ofer

    2015-01-01

    Observations of young open clusters have revealed a bimodal distribution of fast and slower rotation rates that has proven difficult to explain with predictive models of spin down that depend on rotation rates alone. The Metastable Dynamo Model proposed recently by Brown, employing a stochastic transition probability from slow to more rapid spin down regimes, appears to be more successful but lacks a physical basis for such duality. Using detailed 3D MHD wind models computed for idealized multipole magnetic fields, we show that surface magnetic field complexity can provide this basis. Both mass and angular momentum losses decline sharply with increasing field complexity. Combined with observation evidence for complex field morphologies in magnetically active stars, our results support a picture in which young, rapid rotators lose angular momentum in an inefficient way because of field complexity. During this slow spin-down phase, magnetic complexity is eroded, precipitating a rapid transition from weak to str...

  8. 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

  9. Magnetic Complexity as an Explanation for Bimodal Rotation Populations among Young Stars

    NASA Astrophysics Data System (ADS)

    Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer

    2015-07-01

    Observations of young open clusters have revealed a bimodal distribution of fast and slower rotation rates that has proven difficult to explain with predictive models of spin down that depend on rotation rates alone. The Metastable Dynamo Model proposed recently by Brown, employing a stochastic transition probability from slow to more rapid spin down regimes, appears to be more successful but lacks a physical basis for such duality. Using detailed 3D MHD wind models computed for idealized multipole magnetic fields, we show that surface magnetic field complexity can provide this basis. Both mass and angular momentum losses decline sharply with increasing field complexity. Combined with observation evidence for complex field morphologies in magnetically active stars, our results support a picture in which young, rapid rotators lose angular momentum in an inefficient way because of field complexity. During this slow spin-down phase, magnetic complexity is eroded, precipitating a rapid transition from weak to strong wind coupling.

  10. VizieR Online Data Catalog: Young Massive Star Clusters. II. (Larsen, 1999)

    NASA Astrophysics Data System (ADS)

    Larsen, S. S.

    1999-07-01

    Table 4 lists photometric data for Young Massive Star Clusters identified in a sample of 21 nearby galaxies. The photometric data have been corrected for Galactic foreground extinction. Each cluster is identified by the abbreviated NGC number of its host galaxy and an object number: nxxx-yyy is object number yyy in the galaxy NGC xxx. Effective cluster radii have been obtained by modeling the cluster images as MOFFAT15 functions convolved with the point-spread function measured on the CCD images. (1 data file).

  11. POPSTAR evolutionary synthesis models - III. Photometric properties of young star clusters and mixed populations

    NASA Astrophysics Data System (ADS)

    García-Vargas, M. L.; Mollá, M.; Martín-Manjón, M. L.

    2013-07-01

    This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of single stellar populations resulting from our POPSTAR code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, H? and H? luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z = 0.0001-0.05) and age (0.1 Myr to 20 Gyr). We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated star-forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of POPSTAR spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as the H? radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information.

  12. Diffraction-limited infrared observations of the young star Z CMa

    SciTech Connect

    Koresko, C.D.; Beckwith, S.V.W.; Sargent, A.I. (Cornell Univ., Ithaca, NY (USA) California Institute of Technology, Pasadena (USA))

    1989-10-01

    Speckle interferometric observations of Z CMa show a highly elongated light distribution approximately 0.1 arcsec in size at 2.2 microns. The elongation may be the result of light scattered close to the star by a jetlike particle distribution or, alternatively, indicate the presence of an infrared companion similar to that seen toward T Tau. The companion would be cool (2000 K), large (300 solar radii), and more luminous (1000 solar luminosities) than the T Tau companion. If it represents a young object in the initial stages of accretion, its lifetime in the present state is only a few hundred years. 19 refs.

  13. An infrared view of (candidate accretion) disks around massive young stars

    E-print Network

    A. Bik; A. Lenorzer; W-. F. Thi; E. Puga-Antolin; L. B. F. M. Waters; L. Kaper; L. N. Martin-Hernandez

    2007-12-03

    Near-infrared surveys of high-mass star-forming regions start to shed light onto their stellar content. A particular class of objects found in these regions, the so-called massive Young Stellar Objects (YSOs) are surrounded by dense circumstellar material. Several near- and mid-infrared diagnostic tools are used to infer the physical characteristics and geometry of this circumstellar matter. Near-infrared hydrogen emission lines provide evidence for a disk-wind. The profiles of the first overtone of the CO band-heads, originating in the inner 10 AU from the central star, are well fitted assuming a keplerian rotating disk. The mid-infrared spectral energy distribution requires the presence of a more extended envelope containing dust at a temperature of about 200 K. CRIRES observations of CO fundamental absorption lines confirm the presence of a cold envelope. We discuss the evolutionary status of these objects.

  14. Rotational Velocities of Post T Tauri Stars in Young Stellar Associations

    NASA Astrophysics Data System (ADS)

    Rodríguez, J.; Pinzón, G.

    2013-04-01

    This contribution summarizes the preliminary results concerning vsini measurements for a sample of G-K solar type stars in the solar neighborhood based on observations made with the European Southern Observatory telescopes obtained from ESO/ST-ECF Science Archive Facility. We conducted measurements of rotational projected velocities for a sample of 33 young low mass post-T Tauri stars with ages between 10 and 30 Myr belonging to the nearby associations: Beta Pictoris Moving Group (BPMG), Upper Centaurus Lupus (UCL), Lower Centaurus Crux (LCC), and Tucana Horologium (THA). When compared with data of members of the older clusters, the Pleiades and the Hyades, our vsini measurements appear to be consistent with an increase of the rotation between the age of BPMG and THA in agreement with the spin up expected after the disk disappearance.

  15. Stellar contents and Star formation in the young cluster Stock 18

    E-print Network

    Bhatt, Himali; Pandey, J C

    2011-01-01

    We have carried out deep (V$\\sim$21 mag) \\ubvri photometric study of the star cluster Stock 18. These along with archival Infrared data have been used to derive the basic cluster parameters and also to study the star formation processes in and around the cluster region. The distance to the cluster is derived as 2.8$\\pm$0.2 kpc while its age is estimated as $6.0\\pm2.0$ Myr. Present study indicates that interstellar reddening is normal in the direction of the cluster. The mass function slope is found to be -1.37$\\pm$0.27 for the mass range 1$cluster. A young stellar population with age between 1-2 Myr have been found in and around the cluster region. The presence of IRAS and AKARI sources with MSX intensity map also show the youth of the Sh2-170 region.

  16. 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).

  17. Integral-Field Spectroscopy of the Young High-Mass Star IRAS 13481-6124

    NASA Astrophysics Data System (ADS)

    Stecklum, B.; Caratti o Garatti, A.; Linz, H.

    2012-12-01

    We present results of AO-assisted K-band IFU spectroscopy of the massive young star IRAS 13481-6124 performed with ESO's VLT/SINFONI instrument. Our spectro-astrometric analysis of the Br? line revealed a photo-center shift with respect to the adjacent continuum of ˜1 AU at a distance of 3.1 kpc. The position angle of this shift matches with that of the outflow which confirms that the massive star is indeed the driving source. Furthermore, a velocity gradient along the major disk axis was found which hints at the rotational sense of the ionized region, and thus of the disk as well. The gradient is not consistent with Keplerian motion but points to rigid rotation of the innermost disk. Notably, emission of H2 is absent from source while both shocked and fluorescent H2 emission are observed in its immediate surroundings.

  18. 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 [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Baglin, Annie [LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, F-92195, Meudon (France); Alencar, Silvia [Departamento de Física-ICEx-UFMG, Av. Antônio Carlos, 6627, 30270-901, Belo Horizonte, MG (Brazil); Hillenbrand, Lynne A.; Carpenter, John; Findeisen, Krzysztof [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Venuti, Laura; Bouvier, Jerome [UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Turner, Neal J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Plavchan, Peter [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Terebey, Susan [Department of Physics and Astronomy, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Morales-Calderón, María [Centro de Astrobiología, Dpto. de Astrofísica, INTA-CSIC, P.O. Box 78, E-28691, ESAC Campus, Villanueva de la Cañada, Madrid (Spain); Micela, Giusi; Flaccomio, Ettore [INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134, Palermo (Italy); Song, Inseok [Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602-2451 (United States); Gutermuth, Rob [Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States); Hartmann, Lee, E-mail: stauffer@ipac.caltech.edu [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105 (United States); 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 brief—several hours to one day—brightenings 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.

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

    E-print Network

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

    2008-04-28

    MWC 297 is a young massive nearby B[e] star. The central star has a large projected rotational velocity of 350 km/s. Despite the wealth of published observations, the nature of this object and its dust-rich surroundings is not well understood. With the present paper, we shed light on the geometrical structure of the circumstellar matter which produces the near- to mid-infrared flux excess, and construct an overall image of the source's appearance and evolutionary status. The H-, K- and N-band brightness distribution of MWC 297 is probed with the ESO interferometric spectrographs AMBER and MIDI. We have obtained visibility measurements on 3 AMBER and 12 MIDI baselines, covering a wide range of spatial frequencies. We have reconstructed the brightness distribution in H, K and N with a geometric model consisting of three Gaussian disks with different extent and brightness temperature. This model can account for the entire near- to mid-IR emission of MWC 297. 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. We argue that the circumstellar matter in the MWC 297 system is organized in a disk, seen under moderate (i < 40 deg) inclination. The disk displays no inner emission-free gap at the resolution of our interferometric data. The low inclination of the disk implies that the actual rotational velocity of the star exceeds its critical velocity. 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.

  20. The Role of Damped Alfvén Waves in Magnetospheric Accretion Models of Young Stars

    NASA Astrophysics Data System (ADS)

    Vasconcelos, M. J.; Jatenco-Pereira, V.; Opher, R.

    2002-08-01

    We examine the role of Alfvén wave damping in heating the plasma in the magnetic funnels of magnetospheric accretion models of young stars. We study four different damping mechanisms of the Alfvén waves: nonlinear, turbulent, viscous-resistive, and collisional. Two different possible origins for the Alfvén waves are discussed: (1) Alfvén waves generated at the surface of the star by the shock produced by the infalling matter and (2) Alfvén waves generated locally in the funnel by the Kelvin-Helmholtz instability. We find that, in general, the damping lengths are smaller than the tube length. Since thermal conduction in the tube is not efficient, Alfvén waves generated only at the star's surface cannot heat the tube to the temperatures necessary to fit the observations. Only for very low frequency Alfvén waves ~10-5 the ion-cyclotron frequency is the viscous-resistive damping length greater than the tube length. In this case, the Alfvén waves produced at the surface of the star are able to heat the whole tube. Otherwise, local production of Alfvén waves is required to explain the observations. The turbulence level is calculated for different frequencies for optically thin and thick media. We find that turbulent velocites vary greatly for different damping mechanisms, reaching ~100 km s-1 for the collisional damping of low-frequency waves.

  1. New Brown Dwarf Companions to Young Stars in Scorpius-Centaurus

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    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 ~40-100 M jup complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of ~10-30 M 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. Based on Gemini observations from programs GS-2011A-Q-44, GS-2012A-Q-18, and GS-2012A-DD-6, and on ESO observations from program 089.C-0422(A).

  2. 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.

  3. Inner disc rearrangement revealed by dramatic brightness variations in the young star PV Cep

    NASA Astrophysics Data System (ADS)

    Kun, M.; Szegedi-Elek, E.; Moór, A.; Kóspál, Á.; Ábrahám, P.; Apai, D.; Kiss, Z. T.; Klagyivik, P.; Magakian, T. Yu.; Mez?, Gy.; Movsessian, T. A.; Pál, A.; Rácz, M.; Rogers, J.

    2011-06-01

    Young Sun-like stars at the beginning of the pre-main-sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time-scales and wavelength dependence of the variability carry information on the physical mechanisms behind these interactions. We conducted multi-epoch, multiwavelength study of PV Cep, a strongly variable, accreting PMS star. By combining our own observations from 2004 to 2010 with archival and literature data, we show that PV Cep started a spectacular fading in 2005, reaching an IC-band amplitude of 4 mag. Analysis of variation of the optical and infrared fluxes, colour indices and emission line fluxes suggests that the photometric decline in 2005-2009 resulted from an interplay between variable accretion and circumstellar extinction: since the central luminosity of the system is dominated by accretion, a modest drop in the accretion rate could induce the drastic restructuring of the inner disc. Dust condensation in the inner disc region might have resulted in the enhancement of the circumstellar extinction.

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

    SciTech Connect

    Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD (United States); Carlson, Lynn Redding [Johns Hopkins University, 3400 N. Charles St., Baltimore, MD (United States); Whitney, B. [Space Science Institute, Boulder, CO (United States); Babler, B.; Meade, M. [Department of Astronomy, University of Wisconsin, Madison, WI (United States); Indebetouw, R. [Department of Astronomy, University of Virginia, Charlottesville, VA (United States); Hora, J. L., E-mail: k.a.romita@gmail.co, E-mail: carlson@stsci.ed, E-mail: bwhitney@spacescience.or, E-mail: brian@sal.wisc.ed, E-mail: remy@virginia.ed, E-mail: jhora@cfa.harvard.ed [Harvard Smithsonian Center for Astrophysics, Cambridge, MA (United States)

    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.

  5. The Gemini NICI Planet-Finding Campaign: Planet Frequency for Young Moving Group Stars

    NASA Astrophysics Data System (ADS)

    Biller, Beth A.; Liu, M. C.; Wahhaj, Z.; Nielsen, E. L.; Hayward, T. L.; Close, L. M.; Chun, M.; Ftaclas, C.; Toomey, D. W.; Gemini NICI Planet-Finding Campaign Team

    2013-01-01

    We report results of a direct imaging survey for giant planets of a sample of 79 young FGK stars which are members of the ? Pic, TW Hya, AB Dor, Tucana-Horologium, or Hercules-Lyra moving groups and were observed as part of the Gemini-NICI Planet Finding Campaign. For this sample, we obtained median contrasts of ?(mag)=14.0 mag at 1'' in in combined ADI+SDI mode. We found numerous candidate companions in our survey images. The vast majority of these candidates were eliminated as background objects either from archival observations or NICI followup. However, four co-moving brown dwarf or stellar companions were discovered in the moving group sample, including PZ Tel B and CD -35 2722B. From a Bayesian analysis for a wide range of parameters and power-law models of planet distributions, we restrict the planet frequency for 1-20 M_{Jup} objects at semi-major axes from 10-150 AU to <10.5% or less at a 98% confidence level. This survey is the deepest search to date for giant planets around young Moving Group stars.

  6. On the association of young star clusters and their parental clouds: a statistical fractal analysis

    NASA Astrophysics Data System (ADS)

    Hetem, A.; Gregorio-Hetem, J.; Fernandes, B.; Santos-Silva, T.

    2014-10-01

    We present a study of 21 young star clusters aiming to characterize their association to dense clouds. The structure of the clouds was evaluated by means of the Q statistical fractal analysis, designed to compare their geometric structure with the spatial distribution of the cluster members. The sample was selected from the study by Santos-Silva and Gregorio-Hetem (2012, A&A, 547, A107) that evaluated the radial density profile of the stellar superficial distribution of the young clusters. The fractal dimension and other statistical parameters of most of the sample indicate that there is a good cloud-cluster correlation, when compared to other works based on an artificial distribution of points (Lomax et al. 2011, MNRAS, 412, 627). As presented in a previous work (Fernandes et al. 2012, A&A, 541, A95 ), the cluster NGC 6530 is the only object of our sample that presents anomalous statistical behaviour. The fractal analysis shows that this cluster has a centrally concentrated distribution of stars that differs from the substructures found in the density distribution of the cloud projected in the A_{V} map, suggesting that the original cloud geometry was changed by the cluster formation.

  7. Young stars in ? 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 ? 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 ? 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 ? 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 ? Cha. HD 104237C is the lowest mass member of ? 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 ?m 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 ?m on the IRS spectrum of USNO-B120144.7. We find strong signatures of grain growth and crystallization in all ? Cha members with 10 ?m features detected in their IRS spectra. We combine the dust properties derived in the ? Cha sample with those found using identical or similar methods in the MBM 12, Coronet, ? 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.

  8. 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 te

  9. Hubble space telescope observations of young star clusters in NGC-4038/4039, 'the antennae' galaxies

    NASA Technical Reports Server (NTRS)

    Whitmore, Bradley C.; Schweizer, Francois

    1995-01-01

    New, high-resolution images of the disks of NGC 4038/4039 obtained with the Wide Field Camera of the Hubble Space Telescope (HST) are presented. NGC 4038/4039, nicknamed The Antennae, is a prototypical example of a pair of colliding galaxies believed to be at an early stage of a merger. Down to the limiting magnitude of V approximately 23 mag, the HST images reveal a population of over 700 blue pointlike objects within the disks. The mean absolute magnitude of these objects is M(sub V) = -11 mag, with the brightest objects reaching M(sub V) approximately -15. Their mean apparent color indices ar U - V = -0.7 mag and V - 1 = 0.8 mag on the Johnson UVI passband system, while their mean indices corrected for internal reddening are (u - v)(sub 0) = -1.0 mag and (V - I(sub 0) = 0.5. Their mean effective radius, determined from slightly resolved images, is 18 pc (for H(sub 0) = 50 km/s /Mpc). Based on their luminosities and resolution, most of these objects cannot be individual stars, but are likely young compact star clusters. The brighter ones are similar to the objects found in NGC 1275 and NGC 7252, which appear to be young globular clusters formed during recent galazy mergers. Based on their U - V and V - I colors, the brightest, bluest clusters of NGC 4038/4039 appear to be less than 10 Myr old. Most of these bright clusters are relatively tightly clustered themselves, with typically a dozen individual clusters belonging to a complex identified as a giant H II region from ground-based observations. The cluster luminosity function (LF) is approximately a power law, phi(L)dL proportional to L(exp -1.78+/-0.05)dL, with no hint of a turnover at fainter magnitudes. This power-law shape agrees with the LF of Magellanic Cloud clusters and Galactic open clusters, but differs from the LF of old globular cluster systems that is typically Gaussian with a Full Width at Half Maximum (FWHM) of approximately 3 mag. Besides the blue clusters, we also find about a dozen extremely red objects with V - I greater than 3.0. The highest number density of these red objects is found in the SE quadrant, where star formation appears to be most recent. We propose that these objects may be very young star clusters still embedded in their placental dust cocoons.

  10. Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

    E-print Network

    John S. Carr; Alan T. Tokunaga; Joan Najita

    2003-12-04

    We report on the detection and analysis of hot ro-vibrational H2O emission from SVS-13, a young stellar object previously known to have strong CO overtone bandhead emission. Modeling of the high-resolution infrared spectrum shows that the H2O emission is characterized by temperatures ~ 1500 K, significantly lower than the temperatures that characterize the CO bandhead emission. The widths for the H2O lines are also found to be smaller than those for the CO lines. We construct a disk model for the emission that reproduces the CO and H2O spectrum. In this model, the H2O lines originate at somewhat larger disk radii (H2O abundance is about a factor of 10 lower than the calculated chemical equilibrium abundance. Large, approximately transonic, local line broadening is required to fit the profile of the CO bandhead. If this velocity dispersion is identified with turbulence, it is of significant interest regarding the transport of angular momentum in disks. Large local broadening is also required in modeling CO overtone emission from other young stellar objects, suggesting that large turbulent velocities may be characteristic of the upper atmospheres of the inner disks of young stars.

  11. STIS Spectroscopy of Young Star Clusters in "The Antennae" Galaxies (NGC 4038/4039)

    E-print Network

    Bradley C. Whitmore; Diane Gilmore; C. Leitherer; S. Michael Fall; Rupali Chandar; William P. Blair; Francois Schweizer; Qing Zhang; Bryan W. Miller

    2005-07-29

    Long-slit spectra of several dozen young star clusters have been obtained at three positions in the Antennae galaxies with the Space Telescope Imaging Spectrograph (STIS) and its 52"x0.2" slit. Based on H-alpha emission-line measurements, the average cluster-to-cluster velocity dispersion in 7 different cluster aggregates ("knots") is <10 \\kms. The fact that this upper limit is similar to the velocity dispersion of gas in the disks of typical spiral galaxies suggests that the triggering mechanism for the formation of young massive compact clusters ("super star clusters") is unlikely to be high velocity cloud-cloud collisions. On the other hand, models where preexisting giant molecular clouds in the disks of spiral galaxies are triggered into cluster formation are compatible with the observed low velocity dispersions. These conclusions are consistent with those reached by Zhang et al. (2001) based on comparisons between the positions of the clusters and the velocity and density structure of the nearby interstellar medium. We find evidence for systematically lower values of the line ratios [NII]/H-alpha and [SII]/H-alpha in the bright central regions of some of the knots, relative to their outer regions. This suggests that the harder ionizing photons are used up in the regions nearest the clusters, and the diffuse ionized gas farther out is photoionized by 'leakage' of the leftover low-energy photons. The low values of the [SII]/H-alpha line ratio, typically [SII]/H-alpha<0.4, indicates that the emission regions are photoionized rather than shock heated. The absence of evidence for shock-heated gas is an additional indication that high velocity cloud-cloud collisions are not playing a major role in the formation of the young clusters.

  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. Direct Imaging of Jupiter and Saturn-mass planets in wide orbit around nearby young stars

    NASA Astrophysics Data System (ADS)

    Artigau, Etienne; Lafreniere, David; Baron, Frederique; Malo, Lison; Doyon, Rene; Beichman, Charles; Delorme, Philippe; Rameau, Julien; Janson, Markus; Gagne, Jonathan; Naud, Marie-Eve; Albert, Loic

    2014-12-01

    The recent discovery of planetary-mass objects on very wide orbits (hundreds of AU and more) around young stars (e.g. Naud et al. 2014) demonstrates that planets can be found even with arcsecond-level resolution imaging. These massive ( 10MJup) companions are likely formed in-situ via hierarchical collapse and it is not yet known whether this mechanism can form lighter objects. However, dynamical modelling of young planetary systems (Veras et al. 2009) and the relatively large fraction of massive planets in eccentric orbits found by radial velocity surveys suggest that a few percent of planetary systems should host planets, comparable in mass to Jupiter and Saturn, on orbits wide enough to be imaged as isolated objects. We propose to obtain deep IRAC observations combined with J-band imaging gathered by our team to search for such planets around all known nearby young stars (< 70 pc, < 120Myr; 172 stellar systems). This survey will be sensitive to planets down to the mass of Jupiter for all systems and down to the mass of Saturn for 80 of them. Planets lighter than 2MJup are much too faint in the near-infrared to be identified from the ground; Spitzer is the only facility where such a survey can be undertaken. This survey is a unique opportunity to bring direct imaging in a new era with the detection of analogs to our own Solar System Giants, is complementary to the work done on the ground with high-contrast imagers such as GPI and Sphere, and is critical to identify new planets that will be optimally characterized with JWST.

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

    SciTech Connect

    Willis, S.; Marengo, M. [Department of Physics and Astronomy, Iowa State University, Ames, IA 50010 (United States); Allen, L. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Fazio, G. G.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Carey, S., E-mail: swillis@cfa.harvard.edu [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)

    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 ?m. We also analyzed previous observations taken at 24 ?m 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 ?{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.

  15. A Wide-field near- and Mid-infrared Census of Young Stars in NGC 6334

    NASA Astrophysics Data System (ADS)

    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 Ks 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 ?m. We also analyzed previous observations taken at 24 ?m 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 × 105 M ?. The heavy concentration of protostars along the dense filamentary structures indicates that NGC 6334 may be undergoing a "mini-starburst" event with ?SFR > 8.2 M ? Myr–1 pc–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.

  16. 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

  17. Multiwavelength Study of the Starburst Galaxy NGC 7714. II: The Balance between Young, Intermediate Age and Old Stars

    E-print Network

    Ariane Lancon; Jeff D. Goldader; Claus Leitherer; Rosa M. Gonzalez Delgado

    2001-01-18

    We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an optical spectrum, far-IR, Xray and radio fluxes) with new 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 330 pc of the starburst galaxy NGC 7714. [...] We find that the young burst responsible for the UV light is only a small part of an extended episode of enhanced star formation (SF) [...]. The mass of young and intermediate age stars thus formed equals at least 10% of the mass locked in pre-existing stars of the underlying galaxy nucleus [...]. The spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since closest contact with NGC 7715. The trigger of the starburst remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight towards young stars. [...] The different extinction estimates obtained from different indicators 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 diverse properties in terms of obscuration and stellar ages.

  18. Young stellar population and ongoing star formation in the H II complex Sh2-252

    NASA Astrophysics Data System (ADS)

    Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.

    2013-07-01

    In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it is indeed a site of cluster formation at a very early evolutionary stage, sandwiched between the two relatively evolved CH II regions A and B.

  19. On the broad-band spectral-energy distribution of the early-type young star LHalpha 25 = Walker 90

    Microsoft Academic Search

    A. E. Rydgren; F. J. Vrba

    1987-01-01

    New infrared photometry in the wavelength range 1 to 20 microns is presented for the unusual early-type star LHalpha 25 = Walker 90 in the young cluster NGC 2264. Together with previously-published UBVRI photometry, these data show that the broad-band spectral-energy distribution of this star has a minimum near a wavelength of 1 micron and rises rapidly to a wavelength

  20. He I 10830 as a Probe of Winds in Accreting Young Stars

    E-print Network

    Edwards, S; Kwan, J; Hillenbrand, L A; Dupree, A K

    2003-01-01

    He I 10830 profiles acquired with Keck's NIRSPEC for 6 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 4 stars the profiles have the signature of resonance scattering, and possess a deep and broad blueshifted absorption that penetrates more than 50% into the 1 micron 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 2 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 t...

  1. He I 10830 as a Probe of Winds in Accreting Young Stars

    E-print Network

    S. Edwards; W. Fischer; J. Kwan; L. Hillenbrand; A. K. Dupree

    2003-11-12

    He I 10830 profiles acquired with Keck's NIRSPEC for 6 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 4 stars the profiles have the signature of resonance scattering, and possess a deep and broad blueshifted absorption that penetrates more than 50% into the 1 micron 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 2 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.

  2. Young Stars in the Camelopardalis Dust and Molecular Clouds. II. Infrared Objects

    E-print Network

    V. Straizys; V. Laugalys

    2008-03-17

    Using infrared photometric data extracted from the 2MASS, IRAS and MSX databases, 142 suspected young stellar objects (YSOs) are selected from about 2 million stars in the Camelopardalis segment of the Milky Way limited by Galactic longitude 132-158 deg, latitude pm 12 deg. According to radial velocities of the associated CO clouds, the objects are attributed to three molecular and dust cloud layers at 150--300 pc, 900 pc and 2.2 kpc distances from the Sun. These objects concentrate into dust and molecular clouds and exhibit extremely large reddenings (A_V up to 25 mag) which can be caused by the dust in foreground clouds and circumstellar envelopes or disks. In the J-H vs. H-K diagram these objects lie above the intrinsic line of T Tauri variables, roughly along the black-body line. Among the identified objects, some already known YSOs are present, including the well investigated massive object GL 490. The spectral energy distributions between 700 nm and 100 mum suggest that the objects may be YSOs of classes I, II and III. However, we do not exclude the possibility that a small fraction of the objects, especially those without IRAS and MSX photometry, may be unrecognized heavily reddened OB-stars, late-type AGB stars or even galaxies.

  3. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    SciTech Connect

    Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    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.

  4. A new method for measuring metallicities of young super star clusters

    SciTech Connect

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Dr, Honolulu, HI 96822 (United States); Davies, Ben; Bastian, Nate [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Patrick, Lee [Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Schinnerer, Eva [MPI for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany)

    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.

  5. Stellar contents and star formation in the young cluster Stock 18

    NASA Astrophysics Data System (ADS)

    Bhatt, Himali; Sagar, Ram; Pandey, J. C.

    2012-02-01

    We have carried out deep (V ˜ 21 mag) UBVRI photometric study of the star cluster Stock 18. These along with archival Infrared data have been used to derive the basic cluster parameters and also to study the star formation processes in and around the cluster region. The distance to the cluster is derived as 2.8 ± 0.2 kpc while its age is estimated as 6.0 ± 2.0 Myr. Present study indicates that interstellar reddening is normal in the direction of the cluster. The mass function slope is found to be -1.37 ± 0.27 for the mass range 1 < M/ M? < 11.9. There is no evidence found for the effect of mass segregation in main-sequence stars of the cluster. A young stellar population with age between 1-2 Myr have been found in and around the cluster region. The presence of IRAS and AKARI sources with MSX intensity map also show the youth of the Sh2-170 region.

  6. 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 Phot

  7. Young [$\\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?

    E-print Network

    Chiappini, C; Rodrigues, T S; Miglio, A; Montalban, J; Mosser, B; Girardi, L; Valentini, M; Noels, A; Morel, T; Minchev, I; Steinmetz, M; Santiago, B X; Schultheis, M; Martig, M; da Costa, L N; Maia, M A G; Prieto, C Allende; Peralta, R de Assis; Hekker, S; Themeßl, N; Kallinger, T; Garcia, R A; Mathur, S; Baudin, F; Beers, T C; Cunha, K; Harding, P; Holtzman, J; Majewski, S; Meszaros, Sz; Nidever, D; Pan, K; Schiavon, R P; Shetrone, M D; Schneider, D P; Stassun, K

    2015-01-01

    We report the discovery of a group of apparently young CoRoT red-giant stars exhibiting enhanced [alpha/Fe] abundance ratios (as determined from APOGEE spectra) with respect to Solar values. Their existence is not explained by standard chemical evolution models of the Milky Way, and shows that the chemical-enrichment history of the Galactic disc is more complex. We find similar stars in previously published samples for which isochrone-ages could be robustly obtained, although in smaller relative numbers, which could explain why these stars have not received prior attention. The young [alpha/Fe]-rich stars are much more numerous in the CoRoT-APOGEE (CoRoGEE) inner-field sample than in any other high-resolution sample available at present, as only CoRoGEE can explore the inner-disc regions and provide ages for its field stars. The kinematic properties of the young [$\\alpha$/Fe]-rich stars are not clearly thick-disc like, despite their rather large distances from the Galactic mid-plane. Our tentative interpretat...

  8. 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.

  9. Evaluation of Eruption Potential

    Microsoft Academic Search

    Kazuhiro ISHIHARA

    2006-01-01

    Synopsis This manuscript proposed a concept 'eruption potential' and discussed its contents and data and knowledge necessary for its evaluation. As one example, eruption potential at Sakurajima volcano was shown: possibility of eruption in a few decades, possible styles of eruption, eruption scenarios and expected hazards. In Japan, similar evaluation as Sakurajima might be possible at about 20 volcanoes among

  10. Multiwavelength Study of the Starburst Galaxy NGC 7714. II The Balance between Young, Intermediate Age and Old Stars

    E-print Network

    Lançon, A; Leitherer, C; González-Delgado, R M; Lancon, Ariane; Goldader, Jeff D.; Leitherer, Claus; Delgado, Rosa M. Gonzalez

    2001-01-01

    We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an optical spectrum, far-IR, Xray and radio fluxes) with new 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 330 pc of the starburst galaxy NGC 7714. [...] We find that the young burst responsible for the UV light is only a small part of an extended episode of enhanced star formation (SF) [...]. The mass of young and intermediate age stars thus formed equals at least 10% of the mass locked in pre-existing stars of the underlying galaxy nucleus [...]. The spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since closest contact with NGC 7715. The trigger of the starburst remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight towards young stars. [...] The different extinction estimates obtained from different indicators result naturally from the coexistence...

  11. X-ray Emission from Young Stellar Objects in the \\epsilon Chamaeleontis Group: the Herbig Ae Star HD 104237 and Associated Low-Mass Stars

    E-print Network

    Testa, Paola; Schulz, Norbert S; Ishibashi, Kazunori

    2008-01-01

    We present Chandra-HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75\\msol mass range, in their pre-main sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary, and a K3 companion. Its X-ray variability indicates modulation possibly on time scales of the rotation period of the Herbig Ae star, and this would imply that the primary significantly contributes to the overall emission. The spectrum of the Herbig Ae+K3 system shows a soft component significantly more pronounced than in other K-type young stars. This soft emission is reminiscent of the unusually soft spectra observed for the single Herbig Ae stars HD 163296 and AB Aur, and therefore we tentatively attribute it to the Herbig Ae of the binary system. The HETGS spectrum shows strong emission lines corresponding to a wide range of plasma temperatures. The He-like triplet of MgXI and NeIX suggest the presence of plasma ...

  12. Young Low-Mass Stars and Brown Dwarfs in IC 348

    NASA Astrophysics Data System (ADS)

    Luhman, K. L.

    1999-11-01

    I present new results from a continuing program to identify and characterize the low-mass stellar and substellar populations in the young cluster IC 348 (0.5-10 Myr). Optical spectroscopy has revealed young objects with spectral types as late as M8.25. The intrinsic J-H and H-K colors of these sources are dwarflike, whereas the R-I and I-J colors appear intermediate between the colors of dwarfs and giants. Furthermore, the spectra from 6500 to 9500 Å are reproduced well with averages of standard dwarf and giant spectra, suggesting that such averages should be used in the classification of young late-type sources. An H-R diagram is constructed for the low-mass population in IC 348 (K6-M8). The presumably coeval components of the young quadruple system GG Tau (White et al.) and the locus of stars in IC 348 are used as empirical isochrones to test the theoretical evolutionary models. The calculations of Burrows et al. do not appear to be consistent with the data at these earliest stages of stellar evolution. There is fair agreement between the data and the model isochrones of D'Antona & Mazzitelli, except near the hydrogen-burning limit. The agreement cannot be improved by changing the conversion between spectral types and effective temperatures. On the other hand, for the models of Baraffe et al., an adjustment of the temperature scale to progressively warmer temperatures at later M types, intermediate between dwarfs and giants, brings all components of GG Tau onto the same model isochrone and gives the population of IC 348 a constant age and age spread as a function of mass. When other observational constraints are considered, such as the dynamical masses of GM Aur, DM Tau, and GG Tau A, the models of Baraffe et al. are the most consistent with observations of young systems. With compatible temperature scales, the models of both D'Antona & Mazzitelli and Baraffe et al. suggest that the hydrogen-burning mass limit occurs near M6 at ages of <~10 Myr. Thus, several likely brown dwarfs are discovered in this study of IC 348, with masses down to ~20-30 MJ.

  13. GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2

    NASA Astrophysics Data System (ADS)

    Origlia, L.; Oliva, E.; Maiolino, R.; Mucciarelli, A.; Baffa, C.; Biliotti, V.; Bruno, P.; Falcini, G.; Gavriousev, V.; Ghinassi, F.; Giani, E.; Gonzalez, M.; Leone, F.; Lodi, M.; Massi, F.; Montegriffo, P.; Mochi, I.; Pedani, M.; Rossetti, E.; Scuderi, S.; Sozzi, M.; Tozzi, A.

    2013-12-01

    Aims: 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 three red supergiants in the young Scutum cluster RSGC2. Results: Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to identify several tens of atomic and molecular lines suitable for chemical abundance determinations. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc), and of some s-process elements (Y, Sr). We found iron abundances between half and one third solar and solar-scaled [X/Fe] abundance patterns of iron-peak, alpha and most of the light elements, consistent with a thin-disk chemistry. We found a depletion of [C/Fe] and enhancement of [N/Fe], consistent with CN burning, and low 12C/13C abundance ratios (between 9 and 11), requiring extra-mixing processes in the stellar interiors during the post-main-sequence evolution. Finally, we found a slight [Sr/Fe] enhancement and a slight [Y/Fe] depletion (by a factor of ?2), with respect to solar. Table 3 is available in electronic form at http://www.aanda.org

  14. 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. [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); De Mink, S. E. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); De Koter, A.; Sana, H. [Astronomical Institute "Anton Pannekoek", Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands); Gvaramadze, V. V. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992 (Russian Federation); Liermann, A., E-mail: fschneid@astro.uni-bonn.de [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

    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 ?}.

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

    E-print Network

    Fernandes, B; Montmerle, T; Rojas, G

    2015-01-01

    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 (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 H{\\alpha} and lithium lines, observed with multi-objects 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 H{\\alpha} emission, the T Tauri stars were distinguished between classical (17%) and weak-lined (83%), 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 evolut...

  16. A Pulsation Search among Young Brown Dwarfs and Very-low-mass Stars

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie; Hillenbrand, Lynne A.

    2014-12-01

    In 2005, Palla & 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 ? 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.

  17. 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.

  18. Sizes and Shapes of Young Star Cluster Light Profiles in M83

    E-print Network

    Ryon, Jenna E; Adamo, Angela; Gallagher, John S; Konstantopoulos, Iraklis S; Larsen, Søren; Hollyhead, Katherine; Silva-Villa, Esteban; Smith, Linda J

    2015-01-01

    We measure the radii and two-dimensional light profiles of a large sample of young, massive star clusters in M83 using archival HST/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 ($\\eta$). We find lognormal distributions of effective radius and core radius, with medians of $\\approx$2.5 pc and $\\approx$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...

  19. 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 ? 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 ? 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 ? 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).

  20. Discovery of a Nearly Edge-On Disk around the Young Fe Star PDS 453

    NASA Astrophysics Data System (ADS)

    Perrin, Marshall D.; Schnieder, G.; Duchene, G.; Hines, D.; Pinte, C.; Fitzgerald, M.; Wisniewski, J.; HST GO 11155 Team

    2010-01-01

    We present the first spatially-resolved imaging of a protoplanetary disk around PDS 453, a young F2e star intermediate in mass between T Tauri and Herbig Ae stars. Using Lick AO polarimetry and HST NICMOS coronagraphic imaging and polarimetry, we spatially resolve the disk in scattered light from 1-2 microns, achieving an angular resolution of 0.15" and an inner working angle of 0.3" (20 and 40 AU respectively, for an assumed distance of 140 pc). In addition we present spatially-unresolved Gemini T-ReCS mid-IR photometry. Our high-contrast imaging reveals a highly inclined disk (i ~ 80 degrees) with a radius of 220 AU and a sharp outer edge, potentially due to flyby truncation by a nearby candidate stellar companion. Fitting radiative transfer disk models simultaneously to the imaging and SED allows determination of key disk properties as well as constraints on the nature of the scattering dust grains.

  1. YOUNG STELLAR OBJECTS IN LYNDS 1641: DISKS, ACCRETION, AND STAR FORMATION HISTORY

    SciTech Connect

    Fang Min [Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing (China); Kim, Jinyoung Serena; Flaherty, Kevin [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Van Boekel, Roy; Henning, Thomas [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Sicilia-Aguilar, Aurora, E-mail: mfang@pmo.ac.cn [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Cantoblanco, Madrid (Spain)

    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.

  2. A DEEP CHANDRA X-RAY SPECTRUM OF THE ACCRETING YOUNG STAR TW HYDRAE

    SciTech Connect

    Brickhouse, N. S.; Cranmer, S. R.; Dupree, A. K.; Luna, G. J. M.; Wolk, S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2010-02-20

    We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature T{sub e} , electron density N{sub e} , hydrogen column density N{sub H} , relative elemental abundances, and velocities, and reveals its source in three distinct regions of the stellar atmosphere: the stellar corona, the accretion shock, and a very large extended volume of warm postshock plasma. The presence of Mg XII, Si XIII, and Si XIV emission lines in the spectrum requires coronal structures at {approx}10 MK. Lower temperature lines (e.g., from O VIII, Ne IX, and Mg XI) formed at 2.5 MK appear more consistent with emission from an accretion shock. He-like Ne IX line ratio diagnostics indicate that T{sub e} = 2.50 +- 0.25 MK and N{sub e} = 3.0 +- 0.2 x 10{sup 12} cm{sup -3} in the shock. These values agree well with standard magnetic accretion models. However, the Chandra observations significantly diverge from current model predictions for the postshock plasma. This gas is expected to cool radiatively, producing O VII as it flows into an increasingly dense stellar atmosphere. Surprisingly, O VII indicates N{sub e} = 5.7{sup +4.4}{sub -1.2} x 10{sup 11} cm{sup -3}, 5 times lower than N{sub e} in the accretion shock itself and {approx}7 times lower than the model prediction. We estimate that the postshock region producing O VII has roughly 300 times larger volume and 30 times more emitting mass than the shock itself. Apparently, the shocked plasma heats the surrounding stellar atmosphere to soft X-ray emitting temperatures and supplies this material to nearby large magnetic structures-which may be closed magnetic loops or open magnetic field leading to mass outflow. Our model explains the soft X-ray excess found in many accreting systems as well as the failure to observe high N{sub e} signatures in some stars. Such accretion-fed coronae may be ubiquitous in the atmospheres of accreting young stars.

  3. Dynamical star-disk interaction in the young stellar system V354 Monocerotis

    NASA Astrophysics Data System (ADS)

    Fonseca, N. N. J.; Alencar, S. H. P.; Bouvier, J.; Favata, F.; Flaccomio, E.

    2014-07-01

    Aims: The main goal of this work is to characterize the mass accretion and ejection processes of the classical T Tauri star V354 Mon, a member of the young stellar cluster NGC 2264. Methods: In March 2008, photometric and spectroscopic observations of V354 Mon were obtained simultaneously with the CoRoT satellite, the 60 cm telescope at the Observatório Pico dos Dias (LNA, Brazil) equipped with a CCD camera and Johnson/Cousins BV(RI)c filters, and the SOPHIE échelle spectrograph at the Observatoire de Haute-Provence (CNRS, France). Results: The light curve of V354 Mon shows periodical minima (P = 5.26 ± 0.50 days) that vary in depth and width at each rotational cycle. The BV(RI)c observations indicate that the system becomes slightly bluer as the flux increases. The spectra of this T Tauri star exhibit variable emission lines, with blueshifted and redshifted absorption components associated with a disk wind and with the accretion process, respectively, confirming the magnetospheric accretion scenario. From the analysis of the photometric and spectroscopic data, it is possible to identify correlations between the emission line variability and the light-curve modulation of the young system, such as the occurrence of pronounced redshifted absorption in the H? line at the epoch of minimum flux. This is evidence that during photometric minima we see the accretion funnel projected onto the stellar photosphere in our line of sight, implying that the hot spot coincides with the light-curve minima. We applied models of cold and hot spots and a model of occultation by circumstellar material to investigate the source of the observed photometric variations. Conclusions: We conclude that nonuniformly distributed material in the inner part of the circumstellar disk is the main cause of the photometric modulation, which does not exclude the presence of hot and cold spots at the stellar surface. It is believed that the distortion in the inner part of the disk is created by the dynamical interaction between the stellar magnetosphere, inclined with respect to the rotation axis, and the circumstellar disk, as also observed in the classical T Tauri star AA Tau and predicted by magnetohydrodynamical numerical simulations. Based on the observations obtained with the CoRoT satellite, at the Observatório Pico dos Dias, Brazil, and at the Observatoire de Haute Provence, France. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.

  4. 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 ? 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?; ?acc~ 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

  5. 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. [Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); Scaife, Anna M. M. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ (United Kingdom); Green, David A.; Buckle, Jane V., E-mail: rainsworth@cp.dias.ie [Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE (United Kingdom)

    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.

  6. Variable Stars Pulsating Stars: periodic

    E-print Network

    Basu, Shantanu

    Variable Stars · Pulsating Stars: periodic expansion and contraction, e.g., Cepheids, RR Lyrae increases . Why? #12;Pulsating Stars Cepheid variables: giant stars, very luminous Type II Cepheids: lower Z's · Catacylsmic and Eruptive Variables: sudden large changes, e.g., novae and supernovae · Others: changes

  7. Planets Around Low-Mass Stars (PALMS). III. A Young Dusty L Dwarf Companion at the Deuterium-Burning Limit

    E-print Network

    Bowler, Brendan P; Shkolnik, Evgenya L; Dupuy, Trent J

    2013-01-01

    We report the discovery of an L-type companion to the young M3.5V star 2MASS J01225093-2439505 at a projected separation of 1.45" (~52 AU) as part of our adaptive optics imaging search for extrasolar giant planets around young low-mass stars. 2MASS 0122-2439 B has very red near-infrared colors similar to the HR 8799 planets and the reddest known young/dusty L dwarfs in the field. Moderate-resolution (R~3800) 1.5-2.4 $\\mu$m spectroscopy reveals a near-infrared spectral type of L4-L6 and an angular H-band shape, confirming its cool temperature and young age. The kinematics of 2MASS 0122-2439 AB are marginally consistent with members of the ~120 Myr AB Dor young moving group based on the photometric distance to the primary (36 +/- 4 pc) and our radial velocity measurement of 2MASS 0122-2439 A from Keck/HIRES. We adopt the AB Dor group age for the system, but the high energy emission, lack of Li I $\\lambda$6707 absorption, and spectral shape of 2MASS 0122-2439 B suggest a range of ~10-120 Myr is possible. The age...

  8. 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.

  9. THE FIRST X-SHOOTER OBSERVATIONS OF JETS FROM YOUNG STARS

    SciTech Connect

    Bacciotti, F.; Randich, S. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze (Italy); Whelan, E. T. [Laboratoire d'Astrophysique de l'Observatoire de Grenoble, UMR 5521 du CNRS, 38041 Grenoble Cedex (France); Alcala, J. M. [INAF-Osservatorio di Capodimonte, Via Moiariello 16, 80131 Napoli (Italy); Nisini, B. [INAF-Osservatorio di Roma, Via di Frascati 33, 00040, Monteporzio Catone (Italy); Podio, L. [Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen (Netherlands); Stelzer, B. [INAF-Osservatorio di Palermo, Piazza del Parlamento 1, 90134 Palermo (Italy); Cupani, G. [INAF-Osservatorio di Trieste, Via Tiepolo 11, 34143 Trieste (Italy)

    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.

  10. 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. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States)

    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.

  11. 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 3? 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°.

  12. Near-Infrared Polarimetric Imaging of Disks around Young Intermediate-mass Stars in SEEDS

    NASA Astrophysics Data System (ADS)

    Fukagawa, Misato; Hashimoto, Jun; Grady, C. A.; Momose, Munetake; Wisniewski, J. P.; Okamoto, Yoshiko; Muto, Takayuki; Kusakabe, Nobuhiko; Bonnefoy, Mickael; Kotani, Takayuki; Maruta, Yayoi; Tamura, Motohide; Seeds/Hiciao/Ao188 Collaboration,

    2013-07-01

    We present our recent results to directly image circumstellar disks around Herbig Fe/Ae/Be stars in scattered light with Subaru. Observations of such young disks are critically important to understand how disks evolve possibly under the mutual interaction with new-born planets. One of the observational approaches is direct imaging in scattered light, and the progress in this field since PPV can be found in the ability to prove inner regions of disks. This improvement largely owes to the technique of polarization differential imaging (PDI) which provides higher contrast by extracting scattered light from the disk while suppressing unpolarized stellar light. Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) is the project dedicated to exoplanet hunting and study of circumstellar disks by direct imaging. Since its beginning in 2009, thirteen Herbig Fe/Ae/Be stars have been observed primarily in H band (1.6 micron). The PDI method has been employed with adaptive optics, enabling us to look into the inner region as close as 0.2 arcsec (˜30 AU) in radius with the typical angular resolution of 0.06 arcsec (˜8 AU). As a result, the SEEDS imagery has newly uncovered rich structures such as spiral arms, inner holes, and gaps for (pre-)transitional disks while suggested the variably illuminated disks for primordial systems. The highlight is the discovery of two spiral arms each for SAO 206462 and MWC 758. The spiral feature has been uniquely found toward Herbig Fe/Aes so far, which might be due to their warmer disks producing arms loosely wound and more easily detected. The observed morphology can be interpreted by the density-wave model, and those disks are implied to harbor Jupiter-mass companions as the exciting sources of the spiral structures according to these models.

  13. The statistics of triggered star formation: an overdensity of massive young stellar objects around Spitzer bubbles

    NASA Astrophysics Data System (ADS)

    Thompson, M. A.; Urquhart, J. S.; Moore, T. J. T.; Morgan, L. K.

    2012-03-01

    We present a detailed statistical study of massive star formation in the environment of 322 Spitzer mid-infrared bubbles by using the Red MSX Source (RMS) survey for massive young stellar objects (YSOs). Using a combination of simple surface density plots and a more sophisticated angular cross-correlation function analysis, we show that there is a statistically significant overdensity of RMS YSOs towards the bubbles. There is a clear peak in the surface density and angular cross-correlation function of YSOs projected against the rim of the bubbles. By investigating the autocorrelation function of the RMS YSOs, we show that this is not due to intrinsic clustering of the RMS YSO sample. RMS YSOs and Spitzer bubbles are essentially uncorrelated with each other beyond a normalized angular distance of two bubble radii. The bubbles associated with RMS YSOs tend to be both smaller and thinner than those that are not associated with YSOs. We interpret this tendency to be due to an age effect, with YSOs being preferentially found around smaller and younger bubbles. We find no evidence to suggest that the YSOs associated with the bubbles are any more luminous than the rest of the RMS YSO population, which suggests that the triggering process does not produce a top-heavy luminosity function or initial mass function. We suggest that it is likely that the YSOs were triggered by the expansion of the bubbles and estimate that the fraction of massive stars in the Milky Way formed by this process could be between 14 and 30 per cent.

  14. A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1

    NASA Astrophysics Data System (ADS)

    Leitzinger, M.; Odert, P.; Greimel, R.; Korhonen, H.; Guenther, E. W.; Hanslmeier, A.; Lammer, H.; Khodachenko, M. L.

    2014-09-01

    We present a search for stellar activity (flares and mass ejections) in a sample of 28 stars in the young open cluster Blanco-1. We use optical spectra obtained with European Southern Observatory's Visible Multi-Object Spectrograph installed on the Very Large Telescope. From the total observing time of ˜5 h, we find four H? flares but no distinct indication of coronal mass ejections (CMEs) on the investigated dK-dM stars. Two flares show `dips' in their light curves right before their impulsive phases which are similar to previous discoveries in photometric light curves of active dMe stars. We estimate an upper limit of <4 CMEs per day per star and discuss this result with respect to a empirical estimation of the CME rate of main-sequence stars. We find that we should have detected at least one CME per star with a mass of ? 3 × 1017 g depending on the star's X-ray luminosity, but the estimated H? fluxes associated with these masses are below the detection limit of our observations. We conclude that the parameter which mainly influences the detection of stellar CMEs using the method of Doppler-shifted emission caused by moving plasma is not the spectral resolution/velocity but the flux/mass of the CME.

  15. Predicting Volcanic Eruptions

    NSDL National Science Digital Library

    Richard Treves

    This presentation uses data from several eruptive episodes of Mount St. Helens in the 1980's to show the way in which a series of eruptions were accurately predicted by USGS scientists as far as 3 weeks before eruptive activity occurred. Several modules demonstrate the use of earthquakes and deformation of a volcano for predicting eruptions and allow you to predict an actual eruption of Mount St. Helens using data collected by scientists of the USGS Cascades Volcano Observatory.

  16. CCD photometry and proper motions of late-type stars in the young open cluster Stock 2

    Microsoft Academic Search

    D. C. Foster; A. Theissen; C. J. Butler; W. R. J. Rolleston; P. B. Byrne; S. L. Hawley

    2000-01-01

    We present the results of the first CCD BVRI photometric and proper motion study of late-type stars in the young open cluster Stock 2. Twenty-one fields of approximately 5'x 5' size have been observed photometrically, from which we have identified 118 candidate members based on their positions on colour-magnitude diagrams relative to theoretical isochrones. From a comparison of the known

  17. Dust Rings and Filaments around the Isolated Young Star V1331 Cygni

    NASA Astrophysics Data System (ADS)

    Quanz, S. P.; Apai, D.; Henning, Th.

    2007-02-01

    We characterize the small- and large-scale environment of the young star V1331 Cygni with high-resolution HST WFPC2 and Digitized Sky Survey images. In addition to a previously known outer dust ring (~30'' in diameter), the WFPC2 scattered light image reveals an inner dust ring for the first time. This ring has a maximum radius of ~6.5'' and is possibly related to a molecular envelope. Large-scale optical images show that V1331 Cyg is located at the tip of a long dust filament linking it to the dark cloud LDN 981. We discuss the origin of the observed dust morphology and analyze the object's relation to its parent dark cloud LDN 981. Finally, based on recent results from the literature, we investigate the properties of V1331 Cyg and conclude that in its current state the object does not show sufficient evidence to be characterized as an FU Ori object. Based on observations 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 NAS5-26555.

  18. Evolutionary studies of the Young Star Clusters: \\\\NGC 1960, NGC 2453 and NGC 2384

    E-print Network

    Priya Hasan; G. C. Kilambi; S. N. Hasan

    2007-11-20

    We report the analysis of the young star clusters NGC 1960, NGC 2453 and NGC 2384 observed in the $J$ (1.12 $\\mu$m), $H$ (1.65 $\\mu$m) and $K^{'}$ (2.2 $\\mu$m) bands. Estimates of reddening, distance and age as $E(B-V)=0.25$, $d= 1380$ pc and $t=31.6$ to 125 Myr for NGC 1960, $E(B-V)=0.47$, $d=3311$ pc and $t=40$ to 200 Myr for NGC 2453 and $E(B-V)=0.25$, $d=3162$ pc and $t=55$ to 125 Myr for NGC 2384 have been obtained. Also, we have extended the color--magnitude diagrams of these clusters to the fainter end and thus extended the luminosity functions to fainter magnitudes. The evolution of the main sequence and luminosity functions of these clusters have been compared with themselves as well as Lyng\\aa 2 and NGC 1582.

  19. NGC 2782: a merger remnant with young stars in its gaseous tidal tail

    NASA Astrophysics Data System (ADS)

    Torres-Flores, S.; de Oliveira, C. Mendes; de Mello, D. F.; Scarano, S.; Urrutia-Viscarra, F.

    2012-04-01

    We have searched for young star-forming regions around the merger remnant NGC 2782. By using Galaxy Evolution Explorer far-ultraviolet and near-ultraviolet imaging and H I data we found seven ultraviolet sources, located at distances greater than 26 kpc from the centre of NGC 2782, and coinciding with its western H I tidal tail. These regions were resolved in several smaller systems when Gemini/Gemini multi-object spectrograph (GMOS) r-band images were used. We compared the observed colours to stellar population synthesis models and found that these objects have ages of ˜1 to 11 Myr and masses ranging from 103.9 to 104.6 M?. 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 NGC 2782 and also similar to the value presented for an object located close to the main body of NGC 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGC 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the centre 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. a r-band magnitude inside a fixed aperture of 4 arcsec radius and corrected by MW extinction. Region 2 appears to have diffuse emission in the r-band image. b Fixed FUV-band magnitudes corrected by apertures (as described in Section 3.2) and MW extinction. c FUV-r colours. d Magnitudes were measured in a fixed aperture of 4 arcsec radius and corrected by MW extinction. FUV and NUV magnitudes were corrected by aperture, as described in Section 3.2. e Left values: E(B-V) estimated as in Section 3.3. Right values: E(B-V) estimated by using the H I data of NGC 2782. Total extinction is the sum of the internal and Galactic extinctions (0.13 mag in this band). f Ages estimated from FUV-NUV and FUV-r. In parenthesis we show the ages estimated from the H? equivaland SB99 models. g Distance from the centre of the galaxy, assuming a position angle and inclination of 0°.

  20. Galactic Globular Cluster NGC1261: "Young", Low-alpha and Star-to-Star Abundance Variations In Na-O?

    NASA Astrophysics Data System (ADS)

    Filler, Dan; Ivans, I. I.; Simmerer, J.

    2012-01-01

    We present the first high-resolution (R 40,000) chemical abundance analysis of the relatively young (8-9 Gyr), outer halo Galactic globular cluster NGC 1261. Stellar parameters for three stars were derived using spectroscopic constraints. Abundances were deduced using a combination of EWs and fitting synthetic spectra. Our derived metallicity ([Fe/H] = -1.19 ± 0.02) is in excellent agreement with the metallicity scale of Kraft & Ivans (2003, 2004). However, the Na-O anticorrelation spanning 1.1 ± 0.1 dex in sodium, is as large as any other cluster reported to date. In the light element group, we report -0.9 < [C/Fe] < -0.6 with C12/C13 = 4, (for which three regions in the G-band were synthesized); +0.5 < [N/Fe] < +1.1 from the CN band head near 8004A; -0.25 < [O/Fe] < +0.2 from the forbidden lines; -0.3 < [Al/Fe] < +0.15 from the aluminum doublet near 6696A. We also present abundances for the alpha-elements [Mg/Fe] = +0.2 ± 0.1; [Si/Fe] = +0.1 ± 0.1; [Ca/Fe] = +0.15 ± 0.1; [Ti/Fe] = +0.15 ± 0.15. NGC 1261 is distinguished from other clusters of comparable metallicity due to low-alpha abundances. We will discuss the nucleosynthetic histories that may have given rise to these abundances including the possibility of enrichment by Type 1a supernovae. We also report abundances for the iron-peak elements [Sc/Fe] = +0.0 ± 0.2; [V/Fe] = -0.1 ± 0.1; [Cr/Fe] = -0.1 ± 0.15; [Mn/Fe] = -0.1 ± 0.15; [Co/Fe] = +0.2 ± 0.1; [Ni/Fe] = +0.0 ± 0.1; the light neutron-capture elements [Y/Fe] = +0.1 ± 0.1; [Zr/Fe] = +0.35 ± 0.1; the s-process elements [Ba/Fe] = +0.15 ± 0.1; [La/Fe] = +0.1 ± 0.1; [Nd/Fe] = +0.15 ± 0.1; and the r-process element [Eu/Fe] = 0.6 ± 0.2.

  1. Dynamic Young Stars and their Disks: A Temporal View of NGC 2264 with Spitzer and CoRoT

    NASA Astrophysics Data System (ADS)

    Cody, Ann Marie; Stauffer, John; Bouvier, Jèrôme

    2014-01-01

    Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 ("CSI 2264")- a joint30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway. Based on data from the Spitzer and CoRoT missions. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA-s RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.

  2. Kinds of Volcanic Eruptions

    NSDL National Science Digital Library

    At this site, different kinds of eruptions are compared with Hawaiian eruptions. Students will learn that volcanoes can erupt from vents on their summits or flanks, eruptions interact with water in submarine environments as new islands form beneath glaciers and in crater lakes, and volcanic eruptions can be classified by the character of the eruption, including the following types: basaltic flood, Hawaiian, Strombolian, Vulcanian, Peleean, Plinian, rhyolitic flood, ultravulcanian, gas, and fumarolic. As a result of this lesson, students will be able to recognize summit and flank eruptions, know the types of water-related eruptions, and describe different types of volcanic eruptions. The site contains seven activities that range in grade level from kindergarten to grade twelve, and a virtual fieldtrip to Crater Rim Drive.

  3. 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 [Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Marcy, Geoffrey W.; Isaacson, Howard [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Howard, Andrew W. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Johnson, John Asher [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Torres, Guillermo; Carter, Joshua A.; Dawson, Rebekah I.; Geary, John C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Campante, Tiago L.; Chaplin, William J.; Davies, Guy R. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Lund, Mikkel N. [Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Buchhave, Lars A. [Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen (Denmark); Everett, Mark E. [National Optical Astronomy Observatory, 950 N. Cherry Ave, Tucson, AZ 85719 (United States); Fischer, Debra A. [Astronomy Department, Yale University, New Haven, CT (United States); Gilliland, Ronald L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Horch, Elliott P. [Southern Connecticut State University, New Haven, CT 06515 (United States); 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 ?} (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.

  4. Near-IR integral field spectroscopy of ionizing stars and young stellar objects on the borders of HII regions

    E-print Network

    Martins, F; Deharveng, L; Zavagno, A; Bouret, J -C

    2009-01-01

    We present near-IR SINFONI observations of three Galactic HII regions: RVW79, RCW82 and RCW120. We identify the ionizing stars of each region: they are early to late O stars, close to the main sequence. We derive their stellar and wind properties using atmosphere models computed with the code CMFGEN. The cluster ionizing RCW~79 formed 2.3+/-0.5 Myr ago. Similar ages are estimated, albeit with a larger uncertainty, for the ionizing stars of the other two regions. In RCW79 the mechanical wind luminosity represents only 0.1% of the ionizing luminosity, questioning the influence of stellar winds on the dynamics of the the HII region. The young stellar objects show four main types of spectral features: H2 emission, Br gamma emission, CO bandheads emission and CO bandheads absorption. These features are typical of young stellar objects surrounded by disks and/or envelopes. The radial velocities of most YSOs are consistent with that of the ionized gas, firmly establishing that star formation is taking place on the b...

  5. Bruck 88: a young star cluster with an old age resemblance in the outskirts of the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2014-12-01

    We present spectroscopic and photometric results for the Small Magellanic Cloud (SMC) cluster Bruck 88. From the comparison of the cluster integrated spectrum with template cluster spectra, we found that the Milky Way globular cluster template spectra are the ones which best resemble it. However, the extracted cluster colour-magnitude diagram reveals that Bruck 88 is a young cluster (log(t) = 8.1 ± 0.1). The derived cluster age is compatible with the presence of a bright red giant (BRG) star located ˜2.6 arcsec in the sky from the cluster centre. We serendipitously observed HW 33, a star cluster located ?3 arcmin to the south-east from Bruck 88. We obtained for the cluster the same age than Bruck 88 and surprisingly, a BRG star located within the cluster radius also appears to be compatible with the cluster age. We estimated the MK type of the BRG star in the Bruck 88 field to be in the range G9 II/Ib-K1 III. By combining the spectrum of a star within this MK type range with a 100-150 Myr template cluster integrated spectrum, we found that a proportion 85/15 in the sense BRG/template results in a spectrum which best resembles that of Bruck 88. This result confirms that a BRG star dominates the cluster integrated spectrum, so that it causes the globular cluster appearance of its integrated light.

  6. Near-IR integral field spectroscopy of ionizing stars and young stellar objects on the borders of H II regions

    NASA Astrophysics Data System (ADS)

    Martins, F.; Pomarès, M.; Deharveng, L.; Zavagno, A.; Bouret, J. C.

    2010-02-01

    Aims: We study three Galactic H ii regions - RCW 79, RCW 82, and RCW 120 - where triggered star formation is taking place. Two stellar populations are observed: the ionizing stars of each H ii region and young stellar objects on their borders. Our goal is to show that they represent two distinct populations, as expected from successive star-forming events. Methods: We use near-infrared integral field spectroscopy obtained with SINFONI on the VLT to make a spectral classification. We derived the stellar and wind properties of the ionizing stars using atmosphere models computed with the code CMFGEN. The young stellar objects were classified according to their K-band spectra. In combination with published near and mid infrared photometry, we constrained their nature. Linemaps were constructed to study the geometry of their close environment. Results: We identify the ionizing stars of each region. RCW 79 is dominated by a cluster of a dozen O stars, identified for the first time by our observations. RCW 82 and RCW 120 are ionized by two and one O star, respectively. All ionizing stars are early-to-late O stars, close to the main sequence. The cluster ionizing RCW 79 formed 2.3 ± 0.5 Myr ago. Similar ages are estimated, albeit with a larger uncertainty, for the ionizing stars of the other two regions. The total mass-loss rate and ionizing flux is derived for each region. In RCW 79, where the richest cluster of ionizing stars is found, the mechanical wind luminosity represents only 0.1% of the ionizing luminosity, questioning the influence of stellar winds on the dynamics of these three H ii regions. The young stellar objects show four main types of spectral features: H2 emission, Br? emission, CO bandheads emission, and CO bandheads absorption. These features are typical of young stellar objects surrounded by disks and/or envelopes, confirming that star formation is taking place on the borders of the three H ii regions. The radial velocities of most YSOs are consistent with that of the ionized gas, firmly establishing their association with the H ii regions. Exceptions are found in RCW 120 where differences up to 50 km s-1 are observed. Outflows are detected in a few YSOs. All YSOs have moderate-to-strong near-IR excess. In the [24] versus K-[24] diagram, the majority of the sources dominated by H2 emission lines stand out as redder and brighter than the rest of the YSOs. The quantitative analysis of their spectra indicates that, for most of them, the H2 emission is essentially thermal and likely produced by shocks. We tentatively propose that they represent an earlier phase of evolution compared to sources dominated by Br? and CO bandheads. We suggest that they still possess a dense envelope in which jets or winds create shocks. The other YSOs have partly lost their envelopes and show signatures of accretion disks. Overall, the YSOs show distinct spectroscopic signatures compared to the ionizing sources, confirming the presence of two stellar populations. Based on observations collected at the ESO Very Large Telescope (program 081.C-0057).

  7. A "diamond-ring" star: the unusual morphologic structure of a young (multiple?) object

    E-print Network

    Joao L. Yun; Jose M. Torrelles; Nuno C. Santos

    2007-04-24

    We have observed IRAS06468-0325 obtaining optical and infrared images through IJHKs and L' filters, K-band low-resolution spectroscopy, together with millimetre line observations of CO and CS. IRAS06468-0325 has a very unusual and enigmatic morphology with two components: a bright, close to point-like source (the diamond) and a sharp-edge ring-like structure (the ring). The source is not detected in the optical, at wavelengths shorter than the I-band. The diamond is seen in all the imaging bands observed. The ring-like structure in IRAS06468-0325 is clearly seen in the I, J, H, and Ks. It is not detected in the L'-band image. Infrared colours of the diamond are compatible with excess circumstellar emission and a young stellar nature. A strongly non-gaussian and moderately bright CO(1-0) and {13}CO(2-1) lines are seen towards IRAS06468-0325, at v_{LSR} of 30.5 km s{-1} (corresponding to a kinematic distance of 3 kpc). Very weak C{18}O(2-1) and CS(2-1) lines were detected. K-band spectra of the diamond and of the ring are similar both in the slope of the continuum and in the presence of lines supporting the idea that the ring is reflected light from the diamond. With the current data, a few different scenarios are possible to explain the morphology of this object. However, the available data seem to favour that the morphology of IRAS06468-0325 correspond to a young stellar multiple system in a transient stage where a binary co-exists with a circumbinary disc, similar to the case of GG Tau. In this case, the sharpness of the well-defined ring may be due to tidal truncation from dynamic interactions between components in a binary or multiple stellar system. IRAS06468-0325 may be an important rare case that illustrates a short-lived stage of the process of binary or multiple star formation.

  8. Magnetocentrifugally driven flows from young stars and disks. 2: Formulation of the dynamical problem

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.; Najita, Joan; Ruden, Steven P.; Lizano, Susana

    1994-01-01

    We formulate the dynamical problem of a cool wind centrifugally driven from the magnetic interface of a young star and an adjoining Keplerian disk. We examine the situation for mildly accreting T Tauri stars that rotate slowly as well as rapidly accreting protostars that rotate near break-up. In both cases a wind can be driven from a small X-region just outside the stellar magnetopause, where the field lines assume an open geometry and are rooted to material that rotates at an angular speed equal both to the local Keplerian value and to the stellar angular speed. Assuming axial symmetry for the ideal magnetohydrodynamic flow, which requires us to postpone asking how the (lightly ionized) gas is loaded onto field lines, we can formally integrate all the governing equations analytically except for a partial equation that describes how streamlines spread in the meridional plane. Apart from the difficulty of dealing with PDEs of mixed type, finding the functional forms of the conserved quantities along streamlines - the ratio beta of magnetic field to mass flux, the specific energy H of the fluid in the rotating frame, and the total specific angular momentum J carried in the matter and the field - constitutes a standard difficulty in this kind of (Grad-Shafranov) formalism. Fortunately, because the ratio of the thermal speed of the mass-loss regions to the Keplerian speed of rotation of the interface constitutes a small parameter epsilon, we can attack the overall problem by the method of matched asymptotic expansions. This procedure leads to a natural and systematic technique for obtaining the relevant functional dependences of beta, H, and J. Moreover, we are able to solve analytically for the properties of the flow emergent from the small transsonic region driven by gas pressure without having to specify the detailed form of any of the conserved functions, beta, H, and J. This analytical solution provides inner boundary conditions for the numerical computation in a companion paper by Najita & Shu of the larger region where the main acceleration to terminal speeds occurs.

  9. 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 ?m 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-?. Assuming a constant CS abundance throughout the envelope, values of ?=1.0-1.5 are found, which is significantly flatter than the ?=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 ?=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 ?m 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.

  10. Volcanic Eruptions and Hazards

    NSDL National Science Digital Library

    This interactive resource adapted from the National Park Service explains the difference between explosive or effusive (lava pours from a vent onto the ground) volcanic eruptions, and describes the hazards associated with each type of eruption.

  11. GAS SURFACE DENSITY, STAR FORMATION RATE SURFACE DENSITY, AND THE MAXIMUM MASS OF YOUNG STAR CLUSTERS IN A DISK GALAXY. I. THE FLOCCULENT GALAXY M 33

    SciTech Connect

    Gonzalez-Lopezlira, Rosa A.; Pflamm-Altenburg, Jan; Kroupa, Pavel, E-mail: r.gonzalez@crya.unam.mx [Argelander Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2012-12-20

    We analyze the relationship between maximum cluster mass M{sub max} and surface densities of total gas ({Sigma}{sub gas}), molecular gas ({Sigma}{sub H{sub 2}}), and star formation rate ({Sigma}{sub SFR}) in the flocculent galaxy M 33, using published gas data and a catalog of more than 600 young star clusters in its disk. By comparing the radial distributions of gas and most massive cluster masses, we find that M{sub max}{proportional_to}{Sigma}{sup 4.7{+-}0.4}{sub gas}, M{sub max}{proportional_to}{Sigma}{sup 1.3{+-}0.1}{sub H{sub 2}}, and M{sub max}{proportional_to}{Sigma}{sup 1.0{+-}0.1}{sub SFR}. We rule out that these correlations result from the size of the sample; hence, the change of the maximum cluster mass must be due to physical causes.

  12. Extrasolar planets and brown dwarfs around A-F type stars. VIII. A giant planet orbiting the young star HD 113337

    NASA Astrophysics Data System (ADS)

    Borgniet, S.; Boisse, I.; Lagrange, A.-M.; Bouchy, F.; Arnold, L.; Díaz, R. F.; Galland, F.; Delorme, P.; Hébrard, G.; Santerne, A.; Ehrenreich, D.; Ségransan, D.; Bonfils, X.; Delfosse, X.; Santos, N. C.; Forveille, T.; Moutou, C.; Udry, S.; Eggenberger, A.; Pepe, F.; Astudillo, N.; Montagnier, G.

    2014-01-01

    Aims: In the context of the search for extrasolar planets and brown dwarfs around early-type main-sequence stars we present the detection of a giant planet around the young F-type star HD 113337. We estimated the age of the system to be 150-50+100 Myr. Interestingly, an infrared excess attributed to a cold debris disk was previously detected around this star. Methods: We used the SOPHIE spectrograph on the 1.93 m telescope at Observatoire de Haute-Provence to obtain ~300 spectra over six years. We used our tool dedicated to the spectra analysis of A and F stars to derive the radial velocity variations. Results: The data reveal a period of 324.0+1.7-3.3 days that we attribute to a giant planet with a minimum mass of 2.83 ± 0.24 MJup in an eccentric orbit with e = 0.46 ± 0.04. A long-term quadratic drift, which we assign to be probably of stellar origin, is superimposed on the Keplerian solution. Based on observations made with the SOPHIE spectrograph at the Observatoire de Haute-Provence (CNRS, France).Table 2 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/561/A65

  13. Young Stars near Earth: The Octans-Near Association and Castor Moving Group

    NASA Astrophysics Data System (ADS)

    Zuckerman, B.; Vican, Laura; Song, Inseok; Schneider, Adam

    2013-11-01

    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-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-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 "Octans-Near"; 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.

  14. POPULATION SYNTHESIS OF YOUNG ISOLATED NEUTRON STARS: THE EFFECT OF FALLBACK DISK ACCRETION AND MAGNETIC FIELD EVOLUTION

    SciTech Connect

    Fu, Lei; Li, Xiang-Dong, E-mail: lixd@nju.edu.cn [Department of Astronomy, Nanjing University, Nanjing 210093 (China)

    2013-10-01

    The spin evolution of isolated neutron stars (NSs) is dominated by their magnetic fields. The measured braking indices of young NSs show that the spin-down mechanism due to magnetic dipole radiation with constant magnetic fields is inadequate. Assuming that the NS magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we carry out a Monte Carlo simulation of the evolution of young NSs, and show that most of the pulsars have braking indices ranging from –1 to 3. The results are compatible with the observational data of NSs associated with supernova remnants. They also suggest that the initial spin periods of NSs might occupy a relatively wide range.

  15. A ``diamond-ring'' star: the unusual morphology of a young (multiple?) object

    NASA Astrophysics Data System (ADS)

    Yun, J. L.; Torrelles, J. M.; Santos, N. C.

    2007-07-01

    Aims:Our new near-infrared J and Ks-band images taken towards IRAS 06468-0325 revealed the presence of extended emission with very unusual and enigmatic morphology: that of a diamond-ring, that is, a ring or torus with a bright source overlaping the edge of it (not inside it). We report the discovery of this source, explore its nature, and propose possible interpretations of its morphological structure. Methods: We observed IRAS 06468-0325 obtaining optical and infrared images through IJHKs and L' filters, K-band low-resolution spectroscopy, together with millimetre line observations of CO(1-0), 13CO(2-1), C18O(2-1), and CS(2-1). Results: Morphologically, IRAS 06468-0325 has two components: a bright, close to point-like source (the diamond) and a sharp-edge ring-like structure (the ring). The source is not detected in the optical wavelengths shorter than the I-band. The diamond is seen in all the imaging bands observed. The ring-like structure in IRAS 06468-0325 is clearly seen in the I, J, H, and Ks. It is not detected in the L'-band image. Infrared colours of the diamond are compatible with excess circumstellar emission and a young stellar nature. Strongly non-gaussian, moderately bright CO(1-0) and 13CO(2-1) lines are seen towards IRAS 06468-0325, at v_LSR of 30.5 km s-1 (corresponding to a kinematic distance of 3 kpc). Very weak C18O(2-1) and CS(2-1) lines were detected. K-band spectra of the diamond and of the ring are similar both in the slope of the continuum and in the presence of lines supporting the idea that the ring is reflected light from the diamond. Conclusions: With the current data, a few different scenarios are possible to explain the morphology of this object. However, the available data seem to favour the idea that the morphology of IRAS 06468-0325 corresponds to a young, stellar multiple system in a transient stage where a binary co-exists with a circumbinary disc, similar to the case of GG Tau. In this case, the sharpness of the well-defined ring may be due to tidal truncation from dynamic interactions between components in a binary or multiple stellar system. IRAS 06468-0325 may be an important rare case that illustrates a short-lived stage of the process of binary or multiple star formation. Based on observations collected at the ESO 8.2-m VLT-UT1 Antu telescope (programs 072.B-0335, 072.C-0335, 066.C-0015, and 063.I-0097). IJHKsL' images (FITS files) 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/cgi-bin/qcat?J/A+A/470/231

  16. Non-LTE modeling of the structure and spectra of hot accretion spots on the surface of young stars

    NASA Astrophysics Data System (ADS)

    Dodin, A. V.

    2015-05-01

    The results of modeling the structure and spectra of hot accretion spots on the surface of young stars with allowance made for the departures from LTE for hydrogen and helium are presented. The existence of ram pressure of the infalling gas at the outer boundary of the hot spot has been found to lead to Stark broadening of the hydrogen line profiles to ˜1000 km s-1 at the accretion parameters considered. It is shown that allowance for the departures from LTE for carbon and oxygen atoms and ions does not lead to noticeable changes in the structure of the hot spot.

  17. 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 ?m) 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 single telescope into a Fizeau interferometer using a non redundant mask inserted in a pupil plane of the instrument. The analysis of the observations was completed with the sparse aperture mode pipeline. Interference fringes are fitted to obtain complex visibilities of the object, then the closure phases are calibrated and evaluated. Finally, a map of the detection limits is obtained as it is related to the closure phases previously estimated. In order to obtain an estimation of the mass corresponding to the luminosity measured with the reduction pipeline we are using theoretical isochrones interpolated into synthetic color tables. The results are maps of detection limits in unit of Jupiter Mass in a range of up to 450 mas around the stars.

  18. XMM-Newton investigations of the Lambda Orionis star-forming region (XILO). I. The young cluster Collinder 69

    NASA Astrophysics Data System (ADS)

    Barrado, D.; Stelzer, B.; Morales-Calderón, M.; Bayo, A.; Huélamo, N.; Stauffer, J. R.; Hodgkin, S.; Galindo, F.; Verdugo, E.

    2011-02-01

    Context. This is the first paper of a series devoted to the Lambda Orionis star-forming region, Orion's Head, from the X-ray perspective. Our final aim is to provide a comprehensive view of this complex region, which includes several distinct associations and dark clouds. Aims: We aim to uncover the population of the central, young star cluster Collinder 69, and in particular those diskless Class III objects not identified by previous surveys based on near- and mid-infrared searches, and to establish the X-ray luminosity function for the association. Methods: We have combined two exposures taken with the XMM-Newton satellite with an exhaustive data set of optical, near- and mid-infrared photometry to assess the membership of the X-ray sources based on different color-color and color-magnitude diagrams, as well as other properties, such as effective temperatures, masses and bolometric luminosities derived from spectral energy distribution fitting and comparison with theoretical isochrones. The presence of circumstellar disks is discussed using mid-infrared photometry from the Spitzer Space Telescope. Results: With an X-ray flux limit of ~ 5 × 10-15 erg/cm2/s we detected a total of 164 X-ray sources, of which 66 are probable and possible cluster members. A total of 16 are newly identified probable members plus another three possible new members. The two XMM-Newton pointings east and west of the cluster center have allowed us to verify the heterogeneous spatial distribution of young stars, which is probably related to the large scale structure of the region. The disk fraction of the X-ray detected cluster sample (complete down to ~ 0.3 M_?) is very low, close to 10%, in remarkable contrast to the low-mass stellar and substellar population (mostly undetected in X-rays) where the disk fraction reaches about 50%. The X-ray luminosity function of Collinder 69 in different mass bins provides support for an age of several Myr when compared with other well known young associations. Conclusions: The X-ray properties of the young stars in Collinder 69 resemble those found in other young stellar associations, with saturation at log(Lx/Lbol) ~ -3 and low fractional X-ray luminosities for stars with M ? 2 M_?. With our improved cluster census we confirm previous reports on the untypically low disk fraction compared to other clusters of several Myr age. The different disk fractions of X-ray detected (essentially solar-like) and undetected (mostly low-mass stars and brown dwarfs) members can be understood as a consequence of a mass-dependence of the time-scale for disk evolution. Tables 3-6, 8, 9 are only available in electronic form at http://www.aanda.org

  19. Young Stars and Protoplanetary Disks in The Rich Cometary Globule CG 12

    Microsoft Academic Search

    Konstantin Getman

    2005-01-01

    We propose to use four ACIS-I pointings around the sparse and isolated high galactic latitude cometary globule CG 12, the most active star forming cloud among the known cometary globules (CGs). From the known population of BA stars we predict 100 lower mass stars to be detected. With the X-ray and follow up optical and near-IR observations, we will define

  20. Lithium in Young Solar-Type Stars in the Orion Nebula Region

    Microsoft Academic Search

    Douglas K. Duncan; L. M. Rebull

    1996-01-01

    Lithium abundances have been determined for 24 late-type pre-main-sequence stars in the Orion Nebula region with V=12-14 and B-V=0.5-1.4. All of the stars are within 20 arc minutes of the Trapezium; they range from approximately 1.0 to 1.6 solar mass and from 10^6 to 10^7 years old. Approximate chronological ordering of the stars is possible from their location in the

  1. Extremely Active Cool Stars in the Young Open Cluster NGC 2362

    NASA Astrophysics Data System (ADS)

    Berghofer, T. W.; Schmitt, J. H. M. M.

    NGC 2362 is one of the youngest open stellar clusters in our Galaxy and is centered around the massive O-type star tau CMa. This cluster exhibits several hundred cool stars in the pre-main sequence phase. We used the ROSAT PSPC and HRI to obtain deep X-ray images of NGC 2362. Here we present first results of an in-depth study of the X-ray properties of the cool star cluster members.

  2. X-ray emission from young stars in Taurus-Auriga-Perseus: Luminosity functions and the rotation - activity - age - relation

    NASA Astrophysics Data System (ADS)

    Stelzer, B.; Neuhäuser, R.

    2001-10-01

    We report on a systematic search for X-ray emission from pre-main sequence and young main sequence stars in the Taurus-Auriga-Perseus region. Our stellar sample consists of all T Tauri stars from the Taurus-Auriga region, and all late-type stars from the Pleiades and Hyades clusters which have been observed by the ROSAT PSPC in pointed observations. We present the X-ray parameters for all observed stars in tables. Next to the basic results of the data analysis (such as count rates, exposure time, and off-axis angle) we give X-ray luminosities and hardness ratios for all detected stars. Upper limits are given for non-detections. Detection rates for different spectral types are compiled. We use these results to study the connection between coronal X-ray activity and stellar parameters for different subgroups of our sample. In particular we compile X-ray luminosity functions (XLF), and discuss the relations between X-ray emission and spectral type, age, and rotation, which have been disputed extensively in the past. Here, we study these questions with the largest sample so far. The XLF for classical and weak-line T Tauri stars are different, with weak-lines being the stronger X-ray emitters. Proceeding towards the main-sequence (Pleiades, Hyades) the X-ray luminosity declines for all spectral types examined (G, K, and M stars). Within an age group Lx decreases towards later spectral types, while Lx/Lbol remains constant or even increases, reflecting the opposed influence of stellar radius, i.e. emitting area, and convection zone depth. For a given spectral type the fastest rotators show the highest X-ray luminosity. Rotation rate and X-ray emission are clearly correlated for all groups of stars with power law indices for log(Lx/Lbol) versus lg{Prot} of ~ -0.7 to -1.5. The study of XLF for binary stars shows that the known unresolved secondaries likely contribute a significant amount to the X-ray emission. Tables 2 to 7 are only available in electronic form at http://www.edpsciences.org

  3. Stellar contents and star formation in the young cluster Stock 18

    Microsoft Academic Search

    Himali Bhatt; Ram Sagar; J. C. Pandey

    2012-01-01

    We have carried out deep (V ˜ 21 mag) UBVRI photometric study of the star cluster Stock 18. These along with archival Infrared data have been used to derive the basic cluster parameters and also to study the star formation processes in and around the cluster region. The distance to the cluster is derived as 2.8 ± 0.2 kpc while

  4. Search for x ray emitting young stars outside of massive molecular clouds

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.

    1991-01-01

    This project is intended to determine whether X-ray surveys of the sky can uncover previously unrecognized populations of pre-main sequence stars outside of large well-known star forming regions. X-ray observations of large regions such as the Taurus-Auriga complex, Orion molecular cloud, Ophiuchi and Chamaeleon clouds had revealed that low mass pre-main sequence emit X-rays 10(exp 2)-10(exp 4) above main sequence levels, and that X-ray surveys select a large population of 'weak' T Tauri stars that are not easily found in traditional optical and infrared surveys. The present project sought to find 'weak' T Tauri stars around smaller and more distant molecular clouds. X-ray surveys potentially could elucidate the star forming capabilities of small clouds, which are not well understood.

  5. STAR FORMATION IN THE CENTRAL 400 PC OF THE MILKY WAY: EVIDENCE FOR A POPULATION OF MASSIVE YOUNG STELLAR OBJECTS

    SciTech Connect

    Yusef-Zadeh, F.; Hewitt, J. W. [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States); Arendt, R. G. [Science Systems and Applications, Inc., Baltimore County, GSFC, Code 665, Greenbelt, MD 20771 (United States); Whitney, B. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Rieke, G.; Hinz, J. L. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Wardle, M. [Department of Physics and Engineering, Macquarie University, Sydney, NSW 2109 (Australia); Stolovy, S.; Ramirez, S. [Spitzer Science Center, California Institute of Technology, Mail Code 220-6, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Lang, C. C. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States); Burton, M. G. [School of Physics, University of New South Wales, Sydney, NSW 2052 (Australia)], E-mail: zadeh@northwestern.edu

    2009-09-01

    The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gasdynamics and the formation of young stellar objects (YSOs). We probe this possibility with mid-infrared observations obtained with Infrared Array Camera and Multiband Imaging Photometer on Spitzer and with Midcourse Space Experiment. We use color-color diagrams and spectral energy distribution (SED) fits to explore the nature of YSO candidates (including objects with 4.5 {mu}m excesses possibly due to molecular emission). There is an asymmetry in the distribution of the candidate YSOs, which tend to be found at negative Galactic longitudes; this behavior contrasts with that of the molecular gas, approximately 2/3 of which is at positive longitudes. The small-scale height of these objects suggests that they are within the Galactic center region and are dynamically young. They lie between two layers of infrared dark clouds and may have originated from these clouds. We identify new sites for this recent star formation by comparing the mid-IR, radio, submillimeter, and methanol maser data. The methanol masers appear to be associated with young, embedded YSOs characterized by 4.5 {mu}m excesses. We use the SEDs of these sources to estimate their physical characteristics; their masses appear to range from {approx}10 to {approx}20 M{sub sun}. Within the central 400 x 50 pc (|l| < 1.{sup 0}3 and |b| < 10') the star formation rate (SFR) based on the identification of Stage I evolutionary phase of YSO candidates is about 0.14 M{sub sun} yr{sup -1}. Given that the majority of the sources in the population of YSOs are classified as Stage I objects, we suggest that a recent burst of star formation took place within the last 10{sup 5} yr. This suggestion is also consistent with estimates of SFRs within the last {approx}10{sup 7} yr showing a peak around 10{sup 5} yr ago. Lastly, we find that the Schmidt-Kennicutt Law applies well in the central 400 pc of the Galaxy. This implies that star formation does not appear to be dramatically affected by the extreme physical conditions in the Galactic center region.

  6. The young low-mass star ISO-Oph-50: extreme variability induced by a clumpy, evolving circumstellar disc

    NASA Astrophysics Data System (ADS)

    Scholz, Alexander; Muži?, Koraljka; Geers, Vincent

    2015-07-01

    ISO-Oph-50 is a young low-mass object in the ˜1 Myr old Ophiuchus star-forming region undergoing dramatic changes in its optical/near/mid-infrared brightness by 2-4 mag. We present new multi-band photometry and near-infrared spectra, combined with a synopsis of the existing literature data. Based on the spectroscopy, the source is confirmed as a mid-M dwarf, with evidence for ongoing accretion. The near-infrared light curves show large-scale variations, with 2-4 mag amplitude in the bands IJHK, with the object generally being bluer when faint. Near its brightest state, the object shows colour changes consistent with variable extinction of ?AV ˜ 7 mag. High-cadence monitoring at 3.6 ?m reveals quasi-periodic variations with a typical time-scale of 1-2 weeks. The best explanation for these characteristics is a low-mass star seen through circumstellar matter, whose complex variability is caused by changing inhomogeneities in the inner parts of the disc. When faint, the direct stellar emission is blocked; the near-infrared radiation is dominated by scattered light. When bright, the emission is consistent with a photosphere strongly reddened by circumstellar dust. Based on the available constraints, the inhomogeneities have to be located at or beyond ˜0.1 au distance from the star. If this scenario turns out to be correct, a major portion of the inner disc has to be clumpy, structured, and/or in turmoil. In its observational characteristics, this object resembles other types of young stellar objects with variability caused in the inner disc. Compared to other objects, however, ISO-Oph-50 is clearly an extreme case, given the large amplitude of the brightness and colour changes combined with the erratic behaviour. ISO-Oph-50 has been near its brightest state since 2013; further monitoring is highly encouraged.

  7. From Stars to Super-Planets: The Low-Mass IMF in the Young Cluster IC348

    NASA Technical Reports Server (NTRS)

    Najita, Joan R.; Tiede, Glenn P.; Carr, John S.

    2000-01-01

    We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength of the 1.9 micron water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from approximately 0.7 solar mass to 0.015 solar mass. The mass function derived for the cluster in this interval, dN/d log M alpha M(sup 0.5), is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby sun-like stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation vs. as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.

  8. The formation of Lyman alpha fluorescent H2 lines in protoplanetary disks surrounding young solar mass stars

    NASA Astrophysics Data System (ADS)

    Calvet, Nuria

    2014-10-01

    We propose to carry out a theoretical study of the formation of the H2 UV lines created by Lyman alpha fluorescence in protoplanetary disks around solar mass stars. We will use irradiated accretion disks models in which the dust and gas temperatures, as well as the hydrostatic density structure and corresponding chemistry is solved self-consistently, using as input realistic high energy fields, and observed ranges of accretion luminosities. We will include gas opacities in addition to dust to calculate the transfer of high energy radiation, which will enable us to model the gas disk inside the dust destruction radius where a substantial contribution to the flux of the H2 lines arises. The models will also include effects of dust settling by varying the vertical and radial distribution of the dust, which will have a direct effect on the the penetration of high energy radiation with implications for the gas temperature structure, the chemistry, and the strength of the H2 fluorescent lines. We will create a dedicated website with predicted H2 fluorescent line luminosities for a set of models covering ranges of stellar and accretion parameters typical of accreting solar mass stars and different degrees of dust settling. Our study will support efforts of the Ultraviolet Initiative of Cycle 22 by providing the community with the best means to interpret the FUV COS and STIS H2 spectra of young accreting stars.

  9. Young Stars Near Earth: Progress and Prospects ASP Conference Series, Vol. 244, 2001

    E-print Network

    Jensen, Eric L. N.

    such stars do not bias the sample used for subsequent evolutionary studies. 1. Introduction In an influential twenty years later, armed with the benefit of hindsight and data from astrometric space missions and all

  10. Young Stars Near Earth: Progress and Prospects ASP Conference Series, Vol. 244, 2001

    E-print Network

    Jensen, Eric L. N.

    criteria used to locate such stars do not bias the sample used for subsequent evolutionary studies. 1 1978). More than twenty years later, armed with the bene#12;t of hindsight and data from astrometric

  11. 1 Millimeter Polarimetry of Young Stellar Objects: Low-Mass Protostars and T Tauri Stars

    Microsoft Academic Search

    Motohide Tamura; J. H. Hough; Saeko S. Hayashi

    1995-01-01

    We have measured the polarization of the 1.1 mm and 0.8 mm continuum emission for three pr T Tauri stars and two T Tauri stars. Positive detections were made for NGC 1333 IRAS 4A and IRAS 16293 - 2422, while L1551 IRS 5 and HL Tau were only marginally detected. For GG Tau we measured a 2 sigma upper limit

  12. New Very Low-Mass T-Tauri Stars in Taurus: Young Brown Dwarfs?

    Microsoft Academic Search

    Cesar Briceno; Lee Hartmann; John Stauffer

    1998-01-01

    We present initial results of a CCD survey aimed at obtaining the first extensive sample of very low-mass pre-main sequence objects in the Taurus star forming region. Candidate objects for follow up observations were selected from the color-magnitude diagrams. In medium resolution spectra we identified nine new low-mass pre main sequence stars. Using the optical photometry and spectra we derive

  13. Widest Separation and the Lowest Mass Objects among Planetary-mass Companion Candidates around Young Stars

    NASA Astrophysics Data System (ADS)

    Oh, D.

    2014-08-01

    Two substellar companion candidates with planetary mass, around a T-Tauri star in the ? Ophiuchi star-forming region, are discovered by results of near-infrared imaging. Candidates are separated by 1454AU, candi 1 for short, and 542AU, candi 2 for short. There are high possibilities that both candidates are physically related to its primary star from their common proper motions, colors and statistics of YSOs in star forming region. candi 2 is identified as an extremely low-mass object, 0.0070.002 ?, and this is the lowest mass among planetary-mass companion(PMC) candidates imaged to date. In addition, separation from its primary star of candi 1, 0.014 ± 0.002 ?, is the widest among PMC candidates imaged to date. Formation of these extremely wide separated, > 100AU, PMCs, like candi 1 and c, is not fully explained by current planet formation theories, core accretion or gravitational instability. This discovery may suggest that PMCs separated by > 100AU form via extreme mass ratio case of cloud core fragmentation for multiple stars. Apologies : Because of our team policy, we cannot present the name and details of this target currently.

  14. Magnetic activity and differential rotation in the young Sun-like stars KIC 7985370 and KIC 7765135

    NASA Astrophysics Data System (ADS)

    Fröhlich, H.-E.; Frasca, A.; Catanzaro, G.; Bonanno, A.; Corsaro, E.; Molenda-?akowicz, J.; Klutsch, A.; Montes, D.

    2012-07-01

    Aims: We present a detailed study of the two Sun-like stars KIC 7985370 and KIC 7765135, to determine their activity level, spot distribution, and differential rotation. Both stars were previously discovered by us to be young stars and were observed by the NASA Kepler mission. Methods: The fundamental stellar parameters (vsini, spectral type, Teff, log g, and [Fe/H]) were derived from optical spectroscopy by comparison with both standard-star and synthetic spectra. The spectra of the targets allowed us to study the chromospheric activity based on the emission in the core of hydrogen H? and Ca ii infrared triplet (IRT) lines, which was revealed by the subtraction of inactive templates. The high-precision Kepler photometric data spanning over 229 days were then fitted with a robust spot model. Model selection and parameter estimation were performed in a Bayesian manner, using a Markov chain Monte Carlo method. Results: We find that both stars are Sun-like (of G1.5 V spectral type) and have an age of about 100-200 Myr, based on their lithium content and kinematics. Their youth is confirmed by their high level of chromospheric activity, which is comparable to that displayed by the early G-type stars in the Pleiades cluster. The Balmer decrement and flux ratio of their Ca ii-IRT lines suggest that the formation of the core of these lines occurs mainly in optically thick regions that are analogous to solar plages. The spot model applied to the Kepler photometry requires at least seven persistent spots in the case of KIC 7985370 and nine spots in the case of KIC 7765135 to provide a satisfactory fit to the data. The assumption of the longevity of the star spots, whose area is allowed to evolve with time, is at the heart of our spot-modelling approach. On both stars, the surface differential rotation is Sun-like, with the high-latitude spots rotating slower than the low-latitude ones. We found, for both stars, a rather high value of the equator-to-pole differential rotation (d? ? 0.18 rad d-1), which disagrees with the predictions of some mean-field models of differential rotation for rapidly rotating stars. Our results agree instead with previous works on solar-type stars and other models that predict a higher latitudinal shear, increasing with equatorial angular velocity, that can vary during the magnetic cycle. Based on public Kepler data, on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei - INAF at the Observatorio del Roque del los Muchachos, La Palma (Canary Islands), on observations collected at the 2.2-m telescope of the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto (Almería, Spain), operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), and on observations collected at the Catania Astrophysical Observatory (Italy).

  15. V745 Cassiopean interacting young massive binary in a multiple-star system

    NASA Astrophysics Data System (ADS)

    Çak?rl?, Ö.; Ibanoglu, C.; Sipahi, E.

    2014-08-01

    We present spectroscopic observations of the massive early-type system V745 Cas, embedded in a multiple-star system. The brightest star of the system is the eclipsing binary V745 Cas with an orbital period of 1.41 d. The radial velocities of both components and light curves obtained by INTEGRAL and Hipparcos missions were analysed. The components of V745 Cas are shown to be a B0 V primary with a mass Mp = 18.31±0.51 M? and radius Rp = 6.94±0.07 R? and a B(1-2) V secondary with a mass Ms = 10.47±0.28 M? and radius Rs = 5.35 ± 0.05 R?. Our analysis shows that both components fill their corresponding Roche lobes, indicating double contact configuration. Using the UBVJHK magnitudes and interstellar absorption, we estimated the mean distance to the system as 1700 ± 50 pc. The locations of the component stars in the mass-luminosity, mass-radius, effective temperature-mass and surface gravity-mass are in agreement with those of the main-sequence massive stars. We also obtained UBV photometry of the three visual companions and we estimate that all are B-type stars based upon their de-reddened colours. We suspect that this multiple system is probably a member of the Cas OB4 association in the Perseus arm of the Galaxy.

  16. Inhibition of giant-planet formation by rapid gas depletion around young stars.

    PubMed

    Zuckerman, B; Forveille, T; Kastner, J H

    1995-02-01

    Although stars form from clouds of gas and dust, there are insignificant amounts of gas around ordinary (Sun-like) stars. This suggests that hydrogen and helium, the primary constituents of planets such as Jupiter and Saturn, are not easily retained in orbit as a star matures. The gas-giant planets in the Solar System must therefore have formed rapidly. Models of their formation generally suggest that a solid core formed in < or = 10(6) yr, followed by the accretion of the massive gaseous envelope in approximately 10(7) yr (refs 1-5). But how and when the gas of the solar nebula dissipated, and how this compares with the predicted timescale of gas-giant formation, remains unclear, in part because direct observations of circumstellar gas have been made only for stars either younger or older than the critical range of 10(6)-10(7) yr (refs 8-15). Here we report observations of the molecular gas surrounding 20 stars whose ages are likely to be in this range. The gas dissipates rapidly; after a few million years the mass remaining is typically much less than the mass of Jupiter. Thus, if gas-giant planets are common in the Galaxy, they must form even more quickly than present models suggest. PMID:7845460

  17. Seasonality of volcanic eruptions

    Microsoft Academic Search

    B. Mason; D. Pyle; B. Dade; T. Jupp

    2003-01-01

    An analysis of volcanic activity in the last three hundred years reveals that the frequency of onset of volcanic eruptions varies systematically with the time of year. We analysed the Smithsonian catalogue of more than 3200 subaerial eruptions recorded during the last 300 years. We also investigated continuous records, which are not part of the general catalogue, of individual explosions

  18. Seasonality of Volcanic Eruptions

    Microsoft Academic Search

    B. Mason; D. M. Pyle; W. B. Dade; T. Jupp

    2001-01-01

    An analysis of volcanic activity in the last three hundred years reveals that the frequency of onset of volcanic eruptions varies systematically with the time of year. We analysed the Smithsonian catalogue of more than 3200 subaerial eruptions recorded during the last 300 years. We also investigated continuous records, which are not part of the general catalogue, of individual explosions

  19. Generalized Eruptive Syringoma

    PubMed Central

    Avhad, Ganesh; Ghuge, Priyanka; Jerajani, HR

    2015-01-01

    Eruptive syringoma is a very rare variant of syringoma. It is a benign adnexal tumor of the intraepidermal portion of eccrine sweat ducts. Here we report a 32-year-old female presented with classical asymptomatic eruptive syringomas involving her face and extremities. PMID:25814740

  20. Ready to Erupt!

    NSDL National Science Digital Library

    2014-09-18

    Students observe an in-classroom visual representation of a volcanic eruption. The water-powered volcano demonstration is made in advance, using sand, hoses and a waterballoon, representing the main components of all volcanoes. During the activity, students observe, measure and sketch the volcano, seeing how its behavior provides engineers with indicators used to predict an eruption.

  1. The Young, Massive, Star Cluster Sandage-96 After the Explosion of Supernova 2004dj in NGC 2403

    NASA Astrophysics Data System (ADS)

    Vinkó, J.; Sárneczky, K.; Balog, Z.; Immler, S.; Sugerman, B. E. K.; Brown, P. J.; Misselt, K.; Szabó, Gy. M.; Csizmadia, Sz.; Kun, M.; Klagyivik, P.; Foley, R. J.; Filippenko, A. V.; Csák, B.; Kiss, L. L.

    2009-04-01

    The bright Type II-plateau supernova (SN) 2004dj occurred within the young, massive stellar cluster Sandage-96 in a spiral arm of NGC 2403. New multiwavelength observations obtained with several ground-based and space-based telescopes were combined to study the radiation from Sandage-96 after SN 2004dj faded away. Sandage-96 started to dominate the flux in the optical bands starting from 2006 September (~800 days after explosion). The optical fluxes are equal to the pre-explosion ones within the observational uncertainties. An optical Keck spectrum obtained ~900 days after explosion shows the dominant blue continuum from the cluster stars shortward of 6000 Å as well as strong SN nebular emission lines redward. The integrated spectral energy distribution (SED) of the cluster has been extended into the ultraviolet region by archival XMM-Newton and new Swift observations, and compared with theoretical models. The outer parts of the cluster have been resolved by the Hubble Space Telescope, allowing the construction of a color-magnitude diagram (CMD). The fitting of the cluster SED with theoretical isochrones results in cluster ages distributed between 10 and 40 Myr, depending on the assumed metallicity and the theoretical model family. The isochrone fitting of the CMDs indicates that the resolved part of the cluster consists of stars having a bimodal age distribution: a younger population at ~10-16 Myr and an older one at ~32-100 Myr. The older population has an age distribution similar to that of the other nearby field stars. This may be explained with the hypothesis that the outskirts of Sandage-96 are contaminated by stars captured from the field during cluster formation. The young age of Sandage-96 and the comparison of its pre and postexplosion SEDs suggest 12 lsim M prog lsim 20 M sun as the most probable mass range for the progenitor of SN 2004dj. This is consistent with, but perhaps slightly higher than, most of the other Type II-plateau SN progenitor masses determined so far.

  2. The large amplitude outburst of the young star HBC 722 in NGC 7000/IC 5070, a new FU Orionis candidate

    NASA Astrophysics Data System (ADS)

    Semkov, E. H.; Peneva, S. P.; Munari, U.; Milani, A.; Valisa, P.

    2010-11-01

    Context. The investigations of the photometric and spectral variability of PMS stars are essential to a better understanding of the early phases of stellar evolution. We are carrying out a photometric monitoring program of some fields of active star formation. One of our targets is the dark cloud region between the bright nebulae NGC 7000 and IC 5070. Aims: We report the discovery of a large amplitude outburst from the young star HBC 722 (LkH? 188 G4) located in the region of NGC 7000/IC 5070. On the basis of photometric and spectroscopic observations, we argue that this outburst is of the FU Orionis type. Methods: We gathered photometric and spectroscopic observations of the object both in the pre-outburst state and during a phase of increase in its brightness. The photometric BVRI data (Johnson-Cousins system) that we present were collected from April 2009 to September 2010. To facilitate transformation from instrumental measurements to the standard system, fifteen comparison stars in the field of HBC 722 were calibrated in the BVRI bands. Optical spectra of HBC 722 were obtained with the 1.3-m telescope of Skinakas Observatory (Crete, Greece) and the 0.6-m telescope of Schiaparelli Observatory in Varese (Italy). Results: The pre-outburst photometric and spectroscopic observations of HBC 722 show both low amplitude photometric variations and an emission-line spectrum typical of T Tau stars. The observed outburst started before May 2010 and reached its maximum brightness in September 2010, with a recorded ?V ~ 4.7m amplitude. Simultaneously with the increase in brightness the color indices changed significantly and the star became appreciably bluer. The light curve of HBC 722 during the period of rise in brightness is similar to the light curves of the classical FUors - FU Ori and V1057 Cyg. The spectral observations during the time of increase in brightness showed significant changes in both the profiles and intensity of the spectral lines. Only H? remained in emission, while the H?, Na I 5890/5896, Mg I triplet 5174, and Ba II 5854/6497 lines were in strong absorption.

  3. Two Remarkable Spectroscopic Categories of Young O Stars from the VLT-FLAMES Tarantula Survey

    NASA Astrophysics Data System (ADS)

    Walborn, N. R.; Sana, H.; Taylor, W. D.; Simón-Díaz, S.; Evans, C. J.

    2012-12-01

    The spectral and spatial characteristics of two special categories of O stars found in the VFTS dataset are presented. One of them comprises very rapid rotators, including several more extreme than any previously known. These objects are distributed around the peripheries of the main 30 Doradus clusters, suggesting a runaway nature for which their radial velocities already provide preliminary supporting evidence. The other category consists of a large number of Vz stars, previously hypothesized on spectroscopic grounds to be on or very near the ZAMS. Their distribution is the inverse of that of the rapid rotators: the Vz are strongly concentrated to the ionizing clusters, plus a newly recognized band of recent and current star formation to the north, which provides strong circumstantial evidence for their extreme youth.

  4. A Nearly Complete Census Of Young Stars Distribution In The Nearest Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Myers, Philip C.

    2001-01-01

    Under this grant we prepared a program of observations based on our previous plans for observations with the WIRE satellite. Our main effort was to use our WIRE plans to prepare estimates for a SIRTF Legacy Science proposal, From Molecular Cores to Planets (N. Evans, PI). For this purpose, L. Allen compiled catalogs of dense cores with and without associated stars, of stars in the youngest evolutionary stages (Class 0, I, and II), and of embedded clusters observed in the near infrared. Further, Tyler Bourke, Mario van den Ancker, and Chang Won Lee compiled and edited a refined lists of 150 isolated cores in the nearest star-forming regions within several hundred pc of the Sun, suitable for surveying with SIRTF. Our SIRTF Legacy Science proposal was selected for funding, and we are continuing with our planning for the observations.

  5. Results of magnetic field measurements in young stars DO Tau, DR Tau, and DS Tau

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    The results of longitudinal magnetic field measurements B z in the hot accretion spot in three classical T Tauri stars (CTTS) are reported. In all three stars the magnetic field is detected at a level above 2 ? in the formation region of the narrow component of the He I 5876 Å emission line. In the case of DS Tau the longitudinal field B z in the hot spot was also measured from the narrow emission components of the Na I D lines, implying +0.8 ± 0.3 kG, which is equal to the B z field component measured from the He I 5876 Å line. Our results suggest that the 6-m telescope of the Special Astrophysical Observatory can be used to study magnetic fields in the hot spots of CTTS with magnitudes down to 13m, making it possible to double the number of stars of this type with measured B z values in the accretion zone.

  6. WFPC2 Observations of Massive and Compact Young Star Clusters in M31

    E-print Network

    Benjamin F. Williams; Paul W. Hodge

    2000-10-09

    We present color magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values range from E(B-V) = 0.20 +/- 0.10 to 0.31 +/- 0.11. We statistically remove field stars on the basis of completeness, magnitude and color. Isochrone fits to the field-subtracted, reddening-corrected diagrams yield age estimates ranging from 63 +/- 15 Myr to 160 +/- 60 Myr. Implications for the recent evolution of the disk near NGC 206 are discussed.

  7. Initiation of Solar Eruptions

    NASA Technical Reports Server (NTRS)

    Sterling, Alphonse C.; Moore, Ronald L.

    2007-01-01

    We consider processes occurring just prior to and at the start of the onset of flare- and CME-producing solar eruptions. Our recent work uses observations of filament motions around the time of eruption onset as a proxy for the evolution of the fields involved in the eruption. Frequently the filaments show a slow rise prior to fast eruption, indicative of a slow expansion of the field that is about co explode. Work by us and others suggests that reconnection involving emerging or canceling flux results in a lengthening of fields restraining the filament-carrying field, and the consequent upward expansion of the field in and around the filament produces the filament's slow rise: that is, the reconnection weakens the magnetic "tethers" ("tether-weakening" reconnection), and results in the slow rise of the filament. It is still inconclusive, however, what mechanism is responsible for the switch from the slow rise to the fast eruption.

  8. The circumstellar environment of TMR-1 - A young, low-mass star in the Taurus molecular ring

    NASA Technical Reports Server (NTRS)

    Terebey, S.; Beichman, C. A.; Gautier, T. N.; Hester, J. J.

    1990-01-01

    Near-infrared camera and Owens Valley millimeter interferometer data are presented that reveal the circumstellar environment of TMR-1 on scales of roughly 1000 AU. TMR-1 is a deeply embedded, young, low-mass star located in a rotating ring of material in the TMC-1/Heiles Cloud 2 region of the Taurus molecular cloud. The stellar wind cavity, as outlined by the extended infrared continuum emission at 2.2 microns, overlaps with the redshifted outflow detected in the (C-12)O data. High-density circumstellar material is seen in (C-13)O in emission and at 2.2 microns in absorption. The morphology suggests the high-density gas may either be part of a 1000 AU disk or may represent infalling material from the molecular cloud core. TMR-1 appears to be in an early wind-clearing phase of protostar formation.

  9. IUE observations of the chromospheric activity-age relation in young solar-type stars

    NASA Astrophysics Data System (ADS)

    Simon, T.; Boesgaard, A. M.

    1982-04-01

    Ultraviolet data obtained with the IUE spacecraft are presented for a dozen solar-type stars in the field. The stars are of spectral type F6 V - G1 V; on the basis of their high Li content, they range in age from 0.1 to 2.8 Gyr. The evolution of transition regions and chromospheric emission with stellar age is studied along with the surface distribution of magnetically active regions as revealed by rotational modulation of UV emission line fluxes.

  10. Volcanic Eruptions and Climate

    NASA Astrophysics Data System (ADS)

    Robock, A.

    2012-12-01

    Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about one year. The radiative and chemical effects of these aerosol clouds produce responses in the climate system. Observations and numerical models of the climate system show that volcanic eruptions produce global cooling and were the dominant natural cause of climate change for the past millennium, on timescales from annual to century. Major tropical eruptions produce winter warming of Northern Hemisphere continents for one or two years, while high latitude eruptions in the Northern Hemisphere weaken the Asian and African summer monsoon. The Toba supereruption 74,000 years ago caused very large climate changes, affecting human evolution. However, the effects did not last long enough to produce widespread glaciation. An episode of four large decadally-spaced eruptions at the end of the 13th century C.E. started the Little Ice Age. Since the Mt. Pinatubo eruption in the Philippines in 1991, there have been no large eruptions that affected climate, but the cumulative effects of small eruptions over the past decade had a small effect on global temperature trends. The June 13, 2011 Nabro eruption in Eritrea produced the largest stratospheric aerosol cloud since Pinatubo, and the most of the sulfur entered the stratosphere not by direct injection, but by slow lofting in the Asian summer monsoon circulation. Volcanic eruptions warn us that while stratospheric geoengineering could cool the surface, reducing ice melt and sea level rise, producing pretty sunsets, and increasing the CO2 sink, it could also reduce summer monsoon precipitation, destroy ozone, allowing more harmful UV at the surface, produce rapid warming when stopped, make the sky white, reduce solar power, perturb the ecology with more diffuse radiation, damage airplanes flying in the stratosphere, degrade astronomical observations, affect remote sensing, and affect stargazing.

  11. FIRST KECK NULLING OBSERVATIONS OF A YOUNG STELLAR OBJECT: PROBING THE CIRCUMSTELLAR ENVIRONMENT OF THE HERBIG Ae STAR MWC 325

    SciTech Connect

    Ragland, S.; Hrynevich, M. [W. M. Keck Observatory, Kamuela, HI 96743 (United States); Ohnaka, K. [Max-Planck-Institut fuer Radioastronomie, 53121 Bonn (Germany); Hillenbrand, L. [Astrophysics Department, California Institute of Technology, Pasadena, CA 91125 (United States); Ridgway, S. T. [National Optical Astronomy Observatories, Tucson, AZ 85726-6732 (United States); Colavita, M. M.; Traub, W. A. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA, 91109 (United States); Akeson, R. L.; Millan-Gabet, R. [NExScI, California Institute of Technology, Pasadena, CA 91125 (United States); Cotton, W. [National Radio Astronomy Observatory, Charlottesville, VA 22903-2475 (United States); Danchi, W. C., E-mail: sragland@keck.hawaii.edu [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Greenbelt, MD 20771 (United States)

    2012-02-20

    We present the first N-band nulling plus K- and L-band V{sup 2} observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2-12 {mu}m wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative 'sub-micron' (0.1 {mu}m) and 'micron' (2 {mu}m) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast to the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  12. First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae star MWC 325

    NASA Technical Reports Server (NTRS)

    Ragland, S.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Akeson, R. L.; Cotton, W.; Danichi, W. C.; Hrynevych, M.; Milan-Gabet, R.; Traub, W. A.

    2012-01-01

    We present the first N-band nulling plus K- and L-band V(sup 2) observations of a young stellar object, MWC325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2-12 micrometer wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.3 and 2 larger in the Lband and N-band, respectively, compared to that in the K-band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat-disk model, with only slight flaring in the outer regions of the disk, consisting of representative "sub-micron" (0.1 micron) and "micron" (2 micron) grains of a 50:50 ratio of silicate and graphite. This is marked contrast with the disks previously found in other Herbig Ae/Be stars suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  13. Planets around Low-mass Stars. III. A Young Dusty L Dwarf Companion at the Deuterium-burning Limit

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Dupuy, Trent J.

    2013-09-01

    We report the discovery of an L-type companion to the young M3.5V star 2MASS J01225093-2439505 at a projected separation of 1.''45 (?52 AU) as part of our adaptive optics imaging search for extrasolar giant planets around young low-mass stars. 2MASS 0122-2439 B has very red near-infrared colors similar to the HR 8799 planets and the reddest known young/dusty L dwarfs in the field. Moderate-resolution (R ? 3800) 1.5-2.4 ?m spectroscopy reveals a near-infrared spectral type of L4-L6 and an angular H-band shape, confirming its cool temperature and young age. The kinematics of 2MASS 0122-2439 AB are marginally consistent with members of the ~120 Myr AB Dor young moving group based on the photometric distance to the primary (36 ± 4 pc) and our radial velocity measurement of 2MASS 0122-2439 A from Keck/HIRES. We adopt the AB Dor group age for the system, but the high energy emission, lack of Li I ?6707 absorption, and spectral shape of 2MASS 0122-2439 B suggest a range of ~10-120 Myr is possible. The age and luminosity of 2MASS 0122-2439 B fall in a strip where "hot-start" evolutionary model mass tracks overlap as a result of deuterium burning. Several known substellar companions also fall in this region (2MASS J0103-5515 ABb, AB Pic b, ? And b, G196-3 B, SDSS 2249+0044 B, LP 261-75 B, HD 203030 B, and HN Peg B), but their dual-valued mass predictions have largely been unrecognized. The implied mass of 2MASS 0122-2439 B is ?12-13 M Jup or ?22-27 M Jup if it is an AB Dor member, or possibly as low as 11 M Jup if the wider age range is adopted. Evolutionary models predict an effective temperature for 2MASS 0122-2439 B that corresponds to spectral types near the L/T transition (?1300-1500 K) for field objects. However, we find a mid-L near-infrared spectral type, indicating that 2MASS 0122-2439 B represents another case of photospheric dust being retained to cooler temperatures at low surface gravities, as seen in the spectra of young (8-30 Myr) planetary companions. Altogether, the low mass, low temperature, and red colors of 2MASS 0122-2439 B make it a bridge between warm planets like ? Pic b and cool, very dusty ones like HR 8799 bcde. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  14. PLANETS AROUND LOW-MASS STARS. III. A YOUNG DUSTY L DWARF COMPANION AT THE DEUTERIUM-BURNING LIMIT ,

    SciTech Connect

    Bowler, Brendan P.; Liu, Michael C. [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Shkolnik, Evgenya L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Dupuy, Trent J., E-mail: bpbowler@ifa.hawaii.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-09-01

    We report the discovery of an L-type companion to the young M3.5V star 2MASS J01225093-2439505 at a projected separation of 1.''45 ( Almost-Equal-To 52 AU) as part of our adaptive optics imaging search for extrasolar giant planets around young low-mass stars. 2MASS 0122-2439 B has very red near-infrared colors similar to the HR 8799 planets and the reddest known young/dusty L dwarfs in the field. Moderate-resolution (R Almost-Equal-To 3800) 1.5-2.4 {mu}m spectroscopy reveals a near-infrared spectral type of L4-L6 and an angular H-band shape, confirming its cool temperature and young age. The kinematics of 2MASS 0122-2439 AB are marginally consistent with members of the {approx}120 Myr AB Dor young moving group based on the photometric distance to the primary (36 {+-} 4 pc) and our radial velocity measurement of 2MASS 0122-2439 A from Keck/HIRES. We adopt the AB Dor group age for the system, but the high energy emission, lack of Li I {lambda}6707 absorption, and spectral shape of 2MASS 0122-2439 B suggest a range of {approx}10-120 Myr is possible. The age and luminosity of 2MASS 0122-2439 B fall in a strip where ''hot-start'' evolutionary model mass tracks overlap as a result of deuterium burning. Several known substellar companions also fall in this region (2MASS J0103-5515 ABb, AB Pic b, {kappa} And b, G196-3 B, SDSS 2249+0044 B, LP 261-75 B, HD 203030 B, and HN Peg B), but their dual-valued mass predictions have largely been unrecognized. The implied mass of 2MASS 0122-2439 B is Almost-Equal-To 12-13 M{sub Jup} or Almost-Equal-To 22-27 M{sub Jup} if it is an AB Dor member, or possibly as low as 11 M{sub Jup} if the wider age range is adopted. Evolutionary models predict an effective temperature for 2MASS 0122-2439 B that corresponds to spectral types near the L/T transition ( Almost-Equal-To 1300-1500 K) for field objects. However, we find a mid-L near-infrared spectral type, indicating that 2MASS 0122-2439 B represents another case of photospheric dust being retained to cooler temperatures at low surface gravities, as seen in the spectra of young (8-30 Myr) planetary companions. Altogether, the low mass, low temperature, and red colors of 2MASS 0122-2439 B make it a bridge between warm planets like {beta} Pic b and cool, very dusty ones like HR 8799 bcde.

  15. Signatures of Young Star Formation Activity Within Two Parsecs of Sgr A*

    E-print Network

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

    2015-01-01

    We present radio and infrared observations indicating on-going star formation activity inside the $\\sim2-5$ pc circumnuclear ring at the Galactic center. Collectively these measurements suggest a continued disk-based mode of on-going star formation has taken place near Sgr A* over the last few million years. First, VLA observations with spatial resolution 2.17$"\\times0.81"$ 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$\\times10^6$ \\msol\\, black hole. Second, SED modeling of stellar sources indicate massive 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 $\\sim$100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS~5) have bow shock structures suggesting that they have have gaseous disks that are phototoevaporated...

  16. Young Stars Near Earth: Progress and Prospects ASP Conference Series, Vol. ???, 2001

    E-print Network

    Schneider, Glenn

    Jayawardhana and Thomas Greene, eds. HST Observations of Dusty Disks in the TW Hya Association Glenn Schneider evolution. Here we discuss HST near-IR and optical observations of three previously-identi#12;ed members the current competing theories of star, disk, and planetary system formation, evolution and interaction

  17. Young Stars in the Camelopardalis Dust and Molecular Clouds. III. the GL 490 Region

    E-print Network

    V. Straizys; V. Laugalys

    2008-03-17

    Using the infrared photometry data extracted from the 2MASS, IRAS and MSX databases, 50 suspected young stellar objects (YSOs) are selected from about 37500 infrared objects in the 3x3 deg area with the center at Galactic longitude 142.5 deg and latitude +1.0 deg, in the vicinity of the young stellar object GL 490 in the dark cloud DoH 942 (Dobashi et al. 2005). The spectral energy distributions between 700 nm and 100 mum suggest that most of the selected objects may be YSOs of classes I and II. In the color-magnitude diagram K_s vs. H-K_s the suspected YSOs occupy an area right of the main sequence what can be interpreted as being caused by the effects of luminosity, interstellar and circumstellar reddening and infrared thermal emission in circumstellar envelopes and disks.

  18. New constraints on the multiplicity of massive young stars in Upper Scorpius

    NASA Astrophysics Data System (ADS)

    Grellmann, R.; Ratzka, Th.; Köhler, R.; Preibisch, Th.; Mucciarelli, P.

    2015-06-01

    Context. Observations and simulations have clearly established that most stars form in multiple systems. Characterizing their properties is thus important for our understanding of the star formation process. Aims: To provide statistics about the number of companions per star over the full range of angular distances, infrared long-baseline interferometric studies can be employed to fill the gap between spectroscopic and adaptive optics searches. The Upper Scorpius OB association is a good target for such observations, because its stellar content is very well known from both spectroscopic and adaptive optics searches. Methods: We used the ESO Very Large Telescope Interferometer to perform long-baseline interferometric observations of a sample of seven B stars. Furthermore, we used ROSAT X-ray data to search for indications of low-mass companions. Results: With the interferometric observations, we find previously known companions around ? Sco and HR 6027. For the other targets we determine the parameter space in which the presence of companions can be excluded from our data. For two of the B stars in our sample, ? Sco and HR 6026, the detection of X-ray emission provides indirect evidence of previously unknown low-mass companions. Conclusions: In total we find two previously unknown companions. We can exclude the presence of other unknown companions within the separation range of ~2 to ~100 mas and for a brightness ratio ?0.1. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, observing program 085.C-0260.Appendix A is available in electronic form at http://www.aanda.org

  19. A Young Open Cluster Surrounding V838 Monocerotis

    E-print Network

    Howard E. Bond; Melike Afsar

    2006-08-10

    During a program of spectroscopic monitoring of V838 Mon, we serendipitously discovered that a neighboring 16th-mag star is of type B. We then carried out a spectroscopic survey of other stars in the vicinity, revealing two more B-type stars, all within 45" of V838 Mon. We have determined the distance to this sparse, young cluster, based on spectral classification and photometric main-sequence fitting of the three B stars. The distance is found to be 6.2+-1.2 kpc, in excellent agreement with the geometric distance to V838 Mon of 5.9 kpc obtained from Hubble Space Telescope polarimetry of the light echoes. The cluster's age is less than 25 Myr. The absolute luminosity of V838 Mon during its outburst, based on our distance measurement, was very similar to that of M31 RV, an object in the bulge of M31 that was also a cool supergiant throughout its eruption in 1988. However, there is no young population at the site of M31 RV. It does not appear possible to form a nova-like cataclysmic binary system within the young age of the V838 Mon cluster, and the lack of a young population surrounding M31 RV suggests that the outburst mechanism does not require a massive progenitor. These considerations appear to leave stellar-collision or merger scenarios as one of the remaining viable explanations for the outbursts of V838 Mon and M31 RV.

  20. Detached dust shell around Wolf-Rayet star WR60-6 in the young stellar cluster VVV CL036

    SciTech Connect

    Borissova, J.; Amigo, P.; Kurtev, R. [Departamento de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030 (Chile); Kumar, M. S. N. [Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Chené, A.-N. [Gemini Observatory, Northern Operations Center, 670 North A'ohoku Place Hilo, HI 96720 (United States); Minniti, D., E-mail: jura.borissova@uv.cl [Pontificia Universidad Católica de Chile, Facultad de Física, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2014-01-01

    The discovery of a detached dust shell around the Wolf-Rayet (WR) star WR60-6 in the young stellar cluster VVV CL036 is reported. This shell is uncovered through the Spitzer-MIPS 24 ?m image, where it appears brightest, and it is invisible at shorter wavelengths. Using new APEX observations and other data available from the literature, we have estimated some of the shell parameters: the inner and outer radii of 0.15 and 0.90 pc, respectively; the overall systemic velocity of the molecular {sup 12}CO(3 ? 2) emission of –45.7 ± 2.3 km s{sup –1}; an expansion velocity of the gas of 16.3 ± 1 km s{sup –1}; the dust temperature and opacity of 122 ± 12 K and 1.04, respectively; and an age of 2.8 × 10{sup 4} yr. The WR star displays some cyclic variability. The mass computed for the WR60-6 nebula indicates that the material was probably ejected during its previous stages of evolution. In addition, we have identified a bright spot very close to the shell, which can be associated with the Midcourse Space Experiment source G312.13+00.20.

  1. Rapid photometric and spectroscopic evolution of the young planetary nebula Hen 3-1357 and its central star SAO 244567

    NASA Astrophysics Data System (ADS)

    Arkhipova, V. P.; Ikonnikova, N. P.; Kniazev, A. Yu.; Rajoelimanana, Andry

    2013-03-01

    We present the results of spectroscopic and photometric observations for the young compact planetary nebula Hen 3-1357 and its central star SAO 244567. High-resolution spectroscopy has allowed the expansion velocity of the nebula, V exp = 8.4 ± 1.5 km s-1, and the heliocentric velocity of the object, V r = +12.6 ± 1.7 km s-1, to be determined. The gas shell parameters ( N e , T e ), the extinction in the H ? line, and the O, N, Ne, Ar, S, Cl, He, and C abundances have been determined from low-resolution spectra taken in 1992 and 2011. We have found significant changes in the relative intensities of forbidden lines in the spectrum of Hen 3-1357 within the last 20 years: the low-excitation [O I], [O II], and [N II] lines became stronger relative to H ? by a factor of ˜2, while the [O III] lines weakened by a factor of ˜ 2, suggesting a decrease in the excitation class of the nebula. The V-band photometry performed under the ASAS-3 program revealed a decline in the yearly mean brightness of SAO 244 567 from 2001 to 2009 by 0_.^m 5 and rapid variability with an amplitude of a few tenths of a magnitude. Published observational data in a wide spectral range, from the near ultraviolet to the radio band, suggest an appreciable weakening of the flux from the star and the nebula.

  2. Detached Dust Shell around Wolf-Rayet Star WR60-6 in the Young Stellar Cluster VVV CL036

    NASA Astrophysics Data System (ADS)

    Borissova, J.; Kumar, M. S. N.; Amigo, P.; Chené, A.-N.; Kurtev, R.; Minniti, D.

    2014-01-01

    The discovery of a detached dust shell around the Wolf-Rayet (WR) star WR60-6 in the young stellar cluster VVV CL036 is reported. This shell is uncovered through the Spitzer-MIPS 24 ?m image, where it appears brightest, and it is invisible at shorter wavelengths. Using new APEX observations and other data available from the literature, we have estimated some of the shell parameters: the inner and outer radii of 0.15 and 0.90 pc, respectively; the overall systemic velocity of the molecular 12CO(3 ? 2) emission of -45.7 ± 2.3 km s-1 an expansion velocity of the gas of 16.3 ± 1 km s-1 the dust temperature and opacity of 122 ± 12 K and 1.04, respectively; and an age of 2.8 × 104 yr. The WR star displays some cyclic variability. The mass computed for the WR60-6 nebula indicates that the material was probably ejected during its previous stages of evolution. In addition, we have identified a bright spot very close to the shell, which can be associated with the Midcourse Space Experiment source G312.13+00.20. Based on observations gathered as part of observing programs 179.B-2002, VIRCAM, VISTA at ESO, Paranal Observatory, NTT at ESO, and APEX C-090.F-9705B-2012.

  3. Roche-lobe Overflow Systems Powered by Black Holes in Young Star Clusters: The Importance of Dynamical Exchanges

    NASA Astrophysics Data System (ADS)

    Mapelli, Michela; Zampieri, Luca

    2014-10-01

    We have run 600 N-body simulations of intermediate-mass (~3500 M ?) young star clusters (SCs; with three different metallicities (Z = 0.01, 0.1, and 1 Z ?). The simulations include the dependence of stellar properties and stellar winds on metallicity. Massive stellar black holes (MSBHs) with mass >25 M ? are allowed to form through direct collapse of very massive metal-poor stars (Z < 0.3 Z ?). We focus on the demographics of black hole (BH) binaries that undergo mass transfer via Roche lobe overflow (RLO). We find that 44% of all binaries that undergo an RLO phase (RLO binaries) formed through dynamical exchange. RLO binaries that formed via exchange (RLO-EBs) are powered by more massive BHs than RLO primordial binaries (RLO-PBs). Furthermore, the RLO-EBs tend to start the RLO phase later than the RLO-PBs. In metal-poor SCs (0.01-0.1 Z ?), >20% of all RLO binaries are powered by MSBHs. The vast majority of RLO binaries powered by MSBHs are RLO-EBs. We have produced optical color-magnitude diagrams of the simulated RLO binaries, accounting for the emission of both the donor star and the irradiated accretion disk. We find that RLO-PBs are generally associated with bluer counterparts than RLO-EBs. We compare the simulated counterparts with the observed counterparts of nine ultraluminous X-ray sources. We discuss the possibility that IC 342 X-1, Ho IX X-1, NGC 1313 X-2, and NGC 5204 X-1 are powered by an MSBH.

  4. Large grains in disks around young stars: ATCA observations of WW Cha, RU Lup, and CS Cha

    E-print Network

    Dave Lommen; Sarah Maddison; Chris Wright; Ewine van Dishoeck; David Wilner; Tyler Bourke

    2008-12-19

    Grains in disks around young stars grow from interstellar submicron sizes to planetesimals over the course of several Myr. Thermal emission of large grains or pebbles can be best observed at cm wavelengths. However, other emission mechanisms can contribute. We aim to determine the mechanisms of cm emission for 3 T Tauri stars. WW Cha and RU Lup were recently found to have grain growth at least up to mm sizes in their circumstellar disks. CS Cha has similar indications for grain growth in its circumbinary disk. The T Tauri stars WW Cha and RU Lup were monitored over several years at mm and cm wavelengths, using ATCA. The new ATCA 7 mm system was also used to observe CS Cha. WW Cha was detected on several occasions at 7 and 16 mm. We obtained one detection of WW Cha at 3 cm and upper limits only at 6 cm. The emission at 16 mm was stable over days, months and years, but the emission at 3 cm is found to be variable. RU Lup was detected at 7 mm. It was observed at 16 mm 3 times and at 3 and 6 cm 4 times and found to be variable in all 3 wavebands. CS Cha was detected at 7 mm, but the S/N was too low to resolve the gap in the circumbinary disk. The emission at 3, 7 and 16 mm for WW Cha is well explained by thermal emission from mm and cm-sized pebbles. The cm spectral index is consistent with the emission from an optically-thick ionised wind, but the high variability of the cm emission points to a non-thermal contribution. The SEDs of RU Lup and CS Cha from 1 to 7 mm are consistent with thermal emission from mm-sized grains. The variability of the longer-wavelength emission for RU Lup and the negative spectral index suggest non-thermal emission.

  5. A GALEX-based Search for the Sparse Young Stellar Population in the Taurus-Aurigae Star Forming Region

    NASA Astrophysics Data System (ADS)

    Gómez de Castro, Ana I.; Lopez-Santiago, Javier; López-Martínez, Fatima; Sánchez, Néstor; Sestito, Paola; de Castro, Elisa; Cornide, Manuel; Yañez Gestoso, Javier

    2015-02-01

    In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J-K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J-K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.

  6. Measuring Spectra of B-type Stars to Study Young Open Clusters

    NASA Astrophysics Data System (ADS)

    Chiw, Charisee; McSwain, M. V.

    2011-01-01

    We used spectra of the open clusters NGC 1960, NGC 1502, NGC 7160, NGC 2384, NGC 2244, NGC 2422, and IC 1590 to analyze their B-type stellar populations. The spectral lines He I ??4388, 4713, 4471, and H? at 4340 Å were analyzed to measure the stars’ projected rotational velocity, temperature, and surface gravity. Then by comparing our measurements to the evolutionary tracks of Schaller et al., we determined the masses of the stars. We determined the ages of the clusters by comparing the luminosity and temperature measurements to isochrones by Lejeune & Schaerer. Finally, we calculate the interstellar reddening and distance to each cluster. This work is supported by the NSF REU site grant PHY-0849416, NASA DPR No. NNX09AP86G, and Lehigh University.

  7. Activity and rotation of low mass stars in young open clusters

    SciTech Connect

    Seifahrt, Andreas; Reiners, Ansgar [Institut fuer Astrophysik, Georg-August-Universitaet, D-37077 Goettingen (Germany); Scholz, Aleks [SUPA, School of Phys. and Astron., Univ. of St Andrews, North Haugh, St Andrews, KY16 9SS (United Kingdom); Basri, Gibor [Astronomy Department, University of California, Berkeley, CA 94720 (United States)

    2009-02-16

    We present first results from a multi-object spectroscopy campaign in IC2602, the Hyades, the Pleiades, and the Coma cluster using VLT/FLAMES. We analysed the data for radial velocity, rotational velocity (v sin i), and H{alpha}-activity. Here, we highlight three aspects of this study in the context of rotational braking and the rotation-activity relationship among low mass stars. Finally we discuss the cluster membership of sources in IC2602.

  8. The Luminosity Function of Young Star Clusters in ``the Antennae'' Galaxies (NGC 4038-4039)

    Microsoft Academic Search

    Bradley C. Whitmore; Qing Zhang; Claus Leitherer; S. Michael Fall; François Schweizer; Bryan W. Miller

    1999-01-01

    The Wide Field Planetary Camera 2 of the Hubble Space Telescope has been used to obtain high-resolution images of NGC 4038\\/4039 that go roughly 3 mag deeper in V than previous observations made during cycle 2. These new images allow us to measure the luminosity functions (LFs) of clusters and stars over a range of 8 mag (-14

  9. Distributions of short-lived radioactive nuclei produced by young embedded star clusters

    SciTech Connect

    Adams, Fred C. [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States); Fatuzzo, Marco [Physics Department, Xavier University, Cincinatti, OH 45255 (United States); Holden, Lisa [Department of Mathematics, Northern Kentucky University, Highland Heights, KY 41099 (United States)

    2014-07-01

    Most star formation in the Galaxy takes place in clusters, where the most massive members can affect the properties of other constituent solar systems. This paper considers how clusters influence star formation and forming planetary systems through nuclear enrichment from supernova explosions, where massive stars deliver short-lived radioactive nuclei (SLRs) to their local environment. The decay of these nuclei leads to both heating and ionization, and thereby affects disk evolution, disk chemistry, and the accompanying process of planet formation. Nuclear enrichment can take place on two spatial scales: (1) within the cluster itself (? ? 1 pc), the SLRs are delivered to the circumstellar disks associated with other cluster members. (2) On the next larger scale (? ? 2-10 pc), SLRs are injected into the background molecular cloud; these nuclei provide heating and ionization to nearby star-forming regions and to the next generation of disks. For the first scenario, we construct the expected distributions of radioactive enrichment levels provided by embedded clusters. Clusters can account for the SLR mass fractions inferred for the early Solar Nebula, but typical SLR abundances are lower by a factor of ?10. For the second scenario, we find that distributed enrichment of SLRs in molecular clouds leads to comparable abundances. For both the direct and distributed enrichment processes, the masses of {sup 26}Al and {sup 60}Fe delivered to individual circumstellar disks typically fall in the range 10-100 pM {sub ?} (where 1 pM {sub ?} = 10{sup –12} M {sub ?}). The corresponding ionization rate due to SLRs typically falls in the range ?{sub SLR} ? 1-5 × 10{sup –19} s{sup –1}. This ionization rate is smaller than that due to cosmic rays, ?{sub CR} ? 10{sup –17} s{sup –1}, but will be important in regions where cosmic rays are attenuated (e.g., disk mid-planes).

  10. Bright Hot Impacts by Erupted Fragments Falling Back on the Sun: UV Redshifts in Stellar Accretion

    NASA Astrophysics Data System (ADS)

    Reale, F.; Orlando, S.; Testa, P.; Landi, E.; Schrijver, C. J.

    2014-12-01

    A solar eruption after a flare on 2011 June 7 produced EUV-bright impacts of fallbacks far from the eruption site, observed with the Solar Dynamics Observatory. These impacts can be taken as a template for the impact of stellar accretion flows. Broad redshifted UV lines have been commonly observed in young accreting stars. Here we study the emission from the impacts in the Atmospheric Imaging Assembly's UV channels and compare the inferred velocity distribution to stellar observations. We model the impacts with two-dimensional hydrodynamic simulations. We find that the localized UV 1600 Å emission and its timing with respect to the EUV emission can be explained by the impact of a cloud of fragments. The first impacts produce strong initial upflows. The following fragments are hit and shocked by these upflows. The UV emission comes mostly from the shocked front shell of the fragments while they are still falling, and is therefore redshifted when observed from above. The EUV emission instead continues from the hot surface layer that is fed by the impacts. Fragmented accretion can therefore explain broad redshifted UV lines (e.g., C IV 1550 Å) to speeds around 400 km s-1 observed in accreting young stellar objects.

  11. Empirical isochrones and relative ages for young stars, and the radiative-convective gap

    E-print Network

    N. J. Mayne; Tim Naylor; S. P. Littlefair; Eric S. Saunders; R. D. Jeffries

    2006-12-04

    We have selected pre-main-sequence stars in 12 groups of notional ages ranging from 1 Myr to 35 Myrs, using heterogeneous membership criteria. Using these members we have constructed empirical isochrones in V, V-I colour magnitude diagrams (CMDs). This allows us to identify clearly the gap between the radiative main sequence and the convective pre-main-sequence (the R-C gap). We follow the evolution of this gap with age and show that it can be a useful age indicator for groups less than ~15 Myrs old. We also observe a reduction in absolute spreads about the sequences with age. Finally the empirical isochrones allow us to place the groups in order of age, independently of theory. The youngest groups can be collated into three sets of similar ages. The youngest set is the ONC, NGC6530 and IC5146 (nominally 1 Myrs); next Cep OB3b, NGC2362, Lambda Ori and NGC2264 (nominally 3 Myrs); and finally Sigma Ori and IC348 (nominally 4-5 Myrs). This suggests Cep OB3b is younger than previously thought, and IC348 older. For IC348 the stellar rotation rate distribution and fraction of stars with discs imply a younger age than we derive. We suggest this is because of the absence of O-stars in this cluster, whose winds and/or ionising radiation may be an important factor in the removal of discs in other clusters.

  12. Mount Usu Erupts

    NSDL National Science Digital Library

    de Nie, Michael Willem.

    The snow-covered peak of the 2,402-foot (732-meter) Mount Usu erupted today, spewing black smoke and ash and forcing over 15,000 people from their homes. Historically one of Japan's most active volcanoes, Usu last erupted in 1978 after a number of earthquakes which formed a new and smaller volcano by its side. Mudslides triggered by that eruption killed three people in 1978, but so far no casualties have been reported from this eruption, which was predicted by experts. While volcanologists doubt that another major explosion will occur, they have not ruled out further activity. Another concern is mudslides, as the hot ash and smoke could quickly melt the mountain's thick carpet of snow.

  13. Old Faithful Erupting

    USGS Multimedia Gallery

    Photograph of the Old Faithful Geyser erupting in Yellowstone Nationl Park. Old Faithful was named in 1870 during the Washburn-Langford-Doane Yellowstone expedition and was the first geyser in the Park to be named....

  14. Seismic Eruption Teaching Modules

    NSDL National Science Digital Library

    Lawrence Braile

    This site presents educational modules for teaching about earthquakes, volcano eruptions and related plate tectonic concepts using an interactive computer program for mapping called Seismic/Eruption (also called SeisVolE). The program includes up-to-date earthquake and volcanic eruption catalogs and allows the user to display earthquake and volcanic eruption activity in "speeded up real time" on global, regional or local maps that also show the topography of the area in a shaded relief map image. SeisVolE is an interactive program that includes a number of tools that allow the user to analyze earthquake and volcanic eruption data and produce effective displays to illustrate seismicity and volcano patterns. The program can be used to sort data and provide results for statistical analysis, to generate detailed earthquake and volcano activity maps of specific areas or for specific purposes, to investigate earthquake sequences such as foreshocks and aftershocks, and to produce cross section or 3-D perspective views of earthquake locations. The Seismic/Eruption program can be a powerful and effective tool for teaching about plate tectonics and geologic hazards using earthquake and volcano locations, and for learning (or practicing) fundamental science skills such as statistical analysis, graphing, and map skills. The teaching modules describe and illustrate how to use the Seismic/Eruption program effectively in demonstrations, classroom presentations and interactive presentations, and independent study/research. Because the program has many useful options and can be used to examine earthquake activity and volcanic eruption data, the modules provide instructions and examples of quantitative analysis, graphing of results, creating useful maps and cross section diagrams, and performing in-depth exploration and research. The examples are intended to illustrate the features and capabilities of the program and stimulate interest in using the program for discovery learning in Earth science, especially earthquakes, volcanoes and plate tectonics.

  15. IUE observations of the chromospheric activity-age relation in young solar-type stars

    NASA Astrophysics Data System (ADS)

    Simon, T.; Boesgaard, A. M.

    Except for the synoptic observations of the chromospheric Ca II H-K lines by Wilson (1978), in which he sought evidence for magnetic activity cycles, there is still scant data on stellar activity, especially at UV and X-ray wavelengths where 105K transition regions and 106 - 107K coronae are expected to radiate. This paper presents new UV data, obtained with the IUE spacecraft, for a dozen solar-type stars in the field. The purpose is to study the evolution of transition region and chromospheric emission with stellar age, and also the surface distribution of magnetically active regions as revealed by rotational modulation of UV emission line fluxes.

  16. Connecting Flares and Transient Mass Loss Events in Magnetically Active Stars

    E-print Network

    Osten, Rachel A

    2015-01-01

    We explore the ramification of associating the energetics of extreme mag- netic reconnection events with transient mass loss in a stellar analogy with solar eruptive events. We establish energy partitions relative to the total bolometric radiated flare energy for different observed components of stellar flares, and show that there is rough agreement for these values with solar flares. We apply an equipartition between the bolometric radiated flare energy and kinetic energy in an accompanying mass ejection, seen in solar eruptive events and expected from reconnection. This allows an integrated flare rate in a particular waveband to be used to estimate the amount of associated transient mass loss. This approach is supported by a good correspondence between observational flare signatures on high flaring rate stars and the Sun, which suggests a common physical origin. If the frequent and extreme flares that young solar-like stars and low-mass stars experience are accompanied by transient mass loss in the form of ...

  17. Accretion onto Planetary Mass Companions of Low-mass Young Stars

    NASA Astrophysics Data System (ADS)

    Zhou, Yifan; Herczeg, Gregory J.; Kraus, Adam L.; Metchev, Stanimir; Cruz, Kelle L.

    2014-03-01

    Measurements of accretion rates onto planetary mass objects may distinguish between different planet formation mechanisms, which predict different accretion histories. In this Letter, we use Hubble Space Telescope (HST)/WFC3 UVIS optical photometry to measure accretion rates onto three accreting objects, GSC 06214-00210 b, GQ Lup b, and DH Tau b, that are at the planet/brown dwarf boundary and are companions to solar mass stars. The excess optical emission in the excess accretion continuum yields mass accretion rates of 10-9-10-11 M ? yr-1 for these three objects. Their accretion rates are an order of magnitude higher than expected from the correlation between mass and accretion rates measured from the UV excess, which is applicable if these wide planetary mass companions formed by protostellar core fragmentation. The high accretion rates and large separation from the central star demonstrate the presence of massive disks around these objects. Models for the formation and evolution of wide planetary mass companions should account for their large accretion rates. High ratios of H? luminosity over accretion luminosity for objects with low accretion rates suggest that searches for H? emission may be an efficient way to find accreting planets.

  18. Spatially Resolving the Disk Mass Accretion Process In Young Star Binaries

    NASA Astrophysics Data System (ADS)

    Beck, Tracy

    2012-10-01

    We request HST ACS SBC images in the F140LP and F165LP filters in order to spatially resolve UV emission from H2 gas and scattered light emerging from structures in the planet-forming environments of two young binary systems: GG Tau A and UY Aur. These data, in conjunction with a suite of high-angular resolution ground-based observations -- including spectral images of near-IR H2 emission, mm observations of dust continuum and CO gas emission through allocated ALMA "Cycle 0" observations -- will allow us to characterize the morphology of gas and dust passing between the circumbinary and circumstellar disks. Multi-wavelngth mapping of the distribution of material in GG Tau and UY Aur will reveal the role tidal truncation plays in the formation of planets in binary systems and help to constrain a growing number of hydrodynamic simulations of the complex disk-disk interactions.

  19. Infrared observations of NGC 2071/IRS/ and AFGL 490 - Two low-luminosity young stars

    NASA Technical Reports Server (NTRS)

    Harvey, P. M.; Campbell, M. F.; Hoffmann, W. F.; Thronson, H. A., Jr.; Gatley, I.

    1979-01-01

    Infrared observations are presented of two compact sources associated with molecular clouds. Photometry from 2 to 200 microns of the source associated with an OH maser in NGC 2071, OH 205.1-14.1, shows a steep increase in flux from 2 to 50 microns. Scans at several wavelengths fail to resolve the source. Photometry at 50-200 microns of the other object, GL 490, when combined with earlier 2-20-micron spectrophotometry, shows an infrared energy distribution that is much broader than that of the NGC 2071 source. Both sources are interpreted as young, possibly pre-main-sequence objects with differences in energy distributions due principally to differences in the distribution of circumstellar matter.

  20. RX J0513.1+0851 AND RX J0539.9+0956: Two young, rapidly rotating spectroscopic binary stars

    SciTech Connect

    Ruíz-Rodríguez, Dary; Prato, L.; Wasserman, L. H. [Lowell Observatory, 1400 West Mars Hill Road Flagstaff, AZ 86001 (United States); Torres, Guillermo [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Neuhäuser, Ralph, E-mail: dar@lowell.edu [Astrophysikalisches Institut und Universitäts-Sternwarte, FSU Jena, Schillergäßchen 2-3, D-07745 Jena (Germany)

    2013-06-01

    RX J0513.1+0851 and RX J0539.9+0956 were previously identified as young, low-mass, single-lined spectroscopic binary systems and classified as weak-lined T Tauri stars at visible wavelengths. Here we present radial velocities, spectral types, vsin i values, and flux ratios for the components in these systems resulting from two-dimensional cross-correlation analysis. These results are based on high-resolution, near-infrared spectroscopy taken with the Keck II telescope to provide a first characterization of these systems as double-lined rather than single-lined. It applies the power of infrared spectroscopy to the detection of cool secondaries; the flux scales as a less steep function of mass in the infrared than in the visible, thus enabling an identification of low-mass secondaries. We found that the RX J0513.1+0851 and RX J0539.9+0956 primary stars are fast rotators, 60 km s{sup –1} and 80 km s{sup –1}, respectively; this introduces extra difficulty in the detection of the secondary component as a result of the quite broad absorption lines. To date, these are the highest rotational velocities measured for a pre-main sequence spectroscopic binary. The orbital parameters and mass ratios were determined by combining new visible light spectroscopy with our infrared data for both systems. For RX J0513.1+0851, we derived a period of ?4 days and a mass ratio of q = 0.46 ± 0.01 and for RX J0539.9+0956, a period of ?1117 days and a mass ratio of q = 0.66 ± 0.01. Based on our derived properties for the stellar components, we estimate the luminosities and hence distances to these binaries at 220 pc and 90 pc. They appear to be significantly closer than previously estimated.

  1. The structure and dynamics of young star clusters: King 16, NGC 1931, NGC 637 and NGC 189

    E-print Network

    Priya Hasan; S N Hasan; Urmi Shah

    2008-08-13

    In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7', 12', 6' and 5' which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values $E(B-V)$ obtained for the clusters are 0.85, 0.65--0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions ($\\phi(M) = dN/dM \\propto M^{-(1+\\chi)}$) to the parameter $\\tau = t_{age}/t_{relax}$ to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times ($\\tau \\geq 1$). These results suggest mass seggregation due to dynamical effects. The values of $\\chi$, which characterise the overall mass functions for the clusters are 0.96 $\\pm$ 0.11, 1.16 $\\pm$ 0.18, 0.55 $\\pm$ 0.14 and 0.66 $\\pm$ 0.31 respectively. The change in $\\chi$ as a function of radius is a good indicator of the dynamical state of clusters.

  2. Chandra HETGS Multiphase Spectroscopy of the Young Magnetic O Star ?1 Orionis C

    NASA Astrophysics Data System (ADS)

    Gagné, Marc; Oksala, Mary E.; Cohen, David H.; Tonnesen, Stephanie K.; ud-Doula, Asif; Owocki, Stanley P.; Townsend, Richard H. D.; MacFarlane, Joseph J.

    2005-08-01

    We report on four Chandra grating observations of the oblique magnetic rotator ?1 Ori C (O5.5 V), covering a wide range of viewing angles with respect to the star's 1060 G dipole magnetic field. We employ line-width and centroid analyses to study the dynamics of the X-ray-emitting plasma in the circumstellar environment, as well as line-ratio diagnostics to constrain the spatial location, and global spectral modeling to constrain the temperature distribution and abundances of the very hot plasma. We investigate these diagnostics as a function of viewing angle and analyze them in conjunction with new MHD simulations of the magnetically channeled wind shock mechanism on ?1 Ori C. This model fits all the data surprisingly well, predicting the temperature, luminosity, and occultation of the X-ray-emitting plasma with rotation phase.

  3. VizieR Online Data Catalog: Proper motions of young stars in Chamaeleon (Lopez Marti+, 2013)

    NASA Astrophysics Data System (ADS)

    Lopez Marti, B.; Jimenez-Esteban, F.; Bayo, A.; Barrado, D.; Solano, E.; Bouy; H.; Rodrigo, C.

    2013-07-01

    We present the results of a search for new candidate members of the Chamaeleon I and II star forming regions based on proper motions and multiwavelength photometry. Kinematic candidate members are initially selected in an area of 3 degrees around each cloud on the basis of proper motions and colours using the UCAC4 catalogue. The SEDs of the objects are constructed using photometry retrieved from the Virtual Observatory and other resources, and fitted to models of stellar photospheres in order to derive effective temperatures, gravity values and luminosities. Masses and ages are estimated by comparison with theoretical evolutionary tracks in a Hertzprung-Russell diagram. Objects with ages <=20Myr are selected as probable members of the moving groups. The properties of our candidates are compared with those of the previously known members of the clouds. (5 data files).

  4. Emission-line studies of young stars. 4: The optical forbidden lines

    NASA Technical Reports Server (NTRS)

    Hamann, Fred

    1994-01-01

    Optical forbidden line strengths and profiles are discussed for a sample of 30 T Tauri stars and 12 Herbig Ae-Be stars. Transitions of (C I), (N II), (O I), (O II), (S II), (Ca II), (Cr II), (Fe II), and (Ni II) are detected. Profile variability occurred in DG Tau and probably other sources. The ensemble profiles can be divided into four generic components that may represent distinct emitting regions; (1) narrow rest-velocity lines, (2) 'low'-velocity lines (peaking at less than or approximately +/- 50 km s(exp -1)), (3) 'high'-velocity (usually greater than or approximately +/- 100 km s(exp -1)) blueshifted peaks or wings, and (4) high-velocity redshifted peaks. Among T Tauri stars, the rest-velocity lines appear most often in sources with weak and narrow permitted lines, such as the Ca II triplet. The low- and high-velocity blueshifted components usually appear together in sources with strong and broad Ca II triplet lines. If the velocity-shifted lines form in jets, the smallest (full) opening angles required by the profiles are less than or approximately 20 deg for the narrow, blueshifted (Ca II) lines of DG Tau and HL Tau. Other lines in DG Tau are much broader, implying larger opening angles or greater velocity dispersions. The variability in DG Tau also implies significant changes in the collimation or velocity coherence on timescales of a few years. RW Aur and AS 353A have blue- and redshifted line peaks that could form in oppositely directed jets. The strong (S II) lambda 6716 and lambda 6731 lines in RW Aur are exclusively redshifted and require opening angles less than or approximately 60 deg. Measurements of different profiles in the same spectrum show that the physical conditions change with the line-of-sight velocities. The most persistent trends are for more (N II) and (O II) and less (O I) lambda 5577 flux at high velocities. Constraints on the physical conditions are derived by modeling the emission lines via multilevel ions in 'coronal ionization equilibrium.' A single temperature and density cannot fully describe the line spectra in any velocity interval. Temperatures in the (O I) region are 9000 less than or approximately T(sub e) less than 14,000 K, and the ionization fraction (of H) is less than 35%. The densities derived from (O I) include n(sub e) less than or approximately 5 x 10(exp 5) to approximately 10(exp 7) cm(exp -3), but n(sub e) greater than or approximately 10(exp 6) cm(exp -3) obtains only at low velocities. In the (S II) regions the densities are lower, 10(exp 3) less than or approximately n(sub e) less than or approximately 7 x 10(exp 4) cm(exp -3), and the temperatures are probably higher, T(sub e) greater than or approximately 13,000 K. At high velocities (only) there is additional hot gas that produces (N II) and (O II), possibly most of the (S II), and little (O I). This region is characterized by T(sub e) greater than or approximately 15,000 K, n(sub e) less than or approximately 10(exp 5) cm(exp -3), and an ionization fraction greater than or approximately 50%. When combined with the spatially segregated emitting regions observed by others by spectral imaging, these results suggest decreasing n(sub e) and increasing T(sub e) away from the star in at least the high velocity gas.

  5. Chandra HETGS Multi-Phase Spectroscopy of the Young Magnetic O Star theta^1 Orionis C

    E-print Network

    Marc Gagne; Mary E. Oksala; David H. Cohen; Stephanie K. Tonnesen; Asif ud-Doula; Stanley P. Owocki; Richard H. D. Townsend; Joseph J. MacFarlane

    2005-06-06

    We report on four Chandra grating observations of the oblique magnetic rotator theta^1 Ori C (O5.5 V) covering a wide range of viewing angles with respect to the star's 1060 G dipole magnetic field. We employ line-width and centroid analyses to study the dynamics of the X-ray emitting plasma in the circumstellar environment, as well as line-ratio diagnostics to constrain the spatial location, and global spectral modeling to constrain the temperature distribution and abundances of the very hot plasma. We investigate these diagnostics as a function of viewing angle and analyze them in conjunction with new MHD simulations of the magnetically channeled wind shock mechanism on theta^1 Ori C. This model fits all the data surprisingly well, predicting the temperature, luminosity, and occultation of the X-ray emitting plasma with rotation phase.

  6. Water in the envelopes and disks around young high-mass stars

    E-print Network

    Floris van der Tak; Malcolm Walmsley; Fabrice Herpin; Cecilia Ceccarelli

    2005-10-21

    Single-dish spectra and interferometric maps of (sub)mm lines of H2O-18 and HDO are used to study the chemistry of water in eight regions of high-mass star formation. The spectra indicate HDO excitation temperatures of ~110 K and column densities in an 11'' beam of ~2x10^14 cm^-2 for HDO and ~2x10^17 cm^-2 for H2O, with the N(HDO)/N(H2O) ratio increasing with decreasing temperature. Simultaneous observations of CH3OH and SO2 indicate that 20-50% of the single-dish line flux arises in the molecular outflows of these objects. The outflow contribution to the H2O-18 and HDO emission is estimated to be 10-20%. Radiative transfer models indicate that the water abundance is low (~10^-6) outside a critical radius corresponding to a temperature in the protostellar envelope of ~100 K, and `jumps' to H2O/H2 ~ 10^-4 inside this radius. This value corresponds to the observed abundance of solid water and together with the derived HDO/H2O abundance ratios of ~1/1000 suggests that the origin of the observed water is evaporation of grain mantles. This idea is confirmed in the case of AFGL 2591 by interferometer observations of HDO, H2O-18 and SO2 lines, which reveal compact (~800 AU) emission with a systematic velocity gradient. This size is similar to that of the 1.3 mm continuum towards AFGL 2591, from which we estimate a mass of ~0.8 M0, or ~5% of the mass of the central star. We speculate that we may be observing a circumstellar disk in an almost face-on orientation.

  7. X-ray flaring from the young stars in CygnusOB2

    E-print Network

    J. F. Albacete Colombo; M. Caramazza; E. Flaccomio; G. Micela; S. Sciortino

    2007-08-17

    Aims: We characterize individual and ensemble properties of X-ray flares from stars in the CygOB2 and ONC star-forming regions. Method: We analyzed X-ray lightcurves of 1003 CygOB2 sources observed with Chandra for 100 ksec and of 1616 ONC sources detected in the ``Chandra Orion Ultra-deep Project'' 850 ksec observation. We employed a binning-free maximum likelihood method to segment the light-curves into intervals of constants signal and identified flares on the basis of both the amplitude and the time-derivative of the source luminosity. We then derived and compared the flare frequency and energy distribution of CygOB2 and ONC sources. The effect of the length of the observation on these results was investigated by repeating the statistical analysis on five 100 ksec-long segments extracted from the ONC data. Results: We detected 147 and 954 flares from the CygOB2 and ONC sources, respectively. The flares in CygOB2 have decay times ranging from ~0.5 to about 10 hours. The flare energy distributions of all considered flare samples are described at high energies well by a power law with index alpha=-(2.1+-0.1). At low energies, the distributions flatten, probably because of detection incompleteness. We derived average flare frequencies as a function of flare energy. The flare frequency is seen to depend on the source's intrinsic X-ray luminosity, but its determination is affected by the length of the observation. The slope of the high-energy tail of the energy distribution is, however, affected little. A comparison of CygOB2 and ONC sources, accounting for observational biases, shows that the two populations, known to have similar X-ray emission levels, have very similar flare activity.

  8. Variable accretion processes in the young binary-star system UY Aur

    SciTech Connect

    Stone, Jordan M.; Eisner, J. A.; Kulesa, Craig; McCarthy, Don [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Salyk, Colette, E-mail: jstone@as.arizona.edu, E-mail: jeisner@as.arizona.edu, E-mail: csalyk@noao.edu, E-mail: dmccarthy@as.arizona.edu, E-mail: ckulesa@as.arizona.edu [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

    2014-09-01

    We present new K-band spectroscopy of the UY Aur binary star system. Our data are the first to show H{sub 2} emission in the spectrum of UY Aur A and the first to spectrally resolve the Br? line in the spectrum of UY Aur B. We see an increase in the strength of the Br? line in UY Aur A and a decrease in Br? and H{sub 2} line luminosity for UY Aur B compared to previous studies. Converting Br? line luminosity to accretion rate, we infer that the accretion rate onto UY Aur A has increased by 2 × 10{sup –9} M {sub ?} yr{sup –1} per year since a rate of zero was observed in 1994. The Br? line strength for UY Aur B has decreased by a factor of 0.54 since 1994, but the K-band flux has increased by 0.9 mag since 1998. The veiling of UY Aur B has also increased significantly. These data evince a much more luminous disk around UY Aur B. If the lower Br? luminosity observed in the spectrum of UY Aur B indicates an intrinsically smaller accretion rate onto the star, then UY Aur A now accretes at a higher rate than UY Aur B. However, extinction at small radii or mass pile-up in the circumstellar disk could explain decreased Br? emission around UY Aur B even when the disk luminosity implies an increased accretion rate. In addition to our scientific results for the UY Aur system, we discuss a dedicated pipeline we have developed for the reduction of echelle-mode data from the ARIES spectrograph.

  9. Variable Accretion Processes in the Young Binary-star System UY Aur

    NASA Astrophysics Data System (ADS)

    Stone, Jordan M.; Eisner, J. A.; Salyk, Colette; Kulesa, Craig; McCarthy, Don

    2014-09-01

    We present new K-band spectroscopy of the UY Aur binary star system. Our data are the first to show H2 emission in the spectrum of UY Aur A and the first to spectrally resolve the Br? line in the spectrum of UY Aur B. We see an increase in the strength of the Br? line in UY Aur A and a decrease in Br? and H2 line luminosity for UY Aur B compared to previous studies. Converting Br? line luminosity to accretion rate, we infer that the accretion rate onto UY Aur A has increased by 2 × 10–9 M ? yr–1 per year since a rate of zero was observed in 1994. The Br? line strength for UY Aur B has decreased by a factor of 0.54 since 1994, but the K-band flux has increased by 0.9 mag since 1998. The veiling of UY Aur B has also increased significantly. These data evince a much more luminous disk around UY Aur B. If the lower Br? luminosity observed in the spectrum of UY Aur B indicates an intrinsically smaller accretion rate onto the star, then UY Aur A now accretes at a higher rate than UY Aur B. However, extinction at small radii or mass pile-up in the circumstellar disk could explain decreased Br? emission around UY Aur B even when the disk luminosity implies an increased accretion rate. In addition to our scientific results for the UY Aur system, we discuss a dedicated pipeline we have developed for the reduction of echelle-mode data from the ARIES spectrograph. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.

  10. A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER ALLWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy

    NASA Technical Reports Server (NTRS)

    Koening, X. P.; Leisawitz, D. T.

    2014-01-01

    We present an assessment of the performance of WISE and the AllWISE data release in a section of the Galactic Plane. We lay out an approach to increasing the reliability of point source photometry extracted from the AllWISE catalog in Galactic Plane regions using parameters provided in the catalog. We use the resulting catalog to construct a new, revised young star detection and classification scheme combining WISE and 2MASS near and mid-infrared colors and magnitudes and test it in a section of the Outer Milky Way. The clustering properties of the candidate Class I and II stars using a nearest neighbor density calculation and the two-point correlation function suggest that the majority of stars do form in massive star forming regions, and any isolated mode of star formation is at most a small fraction of the total star forming output of the Galaxy. We also show that the isolated component may be very small and could represent the tail end of a single mechanism of star formation in line with models of molecular cloud collapse with supersonic turbulence and not a separate mode all to itself.

  11. High Spatial Resolution Spectroscopy of W51 IRS2E and IRS2W: Two Very Massive Young Stars in Early Formation Stages

    E-print Network

    C. L. Barbosa; R. D. Blum; P. S. Conti; A. Damineli; E. Figueredo

    2008-03-27

    We present $K$-band spectra of the near infrared counterparts to IRS2E and IRS2W which is associated with the ultracompact HII region W51d, both of them embedded sources in the Galactic compact HII region W51 IRS2. The high spatial resolution observations were obtained with the laser guide star facility and Near infrared Integral Field Spectrograph (NIFS) mounted at the Gemini North observatory. The spectrum of the ionizing source of W51d shows the photospheric features NIII (21155 \\AA) in emission and HeII (21897 \\AA) in absorption which lead us to classify it as an young O3 type star. We detected CO overtone in emission at 23000 \\AA in the spectrum of IRS2E, suggesting that it is a massive young object still surrounded by an accretion disc, probably transitioning from the hot core phase to an ultracompact HII region.

  12. A multi-wavelength census of star formation activity in the young embedded cluster around Serpens\\/G3-G6

    Microsoft Academic Search

    A. A. Djupvik; Ph. André; S. Bontemps; F. Motte; G. Olofsson; M. Gålfalk; H.-G. Florén

    2006-01-01

    Aims.The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens\\/G3-G6, located ~45 arcmin (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs). Methods: .Multi-wavelength broadband photometry was obtained to sample the near and mid-IR

  13. The Gemini/NICI Planet-Finding Campaign: The Frequency of Planets around Young Moving Group Stars

    NASA Astrophysics Data System (ADS)

    Biller, B.; Liu, M.; Wahhaj, Z.; Nielsen, E.; NICI Campaign Team

    2014-03-01

    We report results of a direct imaging survey for giant planets around 80 members of the ? Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part of the Gemini/NICI Planet-Finding Campaign. For this sample, we obtained median contrasts of ?H = 13.9 mag at 1'' in combined CH4 narrowband ADI+SDI mode and median contrasts of ?H = 15.1 mag at 2'' in H-band ADI mode. Four co-moving companions of brown dwarf or stellar mass were discovered in this moving group sample: PZ Tel B (36 ± 6 MJup, 16.4 ± 1.0 AU), CDñ35 2722B (31 ± 8 M Jup, 67 ± 4 AU), HD 12894B (0.46 ± 0.08 M., 15.7 ± 1.0 AU), and BD+07 1919C (0.20 ± 0.03 M., 12.5 ± 1.4 AU). From a Bayesian analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1-20 MJup companions at semi-major axes from 10-150 AU to <18% at a 95.4% confidence level using DUSTY models and to <6% at a 95.4% using COND models. This survey is the deepest search to date for giant planets around young moving group stars.

  14. Kinematics of the Outflow from the Young Star DG Tau B: Rotation in the Vicinities of an Optical Jet

    NASA Astrophysics Data System (ADS)

    Zapata, Luis A.; Lizano, Susana; Rodríguez, Luis F.; Ho, Paul T. P.; Loinard, Laurent; Fernández-López, Manuel; Tafoya, Daniel

    2015-01-01

    We present 12CO(2-1) line and 1300 ?m continuum observations made with the Submillimeter Array of the young star DG Tau B. We find, in the continuum observations, emission arising from the circumstellar disk surrounding DG Tau B. The 12CO(2-1) line observations, on the other hand, revealed emission associated with the disk and the asymmetric outflow related with this source. Velocity asymmetries about the flow axis are found over the entire length of the flow. The amplitude of the velocity differences is of the order of 1-2 km s-1 over distances of about 300-400 AU. We interpret them as a result of outflow rotation. The sense of the outflow and disk rotation is the same. Infalling gas from a rotating molecular core cannot explain the observed velocity gradient within the flow. Magneto-centrifugal disk winds or photoevaporated disk winds can produce the observed rotational speeds if they are ejected from a Keplerian disk at radii of several tens of AU. Nevertheless, these slow winds ejected from large radii are not very massive, and cannot account for the observed linear momentum and angular momentum rates of the molecular flow. Thus, the observed flow is probably entrained material from the parent cloud. DG Tau B is a good laboratory to model in detail the entrainment process and see if it can account for the observed angular momentum.

  15. Volcanic eruptions on Io

    NASA Astrophysics Data System (ADS)

    Strom, R. G.; Schneider, N. M.; Terrile, R. J.; Cook, A. F.; Hansen, C.

    1981-09-01

    Nine eruption plumes which were observed during the Voyager 1 encounter with Io are discussed. During the Voyager 2 encounter, four months later, eight of the eruptions were still active although the largest became inactive sometime between the two encounters. Plumes range in height from 60 to over 300 km with corresponding ejection velocities of 0.5 to 1.0 km/s and plume sources are located on several plains and consist of fissures or calderas. The shape and brightness distribution together with the pattern of the surface deposition on a plume 3 is simulated by a ballistic model with a constant ejection velocity of 0.5 km/s and ejection angles which vary from 0-55 deg. The distribution of active and recent eruptions is concentrated in the equatorial regions and indicates that volcanic activity is more frequent and intense in the equatorial regions than in the polar regions. Due to the geologic setting of certain plume sources and large reservoirs of volatiles required for the active eruptions, it is concluded that sulfur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes.

  16. Direct-imaging discovery of a 12-14 Jupiter-mass object orbiting a young binary system of very low-mass stars

    NASA Astrophysics Data System (ADS)

    Delorme, P.; Gagné, J.; Girard, J. H.; Lagrange, A. M.; Chauvin, G.; Naud, M.-E.; Lafrenière, D.; Doyon, R.; Riedel, A.; Bonnefoy, M.; Malo, L.

    2013-05-01

    Context. Though only a handful of extrasolar planets have been discovered via direct-imaging, each of these discoveries had a tremendous impact on our understanding of planetary formation, stellar formation, and cool atmosphere physics. Aims: Since many of these newly imaged giant planets orbit massive A or even B stars, we investigate whether giant planets could be found orbiting low-mass stars at large separations. Methods: We have been conducting an adaptive optic imaging survey to search for planetary-mass companions of young M dwarfs in the solar neigbourhood, in order to probe different initial conditions of planetary formation. Results: We report here the direct-imaging discovery of 2MASS J01033563-5515561(AB)b, a 12-14 MJup companion at a projected separation of 84 AU from a pair of young late-M stars, with which it shares proper motion. We also detected a Keplerian-compatible orbital motion. Conclusions: This young L-type object at the planet/brown dwarf mass boundary is the first ever imaged around a binary system at a separation compatible with formation in a disc. Based on observations obtained with NACO on VLT UT-4 at ESO-Paranal (runs 090.C-0698(A) and 70.D-0444(A).

  17. TECHBOOKS Journal: ASTR MS Code: 190R1 PIPS No: DO00005160 DISK 10-11-2004 15:47 Pages: 11 YOUNG CLOSE-BY NEUTRON STARS: THE GOULD BELT

    E-print Network

    Popov, Sergei

    of close young neutron stars. In compar- ison with our previous investigation we use a different neutronUNCO RRECTED PRO O F TECHBOOKS Journal: ASTR MS Code: 190R1 PIPS No: DO00005160 DISK 10-11-2004 15:47 Pages: 11 YOUNG CLOSE-BY NEUTRON STARS: THE GOULD BELT VS. THE GALACTIC DISC 1 2 S.B. POPOV1,2 , R

  18. Physical parameters of young M-type stars and brown dwarfs with VOSA

    NASA Astrophysics Data System (ADS)

    Bayo, A.; Rodrigo, C.; Barrado, D.; Solano, E.; Allard, F.; Joergens, V.

    Although M dwarfs are the most common stars in our stellar neighborhood they are still among the least understood. This class of objects is dominated by dramatic changes: in their interiors (fully convective, with implications in angular momentum evolution), in their atmospheres (crossing temperatures where dust settling occurs), and in their nature (including both, stellar and substellar objects). Populating efficiently our solar neighborhood, they are very well represented in the databases coming from new and more sensitive surveys that provide photometry at many wavelength ranges and cover large areas of the sky (few examples among many others are GALEX, SDSS, 2MASS, WISE and VISTA). In this context of opulence of objects and data, the Virtual Observatory comes in naturally as an excellent framework to efficiently advance in the knowledge of M-type sources. We put special emphasis in the benefits of using the new capabilities of VOSA (Virtual Observatory SED Analyzer, (2008A&A...492..277B); in operation since 2008 and in constant development) to study large samples of candidate and confirmed M members of Chamaeleon I.

  19. Absolute Parameters of YOung Stars: GG Lup and mu^1 Sco

    E-print Network

    Budding, Edwin; Blackford, Mark

    2015-01-01

    New high-resolution spectroscopy and $BVR$ photometry, together with literature data, on the Gould's Belt close binary systems GG Lup and $\\mu^1$ 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 percent, thus: $M_1$ = 4.16$\\pm$0.12, $M_2$ = 2.64$\\pm$0.12, $R_{1}$ = 2.42$\\pm$0.05, $R_2$ = 1.79$\\pm$0.04, ($\\odot$); $T_{1}$ $\\sim$13000, $T_2$ $\\sim$10600 (K); photometric distance $\\sim$ 160 (pc). The high eccentricity and relatively short period (105 y) of apsidal revolution may be related to an apparent `slow B-type pulsator' (SPB) 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 $\\bar{k_2} = 0.0058 \\pm 0.0004$. This is in agr...

  20. Young Stars and Protostellar Cores near NGC 2023 and the Horsehead Nebula

    NASA Astrophysics Data System (ADS)

    Sandell, G.; Jenness, T.; McMullin, J. P.; Shah, R. Y.

    2001-12-01

    We present new SCUBA images at 850 and 450 ? m as well as extended CO and 13CO J = 2 - 1 maps obtained with the 15 m JCMT telescope on Mauna Kea, Hawaii of NGC 2023 and the Horsehead nebula . We also present BIMA images in 3.5 mm continuum and NH2D of NGC 2023 mm1, the low mass Class 0 protostar in the vicinity of NGC 2023. We detected mm1 in the 3.5 mm continuum, but not the nearby mm2. The NH2D emission is strong and traces the dust emission very well. NGC 2023 mm1 is the strongest sub-mm source in the region and our data cofirm that the dust emission is significantly optically thick in the sub-mm. The Horsehead nebula is readily seen in the dust continuum with a morphology very similar to that seen in the optical. The Horsehead is also very prominent in our CO maps and even the CO emission follows the optical appearance very closely. There are several fainter dust continuum sources in the region: the compact ones appear to coincide with young Class I type sources, the more extended ones are likely dense, pre-stellar cores. There is an elongated dust source in the neck of the Horsehead, which is not seen in the CO maps. The nature of this source is not yet know. The JCMT is operated by the Joint Astronomy Centre, on behalf of UK Particle Physics and Astronomy Research Council, the Netherlands Organization for Scientific Research, and the Canadian National Research Council.

  1. Detection of a Cool, Accretion-Shock-Generated X-Ray Plasma in EX Lupi During the 2008 Optical Eruption

    NASA Technical Reports Server (NTRS)

    Teets, William K.; Weintraub, David A.; Kastner, Joel H.; Grosso, Nicholas; Hamaguchi, Kenji; Richmond, Michael

    2012-01-01

    EX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak of the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for an approx 0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.

  2. Erupting Volcano Mount Etna

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Expedition Five crew members aboard the International Space Station (ISS) captured this overhead look at the smoke and ash regurgitated from the erupting volcano Mt. Etna on the island of Sicily, Italy in October 2002. Triggered by a series of earthquakes on October 27, 2002, this eruption was one of Etna's most vigorous in years. This image shows the ash plume curving out toward the horizon. The lighter-colored plumes down slope and north of the summit seen in this frame are produced by forest fires set by flowing lava. At an elevation of 10,990 feet (3,350 m), the summit of the Mt. Etna volcano, one of the most active and most studied volcanoes in the world, has been active for a half-million years and has erupted hundreds of times in recorded history.

  3. Eta Carinae's Second Eruption and the Light Curves of the eta Carinae Variables

    NASA Astrophysics Data System (ADS)

    Humphreys, Roberta M.; Davidson, Kris; Smith, Nathan

    1999-09-01

    Within the general class of highly unstable massive stars called luminous blue variables (LBVs), four stars have experienced ``giant eruptions'' during which the total luminosities of the stars actually increase. This rare group includes eta Carinae, P Cygni, SN 1961v, and V12 in NGC 2403. Several different observations now suggest that some of the material in eta Car's equatorial region was probably ejected during its lesser or second eruption around 1890. When the old visual observations are corrected for the probable circumstellar extinction at that time, we find that its 1890 eruption is much more significant in terms of its luminosity, energy, and mass loss than previously assumed and resembles the second peak seen in the historical light curve for P Cyg. The light curves of all four eta Carinae variables share a very distinctive appearance with a postmaximum plateau; a second, lesser eruption; and obscuration by circumstellar dust after the giant eruption.

  4. Lichenoid drug eruption.

    PubMed

    Brauer, Jeremy; Votava, Henry J; Meehan, Shane; Soter, Nicholas A

    2009-01-01

    A 78-year-old man presented with an eight-month history of folliculocentric, pink, hyperkeratotic papules and plaques with thick white scale that involved the entire body, with confluence on the buttocks and genitalia. A biopsy specimen demonstrated superficial and focal, mild perivascular and perifollicular, band-like lymphocytic infiltrate and eosinophils. There were lymphocytes extending to the dermo-epidermal junction with vacuolar changes. A diagnosis of lichenoid drug eruption secondary to a proton-pump inhibitor was made. To the best of our knowledge, only one other case of lichenoid drug eruption secondary to a proton-pump inhibitor has been reported. PMID:19891921

  5. Mid-infrared diagnostics of metal-rich HII regions from VLT and Spitzer spectroscopy of young massive stars in W31

    NASA Astrophysics Data System (ADS)

    Furness, J. P.; Crowther, P. A.; Morris, P. W.; Barbosa, C. L.; Blum, R. D.; Conti, P. S.; van Dyk, S. D.

    2010-04-01

    We present near-infrared Very Large Telescope/Infrared Spectrograph and Array Camera and mid-infrared (mid-IR) Spitzer/Infrared Spectrograph spectroscopy of the young massive cluster in the W31 star-forming region. H-band spectroscopy provides refined classifications for four cluster member O stars with respect to Blum et al. In addition, photospheric features are detected in the massive young stellar object (massive YSO) #26. Spectroscopy permits estimates of stellar temperatures and masses, from which a cluster age of ~0.6 Myr and distance of 3.3kpc are obtained, in excellent agreement with Blum et al. IRS spectroscopy reveals mid-IR fine structure line fluxes of [NeII-III] and [SIII-IV] for four O stars and five massive YSOs. In common with previous studies, stellar temperatures of individual stars are severely underestimated from the observed ratios of fine-structure lines, despite the use of contemporary stellar atmosphere and photoionization models. We construct empirical temperature calibrations based upon the W31 cluster stars of known spectral type, supplemented by two inner Milky Way ultracompact (UC) HII regions whose ionizing star properties are established. Calibrations involving [NeIII] 15.5 ?m/[NeII] 12.8 ?m, [SIV] 10.5 ?m/[NeII] 12.8 ?m or [ArIII] 9.0 ?m/[NeII] 12.8 ?m have application in deducing the spectral types of early to mid O stars for other inner Milky Way compact and UC HII regions. Finally, evolutionary phases and time-scales for the massive stellar content in W31 are discussed, due to the presence of numerous young massive stars at different formation phases in a `coeval' cluster. Based on observations made with ESO telescopes at the Paranal Observatory under programme ID 077.C-0550(A) and the Spitzer Space Telescope which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. E-mail: Paul.Crowther@shef.ac.uk

  6. X-ray Modeling of Very Young Early Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications

    E-print Network

    Norbert S. Schulz; Claude R. Canizares; Dave P. Huenemoerder; Kevin J. Tibbetts

    2003-05-30

    We analyzed high resolution X-ray spectra in the wavelength range of 1.5 -- 25 A of three of its X-ray brightest members obtained with the High Energy Transmission Grating Spectrometer (HETGS) on-board the Chandra X-ray Observatory. The DEM derived from over 80 emission lines in the spectrum of Theta Ori C indicates three peaks located at 7.9 MK, 25 MK, and 66 MK. The emission measure varies over the 15.4 day wind period of the star. For the two phases observed, the low temperature emission remains stable, while the high temperature emission shows significant differences. The line widths seem to show a similar bifurcation, where we resolve some of the soft X-ray lines with velocities up to 850 km/s, whereas the bulk of the lines remain unresolved. None of the lines are resolved for Theta Ori A and E. The high temperature emissivity contributes to most of the total X-ray flux in all stars. The bulk of the X-ray emission cannot be produced by shock instabilities in a radiation driven wind and are likely the result of magnetic confinement in all three stars. The fact that all stars appear to be magnetic and are near zero age on the main sequence also raises the issue whether the Orion stars are simply different or whether young massive stars enter the main sequence carrying significant magnetic fields.

  7. A High Dynamic Range Dual Imaging Polarimetric Survey of Circumstellar Disks around Young Stars using Gemini North with Hokupa`a

    NASA Astrophysics Data System (ADS)

    Potter, D.; Baudoz, P.; Guyon, O.; Brandner, W.; Close, L.; Graves, J. E.; Northcott, M.

    2001-05-01

    We present results from a survey of circumstellar disks around young stars in the Taurus star-forming region and in the TW Hydrae association using a dual imaging polarimetric technique with adaptive optics. This technique suppresses speckle noise, which improves our sensitivity in detecting polarized light near bright stars. We present high resolution (75 mas) H-band polarimetry maps of circumstellar disks found around TW Hydrae, LkCa 15, GM Aur, and GG Tau and will discuss techniques used to extract physical properties of these disks from the polarization measurements. These observations were obtained with the University of Hawaii curvature sensing adaptive optics system, Hokupa`a, at the Gemini North 8m telescope. This research acknowledges support by the National Science Foundation.

  8. Spectrophotometric Time Series of ? Carinae's Great Eruption

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Clocchiatti, Alejandro; James, David; Margheim, Steve; Matheson, Thomas; Prieto, Jose Luis; Smith, Chris; Smith, Nathan; Walborn, Nolan; Welch, Doug; Zenteno, Alfredo

    2014-08-01

    ? Car serves as our most important template for understanding non-SN transients from massive stars in external galaxies. However, until recently, no spectra were available because its historic ``Great Eruption'' (GE) occurred from 1838-1858, before the invention of the astronomical spectrograph, and only visual estimates of its brightness were recorded teSF11. Now we can also obtain a spectral sequence of the eruption through its light echoes we discovered, which will be of great value since spectra are our most important tool for inferring physical properties of extragalactic transients. Subsequent spectroscopic follow-up revealed that its outburst was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) teRest12_eta. These differences between the GE and the extragalactic transients presumed to be its analogues raise questions about traditional scenarios for the outburst. We propose to obtain a spectrophotometric time series of the GE from different directions, allowing the original eruption of ? Car to be studied as a function of time as well as latitude, something only possible with light echoes. This unique detailed spectroscopic study of the light echoes of ? Car will help us understand (episodic) mass- loss in the most massive evolved stars and their connection to the most energetic core-collapse SNe.

  9. First spectroscopic observations of the substellar companion of the young debris disk star PZ Telescopii

    NASA Astrophysics Data System (ADS)

    Schmidt, T. O. B.; Mugrauer, M.; Neuhäuser, R.; Vogt, N.; Witte, S.; Hauschildt, P. H.; Helling, Ch.; Seifahrt, A.

    2014-06-01

    Context. In 2010 a substellar companion to the solar analog pre-main sequence star PZ Tel and member of the approximately 12 Myr old ? Pic moving group was found by high-contrast direct imaging independently by two teams. Aims: In order to determine the basic parameters of this companion more precisely and independent of evolutionary models, hence age-independent, we obtained follow-up spectroscopic observations of the primary and companion. Methods: We used the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope Unit 4/Yepun of ESO's Paranal Observatory in the H + K band and processed the data using the spectral deconvolution technique. The resulting spectrum of the companion was then compared to a grid of Drift-Phoenix synthetic model spectra, a combination of a general-purpose model atmosphere code with a non-equilibrium, stationary cloud and dust model, using a ?2 minimization analysis. Results: We find a best fitting spectral type of G6.5 for PZ Tel A. The extracted spectrum of the substellar companion, at a spatial position compatible with earlier orbit estimates, yields a temperature Teff = 2500-115+138 K, a visual extinction AV = 0.53-0.53+0.84 mag, a surface gravity of log g = 3.50-0.30+0.51 dex, and a metallicity at the edge of the grid of [M/H] = 0.30-0.30 dex. Conclusions: We derive a luminosity of log(Lbol/L?) = -2.66-0.08+0.06, a radius of R = 2.42-0.34+0.28 RJup, and a mass of M = 7.5-4.3+16.9 MJup for the PZ Tel companion, which is consistent with most earlier estimates using photometry alone. Combining our results with evolutionary models, we find a best-fitting mass of about 21 Jupiter masses at an age corresponding to the recently determined lithium depletion age of 7-2+4 Myr. Hence, the PZ Tel companion is most likely a wide brown dwarf companion in the 12-4+8 Myr old ? Pic moving group. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 087.C-0109(A).

  10. STARS DO NOT EAT THEIR YOUNG MIGRATING PLANETS: EMPIRICAL CONSTRAINTS ON PLANET MIGRATION HALTING MECHANISMS

    SciTech Connect

    Plavchan, Peter [NASA Exoplanet Science Institute, California Institute of Technology, M/C 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Bilinski, Christopher [University of Arizona, Tucson, AZ 85721 (United States)

    2013-06-01

    The discovery of ''hot Jupiters'' very close to their parent stars confirmed that Jovian planets migrate inward via several potential mechanisms. We present empirical constraints on planet migration halting mechanisms. We compute model density functions of close-in exoplanets in the orbital semi-major axis-stellar mass plane to represent planet migration that is halted via several mechanisms, including the interior 1:2 resonance with the magnetospheric disk truncation radius, the interior 1:2 resonance with the dust sublimation radius, and several scenarios for tidal halting. The models differ in the predicted power-law dependence of the exoplanet orbital semi-major axis as a function of stellar mass, and thus we also include a power-law model with the exponent as a free parameter. We use a Bayesian analysis to assess the model success in reproducing empirical distributions of confirmed exoplanets and Kepler candidates that orbit interior to 0.1 AU. Our results confirm a correlation of the halting distance with stellar mass. Tidal halting provides the best fit to the empirical distribution of confirmed Jovian exoplanets at a statistically robust level, consistent with the Kozai mechanism and the spin-orbit misalignment of a substantial fraction of hot Jupiters. We can rule out migration halting at the interior 1:2 resonances with the magnetospheric disk truncation radius and the interior 1:2 resonance with the dust disk sublimation radius, a uniform random distribution, and a distribution with no dependence on stellar mass. Note that our results do not rule out Type-II migration, but rather eliminate the role of a circumstellar disk in stopping exoplanet migration. For Kepler candidates, which have a more restricted range in stellar mass compared to confirmed planets, we are unable to discern between the tidal dissipation and magnetospheric disk truncation braking mechanisms at a statistically significant level. The power-law model favors exponents in the range of 0.38-0.9. This is larger than that predicted for tidal halting (0.23-0.33), which suggests that additional physics may be missing in the tidal halting theory.

  11. Planets Around Low-mass Stars (PALMS). V. Age-dating Low-mass Companions to Members and Interlopers of Young Moving Groups

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan P.; Shkolnik, Evgenya L.; Liu, Michael C.; Schlieder, Joshua E.; Mann, Andrew W.; Dupuy, Trent J.; Hinkley, Sasha; Crepp, Justin R.; Johnson, John Asher; Howard, Andrew W.; Flagg, Laura; Weinberger, Alycia J.; Aller, Kimberly M.; Allers, Katelyn N.; Best, William M. J.; Kotson, Michael C.; Montet, Benjamin T.; Herczeg, Gregory J.; Baranec, Christoph; Riddle, Reed; Law, Nicholas M.; Nielsen, Eric L.; Wahhaj, Zahed; Biller, Beth A.; Hayward, Thomas L.

    2015-06-01

    We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (?10–100 MJup) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 MJup) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ?40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (?100 AU) configuration. In addition, Li i ?6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (?200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1?) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (?1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest-known member of the Pleiades. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (ESO Program 090.A-9010(A)).

  12. 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.

  13. Eruption on Io

    NASA Technical Reports Server (NTRS)

    1996-01-01

    This image, taken by NASA's Galileo spacecraft, shows a new blue-colored volcanic plume extending about 100 kilometers (about 60 miles) into space from Jupiter's moon Io (see inset at lower left). The blue color of the plume is consistent with the presence of sulfur dioxide gas and 'snow' condensing from the gas as the plume expands and cools. Galileo images have also shown that the Ra Patera plume glows in the dark, perhaps due to the fluorescence of sulfur and oxygen ions created by the breaking apart of sulfur dioxide molecules by energetic particles in the Jovian magnetosphere. The images at right show a comparison of changes seen near the volcano Ra Patera since the Voyager spacecraft flybys of 1979 (windows at right show Voyager image at top and Galileo image at bottom). This eruptive plume is an example of a new type of volcanic activity discovered during Voyager's flyby in 1979, believed to be geyser-like eruptions driven by sulfur dioxide or sulfur gas erupting and freezing in Io's extremely tenuous atmosphere. Volcanic eruptions on Earth cannot throw materials to such high altitudes. Ra Patera is the site of dramatic surface changes. An area around the volcano of about 40,000 square kilometers, area about the size of New Jersey, has been covered by new volcanic deposits. The image was taken in late June 28, 1996 from a distance of 972,000 kilometers (604,000 miles). The Galileo mission is managed by NASA's Jet Propulsion Laboratory.

  14. Young pumice deposits on Nisyros, Greece

    Microsoft Academic Search

    Ellen M Limburg; Johan C Varekamp

    1991-01-01

    The island of Nisyros (Aegean Sea) consists of a silicic volcanic sequence upon a base of mafic-andesitic hyaloclastites, lava flows, and breccias. We distinguish two young silicic eruptive cycles each consisting of an explosive phase followed by effusions, and an older silicic complex with major pyroclastic deposits. The caldera that formed after the last plinian eruption is partially filled with

  15. Gemini GMOS/IFU spectroscopy of NGC 1569 - I: Mapping the properties of a young star cluster and its environment

    E-print Network

    M. S. Westmoquette; K. M. Exter; L. J. Smith; J. S. Gallagher III

    2007-08-17

    [Abridged] We present Gemini-North GMOS/IFU observations of a young star cluster (cluster 10) and its environment near the centre of the dwarf irregular starburst galaxy NGC 1569. This forms part of a larger and on-going study of the formation and collimation mechanisms of galactic winds, including three additional IFU pointings in NGC 1569 covering the base of the galactic wind which are analysed in a companion paper. The good spatial- and spectral-resolution of these GMOS/IFU observations, covering 4740-6860 A, allow us to probe the interactions between clusters and their environments on small scales. Combining our GMOS spectrum with HST imaging, we find that cluster 10 is composed of two very close components with ages of 5-7 Myr and <5 Myr, and a combined mass of 7 +/- 5 x 10^3 Msun. A detailed analysis of the H_alpha emission line profile shapes across the whole field-of-view shows them to be composed of a bright narrow feature (intrinsic FWHM ~ 50 km/s) superimposed on a fainter broad component (FWHM < 300 km/s). By mapping the properties of each individual component, we investigate the small-scale structure and properties of the ionized ISM, including reddening, excitation and electron densities, and for the first time find spatial correlations between the line component properties. We discuss in detail the possible mechanisms that could give rise to the two components and these correlations, and conclude that the most likely explanation for the broad emission is that it is produced in a turbulent mixing layer on the surface of the cool gas clumps embedded within the hot, fast-flowing cluster winds. We conclude we are sampling well within the outer bounding shocks of the expanding superbubbles and within the outflow 'energy injection zone'.

  16. Quiet-Region Filament Eruptions

    NASA Technical Reports Server (NTRS)

    Choudhary, Debi Prasad; Moore, Ronald L.

    2004-01-01

    We report characteristics of quiescent filament eruptions that did not produce coronal mass ejections (CMEs). It is known that there is a dichotomy of quiescent filament eruptions: those that produce CMEs and those that do not. We examined the quiescent filament eruptions, each of which was located far from disk center (greater than or equal to 0.7 R(sub Sun)) in diffuse remnant magnetic fields of decayed active regions, was well observed in Ha observations and Fe XII, and had good coronagraph coverage. We present the similarity and differences of two classes of filament eruptions. From their lack of CME production and the appearance of their eruptive motion in Fe XII movies, we conclude that the non-CME-producing filament eruptions are confined eruptions like the confined filament eruptions in active regions. We take the similarity of the confined and eruptive quiescent filament eruptions with their active-region counterparts to favor runaway tether-cutting connection for unleashing the magnetic explosion in all these eruptions.

  17. Planets Around Low-Mass Stars (PALMS). I. A Substellar Companion to the Young M Dwarf 1RXS J235133.3+312720

    E-print Network

    Bowler, Brendan P; Shkolnik, Evgenya L; Dupuy, Trent J; Cieza, Lucas A; Kraus, Adam L; Tamura, Motohide

    2012-01-01

    We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2.4" (~120 AU) pair is confirmed to be comoving from two epochs of high resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0$^{+2}_{-1}$. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 +/- 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to t...

  18. Massive stars: flare activity due to infalls of comet-like bodies

    NASA Astrophysics Data System (ADS)

    Ibadov, Subhon; Ibodov, Firuz S.

    2015-01-01

    Passages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as ``blast'' shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and ``exploding'' comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.

  19. Planets Around Low-Mass Stars (PALMS). V. Age-Dating Low-Mass Companions to Members and Interlopers of Young Moving Groups

    E-print Network

    Bowler, Brendan P; Liu, Michael C; Schlieder, Joshua E; Mann, Andrew W; Dupuy, Trent J; Hinkley, Sasha; Crepp, Justin R; Johnson, John Asher; Howard, Andrew W; Flagg, Laura; Weinberger, Alycia J; Aller, Kimberly M; Allers, Katelyn N; Best, William M J; Kotson, Michael C; Montet, Benjamin T; Herczeg, Gregory J; Baranec, Christoph; Riddle, Reed; Law, Nicholas M; Nielsen, Eric L; Wahhaj, Zahed; Biller, Beth A; Hayward, Thomas L

    2015-01-01

    We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7-M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8-120 Myr) in the literature. The inferred masses of the companions (~10-100 Mjup) are highly sensitive to the ages of the primary stars so we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. 2MASS J02155892-0929121 C is a new M7 substellar companion (40-60 Mjup) with clear spectroscopic signs of low gravity and hence youth. The primary, possibly a member of the ~40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (1 Gyr) tidally-locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with ...

  20. Stars

    NSDL National Science Digital Library

    Roberta Johnson

    2000-07-01

    This section of the Windows to the Universe web site provides information and images about stars including star statistics, and a star gallery. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging web site that spans the Earth and Space sciences and includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

  1. Summertime actinic lichenoid eruption.

    PubMed

    Bedi, T R

    1978-01-01

    A distinct summertime skin disorder seen in 25 Indian patients is described under a tentative designation of summertime actinic lichenoid eruption (SALE). The eruption predominantly affects females in their 2nd to 4th decade. The initial lesions are in the form of closely aggregated pruritic lichenoid papules starting during summer months on the exposed parts of the body. The lesions respond favourably to sun protection and corticosteroid cream but the recurrences are common during the subsequent summers when the lesions tend to become more persistent, pruritic and lichenified. Histopathologic features include early basal cell degeneration, spongiotic vesiculation with or without focal parakeratosis and an intense lymphocytic infiltrate in the dermis. In spite of strong clinical evidence of relation to sunlight, the lesions are not easily reproducible by artificial light. PMID:307503

  2. Neutrophilic Fixed Drug Eruption.

    PubMed

    Waldman, Leah; Reddy, Swathi B; Kassim, Andrea; Dettloff, Jennifer; Reddy, Vijaya B

    2015-07-01

    Fixed drug eruption (FDE) is a cutaneous reaction to a medication that recurs in the same fairly localized site with each exposure to the offending drug. The classical histopathologic findings in FDE consist of an interface dermatitis with predominantly lymphocytic inflammatory cell infiltrate. An unusual case of FDE in a 27-year-old pregnant woman who presented with widespread lesions and a predominantly neutrophilic infiltrate on histopathologic examination is reported. PMID:25072682

  3. PLANETS AROUND LOW-MASS STARS (PALMS). I. A SUBSTELLAR COMPANION TO THE YOUNG M DWARF 1RXS J235133.3+312720

    SciTech Connect

    Bowler, Brendan P.; Liu, Michael C.; Cieza, Lucas A.; Kraus, Adam L. [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Dupuy, Trent J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tamura, Motohide, E-mail: bpbowler@ifa.hawaii.edu [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2012-07-10

    We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2.''4 ({approx}120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0{sup +2}{sub -1}. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of {approx}10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 {+-} 10 pc) indicate it is likely a member of the {approx}50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the {approx}200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 {+-} 6 M{sub Jup} for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages.

  4. Eruption rates in explosive eruptions: Ground truth and models

    NASA Astrophysics Data System (ADS)

    Tumi Gudmundsson, Magnus; Durig, Tobias; Höskuldsson, Ármann; Thordarson, Thorvaldur; Larsen, Gudrún; Óladóttir, Bergrún A.; Högnadóttir, Thórdís; Oddsson, Björn; Björnsson, Halldór; Gudmundsdóttir, Esther R.

    2015-04-01

    Estimations of eruption rates in explosive eruptions are difficult and error margins are invariably high. In small to moderate sized eruptions effects of wind on plume height can be large and in larger eruptions observations are often difficult due to masking of source by low cloud, pyroclastic density currents and monitoring system saturation. Several medium-sized explosive eruptions in recent years have been an important in sparking off intense research on e.g. atmosphere-plume interaction and associated effects of wind on plume height. Other methods that do not rely on plume height are e.g. infrared satellite monitoring of atmospheric loading of fine tephra, infrasound, analysis of video recordings from vents, and it has been suggested that co-eruptive tilt-meter deformation data can predict eruption intensity. The eruptions of Eyjafjallajökull in 2010 and Grímsvötn in 2011 provided a wealth of data that potentially can be of use in developing constraints of eruption rates in explosive eruptions. A key parameter in all such comparisons between models and data is as detailed knowledge as possible on tephra fallout. For both Eyjafjallajökull and Grímsvötn intensive field efforts took place to map out the deposits during and immediately after the eruptions. The resulting maps cover both individual phases as well as total fallout. Comparison of these data with plume-based and other models of mass discharge rates is presently work in progress. A desirable future aim is near real time estimates of mass eruption rates based several of the parameters mentioned above. This type of work is currently ongoing within the framework of the EU-funded supersite project FUTUREVOLC.

  5. Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4

    NASA Astrophysics Data System (ADS)

    Donati, J.-F.; Hébrard, E.; Hussain, G.; Moutou, C.; Grankin, K.; Boisse, I.; Morin, J.; Gregory, S. G.; Vidotto, A. A.; Bouvier, J.; Alencar, S. H. P.; Delfosse, X.; Doyon, R.; Takami, M.; Jardine, M. M.; Fares, R.; Cameron, A. C.; Ménard, F.; Dougados, C.; Herczeg, G.; Matysse Collaboration

    2014-11-01

    We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa 4 within the Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets (MaTYSSE) programme, involving ESPaDOnS at the Canada-France-Hawaii Telescope. Despite an age of only 2 Myr and a similarity with prototypical classical T Tauri stars, LkCa 4 shows no evidence for accretion and probes an interesting transition stage for star and planet formation. Large profile distortions and Zeeman signatures are detected in the unpolarized and circularly polarized lines of LkCa 4 using Least-Squares Deconvolution (LSD), indicating the presence of brightness inhomogeneities and magnetic fields at the surface of LkCa 4. Using tomographic imaging, we reconstruct brightness and magnetic maps of LkCa 4 from sets of unpolarized and circularly polarized LSD profiles. The large-scale field is strong and mainly axisymmetric, featuring a ?2 kG poloidal component and a ?1 kG toroidal component encircling the star at equatorial latitudes - the latter making LkCa 4 markedly different from classical T Tauri stars of similar mass and age. The brightness map includes a dark spot overlapping the magnetic pole and a bright region at mid-latitudes - providing a good match to the contemporaneous photometry. We also find that differential rotation at the surface of LkCa 4 is small, typically ?5.5 times weaker than that of the Sun, and compatible with solid-body rotation. Using our tomographic modelling, we are able to filter out the activity jitter in the radial velocity curve of LkCa 4 (of full amplitude 4.3 km s-1) down to an rms precision of 0.055 km s-1. Looking for hot Jupiters around young Sun-like stars thus appears feasible, even though we find no evidence for such planets around LkCa 4.

  6. Disks around the Young Stars TW Hya and HD 100546 Imaged at 3.4 Millimeters with the Australia Telescope Compact Array

    E-print Network

    D. J. Wilner; T. L. Bourke; C. M. Wright; J. K. Jorgensen; E. F. van Dishoeck; T. Wong

    2003-06-19

    We present observations of the young stars TW Hya and HD 100546 made with the Australia Telescope Compact Array at 89 GHz with $\\sim2''$ resolution and $\\sim3$ mJy continuum sensitivity. Compact thermal dust continuum emission is detected from disks surrounding both stars. HD 100546 also shows hints of extended emission, presumably a residual protostellar envelope, which is also visible in scattered light at optical wavelengths. For TW Hya, HCO$^+$ J=1--0 line emission from the circumstellar disk is detected and spatially resolved. The observed size and intensity are in good agreement with model calculations based on an irradiated disk with substantial depletions derived previously from single dish observations of higher-J HCO$^+$ transitions.

  7. The Gemini/NICI Planet-Finding Campaign: The Frequency of Planets around Young Moving Group Stars

    NASA Astrophysics Data System (ADS)

    Biller, Beth A.; Liu, Michael C.; Wahhaj, Zahed; Nielsen, Eric L.; Hayward, Thomas L.; Males, Jared R.; Skemer, Andrew; Close, Laird M.; Chun, Mark; Ftaclas, Christ; Clarke, Fraser; Thatte, Niranjan; Shkolnik, Evgenya L.; Reid, I. Neill; Hartung, Markus; Boss, Alan; Lin, Douglas; Alencar, Silvia H. P.; de Gouveia Dal Pino, Elisabete; Gregorio-Hetem, Jane; Toomey, Douglas

    2013-11-01

    We report results of a direct imaging survey for giant planets around 80 members of the ? Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part of the Gemini/NICI Planet-Finding Campaign. For this sample, we obtained median contrasts of ?H = 13.9 mag at 1'' in combined CH4 narrowband ADI+SDI mode and median contrasts of ?H = 15.1 mag at 2'' in H-band ADI mode. We found numerous (>70) candidate companions in our survey images. Some of these candidates were rejected as common-proper motion companions using archival data; we reobserved with Near-Infrared Coronagraphic Imager (NICI) all other candidates that lay within 400 AU of the star and were not in dense stellar fields. The vast majority of candidate companions were confirmed as background objects from archival observations and/or dedicated NICI Campaign followup. Four co-moving companions of brown dwarf or stellar mass were discovered in this moving group sample: PZ Tel B (36 ± 6 M Jup, 16.4 ± 1.0 AU), CD-35 2722B (31 ± 8 M Jup, 67 ± 4 AU), HD 12894B (0.46 ± 0.08 M ?, 15.7 ± 1.0 AU), and BD+07 1919C (0.20 ± 0.03 M ?, 12.5 ± 1.4 AU). From a Bayesian analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1-20 M Jup companions at semi-major axes from 10-150 AU to <18% at a 95.4% confidence level using DUSTY models and to <6% at a 95.4% using COND models. Our results strongly constrain the frequency of planets within semi-major axes of 50 AU as well. We restrict the frequency of 1-20 M Jup companions at semi-major axes from 10-50 AU to <21% at a 95.4% confidence level using DUSTY models and to <7% at a 95.4% using COND models. This survey is the deepest search to date for giant planets around young moving group stars. 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 Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  8. Silicic Submarine Eruptions: what can erupted pyroclasts tell us?

    NASA Astrophysics Data System (ADS)

    Carey, R.; Allen, S.; McPhie, J.; Fiske, R. S.; Tani, K.

    2013-12-01

    Our understanding of submarine volcanism is in its infancy with respect to subaerial eruption processes. Two fundamental differences between eruptions in seawater compared to those on land are that (1) eruptions occur at higher confining pressures, and (2) in a seawater medium, which has a higher heat capacity, density and viscosity than air. Together with JAMSTEC collaborators we have a sample suite of submarine pumice deposits from modern volcanoes of known eruption depths. This sample suite spans a spectrum of eruption intensities, from 1) powerful explosive caldera-forming (Myojin Knoll caldera); to 2) weakly explosive cone building (pre-caldera Myojin Knoll pumice and Kurose-Nishi pumice); to 3) volatile-driven effusive dome spalling (Sumisu knoll A); to 4) passive dome effusion (Sumisu knoll B and C). This sample suite has exceptional potential, not simply because the samples have been taken from well-constrained, sources but because they have similar high silica contents, are unaltered and their phenocrysts contain melt inclusions. Microtextural quantitative analysis has revealed that (i) clast vesicularities remain high (69-90 vol.%) regardless of confining pressure, mass eruption rate or eruption style , (ii) vesicle number densities scale with inferred eruption rate, and (iii) darcian and inertial permeabilities of submarine effusive and explosive pyroclasts overlap with explosively-erupted subaerial pyroclasts.

  9. The intensity of plinian eruptions

    Microsoft Academic Search

    Steven Carey; Haraldur Sigurdsson

    1989-01-01

    Peak intensities (magma discharge rate) of 45 Pleistocene and Holocene plinian eruptions have been inferred from lithic dispersal patterns by using a theoretical model of pyroclast fallout from eruption columns. Values range over three orders of magnitude from 1.6 × 106 to 1.1 × 109 kg\\/s. Magnitudes (total erupted mass) also vary over about three orders of magnitude from 2.0

  10. Massive Stars

    NASA Astrophysics Data System (ADS)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  11. The Massive Star Population in M101

    NASA Astrophysics Data System (ADS)

    Grammer, Skyler H.

    An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these giant eruptions and their progenitors which are presumably very-massive, evolved stars such as luminous blue variables, hypergiants, and supergiants. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the luminous and evolved massive star populations in several nearby galaxies. We aim to identify the likely progenitors of the giant eruptions, study the spatial variations in the stellar populations, and examine the relationship between massive star populations and their environment. The work presented here is focused on stellar populations in the relatively nearby, giant, spiral galaxy M101 from sixteen archival BVI HST/ACS images. We create a catalog of stars in the direction to M101 with photometric errors < 10% for V < 24.5 and 50% completeness down to V ˜ 26.5 even in regions of high stellar crowding. Using color and magnitude criteria we have identified candidate luminous OB type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent. From our catalog, we derive the star formation history (SFH) for the stellar populations in five 2' wide annuli by fitting the color-magnitude diagrams. Binning the SFH into time frames corresponding to populations traced by Halpha, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we show that the fraction of stellar populations young enough to contribute in Halpha is 15% " 35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Halpha emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant. Though photometry has proven to be a powerful tool to identify candidate evolved massive stars and their effects on their host galaxy, spectroscopy is necessary to study the physical properties of individual stars. We observed moderate-resolution optical spectra for 56 of the brightest stars in the direction to M101 using the Multiple Mirror Telescope. We also created light curves for each target using multi-epoch U BV R images from the Large Binocular Telescope. We separate the spectroscopially confirmed members of M101 into four groups: hot supergiants, intermediate supergiants, emission-line stars, and LBVs. Several stars in each group are discussed in detail. Of the spectroscopically confirmed members, we find that eight meet our criterion for variability. We present light curves for the known LBV candidates, V2, V4, and V9, and introduce a new candidate: 9492 &barbelow;14 &barbelow;11998. Additionally, we identify 20 new variables in M101. Lacking spectra, we separated the variables, by their photometric properties, into three groups: hot, intermediate, and cool. We find two hot stars with V-band variability of +/-1 magnitude; we flag these stars as LBV candidates. Of the intermediate and cool variables, we identify several stars with low- to moderate-amplitude variability (0.1--0.5 magnitudes).

  12. A Blast Wave from the 1843 Eruption of Eta Carinae

    E-print Network

    Nathan Smith

    2008-09-09

    Very massive stars shed much of their mass in violent precursor eruptions as luminous blue variables (LBVs) before reaching their most likely end as supernovae, but the cause of LBV eruptions is unknown. The 19th century eruption of Eta Carinae, the prototype of these events, ejected about 12 solar masses at speeds of 650 km/s, with a kinetic energy of almost 10^50 ergs. Some faster material with speeds up to 1000-2000 km/s had previously been reported but its full distribution was unknown. Here I report observations of much faster material with speeds up to 3500-6000 km/s, reaching farther from the star than the fastest material in earlier reports. This fast material roughly doubles the kinetic energy of the 19th century event, and suggests that it released a blast wave now propagating ahead of the massive ejecta. Thus, Eta Car's outer shell now mimics a low-energy supernova remnant. The eruption has usually been discussed in terms of an extreme wind driven by the star's luminosity, but fast material reported here suggests that it was powered by a deep-seated explosion rivalling a supernova, perhaps triggered by the pulsational pair instability. This may alter interpretations of similar events seen in other galaxies.

  13. Drug Rash (Unclassified Drug Eruption) in Adults

    MedlinePLUS

    newsletter | contact Share | Drug Eruption, Unclassified Information for adults A A A Acute drug eruption with numerous red, raised lesions. Overview A drug rash (drug eruption), also known as a drug ...

  14. Planet Formation in Action? - Astronomers may have found the first object clearing its path in the natal disc surrounding a young star

    NASA Astrophysics Data System (ADS)

    2011-02-01

    Using ESO's Very Large Telescope an international team of astronomers has been able to study the short-lived disc of material around a young star that is in the early stages of making a planetary system. For the first time a smaller companion could be detected that may be the cause of the large gap found in the disc. Future observations will determine whether this companion is a planet or a brown dwarf. Planets form from the discs of material around young stars, but the transition from dust disc to planetary system is rapid and few objects are caught during this phase [1]. One such object is T Chamaeleontis (T Cha), a faint star in the small southern constellation of Chamaeleon that is comparable to the Sun, but very near the beginning of its life [2]. T Cha lies about 350 light-years from the Earth and is only about seven million years old. Up to now no forming planets have been found in these transitional discs, although planets in more mature discs have been seen before (eso0842, heic0821). "Earlier studies had shown that T Cha was an excellent target for studying how planetary systems form," notes Johan Olofsson (Max Planck Institute for Astronomy, Heidelberg, Germany), one of the lead authors of two papers in the journal Astronomy & Astrophysics that describe the new work. "But this star is quite distant and the full power of the Very Large Telescope Interferometer (VLTI) was needed to resolve very fine details and see what is going on in the dust disc." The astronomers first observed T Cha using the AMBER instrument and the VLT Interferometer (VLTI) [3]. They found that some of the disc material formed a narrow dusty ring only about 20 million kilometres from the star. Beyond this inner disc, they found a region devoid of dust with the outer part of the disc stretching out into regions beyond about 1.1 billion kilometres from the star. Nuria Huélamo (Centro de Astrobiología, ESAC, Spain), the lead author of the second paper takes up the story: "For us the gap in the dust disc around T Cha was a smoking gun, and we asked ourselves: could we be witnessing a companion digging a gap inside its protoplanetary disc?" However, finding a faint companion so close to a bright star is a huge challenge and the team had to use the VLT instrument NACO in a novel and powerful way, called sparse aperture masking, to reach their goal [4]. After careful analysis they found the clear signature of an object located within the gap in the dust disc, about one billion kilometres from the star - slightly further out than Jupiter is within our Solar System and close to the outer edge of the gap. This is the first detection of an object much smaller than a star within a gap in the planet-forming dust disc around a young star. The evidence suggests that the companion object cannot be a normal star [5] but it could be either a brown dwarf [6] surrounded by dust or, most excitingly, a recently formed planet. Huélamo concludes: "This is a remarkable joint study that combines two different state-of-the-art instruments at ESO's Paranal Observatory. Future observations will allow us to find out more about the companion and the disc, and also understand what fuels the inner dusty disc." Notes [1] The transitional discs can be spotted because they give off less radiation at mid-infrared wavelengths. The clearing of the dust close to the star and the creation of gaps and holes can explain this missing radiation. Recently formed planets may have created these gaps, although there are also other possibilities. [2] T Cha is a T Tauri star, a very young star that is still contracting towards the main sequence. [3] The astronomers used the AMBER instrument (Astronomical Multi-BEam combineR) and the VLTI to combine the light from all four of the 8.2-metre VLT Unit Telescopes and create a "virtual telescope" 130 metres across. [4] NACO (or NAOS-CONICA in full) is an adaptive optics instrument attached to ESO's Very Large Telescope. Thanks to adaptive optics, astronomers can remove most of the blurring

  15. Granulomatous Drug Eruptions.

    PubMed

    Dodiuk-Gad, Roni P; Shear, Neil H

    2015-07-01

    Granuloma formation is usually regarded as a means of defending the host from persistent irritants of either exogenous or endogenous origin. Noninfectious granulomatous disorders of the skin encompass a challenging group of diseases owing to their clinical and histologic overlap. Drug reactions characterized by a granulomatous reaction pattern are rare, and defined by a predominance of histiocytes in the inflammatory infiltrate. This review summarizes current knowledge on the various types of granulomatous drug eruptions, focusing on the 4 major types: interstitial granulomatous drug reaction, drug-induced accelerated rheumatoid nodulosis, drug-induced granuloma annulare, and drug-induced sarcoidosis. PMID:26143430

  16. Hydrogen lines as a diagnostic tool for studying multicomponent emitting regions in hot young stars: magnetosphere, X-wind, and disk wind

    NASA Astrophysics Data System (ADS)

    Tambovtseva, L. V.; Grinin, V. P.; Weigelt, G.

    2014-02-01

    Infrared interferometric observations with high spatial and spectral resolution and their quantitative modeling provide us with a unique opportunity to improve our understanding of the circumstellar environment of young stars and the accretion-ejection process. The goal of this paper is to investigate various models of the emitting regions in young Herbig Ae/Be stars that consist of (i) a compact rotating magnetosphere; (ii) an X-wind; and (iii) a disk wind. These models can be used, for example, to quantitatively interpret line profile measurements and infrared interferometric observations with the AMBER instrument of the Very Large Telescope Interferometer (VLTI) in the high spectral resolution mode (R = 12 000). VLTI/AMBER observations allow us to resolve the disk wind region and study the flux contribution of the unresolved magnetosphere and X-wind region to the total line flux. Analyzing the results of our non-LTE calculations, we conclude that the mechanisms of the different broadening of emission lines of different series include (1) the kinematic expansion due to the motion of the outflowing, accelerating gas in the magneto-centrifugal disk wind; (2) the Stark effect; and (3) the rotation of the magnetosphere. We also investigated extinction effects that can influence the shape of the line profiles. We considered the obscuration of the outer disk wind by an opaque dust and gas disk, the obscuration of the disk wind by a flared disk or by dust in the disk wind itself, and absorption of the star and disk continuum radiation in the disk wind along the line of sight. We show that due to extinction effects, the line profiles can change from double-peaked to single-peaked and P Cygni profiles. We studied the contribution of the different components of the stellar environment to different hydrogen emission lines and investigated how this contribution is dependent on the model parameters. The results of this study can be used for the detailed modeling of the emitting regions of individual young stars.

  17. The physics of large eruptions

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2015-04-01

    Based on eruptive volumes, eruptions can be classified as follows: small if the volumes are from less than 0.001 km3 to 0.1 km3, moderate if the volumes are from 0.1 to 10 km3, and large if the volumes are from 10 km3 to 1000 km3 or larger. The largest known explosive and effusive eruptions have eruptive volumes of 4000-5000 km3. The physics of small to moderate eruptions is reasonably well understood. For a typical mafic magma chamber in a crust that behaves as elastic, about 0.1% of the magma leaves the chamber (erupted and injected as a dyke) during rupture and eruption. Similarly, for a typical felsic magma chamber, the eruptive/injected volume during rupture and eruption is about 4%. To provide small to moderate eruptions, chamber volumes of the order of several tens to several hundred cubic kilometres would be needed. Shallow crustal chambers of these sizes are common, and deep-crustal and upper-mantle reservoirs of thousands of cubic kilometres exist. Thus, elastic and poro-elastic chambers of typical volumes can account for small to moderate eruptive volumes. When the eruptions become large, with volumes of tens or hundreds of cubic kilometres or more, an ordinary poro-elastic mechanism can no longer explain the eruptive volumes. The required sizes of the magma chambers and reservoirs to explain such volumes are simply too large to be plausible. Here I propose that the mechanics of large eruptions is fundamentally different from that of small to moderate eruptions. More specifically, I suggest that all large eruptions derive their magmas from chambers and reservoirs whose total cavity-volumes are mechanically reduced very much during the eruption. There are two mechanisms by which chamber/reservoir cavity-volumes can be reduced rapidly so as to squeeze out much of, or all, their magmas. One is piston-like caldera collapse. The other is graben subsidence. During large slip on the ring-faults/graben-faults the associated chamber/reservoir shrinks in volume, thereby maintaining the excess magmatic pressure much longer than is possible in the ordinary poro-elastic mechanism. Here the physics of caldera subsidence and graben subsidence is regarded as basically the same. The geometric difference in the surface expression is simply a reflection of the horizontal cross-sectional shape of the underlying magma body. In this new mechanism, the large eruption is the consequence -- not the cause -- of the caldera/graben subsidence. Thus, once the conditions for large-scale subsidence of a caldera/graben during an unrest period are established, then the likelihood of large to very large eruptions can be assessed and used in reliable forecasting. Gudmundsson, A., 2012. Strengths and strain energies of volcanic edifices: implications for eruptions, collapse calderas and landslides. Nat. Hazards Earth Syst. Sci., 12, 2241-2258. Gudmundsson, A., 2014. Energy release in great earthquakes and eruptions. Front. Earth Science 2:10. doi: 10.3389/feart.2014.00010 Gudmundsson, A., Acocella, V., 2015.Volcanotectonics: Understanding the Structure, Deformation, and Dynamics of Volcanoes. Cambridge University Press (published 2015).

  18. Physicochemical Controls on Eruption Style

    NSDL National Science Digital Library

    Victor Camp

    This site describes the nature of pressure surfaces and explains the dynamic processes associated with the eruption model. Magma composition and viscosity are discussed, as well as vesiculation. Also, there is a link to a computer program which allows the user to construct a diverse group of volcanic landforms through the simulation of variable types of eruptions. It can be downloaded free of charge.

  19. Automated Detection of Solar Eruptions

    E-print Network

    Hurlburt, Neal

    2015-01-01

    Observation of the solar atmosphere reveals a wide range of motions, from small scale jets and spicules to global-scale coronal mass ejections. Identifying and characterizing these motions are essential to advancing our understanding the drivers of space weather. Both automated and visual identifications are currently used in identifying CMEs. To date, eruptions near the solar surface (which may be precursors to CMEs) have been identified primarily by visual inspection. Here we report on EruptionPatrol (EP): a software module that is designed to automatically identify eruptions from data collected by SDO/AIA. We describe the method underlying the module and compare its results to previous identifications found in the Heliophysics Event Knowledgebase. EP identifies eruptions events that are consistent with those found by human annotations, but in a significantly more consistent and quantitative manner. Eruptions are found to be distributed within 15Mm of the solar surface. They possess peak speeds ranging from...

  20. CK Vul as a candidate eruptive stellar merging event

    NASA Astrophysics Data System (ADS)

    Kato, T.

    2003-02-01

    CK Vul (Nova Vul 1670) is one of the most mysterious objects among erupting stellar objects. Past studies have suggested that CK Vul is a final helium-flash object resembling V605 Aql and V4334 Sgr (Sakurai's object). The peculiar outburst light curve of CK Vul, however, had no similar counterpart among the known eruptive objects. Furthermore, the presence of hydrogen in the proposed remnant seems to contradict with the final helium-flash scenario. We propose that the peculiarities of CK Vul can be naturally understood if we consider a merging of main-sequence stars, following a new interpretation by Soker & Tylenda (\\cite{sok02v838mon}) which was proposed to explain the peculiar eruptive object V838 Mon. In this case, the 1670 outburst of CK Vul may be best understood as a V838 Mon-like event which occurred in our vicinity.

  1. SPECTRAL TYPING OF LATE-TYPE STELLAR COMPANIONS TO YOUNG STARS FROM LOW-DISPERSION NEAR-INFRARED INTEGRAL FIELD UNIT DATA

    SciTech Connect

    Roberts, Lewis C.; Beichman, Charles A.; Burruss, Rick; Ligon, E. Robert; Lockhart, Thomas G.; Roberts, Jennifer E.; Shao, Michael [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Rice, Emily L.; Brenner, Douglas; Oppenheimer, Ben R. [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Crepp, Justin R.; Dekany, Richard G.; Hillenbrand, Lynne A.; Hinkley, Sasha [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); King, David; Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom); Metchev, Stanimir [Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800 (United States); Pueyo, Laurent; Sivaramakrishnan, Anand; Soummer, Remi, E-mail: lewis.c.roberts@jpl.nasa.gov [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2012-07-15

    We used the Project 1640 near-infrared coronagraph and integral field spectrograph to observe 19 young solar-type stars. Five of these stars are known binary stars and we detected the late-type secondaries and were able to measure their JH spectra with a resolution of R {approx} 30. The reduced, extracted, and calibrated spectra were compared to template spectra from the IRTF spectral library. With this comparison, we test the accuracy and consistency of spectral-type determination with the low-resolution near-infrared spectra from P1640. Additionally, we determine effective temperature and surface gravity of the companions by fitting synthetic spectra calculated with the PHOENIX model atmosphere code. We also present several new epochs of astrometry of each of the systems. Together, these data increase our knowledge and understanding of the stellar make up of these systems. In addition to the astronomical results, the analysis presented helps validate the Project 1640 data reduction and spectral extraction processes and the utility of low-resolution, near-infrared spectra for characterizing late-type companions in multiple systems.

  2. Near-IR integral field spectroscopy of ionizing stars and young stellar objects on the borders of HII regions

    Microsoft Academic Search

    F. Martins; M. Pomares; L. Deharveng; A. Zavagno; J.-C. Bouret

    2009-01-01

    We present near-IR SINFONI observations of three Galactic HII regions: RVW79,\\u000aRCW82 and RCW120. We identify the ionizing stars of each region: they are early\\u000ato late O stars, close to the main sequence. We derive their stellar and wind\\u000aproperties using atmosphere models computed with the code CMFGEN. The cluster\\u000aionizing RCW~79 formed 2.3+\\/-0.5 Myr ago. Similar ages are

  3. A SEARCH FOR YOUNG STARS IN THE S0 GALAXIES OF A SUPER-GROUP AT z = 0.37

    SciTech Connect

    Just, Dennis W.; Zaritsky, Dennis [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Tran, Kim-Vy H. [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics, Texas A and M University, College Station, TX 77843 (United States); Gonzalez, Anthony H. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Kautsch, Stefan J. [Department of Physics, Computer Science and Engineering, Christopher Newport University, Newport News, VA 23606 (United States); Moustakas, John [Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093 (United States)

    2011-10-20

    We analyze Galaxy Evolution Explorer UV data for a system of four gravitationally bound groups at z = 0.37, SG1120, which is destined to merge into a Coma-mass cluster by z = 0, to study how galaxy properties may change during cluster assembly. Of the 38 visually classified S0 galaxies, with masses ranging from log (M{sub *})[M{sub sun}] {approx} 10-11, we detect only one in the near-UV (NUV) channel, a strongly star-forming S0 that is the brightest UV source with a measured redshift placing it in SG1120. Stacking the undetected S0 galaxies (which generally lie on or near the optical red sequence of SG1120) still results in no NUV/far-UV (FUV) detection (<2{sigma}). Using our limit in the NUV band, we conclude that for a rapidly truncating star formation rate, star formation ceased at least {approx}0.1-0.7 Gyr ago, depending on the strength of the starburst prior to truncation. With an exponentially declining star formation history over a range of timescales, we rule out recent star formation over a wide range of ages. We conclude that if S0 formation involves significant star formation, it occurred well before the groups were in this current pre-assembly phase. As such, it seems that S0 formation is even more likely to be predominantly occurring outside of the cluster environment.

  4. 40Ar/39Ar ages of the AD 79 eruption of Vesuvius, Italy

    USGS Publications Warehouse

    Lanphere, M.; Champion, D.; Melluso, L.; Morra, V.; Perrotta, A.; Scarpati, C.; Tedesco, D.; Calvert, A.

    2007-01-01

    The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925??66 years in 2004 (1?? uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and Renne and Min (1998) demonstrate the validity of the 40Ar/39Ar method to reconstruct the recent eruptive history of young, active volcanoes. ?? Springer-Verlag 2006.

  5. On the Mid-infrared Variability of Candidate Eruptive Variables (EXors): A Comparison between Spitzer and WISE Data

    NASA Astrophysics Data System (ADS)

    Antoniucci, S.; Giannini, T.; Li Causi, G.; Lorenzetti, D.

    2014-02-01

    Aiming to statistically study the variability in the mid-IR of young stellar objects, we have compared the 3.6, 4.5, and 24 ?m Spitzer fluxes of 1478 sources belonging to the C2D (Cores to Disks) legacy program with the WISE fluxes at 3.4, 4.6, and 22 ?m. From this comparison, we have selected a robust sample of 34 variable sources. Their variations were classified per spectral Class (according to the widely accepted scheme of Class I/flat/II/III protostars), and per star forming region. On average, the number of variable sources decreases with increasing Class and is definitely higher in Perseus and Ophiuchus than in Chamaeleon and Lupus. According to the paradigm Class ? Evolution, the photometric variability can be considered to be a feature more pronounced in less evolved protostars, and, as such, related to accretion processes. Moreover, our statistical findings agree with the current knowledge of star formation activity in different regions. The 34 selected variables were further investigated for similarities with known young eruptive variables, namely the EXors. In particular, we analyzed (1) the shape of the spectral energy distribution, (2) the IR excess over the stellar photosphere, (3) magnitude versus color variations, and (4) output parameters of model fitting. This first systematic search for EXors ends up with 11 bona fide candidates that can be considered as suitable targets for monitoring or future investigations.

  6. On the mid-infrared variability of candidate eruptive variables (exors): A comparison between Spitzer and WISE data

    SciTech Connect

    Antoniucci, S.; Giannini, T.; Li Causi, G.; Lorenzetti, D., E-mail: simone.antoniucci@oa-roma.inaf.it, E-mail: teresa.giannini@oa-roma.inaf.it, E-mail: gianluca.licausi@oa-roma.inaf.it, E-mail: dario.lorenzetti@oa-roma.inaf.it [INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monte Porzio (Italy)

    2014-02-10

    Aiming to statistically study the variability in the mid-IR of young stellar objects, we have compared the 3.6, 4.5, and 24 ?m Spitzer fluxes of 1478 sources belonging to the C2D (Cores to Disks) legacy program with the WISE fluxes at 3.4, 4.6, and 22 ?m. From this comparison, we have selected a robust sample of 34 variable sources. Their variations were classified per spectral Class (according to the widely accepted scheme of Class I/flat/II/III protostars), and per star forming region. On average, the number of variable sources decreases with increasing Class and is definitely higher in Perseus and Ophiuchus than in Chamaeleon and Lupus. According to the paradigm Class ? Evolution, the photometric variability can be considered to be a feature more pronounced in less evolved protostars, and, as such, related to accretion processes. Moreover, our statistical findings agree with the current knowledge of star formation activity in different regions. The 34 selected variables were further investigated for similarities with known young eruptive variables, namely the EXors. In particular, we analyzed (1) the shape of the spectral energy distribution, (2) the IR excess over the stellar photosphere, (3) magnitude versus color variations, and (4) output parameters of model fitting. This first systematic search for EXors ends up with 11 bona fide candidates that can be considered as suitable targets for monitoring or future investigations.

  7. [Captopril induced lichenoid eruption].

    PubMed

    Bravard, P; Barbet, M; Eich, D; Weber, M; Daniel, F; Lauret, P

    1983-01-01

    The authors report three cases of Captopril induced lichenoid eruption, already unmentionned, as far as they know. This cutaneous adverse reaction seemed to be dose related. Late onset was possible, even after six months of therapy. Violaceous papules or plaques were localized (two cases) or disseminated (one case) on the skin. The oral cavity was spared, but mucous membrane may be involved (localisation on the glans penis in one case). Histopathology was suggestive of lichen, but cellular dermal infiltrate was rather sparse. Immunofluorescent study in one case showed anti-IgM and C4 deposits on dermal colloid bodies. Captopril withdrawal was followed by improvement. Reviewing the literature, the authors are questionning about the fact that chemical structures of Penicillamine, Pyritinol and Captopril are strikingly similar and perhaps causative. PMID:6354041

  8. Solar Eruptive Events

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2012-01-01

    It s long been known that the Sun plays host to the most energetic explosions in the solar system. But key insights into the forms that energy takes have only recently become available. Solar flares have been phenomena of both academic and practical interest since their discovery in 1859. From the academic point of view, they are the nearest events for studying the explosive release of energy in astrophysical magnetized plasmas. From the practical point of view, they disrupt communication channels on Earth, from telegraph communications in 1859 to radio and television signals today. Flares also wreak havoc on the electrical power grid, satellite operations, and GPS signals, and energetic charged particles and radiation are dangerous to passengers on high-altitude polar flights and to astronauts. Flares are not the only explosive phenomena on the Sun. More difficult to observe but equally energetic are the large coronal mass ejections (CMEs), the ejection of up to ten billion tons of magnetized plasma into the solar wind at speeds that can exceed 1000 km/s. CMEs are primarily observed from the side, with coronagraphs that block out the bright disk of the Sun and lower solar atmosphere so that light scattered from the ejected mass can be seen. Major geomagnetic storms are now known to arise from the interaction of CMEs with Earth's magnetosphere. Solar flares are observed without CMEs, and CMEs are observed without flares. The two phenomena often occur together, however, and almost always do in the case of large flares and fast CMEs. The term solar eruptive event refers to the combination of a flare and a CME. Solar eruptive events generate a lot of heat: They can heat plasma to temperatures as high at 50 million Kelvin, producing radiation across the electromagnetic spectrum. But that s not all. A fascinating aspect of solar eruptive events is the acceleration of electrons and ions to suprathermal often relativistic energies. The accelerated particles are primarily observed through their emissions in the higher energy x-ray, gamma-ray, and rf regimes. The radio and x-ray emissions are both from mildly relativistic electrons with energies of tens of keV and above. Gamma-ray line emission comes indirectly from accelerated protons and heavier ions with MeV and higher energies. The difficulty in collecting spatially and spectrally resolved x-ray and gamma-ray data has long been a barrier to learning about the accelerated particles. Considerable progress has been made in the last decade in understanding the relationship between the flare, the CME, energy release, and particle acceleration. But many new questions have also arisen. In this article, I describe those new insights and our evolving understanding of solar eruptive events.

  9. High-resolution imaging of young M-type stars of the solar neighbourhood: probing for companions down to the mass of Jupiter

    NASA Astrophysics Data System (ADS)

    Delorme, P.; Lagrange, A. M.; Chauvin, G.; Bonavita, M.; Lacour, S.; Bonnefoy, M.; Ehrenreich, D.; Beust, H.

    2012-03-01

    Context. High-contrast imaging is a powerful technique when searching for gas giant planets and brown dwarfs orbiting at separations greater than several AU. Around solar-type stars, giant planets are expected to form by core accretion or by gravitational instability, but since core accretion is increasingly difficult as the primary star becomes lighter, gravitational instability would be a probable formation scenario for still-to-find distant giant planets around a low-mass star. A systematic survey for such planets around M dwarfs would therefore provide a direct test of the efficiency of gravitational instability. Aims: We search for gas giant planets orbiting late-type stars and brown dwarfs of the solar neighbourhood. Methods: We obtained deep high-resolution images of 16 targets with the adaptive optic system of VLT-NACO in the L' band, using direct imaging and angular differential imaging. This is currently the largest and deepest survey for Jupiter-mass planets around M-dwarfs. We developed and used an integrated reduction and analysis pipeline to reduce the images and derive our 2D detection limits for each target. The typical contrast achieved is about 9 mag at 0.5? and 11 mag beyond 1?. For each target we also determine the probability of detecting a planet of a given mass at a given separation in our images. Results: We derived accurate detection probabilities for planetary companions, taking orbital projection effects into account, with in average more than 50% probability to detect a 3 MJup companion at 10 AU and a 1.5 MJup companion at 20 AU, bringing strong constraints on the existence of Jupiter-mass planets around this sample of young M-dwarfs. Based on observations made with the NACO at VLT UT-4 at the Paranal Observatory under programme IDs 084.C-0739, 085.C-0675(A), 087.C-0413(A) and 087.C-0450(B).

  10. High-velocity outflows from young star-forming galaxies in the UKIDSS Ultra-Deep Survey

    NASA Astrophysics Data System (ADS)

    Bradshaw, E. J.; Almaini, O.; Hartley, W. G.; Smith, K. T.; Conselice, C. J.; Dunlop, J. S.; Simpson, C.; Chuter, R. W.; Cirasuolo, M.; Foucaud, S.; McLure, R. J.; Mortlock, A.; Pearce, H.

    2013-07-01

    We investigate galactic-scale outflows in the redshift range 0.71 ? z ? 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ˜109.5 M? and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [O II] equivalent width, star formation rate, specific star formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spectral stacks, with velocities ranging from 100 to 1000 km s-1, indicating that large-scale outflowing winds are a common property at these redshifts. The highest velocity outflows (>500 km s-1) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high-velocity galactic outflows are mostly driven by star-forming processes rather than active galactic nuclei, with implied mass outflow rates comparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high-redshift mass-metallicity relation.

  11. A Young Stellar and Protostellar Census of Galactic Ultracompact HII Regions -- Exploring Massive Star Formation with MIPS and IRAC

    NASA Astrophysics Data System (ADS)

    Carey, Sean; Conti, Peter; Crowther, Paul; Noreiga-Crespo, Alberto; Rho, Jeonghee

    2005-06-01

    We will map regions around 41 ultracompact HII (UCHII) regions from the radio selected Midcourse Space Experiment (MSX) sample of Crowther & Conti (2003) using IRAC and MIPS to (i) determine their embedded source contents; (ii) the multiplicity of high mass star formation and (iii) estimate the initial mass function of the sample. Our sample spans a range of UCHII morphology and Galactic environment. The proposed observations will detect all massive star formation ongoing in these objects and permit robust determination of the number of stars powering each UCHII, in contrast with previous mid-IR observations which were poorly spatially matched with radio observations. Deep imaging with IRAC will look for molecular line emission associated with shocked massive outflows, and MIPS observations will be critical to detect the earliest and most massive protostars and to construct the spectral energy distributions of the protostars. The data will be used to examine various theories of massive star formation and to examine the role of triggered star formation in these early massive objects.

  12. An Analysis of Eruptions Detected by the LMSAL Eruption Patrol

    NASA Astrophysics Data System (ADS)

    Hurlburt, N. E.; Higgins, P. A.; Jaffey, S.

    2014-12-01

    Observations of the solar atmosphere reveals a wide range of real and apparent motions, from small scale jets and spicules to global-scale coronal mass ejections. Identifying and characterizing these motions are essential to advance our understanding the drivers of space weather. Automated and visual identifications are used in identifying CMEs. To date, the precursors to these — eruptions near the solar surface — have been identified primarily by visual inspection. Here we report on an analysis of the eruptions detected by the Eruption Patrol, a data mining module designed to automatically identify eruptions from data collected by Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA). We describe the module and use it both to explore relations with other solar events recorded in the Heliophysics Event Knowledgebase and to identify and access data collected by the Interface Region Imaging Spectrograph (IRIS) and Solar Optical Telescope (SOT) on Hinode for further analysis.

  13. LOCAL LYMAN BREAK GALAXY ANALOGS: THE IMPACT OF MASSIVE STAR-FORMING CLUMPS ON THE INTERSTELLAR MEDIUM AND THE GLOBAL STRUCTURE OF YOUNG, FORMING GALAXIES

    SciTech Connect

    Overzier, Roderik A. [Max-Planck-Institut for Astrophysics, D-85748 Garching (Germany); Heckman, Timothy M.; Ptak, Andy; Ford, Holland C. [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Tremonti, Christy [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117, Heidelberg (Germany); Armus, Lee [Spitzer Science Center, California Institute of Technology, Pasadena, CA (United States); Basu-Zych, Antara [NASA Goddard Space Flight Center, Laboratory for X-ray Astrophysics, Greenbelt, MD 20771 (United States); Goncalves, Thiago; Martin, D. Christopher [California Institute of Technology, MC 405-47, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Rich, R. Michael [Deptartment of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562 (United States); Schiminovich, David [Department of Astronomy, Columbia University, MC 2457, 550 West 120th Street, New York, NY 10027 (United States); Madore, Barry; Seibert, Mark, E-mail: overzier@mpa-garching.mpg.d [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

    2009-11-20

    We report on the results of Hubble Space Telescope optical and UV imaging, Spitzer mid-IR photometry, and optical spectroscopy of a sample of 30 low-redshift (z approx 0.1 to 0.3) galaxies chosen from the Sloan Digital Sky Survey and Galaxy Evolution Explorer surveys to be accurate local analogs of the high-redshift Lyman break galaxies. The Lyman break analogs (LBAs) are similar in stellar mass, metallicity, dust extinction, star formation rate (SFR), physical size, and gas velocity dispersion, thus enabling a detailed investigation of many processes that are important in star-forming galaxies at high redshift. The main optical emission-line properties of LBAs, including evidence for outflows, are also similar to those typically found at high redshift. This indicates that the conditions in their interstellar medium are comparable. In the UV, LBAs are characterized by complexes of massive clumps of star formation, while in the optical they most often show evidence for (post-)mergers and interactions. In six cases, we find a single extremely massive (up to several x10{sup 9} M{sub sun}) compact (radius approx10{sup 2} pc) dominant central object (DCO). The DCOs are preferentially found in LBAs with the highest mid-IR luminosities (L{sub 24m}u{sub m} = 10{sup 10.3}-10{sup 11.2} L{sub sun}) and correspondingly high SFRs (15-100 M{sub sun} yr{sup -1}). We show that the massive star-forming clumps (including the DCOs) have masses much larger than the nuclear super star clusters seen in normal late-type galaxies. However, the DCOs do have masses, sizes, and densities similar to the excess light/central cusps seen in typical elliptical galaxies with masses similar to the LBA galaxies. We suggest that the DCOs form in the present-day examples of the dissipative mergers at high redshift that are believed to have produced the central cusps in local ellipticals (consistent with the disturbed optical morphologies of the LBAs). More generally, the properties of the LBAs are consistent with the idea that instabilities in a gas-rich disk lead to very massive star-forming clumps that eventually coalesce to form a spheroid. Finally, we comment on the apparent lack of energetically significant active galactic nuclei in the DCOs. We speculate that the DCOs are too young at present to grow a supermassive black hole because they are still in a supernova-dominated outflow phase (age less than 50 Myr).

  14. Research Spotlight Eruptive Behaviour Science be inspired

    Microsoft Academic Search

    Mount Etna; Photo D. Pyle

    All volcanoes erupt differently. Research into volcanic activity relies on being in the right place at the right time to capture unique information on eruption characteristics. The low frequency of eruptions means that such observational data are scarce. Whilst studying volcanic activity on Santorini, Dr Pyle and colleagues re-analysed previous descriptions of eruption behaviour stretching back to the early 1700's.

  15. How does a low-mass cut-off in the stellar IMF affect the evolution of young star clusters?

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, M. B. N.; Goodwin, S. P.; de Grijs, R.; Rose, M.; Kim, Sungsoo S.

    2014-12-01

    We investigate how different stellar initial mass functions (IMFs) can affect the mass-loss and survival of star clusters. We find that IMFs with radically different low-mass cut-offs (between 0.1 and 2 M?) do not change cluster destruction time-scales as much as might be expected. Unsurprisingly, we find that clusters with more high-mass stars lose relatively more mass through stellar evolution, but the response to this mass-loss is to expand and hence significantly slow their dynamical evolution. We also argue that it is very difficult, if not impossible, to have clusters with different IMFs that are initially `the same', since the mass, radius and relaxation times depend on each other and on the IMF in a complex way. We conclude that changing the IMF to be biased towards more massive stars does speed up mass-loss and dissolution, but that it is not as dramatic as might be thought.

  16. THE YOUNG OPEN CLUSTERS KING 12, NGC 7788, AND NGC 7790: PRE-MAIN-SEQUENCE STARS AND EXTENDED STELLAR HALOS

    SciTech Connect

    Davidge, T. J. [Dominion Astrophysical Observatory, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

    2012-12-20

    The stellar contents of the open clusters King 12, NGC 7788, and NGC 7790 are investigated using MegaCam images. Comparisons with isochrones yield an age <20 Myr for King 12, 20-40 Myr for NGC 7788, and 60-80 Myr for NGC 7790 based on the properties of stars near the main-sequence turnoff (MSTO) in each cluster. The reddening of NGC 7788 is much larger than previously estimated. The luminosity functions (LFs) of King 12 and NGC 7788 show breaks that are attributed to the onset of pre-main-sequence (PMS) objects, and comparisons with models of PMS evolution yield ages that are consistent with those measured from stars near the MSTO. In contrast, the r' LF of main-sequence stars in NGC 7790 is matched to r' = 20 by a model that is based on the solar neighborhood mass function. The structural properties of all three clusters are investigated by examining the two-point angular correlation function of blue main-sequence stars. King 12 and NGC 7788 are each surrounded by a stellar halo that extends out to a radius of 5 arcmin ({approx}3.4 pc). It is suggested that these halos form in response to large-scale mass ejection early in the evolution of the clusters, as predicted by models. In contrast, blue main-sequence stars in NGC 7790 are traced out to a radius of {approx}7.5 arcmin ({approx}5.5 pc), with no evidence of a halo. It is suggested that all three clusters may have originated in the same star-forming complex, but not in the same giant molecular cloud.

  17. VLBA DETERMINATION OF THE DISTANCE TO NEARBY STAR-FORMING REGIONS. VI. THE DISTANCE TO THE YOUNG STELLAR OBJECT HW 9 IN CEPHEUS A

    SciTech Connect

    Dzib, Sergio; Loinard, Laurent; RodrIguez, Luis F. [Centro de RadioastronomIa y Astrofisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 3-72, 58090, Morelia, Michoacan (Mexico); Mioduszewski, Amy J. [National Radio Astronomy Observatory, Domenici Science Operations Center, 1003 Lopezville Road, Socorro, NM 87801 (United States); Torres, Rosa M., E-mail: s.dzib@crya.unam.mx [Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, 53121 Bonn (Germany)

    2011-05-20

    Using the Very Long Baseline Array (VLBA), we have observed the radio continuum emission from the young stellar object HW 9 in the Cepheus A star-forming region at 10 epochs between 2007 February and 2009 November. Due to its strong radio variability, the source was detected at only four of the ten epochs. From these observations, the trigonometric parallax of HW 9 was determined to be {pi} = 1.43 {+-} 0.07 mas, in excellent agreement with a recent independent determination by Moscadelli et al. of the trigonometric parallax of a methanol maser associated with the nearby young stellar source HW 2 ({pi} = 1.43 {+-} 0.08 mas). This concordance in results, obtained in one case from continuum and in the other from line observations, confirms the reliability of VLBA trigonometric parallax measurements. By combining the two results, we constrain the distance to Cepheus A to be 700{sup +31}-{sub 28} pc, an uncertainty of 3.5%.

  18. Overview of the Kamoamoa Eruption

    USGS Multimedia Gallery

    Overview of the Kamoamoa eruption looking northeast toward Pu'u 'O 'o, in the background. The southwestern vent is in the foreground, while the northeastern vent is the distant fume at the base of Pu'u 'O 'o....

  19. Eruptive Behaviour of Forest Fires

    Microsoft Academic Search

    D. X. Viegas; A. Simeoni

    2011-01-01

    A critical review of the mechanisms that are described in the literature to explain the onset and development of eruption\\u000a or blow up in forest fires is presented, given their great relevance for fire safety, particularly in canyons. The various\\u000a processes described in the literature that are considered as potential causes of fire eruption are discussed. Some of them\\u000a seem

  20. A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6

    E-print Network

    Djupvik, A A; Bontemps, S; Motte, F; Olofsson, G; Gaalfalk, M; Floren, H G; Andre, Ph.

    2006-01-01

    Aims. The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~ 45' (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs). Methods. Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 um) and LW3 (12-18 um) of a 19' x 16' field was combined with JHKs data from 2MASS, Ks data from Arnica/NOT, and L' data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 um S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows. Results. We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sour...

  1. Dynamics of a geyser eruption

    NASA Astrophysics Data System (ADS)

    Dowden, John; Kapadia, Phiroze; Brown, Geoff; Rymer, Hazel

    1991-10-01

    Geyser action is characterised by the eruption of a mixture of steam, water and, in some cases, mud to substantial heights above surface level. The role of vaporisation in the ejection process is investigated with the aid of a mathematical model which treats geyser eruptions as isolated, steady state, one-dimensional phenomena; they are treated from an Eulerian point of view. It is found that large scale boiling of water occurs close to the surface, even though the instabilities that initiate the cycle may occur much lower down. Somewhat different models characterise superficially similar geyser eruptions from narrow confined tubes and from pools such as crater lakes. In the latter case the model predicts a root zone for steam flash at a depth of a few metres below the water surface, compared to a depth of tens of metres below the exit plane when eruption is from a confining tube, for normal eruptions ten to one hundred metres high. Relationships are obtained between geyser height, water content, depth of vaporisation, and such parameters as temperature and pressure at the onset of vaporisation. These relationships are used to provide a simple model of an eruption of Old Faithful, which reflects its main characteristics. They are also used to discuss geysering in the crater lake of Poás volcano in Costa Rica. A triggering mechanism which depends on progressive compression of a volume of steam is considered briefly. The system ultimately becomes unstable and results in the ejection of a volume of fluid.

  2. SPITZER DETECTION OF POLYCYCLIC AROMATIC HYDROCARBONS AND SILICATE FEATURES IN POST-AGB STARS AND YOUNG PLANETARY NEBULAE

    SciTech Connect

    Cerrigone, Luciano [Max-Planck-Institut fuer Radioastronomie, Bonn (Germany); Hora, Joseph L. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Umana, Grazia; Trigilio, Corrado [INAF, Catania Astrophysical Observatory, Catania (Italy)

    2009-09-20

    We have observed a small sample of hot post-asymptotic giant branch (AGB) stars with the Infrared Array Camera (IRAC) and the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The stars were selected from the literature on the basis of their far-infrared (IR) excess (i.e., post-AGB candidates) and B spectral type (i.e., close to the ionization of the envelope). The combination of our IRAC observations with Two Micron All Sky Survey and IRAS catalog data, along with previous radio observations in the cm range (where available) allowed us to model the spectral energy distributions of our targets and find that in almost all of them at least two shells of dust at different temperatures must be present, the hot dust component ranging up to 10{sup 3} K. In several targets, grains larger than 1 {mu}m are needed to match the far-IR data points. In particular, in IRAS 17423-1755 grains up to 100 {mu}m must be introduced to match the emission in the millimeter range. We obtained IRS spectra to identify the chemistry of the envelopes and found that more than one-third of the sources in our sample have mixed chemistry, showing both mid-IR bands attributed to polycyclic aromatic hydrocarbons (PAHs) and silicate features. The analysis of the PAH features indicates that these molecules are located in the outflows, far away from the central stars. We consider the larger than expected percentage of mixed-chemistry targets as a selection bias toward stars with a disk or torus around them. Our results strengthen the current picture of mixed chemistry being due to the spatial segregation of different dust populations in the envelopes.

  3. Automated Detection of Eruptive Structures for Solar Eruption Prediction

    NASA Astrophysics Data System (ADS)

    Georgoulis, Manolis K.

    2012-07-01

    The problem of data processing and assimilation for solar eruption prediction is, for contemporary solar physics, more pressing than the problem of data acquisition. Although critical solar data, such as the coronal magnetic field, are still not routinely available, space-based observatories deliver diverse, high-quality information at such a high rate that a manual or semi-manual processing becomes meaningless. We discuss automated data analysis methods and explain, using basic physics, why some of them are unlikely to advance eruption prediction. From this finding we also understand why solar eruption prediction is likely to remain inherently probabilistic. We discuss some promising eruption prediction measures and report on efforts to adapt them for use with high-resolution, high-cadence photospheric and coronal data delivered by the Solar Dynamics Observatory. Concluding, we touch on the problem of physical understanding and synthesis of different results: combining different measures inferred by different data sets is a yet-to-be-done exercise that, however, presents our best opportunity of realizing benefits in solar eruption prediction via a meaningful, targeted assimilation of solar data.

  4. Explosive volcanism lessons learned from Mentos and soda eruptions

    NASA Astrophysics Data System (ADS)

    Wright, H. M.; Rust, A. C.; Cashman, K. V.

    2006-12-01

    When hard Mentos candies are dropped into a bottle of carbonated beverage, the resultant rapid CO2 exsolution and gas expansion causes an impressive soda `eruption'. We explore the ways in which this simple example can be used to demonstrate explosive volcanic processes. Through hands-on experiments, students can vary the type of candy, the type of beverage, and the shape of the vent (by making a hole in the cap of the soda bottle) to understand the processes that are influencing the height and duration of the eruption column. The activity can be tailored to demonstrate basic principles of gas exsolution and expansion for young students, but can also be extended to more complex principles of heterogeneous bubble nucleation and decreasing surface tension for college students. We present results from Mentos and soda experiments by a group of college freshman in the elementary education program (with no real science background). We compare students' resultant understanding of the similarities and differences between volcanic eruptions and the experiments with the results from a similar activity performed by a group of graduate geology students. The Mentos and soda reaction is dramatic. Video clips of people, young and old, trying this experiment across the world can be found on the world wide web. We suggest that the popularity of this demonstration be used to help teach fundamental concepts in both volcanology and scientific experimentation.

  5. Most Powerful Eruption in the Universe Discovered

    NASA Astrophysics Data System (ADS)

    2005-01-01

    Astronomers have found the most powerful eruption seen in the Universe using NASA's Chandra X-ray Observatory. A supermassive black hole generated this eruption by growing at a remarkable rate. This discovery shows the enormous appetite of large black holes, and the profound impact they have on their surroundings. The huge eruption is seen in a Chandra image of the hot, X-ray emitting gas of a galaxy cluster called MS 0735.6+7421. Two vast cavities extend away from the supermassive black hole in the cluster's central galaxy. The eruption - which has lasted for 100 million years and is still going - has generated the energy equivalent to hundreds of millions of gamma-ray bursts. Animation of Eruption from Supermassive Black Hole Animation of Eruption from Supermassive Black Hole This event was caused by gravitational energy release as enormous amounts of matter fell toward a black hole. Most of the matter was swallowed, but some of it was violently ejected before being captured by the black hole. "I was stunned to find that a mass of about 300 million Suns was swallowed," said Brian McNamara of Ohio University in Athens, lead author of the study that appears in the January 6, 2005 issue of Nature. "This is almost as massive as the supermassive black hole that swallowed it." Astronomers are not sure where such large amounts of matter came from. One theory is that gas from the host galaxy catastrophically cooled and was then swallowed by the black hole. Illustration of MS 0735.6+742 Illustration of MS 0735.6+742 The energy released shows that the black hole in MS 0735 has grown very dramatically during this eruption. Previous studies suggest that other large black holes have grown very little in the recent past, and that only smaller black holes are still growing quickly. "This new result is as surprising as it is exciting", said co-author Paul Nulsen of the Harvard-Smithsonian Center of Astrophysics. "This black hole is feasting when it should be fasting." Radio emission within the cavities shows that jets from the black hole erupted to create the cavities. Gas is being pushed away from the black hole at supersonic speeds over a distance of about a million light years. The mass of the displaced gas equals about a trillion Suns, more than the mass of all the stars in the Milky Way. LA Radio & Chandra X-ray Composite of MS 0735.6+7421 VLA Radio & Chandra X-ray Composite of MS 0735.6+7421 The rapid growth of supermassive black holes is usually detected by observing very bright radiation from the centers of galaxies in the optical and X-ray wavebands, or luminous radio jets. In MS 0735 no bright central radiation is found and the radio jets are faint. Therefore, the true nature of MS 0735 is only revealed through X-ray observations of the hot cluster gas. "Until now we had no idea that this black hole was gorging itself", said co-author Michael Wise of the Massachusetts Institute of Technology. "The discovery of this eruption shows that X-ray telescopes are necessary to understand some of the most violent events in the Universe." The astronomers estimated how much energy was needed to create the cavities by calculating the density, temperature and pressure of the hot gas. By making a standard assumption, that 10% of the gravitational energy goes into launching the jets, they estimated how much material the black hole swallowed. Size Comparison of MS 0735.6+7421 & Perseus Cluster Size Comparison of MS 0735.6+7421 & Perseus Cluster Besides generating the cavities, some of the energy from this eruption should keep the hot gas around the black hole from cooling, and some of it may also generate large-scale magnetic fields in the galaxy cluster. Chandra observers have discovered other cavities in galaxy clusters, but this one is easily the largest and the most powerful. For example, the energy content here exceeds that of the Perseus cavities by 250 times, and dwarfs the cavities in M87 by a factor of 10,000. NASA's Marshall Space Flight Center, Huntsville,

  6. Eruptive modes and hiatus of volcanism at West Mata seamount, NE Lau basin: 1996-2012

    NASA Astrophysics Data System (ADS)

    Embley, Robert W.; Merle, Susan G.; Baker, Edward T.; Rubin, Kenneth H.; Lupton, John E.; Resing, Joseph A.; Dziak, Robert P.; Lilley, Marvin D.; Chadwick, William W.; Shank, T.; Greene, Ron; Walker, Sharon L.; Haxel, Joseph; Olson, Eric; Baumberger, Tamara

    2014-10-01

    present multiple lines of evidence for years to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996-2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at ˜2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996-2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.

  7. Short- and long-term variability of young stars in the Orion Nebula Cluster and Molecular Cloud

    E-print Network

    Rivilla, V M; Sanz-Forcada, J; Jiménez-Serra, I; Forbrich, J; Martín-Pintado, J

    2015-01-01

    We used the Very Large Array to carry out a multi-epoch radio continuum monitoring of the Orion Nebula Cluster and Orion Molecular Cloud. Our observations reveal the presence of 19 sources. With the exception of the sources BN and C the sources show variability between the different epochs. We have found tentative evidence of variability in the massive object related with source I. Our observations also confirm radio flux density variations of a factor >2 on timescales of hours to days in 5 sources. One of these flaring sources, OHC-E, has been detected for the first time. We conclude that the radio emission arises from: i) highly-variable non-thermal gyrosynchrotron emission produced by electrons accelerated in the magnetospheres of pre-main sequence stars; ii) thermal emission from ionized gas and/or heated dust around massive objects and proplyds. Combining our sample with other radio monitoring and a X-ray catalog, we have studied the properties of 51 radio/X-ray stars. We have found severals hints of a d...

  8. Physical Properties of Young Brown Dwarfs and Very Low Mass Stars Inferred from High-resolution Model Spectra

    NASA Astrophysics Data System (ADS)

    Rice, Emily L.; Barman, T.; Mclean, Ian S.; Prato, L.; Kirkpatrick, J. Davy

    2010-01-01

    By comparing ne