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Sample records for southern low-mass protostars

  1. Winds from Low Mass Protostars

    NASA Astrophysics Data System (ADS)

    Shu, Frank H.; Lizano, Susana; Adams, Fred C.; Ruden, Steven P.

    In its last stages, star formation in molecular clouds includes the onset of a stellar wind that helps to clear away the surrounding placenta of gas and dust, thereby making the young stellar object optically visible. The authors discuss new observational evidence that the emerging wind is largely neutral and atomic in low-mass protostars. They then suggest a simple theoretical mechanism for the generation of such powerful neutral winds.

  2. COMPLEX MOLECULES TOWARD LOW-MASS PROTOSTARS: THE SERPENS CORE

    SciTech Connect

    Oeberg, Karin I.; Van der Marel, Nienke; Kristensen, Lars E.; Van Dishoeck, Ewine F.

    2011-10-10

    Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is the key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH{sub 3}OH-rich ices and thermally or non-thermally evaporate with CH{sub 3}OH, we have identified three sight lines in the Serpens core-SMM1, SMM4, and SMM4-W-which are likely to be rich in complex organics. Using the IRAM 30 m telescope, narrow lines (FWHM of 1-2 km s{sup -1}) of CH{sub 3}CHO and CH{sub 3}OCH{sub 3} are detected toward all sources, HCOOCH{sub 3} toward SMM1 and SMM4-W, and C{sub 2}H{sub 5}OH not at all. Beam-averaged abundances of individual complex organics range between 0.6% and 10% with respect to CH{sub 3}OH when the CH{sub 3}OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of low-mass sources. Complex organic abundances are of the same order of magnitude toward low-mass protostars and high-mass hot cores, but HCOOCH{sub 3} is relatively more important toward low-mass protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times.

  3. Observations of Carbon Chain Chemistry in the Envelopes of Low-Mass Protostars

    NASA Technical Reports Server (NTRS)

    Cordiner, M.; Charnley, S.; Buckle, J. V.; Walsh, C.; Millar, T. J.

    2012-01-01

    Observational results are reported from our surveys in the Northern Hemisphere (using the Onsala 20 m telescope) and the Southern Hemisphere (using the Mopra 22 m telescope) to search for 3 mm emission lines from carbon-chain-bearing species and other complex molecules in the envelopes of low-mass protostars. Based on a sample of approximately 60 sources, we find that carbon-chain-bearing species including HC3N (and C4H) are highly abundant in the vicinity of more than half of the observed protostars. The origin and evolution of these species, including their likely incorporation into ices in protoplanetary disks will be discussed

  4. A Complex Organic Slushy Bathing Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Drozdovskaya, Maria; Walsh, Catherine; Visser, Ruud; Harsono, Daniel; van Dishoeck, Ewine

    2015-08-01

    Complex organic molecules are ubiquitous companions of young forming stars. They were first observed in hot cores surrounding high-mass protostars [e.g., 1], but have since also been detected in the environs of several low-mass counterparts [e.g., 2]. Recent studies have shown that colder envelopes and positions with impinging outflows may also glow with emission from complex organic species [e.g., 3, 4]. For this meeting, I would like to present physicochemical modeling results on the synthesis of complex organics in an envelope-cavity system that is subject to non-thermal processing. This includes wavelength-dependent radiative transfer calculations with RADMC [5] and a comprehensive gas-grain chemical network [6]. The results show that the morphology of such a system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances; and the remaining outer envelope abundant in simpler solid and gaseous molecules. Within the adopted paradigm, complex organic molecules are demonstrated to have unique lifetimes and be grouped into early and late species [7]. Key chemical processes for forming and destroying complex organic molecules will be discussed. In addition, the results of adding newly experimentally verified routes [8] into the existing chemical networks will be shown.[1] Blake G. A., Sutton E. C., Masson C. R., Phillips T. G., 1987, ApJ, 315, 621[2] Jørgensen J. K., Favre C., Bisschop S. E., Bourke T. L., van Dishoeck E. F., Schmalzl M., 2012, ApJ, 757, L4[3] Arce H. G., Santiago-García J., Jørgensen J. K., Tafalla M., Bachiller R., 2008, ApJ, 681, L21[4] Öberg K. I., Bottinelli S., Jørgensen J. K., van Dishoeck E. F., 2010, ApJ, 716, 825[5] Dullemond C. P., Dominik C., 2004, A&A, 417, 159[6] Walsh C., Millar T. J., Nomura H., Herbst E., Widicus Weaver S., Aikawa Y., Laas J. C., Vasyunin A. I., 2014, A&A, 563, A33[7] Drozdovskaya

  5. Probing the effects of external irradiation on low-mass protostars through unbiased line surveys

    NASA Astrophysics Data System (ADS)

    Lindberg, J. E.; Jørgensen, J. K.; Watanabe, Y.; Bisschop, S. E.; Sakai, N.; Yamamoto, S.

    2015-12-01

    Context. The envelopes of molecular gas around embedded low-mass protostars show different chemistries, which can be used to trace their formation history and physical conditions. The excitation conditions of some molecular species can also be used to trace these physical conditions, making it possible to constrain for instance sources of heating and excitation. Aims: We study the range of influence of an intermediate-mass Herbig Be protostar. We also study the effect of feedback from the environment on the chemical and physical properties of embedded protostars. Methods: We followed up on an earlier line survey of the Class 0/I source R CrA IRS7B in the 0.8 mm window with an unbiased line survey of the same source in the 1.3 mm window using the Atacama Pathfinder Experiment (APEX) telescope. We also studied the excitation of the key species H2CO, CH3OH, and c-C3H2 in a complete sample of the 18 embedded protostars in the Corona Australis star-forming region. Radiative transfer models were employed to establish abundances of the molecular species. Results: We detect line emission from 20 molecular species (32 including isotopologues) in the two surveys. The most complex species detected are CH3OH, CH3CCH, CH3CHO, and CH3CN (the latter two are only tentatively detected). CH3CN and several other complex organic molecules are significantly under-abundant in comparison with what is found towards hot corino protostars. The H2CO rotational temperatures of the sources in the region decrease with the distance to the Herbig Be star R CrA, whereas the c-C3H2 temperatures remain constant across the star-forming region. Conclusions: The high H2CO temperatures observed towards objects close to R CrA suggest that this star has a sphere of influence of several 10 000 AU in which it increases the temperature of the molecular gas to 30-50 K through irradiation. The chemistry in the IRS7B envelope differs significantly from many other embedded protostars, which could be an effect of

  6. Infrared Observations of Hot Gas and Cold Ice Toward the Low Mass Protostar Elias 29

    NASA Technical Reports Server (NTRS)

    Boogert, A. C. A.; Tielens, A. G. G. M.; Ceccarelli, C.; Boonman, A. M. S.; vanDishoeck, E. F.; Keane, J. V.; Whittet, D. C. B.; deGraauw, T.

    2000-01-01

    We have obtained the full 1-200 micrometer spectrum of the low luminosity (36 solar luminosity Class I protostar Elias 29 in the rho Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of interstellar ice and the interrelationship of interstellar ice and hot core gases around low mass protostars. We see abundant hot CO and H2O gas, as well as the absorption bands of CO, CO2, H2O and "6.85 micrometer" ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 with the conditions around several well studied luminous, high mass protostars. The high gas temperature and gas/solid ratios resemble those of relatively evolved high mass objects (e.g. GL 2591). However, none of the ice band profiles shows evidence for significant thermal processing, and in this respect Elias 29 resembles the least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude that the heating of the envelope of the low mass object Elias 29 is qualitatively different from that of high mass protostars. This is possibly related to a different density gradient of the envelope or shielding of the ices in a circumstellar disk. This result is important for our understanding of the evolution of interstellar ices, and their relation to cometary ices.

  7. Water deuterium fractionation in the low-mass protostar NGC1333-IRAS2A

    NASA Astrophysics Data System (ADS)

    Liu, F.-C.; Parise, B.; Kristensen, L.; Visser, R.; van Dishoeck, E. F.; Güsten, R.

    2011-03-01

    Context. Although deuterium enrichment of water may provide an essential piece of information in the understanding of the formation of comets and protoplanetary systems, only a few studies up to now have aimed at deriving the HDO/H2O ratio in low-mass star forming regions. Previous studies of the molecular deuteration toward the solar-type class 0 protostar, IRAS 16293-2422, have shown that the D/H ratio of water is significantly lower than other grain-surface-formed molecules. It is not clear if this property is general or particular to this source. Aims: In order to see if the results toward IRAS 16293-2422 are particular, we aimed at studying water deuterium fractionation in a second low-mass solar-type protostar, NGC1333-IRAS2A. Methods: Using the 1-D radiative transfer code RATRAN, we analyzed five HDO transitions observed with the IRAM 30 m, JCMT, and APEX telescopes. We assumed that the abundance profile of HDO in the envelope is a step function, with two different values in the inner warm (T > 100 K) and outer cold (T < 100 K) regions of the protostellar envelope. Results: The inner and outer abundance of HDO is found to be well constrained at the 3σ level. The obtained HDO inner and outer fractional abundances are xHDO_in = 6.6 × 10-8-1.0 × 10-7(3σ) and x^{HDO}out=9×10-11= 9 × 10-11-1.0-1.8 × 10-9(3σ). These values are close to those in IRAS 16293-2422, which suggests that HDO may be formed by the same mechanisms in these two solar-type protostars. Taking into account the (rather poorly onstrained) H2O abundance profile deduced from Herschel observations, the derived HDO/H2O in the inner envelope is ≥1% and in the outer envelope it is 0.9%-18%. These values are more than one order of magnitude higher than what is measured in comets. If the same ratios apply to the protosolar nebula, this would imply that there is some efficient reprocessing of the material between the protostellar and cometary phases. Conclusions: The H2O inner fractional

  8. Infrared observations of hot gas and cold ice toward the low mass protostar Elias 29

    NASA Astrophysics Data System (ADS)

    Boogert, A. C. A.; Tielens, A. G. G. M.; Ceccarelli, C.; Boonman, A. M. S.; van Dishoeck, E. F.; Keane, J. V.; Whittet, D. C. B.; de Graauw, Th.

    2000-08-01

    We have obtained the full 1-200 μm spectrum of the low luminosity (36 Lsolar) Class I protostar Elias 29 in the ρ Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of interstellar ice and the interrelationship of interstellar ice and hot core gases around low mass protostars. We see abundant hot CO and H2O gas, as well as the absorption bands of CO, CO2, H2O and "6.85 μm" ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 with the conditions around several well studied luminous, high mass protostars. The high gas temperature and gas/solid ratios resemble those of relatively evolved high mass objects (e.g. GL 2591). However, none of the ice band profiles shows evidence for significant thermal processing, and in this respect Elias 29 resembles the least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude that the heating of the envelope of the low mass object Elias 29 is qualitatively different from that of high mass protostars. This is possibly related to a different density gradient of the envelope or shielding of the ices in a circumstellar disk. This result is important for our understanding of the evolution of interstellar ices, and their relation to cometary ices. 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 United Kingdom) and with the participation of ISAS and NASA.

  9. Water in embedded low-mass protostars: cold envelopes and warm outflows

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; van Dishoeck, Ewine; Mottram, Joseph; Schmalzl, Markus; Visser, Ruud

    2015-08-01

    As stars form, gas from the parental cloud is transported through the molecular envelope to the protostellar disk from which planets eventually form. Water plays a crucial role in such systems: it forms the backbone of the oxygen chemistry, it is a unique probe of warm and hot gas, and it provides a unique link between the grain surface and gas-phase chemistries. The distribution of water, both as ice and gas, is a fundamental question to our understanding of how planetary systems, such as the Solar System, form.The Herschel Space Observatory observed many tens of embedded low-mass protostars in a suite of gas-phase water transitions in several programs (e.g. Water in Star-forming regions with Herschel, WISH, and the William Herschel Line Legacy Survey, WILL), and related species (e.g. CO in Protostars with HIFI, COPS-HIFI). I will summarize what Herschel has revealed about the water distribution in the cold outer molecular envelope of low-mass protostars, and the warm gas in outflows, the two components predominantly traced by Herschel observations. I will present our current understanding of where the water vapor is in protostellar systems and the underlying physical and chemical processes leading to this distribution. Through these dedicated observational surveys and complementary modeling efforts, we are now at a stage where we can quantify where the water is during the early stages of star formation.

  10. Deep O2 observations toward a low-mass protostar with Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Yildiz, Umut; Acharyya, Kinsuk; Goldsmith, Paul; van Dishoeck, Ewine; Melnick, Gary; Snell, Ronald; Liseau, Rene; Chen, Jo-Hsin; Pagani, Laurent; Bergin, Edwin; Caselli, Paola; Herbst, Eric; Kristensen, Lars; Visser, Ruud; Lis, Dariusz; Gerin, Maryvonne

    2013-07-01

    Oxygen is the third most abundant element in the Universe, after hydrogen and helium. According to traditional gas-phase chemical models, O2 should be abundant in molecular clouds (X(O2)~7e-5 relative to H2), but until recently, attempts to detect interstellar O2 line emission with ground- and space-based observatories have failed. Following the multi-line detection of O2 with low abundances in the Orion and rho OphA molecular clouds with Herschel, it is important to investigate other environments, and we here quantify the O2 abundance near a solar-mass protostar. Observations of molecular oxygen, O2, at 487 GHz toward a deeply embedded low-mass Class 0 protostar, NGC 1333 IRAS 4A, are presented, using the HIFI on the Herschel Space Observatory. The high spectral resolution data are analysed using radiative transfer models to infer column densities and abundances, and are tested directly against full gas-grain chemical models. The deep HIFI spectrum (rms=1.3 mK) fails to show O2 at the velocity of the dense protostellar envelope, implying one of the deepest abundance upper limits of O2/H2 at <6x10e-9 (3 sigma). The O2/CO abundance ratio is less than 0.005. However, a tentative (4.5 sigma) detection of O2 is seen at the velocity of the surrounding NGC~1333 cloud, shifted by 1 km/s relative to the protostar. Pure gas-phase models and gas-grain chemical models require a long pre-collapse phase (~0.7-1x10e6 years) during which atomic and molecular oxygen are frozen out onto dust grains and fully converted to H2O to avoid overproduction of O2 in the dense envelope. The tentative detection of O2 in the surrounding cloud is consistent with a low-density PDR model with a small enhancement of the water-ice photodesorption yield of a factor of two. The low O2 abundance in the collapsing envelope around a low-mass protostar suggests that the gas and ice entering protoplanetary disks is very poor in O2. This research is described in Yildiz et al. (2013, A&A, astro-ph: 1307.8031).

  11. Deep observations of O2 toward a low-mass protostar with Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Yıldız, Umut A.; Acharyya, Kinsuk; Goldsmith, Paul F.; van Dishoeck, Ewine F.; Melnick, Gary; Snell, Ronald; Liseau, René; Chen, Jo-Hsin; Pagani, Laurent; Bergin, Edwin; Caselli, Paola; Herbst, Eric; Kristensen, Lars E.; Visser, Ruud; Lis, Dariusz C.; Gerin, Maryvonne

    2013-10-01

    Context. According to traditional gas-phase chemical models, O2 should be abundant in molecular clouds, but until recently, attempts to detect interstellar O2 line emission with ground- and space-based observatories have failed. Aims: Following the multi-line detections of O2 with low abundances in the Orion and ρ Oph A molecular clouds with Herschel, it is important to investigate other environments, and we here quantify the O2 abundance near a solar-mass protostar. Methods: Observations of molecular oxygen, O2, at 487 GHz toward a deeply embedded low-mass Class 0 protostar, NGC 1333-IRAS 4A, are presented, using the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory. Complementary data of the chemically related NO and CO molecules are obtained as well. The high spectral resolution data are analysed using radiative transfer models to infer column densities and abundances, and are tested directly against full gas-grain chemical models. Results: The deep HIFI spectrum fails to show O2 at the velocity of the dense protostellar envelope, implying one of the lowest abundance upper limits of O2/H2 at ≤6 × 10-9 (3σ). The O2/CO abundance ratio is less than 0.005. However, a tentative (4.5σ) detection of O2 is seen at the velocity of the surrounding NGC 1333 molecular cloud, shifted by 1 km s-1 relative to the protostar. For the protostellar envelope, pure gas-phase models and gas-grain chemical models require a long pre-collapse phase (~0.7-1 × 106 years), during which atomic and molecular oxygen are frozen out onto dust grains and fully converted to H2O, to avoid overproduction of O2 in the dense envelope. The same model also reproduces the limits on the chemically related NO molecule if hydrogenation of NO on the grains to more complex molecules such as NH2OH, found in recent laboratory experiments, is included. The tentative detection of O2 in the surrounding cloud is consistent with a low-density PDR model with small changes in

  12. Submillimeter-Wave Observations toward the Low-Mass Protostar IRAS 15398-3359 at Subarcsecond Resolution

    NASA Astrophysics Data System (ADS)

    Oya, Y.; Sakai, N.; Watanabe, Y.; Yamamoto, S.; Sakai, T.; Hirota, T.; Lindberg, J. E.; Bisschop, S. E.; Jørgensen, J. K.; van Dishoeck, E. F.

    2015-12-01

    Subarcsecond 0."5 images of H2CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud with ALMA. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be almost edge-on (20°) based on the kinematic structure of the outflow cavity. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle, and the mass of the protostar is estimated to be less than 0.09 ⊙.

  13. The complex chemistry of outflow cavity walls exposed: the case of low-mass protostars

    NASA Astrophysics Data System (ADS)

    Drozdovskaya, Maria N.; Walsh, Catherine; Visser, Ruud; Harsono, Daniel; van Dishoeck, Ewine F.

    2015-08-01

    Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude. This mechanism remains to be quantified with laboratory experiments. Direct photodesorption is found to be relatively inefficient. If radicals are not produced directly in the icy mantle, the formation of complex organics is impeded. For efficiency, a sufficient number of FUV photons needs to penetrate the envelope, and elevated cool dust temperatures need to enable grain-surface radical mobility. As a result, a high stellar luminosity and a sufficiently wide cavity favour chemical complexity. Furthermore within this paradigm, complex organics are demonstrated to have unique lifetimes and be grouped into early (formaldehyde, ketene, methanol, formic acid, methyl formate, acetic acid and glycolaldehyde) and late (acetaldehyde, dimethyl ether and ethanol) species.

  14. High-J CO survey of low-mass protostars observed with Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; San José-García, I.; Karska, A.; Harsono, D.; Tafalla, M.; Fuente, A.; Visser, R.; Jørgensen, J. K.; Hogerheijde, M. R.

    2013-08-01

    Context. In the deeply embedded stage of star formation, protostars start to heat and disperse their surrounding cloud cores. The evolution of these sources has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to the lack of high-J CO observations. Aims: The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas in low-mass protostellar envelopes using spectrally resolved Herschel data of CO and compare those with the colder gas traced by lower excitation lines. Methods: Herschel-HIFI observations of high-J lines of 12CO, 13CO, and C18O (up to Ju = 10, Eu up to 300 K) are presented toward 26 deeply embedded low-mass Class 0 and Class I young stellar objects, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. Complementary lower J CO maps were observed using ground-based telescopes, such as the JCMT and APEX and convolved to matching beam sizes. Results: The 12CO 10-9 line is detected for all objects and can generally be decomposed into a narrow and a broad component owing to the quiescent envelope and entrained outflow material, respectively. The 12CO excitation temperature increases with velocity from ~60 K up to ~130 K. The median excitation temperatures for 12CO, 13CO, and C18O derived from single-temperature fits to the Ju = 2-10 integrated intensities are ~70 K, 48 K and 37 K, respectively, with no significant difference between Class 0 and Class I sources and no trend with Menv or Lbol. Thus, in contrast to the continuum SEDs, the spectral line energy distributions (SLEDs) do not show any evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is

  15. A RECENT ACCRETION BURST IN THE LOW-MASS PROTOSTAR IRAS 15398-3359: ALMA IMAGING OF ITS RELATED CHEMISTRY

    SciTech Connect

    Jørgensen, Jes K.; Brinch, Christian; Lindberg, Johan E.; Bisschop, Suzanne E.; Visser, Ruud; Bergin, Edwin A.; Sakai, Nami; Yamamoto, Satoshi; Harsono, Daniel; Van Dishoeck, Ewine F.; Persson, Magnus V.

    2013-12-20

    Low-mass protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C{sup 17}O, H{sup 13}CO{sup +}, CH{sub 3}OH, C{sup 34}S and C{sub 2}H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H{sup 13}CO{sup +} is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO{sup +} is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH{sub 3}OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other protostars.

  16. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2016-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  17. Is Episodic Accretion Necessary to Resolve the Luminosity Problem in Low-Mass Protostars?

    NASA Astrophysics Data System (ADS)

    Sevrinsky, Raymond Andrew; Dunham, Michael

    2017-01-01

    In this contribution, we compare the results of protostellar accretion simulations for scenarios both containing and lacking episodic accretion activity. We determine synthetic observational signatures for collapsing protostars by taking hydrodynamical simulations predicting highly variable episodic accretion events, filtering out the stochastic behavior by applying power law fits to the mass accretion rates onto the disk and central star, and using the filtered rates as inputs to two-dimensional radiative transfer calculations. The spectral energy distributions generated by these calculations are used to calculate standard observational signatures of Lbol and Tbol, and compared directly to a sample of 230 embedded protostars. We explore the degree to which these continually declining accretion models successfully reproduce the observed spread of protostellar luminosities, and examine their consistency with the prior variable models to investigate the degree to which episodic accretion bursts are necessary in protostellar formation theories to match observations of field protostars. The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.

  18. 183 GHz H{sub 2}O MASER EMISSION AROUND THE LOW-MASS PROTOSTAR SERPENS SMM1

    SciTech Connect

    Van Kempen, T. A.; Wilner, D.; Gurwell, M.

    2009-11-20

    We report the first interferometric detection of 183 GHz water emission in the low-mass protostar Serpens SMM1 using the Submillimeter Array with a resolution of 3'' and rms of approx7 Jy in a 3 km s{sup -1} bin. Due to the small size and high brightness of more than 240 Jy beam{sup -1}, it appears to be maser emission. In total, three maser spots were detected out to approx700 AU from the central protostar, lying along the redshifted outflow axis, outside the circumstellar disk but within the envelope region as evidenced by the continuum measurements. Two of the maser spots appear to be blueshifted by about 1-2 km s{sup -1}. No extended or compact thermal emission from a passively heated protostellar envelope was detected with a limit of 7 Jy (16 K), in agreement with recent modeling efforts. We propose that the maser spots originate within the cavity walls due to the interaction of the outflow jet with the surrounding protostellar envelope. Hydrodynamical models predict that such regions can be dense and warm enough to invert the 183 GHz water transition.

  19. The deuterium fractionation of water on solar-system scales in deeply-embedded low-mass protostars

    NASA Astrophysics Data System (ADS)

    Persson, M. V.; Jørgensen, J. K.; van Dishoeck, E. F.; Harsono, D.

    2014-03-01

    Context. The chemical evolution of water through the star formation process directly affects the initial conditions of planet formation. The water deuterium fractionation (HDO/H2O abundance ratio) has traditionally been used to infer the amount of water brought to Earth by comets. Measuring this ratio in deeply-embedded low-mass protostars makes it possible to probe the critical stage when water is transported from clouds to disks in which icy bodies are formed. Aims: We aim to determine the HDO/H2O abundance ratio in the warm gas in the inner 150 AU for three deeply-embedded low-mass protostars NGC 1333-IRAS 2A, IRAS 4A-NW, and IRAS 4B through high-resolution interferometric observations of isotopologues of water. Methods: We present sub-arcsecond resolution observations of the 31,2-22,1 transition of HDO at 225.89672 GHz in combination with previous observations of the 31,3-22,0 transition of H218O at 203.40752 GHz from the Plateau de Bure Interferometer toward three low-mass protostars. The observations have similar angular resolution (0.̋7-1.̋3), probing scales R ≲ 150 AU. In addition, observations of the 21,1-21,2 transition of HDO at 241.561 GHz toward IRAS 2A are presented to constrain the excitation temperature. A direct and model independent HDO/H2O abundance ratio is determined for each source and compared with HDO/H2O ratios derived from spherically symmetric full radiative transfer models for two sources. Results: From the two HDO lines observed toward IRAS 2A, the excitation temperature is found to be Tex = 124 ± 60 K. Assuming a similar excitation temperature for H218O and all sources, the HDO/H2O ratio is 7.4 ± 2.1 × 10-4 for IRAS 2A, 19.1 ± 5.4 × 10-4 for IRAS 4A-NW, and 5.9 ± 1.7 × 10-4 for IRAS 4B. The abundance ratios show only a weak dependence on the adopted excitation temperature. The abundances derived from the radiative transfer models agree with the direct determination of the HDO/H2O abundance ratio for IRAS 16293-2422 within a

  20. Neutral stellar winds that drive bipolar outflows in low-mass protostars

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Heiles, Carl; Koo, Bon-Ghul; Shu, Frank H.; Rodriguez, Luis F.

    1988-01-01

    The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

  1. UNVEILING THE EVOLUTIONARY SEQUENCE FROM INFALLING ENVELOPES TO KEPLERIAN DISKS AROUND LOW-MASS PROTOSTARS

    SciTech Connect

    Yen, Hsi-Wei; Takakuwa, Shigehisa; Ohashi, Nagayoshi; Ho, Paul T. P.

    2013-07-20

    We performed Submillimeter Array observations in the C{sup 18}O (2-1) emission line toward six Class 0 and I protostars to study rotational motions of their surrounding envelopes and circumstellar material on 100-1000 AU scales. C{sup 18}O (2-1) emission with intensity peaks located at the protostellar positions is detected toward all six sources. The rotational velocities of the protostellar envelopes as a function of radius were measured from the position-velocity diagrams perpendicular to the outflow directions passing through the protostellar positions. Two Class 0 sources, B335 and NGC 1333 IRAS 4B, show no detectable rotational motion, while L1527 IRS (Class 0/I) and L1448-mm (Class 0) exhibit rotational motions with radial profiles of V{sub rot}{proportional_to}r {sup -1.0{+-}0.2} and {proportional_to}r {sup -1.0{+-}0.1}, respectively. The other Class I sources, TMC-1A and L1489 IRS, exhibit the fastest rotational motions among the sample, and their rotational motions have flatter radial profiles of V{sub rot}{proportional_to}r {sup -0.6{+-}0.1} and {proportional_to}r {sup -0.5{+-}0.1}, respectively. The rotational motions with the radial dependence of {approx}r {sup -1} can be interpreted as rotation with a conserved angular momentum in a dynamically infalling envelope, while those with the radial dependence of {approx}r {sup -0.5} can be interpreted as Keplerian rotation. These observational results demonstrate categorization of rotational motions from infalling envelopes to Keplerian-disk formation. Models of the inside-out collapse where the angular momentum is conserved are discussed and compared with our observational results.

  2. Constraining the physical structure of the inner few 100 AU scales of deeply embedded low-mass protostars

    NASA Astrophysics Data System (ADS)

    Persson, M. V.; Harsono, D.; Tobin, J. J.; van Dishoeck, E. F.; Jørgensen, J. K.; Murillo, N.; Lai, S.-P.

    2016-05-01

    Context. The physical structure of deeply embedded low-mass protostars (Class 0) on scales of less than 300 AU is still poorly constrained. While molecular line observations demonstrate the presence of disks with Keplerian rotation toward a handful of sources, others show no hint of rotation. Determining the structure on small scales (a few 100 AU) is crucial for understanding the physical and chemical evolution from cores to disks. Aims: We determine the presence and characteristics of compact, disk-like structures in deeply embedded low-mass protostars. A related goal is investigating how the derived structure affects the determination of gas-phase molecular abundances on hot-core scales. Methods: Two models of the emission, a Gaussian disk intensity distribution and a parametrized power-law disk model, are fitted to subarcsecond resolution interferometric continuum observations of five Class 0 sources, including one source with a confirmed Keplerian disk. Prior to fitting the models to the de-projected real visibilities, the estimated envelope from an independent model and any companion sources are subtracted. For reference, a spherically symmetric single power-law envelope is fitted to the larger scale emission (~1000 AU) and investigated further for one of the sources on smaller scales. Results: The radii of the fitted disk-like structures range from ~90-170 AU, and the derived masses depend on the method. Using the Gaussian disk model results in masses of 54-556 × 10-3 M⊙, and using the power-law disk model gives 9-140 × 10-3 M⊙. While the disk radii agree with previous estimates the masses are different for some of the sources studied. Assuming a typical temperature distribution (r-0.5), the fractional amount of mass in the disk above 100 K varies from 7% to 30%. Conclusions: A thin disk model can approximate the emission and physical structure in the inner few 100 AU scales of the studied deeply embedded low-mass protostars and paves the way for

  3. Outflows, infall and evolution of a sample of embedded low-mass protostars. The William Herschel Line Legacy (WILL) survey

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; van Dishoeck, E. F.; Kristensen, L. E.; Karska, A.; San José-García, I.; Khanna, S.; Herczeg, G. J.; André, Ph.; Bontemps, S.; Cabrit, S.; Carney, M. T.; Drozdovskaya, M. N.; Dunham, M. M.; Evans, N. J.; Fedele, D.; Green, J. D.; Harsono, D.; Johnstone, D.; Jørgensen, J. K.; Könyves, V.; Nisini, B.; Persson, M. V.; Tafalla, M.; Visser, R.; Yıldız, U. A.

    2017-04-01

    Context. Herschel observations of water and highly excited CO (J > 9) have allowed the physical and chemical conditions in the more active parts of protostellar outflows to be quantified in detail for the first time. However, to date, the studied samples of Class 0/I protostars in nearby star-forming regions have been selected from bright, well-known sources and have not been large enough for statistically significant trends to be firmly established. Aims: We aim to explore the relationships between the outflow, envelope and physical properties of a flux-limited sample of embedded low-mass Class 0/I protostars. Methods: We present spectroscopic observations in H2O, CO and related species with Herschel HIFI and PACS, as well as ground-based follow-up with the JCMT and APEX in CO, HCO+ and isotopologues, of a sample of 49 nearby (d < 500 pc) candidate protostars selected from Spitzer and Herschel photometric surveys of the Gould Belt. This more than doubles the sample of sources observed by the WISH and DIGIT surveys. These data are used to study the outflow and envelope properties of these sources. We also compile their continuum spectral energy distributions (SEDs) from the near-IR to mm wavelengths in order to constrain their physical properties (e.g. Lbol, Tbol and Menv). Results: Water emission is dominated by shocks associated with the outflow, rather than the cooler, slower entrained outflowing gas probed by ground-based CO observations. These shocks become less energetic as sources evolve from Class 0 to Class I. Outflow force, measured from low-J CO, also decreases with source evolutionary stage, while the fraction of mass in the outflow relative to the total envelope (i.e. Mout/Menv) remains broadly constant between Class 0 and I. The median value of 1% is consistent with a core to star formation efficiency on the order of 50% and an outflow duty cycle on the order of 5%. Entrainment efficiency, as probed by FCO/Ṁacc, is also invariant with source

  4. Molecular outflows driven by low-mass protostars. I. Correcting for underestimates when measuring outflow masses and dynamical properties

    SciTech Connect

    Dunham, Michael M.; Arce, Héctor G.; Mardones, Diego; Lee, Jeong-Eun; Matthews, Brenda C.; Stutz, Amelia M.; Williams, Jonathan P.

    2014-03-01

    We present a survey of 28 molecular outflows driven by low-mass protostars, all of which are sufficiently isolated spatially and/or kinematically to fully separate into individual outflows. Using a combination of new and archival data from several single-dish telescopes, 17 outflows are mapped in {sup 12}CO (2-1) and 17 are mapped in {sup 12}CO (3-2), with 6 mapped in both transitions. For each outflow, we calculate and tabulate the mass (M {sub flow}), momentum (P {sub flow}), kinetic energy (E {sub flow}), mechanical luminosity (L {sub flow}), and force (F {sub flow}) assuming optically thin emission in LTE at an excitation temperature, T {sub ex}, of 50 K. We show that all of the calculated properties are underestimated when calculated under these assumptions. Taken together, the effects of opacity, outflow emission at low velocities confused with ambient cloud emission, and emission below the sensitivities of the observations increase outflow masses and dynamical properties by an order of magnitude, on average, and factors of 50-90 in the most extreme cases. Different (and non-uniform) excitation temperatures, inclination effects, and dissociation of molecular gas will all work to further increase outflow properties. Molecular outflows are thus almost certainly more massive and energetic than commonly reported. Additionally, outflow properties are lower, on average, by almost an order of magnitude when calculated from the {sup 12}CO (3-2) maps compared to the {sup 12}CO (2-1) maps, even after accounting for different opacities, map sensitivities, and possible excitation temperature variations. It has recently been argued in the literature that the {sup 12}CO (3-2) line is subthermally excited in outflows, and our results support this finding.

  5. The ALMA-PILS survey: First detections of ethylene oxide, acetone and propanal toward the low-mass protostar IRAS 16293-2422

    NASA Astrophysics Data System (ADS)

    Lykke, J. M.; Coutens, A.; Jørgensen, J. K.; van der Wiel, M. H. D.; Garrod, R. T.; Müller, H. S. P.; Bjerkeli, P.; Bourke, T. L.; Calcutt, H.; Drozdovskaya, M. N.; Favre, C.; Fayolle, E. C.; Jacobsen, S. K.; Öberg, K. I.; Persson, M. V.; van Dishoeck, E. F.; Wampfler, S. F.

    2017-01-01

    Context. One of the open questions in astrochemistry is how complex organic and prebiotic molecules are formed. The unsurpassed sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) takes the quest for discovering molecules in the warm and dense gas surrounding young stars to the next level. Aims: Our aim is to start the process of compiling an inventory of oxygen-bearing complex organic molecules toward the solar-type Class 0 protostellar binary IRAS 16293-2422 from an unbiased spectral survey with ALMA, Protostellar Interferometric Line Survey (PILS). Here we focus on the new detections of ethylene oxide (c-C2H4O), acetone (CH3COCH3), and propanal (C2H5CHO). Methods: With ALMA, we surveyed the spectral range from 329 to 363 GHz at 0.5″ (60 AU diameter) resolution. Using a simple model for the molecular emission in local thermodynamical equilibrium, the excitation temperatures and column densities of each species were constrained. Results: We successfully detect propanal (44 lines), ethylene oxide (20 lines) and acetone (186 lines) toward one component of the protostellar binary, IRAS 16293B. The high resolution maps demonstrate that the emission for all investigated species originates from the compact central region close to the protostar. This, along with a derived common excitation temperature of Tex ≈ 125 K, is consistent with a coexistence of these molecules in the same gas. Conclusions: The observations mark the first detections of acetone, propanal and ethylene oxide toward a low-mass protostar. The relative abundance ratios of the two sets of isomers, a CH3COCH3/C2H5CHO ratio of 8 and a CH3CHO/c-C2H4O ratio of 12, are comparable to previous observations toward high-mass protostars. The majority of observed abundance ratios from these results as well as those measured toward high-mass protostars are up to an order of magnitude above the predictions from chemical models. This may reflect either missing reactions or uncertain rates in the

  6. HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A

    SciTech Connect

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Van Dishoeck, E. F.; Vastel, C.; Taquet, V.

    2014-09-01

    Water plays a crucial role both in the interstellar medium and on Earth. To constrain its formation mechanisms and its evolution through the star formation process, the determination of the water deuterium fractionation ratios is particularly suitable. Previous studies derived HDO/H{sub 2}O ratios in the warm inner regions of low-mass protostars. We here report a detection of the D{sub 2}O 1{sub 1,} {sub 0}-1{sub 0,} {sub 1} transition toward the low-mass protostar NGC 1333 IRAS2A with the Plateau de Bure interferometer: this represents the first interferometric detection of D{sub 2}O—and only the second solar-type protostar for which this isotopologue is detected. Using the observations of the HDO 5{sub 4,} {sub 2}-6{sub 3,} {sub 3} transition simultaneously detected and three other HDO lines previously observed, we show that the HDO line fluxes are well reproduced with a single excitation temperature of 218 ± 21 K and a source size of ∼0.''5. The D{sub 2}O/HDO ratio is ∼(1.2 ± 0.5) × 10{sup –2}, while the use of previous H{sub 2}{sup 18}O observations give an HDO/H{sub 2}O ratio of ∼(1.7 ± 0.8) × 10{sup –3}, i.e., a factor of seven lower than the D{sub 2}O/HDO ratio. These results contradict the predictions of current grain surface chemical models and indicate that either the surface deuteration processes are poorly understood or that both sublimation of grain mantles and water formation at high temperatures (≳230 K) take place in the inner regions of this source. In the second scenario, the thermal desorption of the grain mantles would explain the high D{sub 2}O/HDO ratio, while water formation at high temperature would explain significant extra production of H{sub 2}O leading to a decrease of the HDO/H{sub 2}O ratio.

  7. COMPUTATIONAL MODELING OF THE CLASS I LOW-MASS PROTOSTAR ELIAS 29 APPLYING OPTICAL CONSTANTS OF ICES PROCESSED BY HIGH ENERGY COSMIC RAY ANALOGS

    SciTech Connect

    Rocha, W. R. M.; Pilling, S. E-mail: sergiopilling@yahoo.com.br

    2015-04-10

    We present a study of the effects of high energy cosmic rays (CRs) over the astrophysical ices, observed toward the embedded class I protostar Elias 29, by using computational modeling and laboratory data. Its spectrum was observed with the Infrared Space Observatory (ISO) covering 2.3–190 μm. The modeling employed the three-dimensional Monte Carlo radiative transfer code RADMC-3D and laboratory data of bombarded ice grains by CR analogs and unprocessed ices (not bombarded). We are assuming that Elias 29 has a self-irradiated disk with inclination i = 60.°0, surrounded by an envelope with a bipolar cavity. The results show that absorption features toward Elias 29 are better reproduced by assuming a combination between unprocessed astrophysical ices at low temperature (H{sub 2}O, CO, CO{sub 2}) and bombarded ices (H{sub 2}O:CO{sub 2}) by high energy CRs. Evidences of the ice processing around Elias 29 can be observed by the good fitting around 5.5–8.0 μm, by polar and apolar ice segregation in 15.15–15.25 μm, and by the presence of the CH{sub 4} and HCOOH ices. Given that non-nitrogen compounds were employed in this work, we assume that absorption around 5.5–8.0 μm should not be associated with the NH{sub 4}{sup +} ion (see the 2003 work of Shutte and Khanna ), but more probably with aliphatic ethers (e.g., R1-OCH{sub 2}-R2), CH{sub 3}CHO, and related species. The results obtained in this paper are important because they show that the environment around protostars is better modeled considering processed samples and, consequently, demonstrate the chemical evolution of the astrophysical ices.

  8. Computational Modeling of the Class I Low-Mass Protostar Elias 29 Applying Optical Constants of Ices Processed By High Energy Cosmic Ray Analogs

    NASA Astrophysics Data System (ADS)

    Rocha, W. R. M.; Pilling, S.

    2015-04-01

    We present a study of the effects of high energy cosmic rays (CRs) over the astrophysical ices, observed toward the embedded class I protostar Elias 29, by using computational modeling and laboratory data. Its spectrum was observed with the Infrared Space Observatory (ISO) covering 2.3-190 μm. The modeling employed the three-dimensional Monte Carlo radiative transfer code RADMC-3D and laboratory data of bombarded ice grains by CR analogs and unprocessed ices (not bombarded). We are assuming that Elias 29 has a self-irradiated disk with inclination i = 60.°0, surrounded by an envelope with a bipolar cavity. The results show that absorption features toward Elias 29 are better reproduced by assuming a combination between unprocessed astrophysical ices at low temperature (H2O, CO, CO2) and bombarded ices (H2O:CO2) by high energy CRs. Evidences of the ice processing around Elias 29 can be observed by the good fitting around 5.5-8.0 μm, by polar and apolar ice segregation in 15.15-15.25 μm, and by the presence of the CH4 and HCOOH ices. Given that non-nitrogen compounds were employed in this work, we assume that absorption around 5.5-8.0 μm should not be associated with the NH4+ ion (see the 2003 work of Shutte & Khanna ), but more probably with aliphatic ethers (e.g., R1-OCH2-R2), CH3CHO, and related species. The results obtained in this paper are important because they show that the environment around protostars is better modeled considering processed samples and, consequently, demonstrate the chemical evolution of the astrophysical ices.

  9. HERSCHEL KEY PROGRAM, ''DUST, ICE, AND GAS IN TIME'' (DIGIT): THE ORIGIN OF MOLECULAR AND ATOMIC EMISSION IN LOW-MASS PROTOSTARS IN TAURUS

    SciTech Connect

    Lee, Jeong-Eun; Lee, Seokho; Lee, Jinhee; Evans II, Neal J.; Green, Joel D.

    2014-10-01

    Six low-mass embedded sources (L1489, L1551-IRS5, TMR1, TMC1-A, L1527, and TMC1) in Taurus have been observed with Herschel-PACS to cover the full spectrum from 50 to 210 μm as part of the Herschel key program, ''Dust, Ice, and Gas In Time''. The relatively low intensity of the interstellar radiation field surrounding Taurus minimizes contamination of the [C II] emission associated with the sources by diffuse emission from the cloud surface, allowing study of the [C II] emission from the source. In several sources, the [C II] emission is distributed along the outflow, as is the [O I] emission. The atomic line luminosities correlate well with each other, as do the molecular lines, but the atomic and molecular lines correlate poorly. The relative contribution of CO to the total gas cooling is constant at ∼30%, while the cooling fraction by H{sub 2}O varies from source to source, suggesting different shock properties resulting in different photodissociation levels of H{sub 2}O. The gas with a power-law temperature distribution with a moderately high density can reproduce the observed CO fluxes, indicative of CO close to LTE. However, H{sub 2}O is mostly subthermally excited. L1551-IRS5 is the most luminous source (Ł{sub bol} = 24.5 L {sub ☉}) and the [O I] 63.1 μm line accounts for more than 70% of its FIR line luminosity, suggesting complete photodissociation of H{sub 2}O by a J shock. In L1551-IRS5, the central velocity shifts of the [O I] line, which exceed the wavelength calibration uncertainty (∼70 km s{sup –1}) of PACS, are consistent with the known redshifted and blueshifted outflow direction.

  10. FORCAST Spectroscopy of Orion Protostars: Probing Intermediate Luminosities

    NASA Astrophysics Data System (ADS)

    Megeath, Tom

    2015-10-01

    We propose FORECAST low resolution spectroscopy of seven protostars in the Orion molecular clouds. These protostars have luminosities between those of low mass protostars which were the primary focus of the Herschel Orion Protostar Survey (HOPS) and those of the high mass protostars in the Orion Nebula. Although we have constructed 1-870 micron SEDs from 2MASS, Spitzer, Herschel and APEX photometry of these intermediate (40-600 Lsun) luminosity protostars, we do not have Spitzer IRS spectra showing the shape and depth of the 10 micron silicate features and the slope of the mid-IR spectral energy distribution (SED). Given the importance of such spectra for constraining the properties of the protostars through radiative transfer modeling, we request time to obtain FORCAST FOR-G111 (8.4-13.7 micron) and FOR-G227 (17.6-27.7 micron) grism spectra. With these data, we can extend our study of protostars in Orion to include a sample of more luminous protostar which are expected to include both intermediate mass protostars and low mass protostars undergoing outbursts. To investigate potential variability between Spitzer and WISE epochs, we also request photomety of a protostar potentially undergoing an episodic outburst.

  11. Distributed low-mass star formation in the IRDC G34.43+00.24

    SciTech Connect

    Foster, Jonathan B.; Arce, Héctor G.; Offner, Stella; Kassis, Marc; Sanhueza, Patricio; Jackson, James M.; Finn, Susanna C.; Sakai, Takeshi; Sakai, Nami; Yamamoto, Satoshi; Guzmán, Andrés E.; Rathborne, Jill M.

    2014-08-20

    We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in the K band, which comes from excited H{sub 2} in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow line-width SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.

  12. ORPHANED PROTOSTARS

    SciTech Connect

    Reipurth, Bo; Connelley, Michael; Mikkola, Seppo; Valtonen, Mauri

    2010-12-10

    We explore the origin of a population of distant companions ({approx}1000-5000 AU) to Class I protostellar sources recently found by Connelley and coworkers, who noted that the companion fraction diminished as the sources evolved. Here, we present N-body simulations of unstable triple systems embedded in dense cloud cores. Many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes as the cloud cores gradually disappear. We use the term orphans to denote protostellar objects that are dynamically ejected from their placental cloud cores, either escaping or for a time being tenuously bound at large separations. Half of all triple systems are found to disintegrate during the protostellar stage, so if multiple systems are a frequent outcome of the collapse of a cloud core, then orphans should be common. Bound orphans are associated with embedded close protostellar binaries, but escaping orphans can travel as far as {approx}0.2 pc during the protostellar phase. The steep climb out of a potential well ensures that orphans are not kinematically distinct from young stars born with a less violent pre-history. The identification of orphans outside their heavily extincted cloud cores will allow the detailed study of protostars high up on their Hayashi tracks at near-infrared and in some cases even at optical wavelengths.

  13. The Birth of Disks Around Protostars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-03-01

    The dusty disks around young stars make the news regularly due to their appeal as the birthplace of early exoplanets. But how do disks like these first form and evolve around their newly born protostars? New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) are helping us to better understand this process.Formation from CollapseStars are born from the gravitational collapse of a dense cloud of molecular gas. Long before they start fusing hydrogen at their centers when they are still just hot overdensities in the process of contracting we call them protostars. These low-mass cores are hidden at the hearts of the clouds of molecular gas from which they are born.Aerial image of the Atacama Large Millimeter/submillimeter Array. [EFE/Ariel Marinkovic]During this contraction phase, before a protostar transitions to a pre-main-sequence star (which it does by blowing away its outer gas envelope, halting the stars growth), much of the collapsing material will spin into a centrifugally supported Keplerian disk that surrounds the young protostar. Later, these circumstellar disks will become the birthplace for young planets something for which weve seen observational evidence in recent years.But how do these Keplerian disks which eventually have scales of hundreds of AU first form and grow around protostars? We need observations of these disks in their early stages of formation to understand their birth and evolution a challenging prospect, given the obscuring molecular gas that hides them at these stages. ALMA, however, is up to the task: it can peer through to the center of the gas clouds to see the emission from protostellar cores and their surroundings.ALMA observations of the protostar Lupus 3 MMS. The molecular outflows from the protostar are shown in panel a. Panel b shows the continuum emission, which has a compact component that likely traces a disk surrounding the protostar. [Adapted from Yen et al. 2017]New Disks Revealed?In a recent

  14. Protostar mass functions in young clusters

    SciTech Connect

    Myers, Philip C.

    2014-01-20

    In an improved model of protostar mass functions (PMFs), protostars gain mass from isothermal cores in turbulent clumps. Their mass accretion rate is similar to Shu accretion at low mass and to reduced Bondi accretion at high mass. Accretion durations follow a simple expression in which higher-mass protostars accrete for longer times. These times are set by ejections, stellar feedback, and gravitational competition, which terminate accretion and reduce its efficiency. The mass scale is the mass of a critically stable isothermal core. In steady state, the PMF approaches a power law at high mass because of competition between clump accretion and accretion stopping. The power law exponent is the ratio of the timescales of accretion and accretion stopping. The protostar luminosity function (PLF) peaks near 1 L {sub ☉} because of inefficient accretion of core gas. Models fit observed PLFs in four large embedded clusters. These indicate that their underlying PMFs may be top-heavy compared with the initial mass function, depending on the protostar radius model.

  15. Studies of low-mass star formation with the large deployable reflector

    NASA Technical Reports Server (NTRS)

    Hollenbach, D. J.; Tielens, Alexander G. G. M.

    1984-01-01

    Estimates are made of the far-infrared and submillimeter continuum and line emission from regions of low mass star formation. The intensity of this emission is compared with the sensitivity of the large deployable reflector (LDR), a large space telescope designed for this wavelength range. The proposed LDR is designed to probe the temperature, density, chemical structure, and the velocity field of the collapsing envelopes of these protostars. The LDR is also designed to study the accretion shocks on the cores and circumstellar disks of low-mass protostars, and to detect shock waves driven by protostellar winds.

  16. Molecule formation in fast neutral winds from protostars

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Mamon, G. A.; Huggins, P. J.

    1989-01-01

    A time-dependent chemical model is used to analyze the processes generating and destroying molecules in very high velocity winds from low-mass protostars. CO and SiO are found to be generated in significant quantities despite the persistence of H in atomic form, consistently with recent protostellar wind detections of CO and H I at velocities in excess of 100 km/sec. A moderate mass-loss rate, in conjunction with a temperature distribution that decreases rather rapidly with distance from the protostar, are the conditions for substantial molecule formation.

  17. Episodic Accretion among the Orion Protostars

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Safron, Emily; Megeath, S. Thomas

    2016-06-01

    Episodic accretion, where a young stellar object undergoes stochastic spikes in its disk-to-star accretion rate one or more times over its formation period, may be a crucial process in the formation of low-mass stars. These spikes result in a factor of 10 to 100 increase in the source luminosity over the course of several months that may persist for years. Six years after the Spitzer survey of the Orion molecular clouds, the WISE telescope mapped Orion with similar wavelength coverage. Thus, the two surveys can be used to explore the mid-infrared variability of young stars on this timescale, which is suitable for discovering episodic accretion events. Out of 319 Orion protostars that were targets of the Herschel Orion Protostar Survey, we identified two examples of episodic accretion with this method. One of them, HOPS 223, was previously known. The other, HOPS 383, is the first known example of episodic accretion in a Class 0 protostar (age < 0.2 Myr). With these and one other outburst that began early in the Spitzer mission, we estimate that the most likely interval between protostellar outbursts is 740 years, with a 90% confidence interval of 470 to 6200 years. These outbursts are weaker than the optically revealed FU Ori events. We will update the mid-infrared light curves of HOPS 223 and HOPS 383 with recent data from FORCAST aboard SOFIA; HOPS 223 shows signs of fading.

  18. VLBI multi-epoch water maser observations toward massive protostars

    NASA Astrophysics Data System (ADS)

    Torrelles, José M.; Gómez, José F.; Patel, Nimesh A.; Curiel, Salvador; Anglada, Guillem; Estalella, Robert

    2012-07-01

    VLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated ``short-lived'' pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simultaneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similar to what is observed in low-mass protostars). In addition, with these observations it has been possible to identify new, previously unseen centers of high-mass star formation through outflow activity.

  19. Analysis of the southern pre-contact W UMa binary ZZ Eridani: A 34 year period study yields a possible low-mass companion

    SciTech Connect

    Samec, R. G.; Clark, J. D.; Hamme, W. Van; Faulkner, D. R.

    2015-02-01

    Complete Bessel BVRI light curves of ZZ Eridani [2MASS J04130109-1044545, HV 6280, NSVS 14888164 α(2000) = 04{sup h}13{sup m}1{sub ·}{sup s}10, δ(2000) = −10°44′54{sub ·}{sup ″}5 (ICRS), V = 13.9-14.4-15.0] are observed and analyzed. The system is a southern pre-contact W UMa binary. Its light curve has the appearance of an Algol (EA) light curve, however, it is made up of dwarf solar-type components with a period of only 0.4521 days. Our 34 year period study yields a sinusoidal fit or an increasing quadratic fit. The sinusoid may indicate that a third body is orbiting the close binary. The lower-limit mass of the third body is near that of the brown dwarf limit (0.095 M α). Also included is an improved ephemeris, a mass ratio search, and a simultaneous BVRI Wilson–Devinney solution.

  20. Characterizing Dust and Ice Toward Protostars in the Orion Molecular Cloud Complex

    NASA Astrophysics Data System (ADS)

    Poteet, Charles Allen

    Protostars are young stars in the process of accreting infalling envelopes of gas and dust which are transported from the diffuse interstellar medium through gravitational collapse. Although the envelopes are commonly thought to be comprised of cold, pristine material from the interstellar medium, recent space-based studies suggest that protostellar envelopes of low- and high-mass protostars contain thermally processed dust and ice. Unlike the envelope material from luminous, massive protostars, where dust and ice are subject to processing by direct stellar irradiation, thermally processed materials in low-mass protostars may be the consequence of accretion-driven outbursts, shocks in protostellar outflows, or transport of materials from the inner disk to the envelope by outflows and winds. We present an analysis of mid-infrared spectra of a large sample of protostars from the Orion Molecular Cloud complex, the most active region of star formation within the nearest 500 pc. The spectra, obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope , reveal strong silicate and solid molecular absorption bands. Using spectral decomposition analyses to determine the dust and ice composition toward the protostars, we find that the amorphous silicate composition is more dominated by amorphous pyroxene than dust in the Galactic diffuse interstellar medium, and that the mass fraction of amorphous pyroxene varies between protostars. Toward the perplexing protostar HOPS-68, we report the first unambiguous detection of (1) crystalline silicate absorption in a cold, infalling protostellar envelope and (2) highly processed carbon dioxide ice mantles. Moreover, we find evidence for crystalline silicate absorption towards two additional protostars. These results provide strong evidence that dust and ice delivered to planet-forming disks around low-mass stars in the protostellar phase may be processed by feedback from the central protostar.

  1. Protostars and Planets VI

    NASA Astrophysics Data System (ADS)

    Beuther, Henrik; Klessen, Ralf S.; Dullemond, Cornelis P.; Henning, Thomas

    The Protostars and Planets book and conference series has been a long-standing tradition that commenced with the first meeting led by Tom Gehrels and held in Tucson, Arizona, in 1978. The goal then, as it still is today, was to bridge the gap between the fields of star and planet formation as well as the investigation of planetary systems and planets. As Tom Gehrels stated in the preface to the first Protostars and Planets book, "Cross-fertilization of information and understanding is bound to occur when investigators who are familiar with the stellar and interstellar phases meet with those who study the early phases of solar system formation." The central goal remained the same for the subsequent editions of the books and conferences Protostars and Planets II in 1984, Protostars and Planets III in 1990, Protostars and Planets IV in 1998, and Protostars and Planets V in 2005, but has now been greatly expanded by the flood of new discoveries in the field of exoplanet science. The original concept of the Protostars and Planets series also formed the basis for the sixth conference in the series, which took place on July 15-20, 2013. It was held for the first time outside of the United States in the bustling university town of Heidelberg, Germany. The meeting attracted 852 participants from 32 countries, and was centered around 38 review talks and more than 600 posters. The review talks were expanded to form the 38 chapters of this book, written by a total of 250 contributing authors. This Protostars and Planets volume reflects the current state-of-the-art in star and planet formation, and tightly connects the fields with each other. It is structured into four sections covering key aspects of molecular cloud and star formation, disk formation and evolution, planetary systems, and astrophysical conditions for life. All poster presentations from the conference can be found at www.ppvi.org. In the eight years that have passed since the fifth conference and book in the

  2. TRACING EMBEDDED STELLAR POPULATIONS IN CLUSTERS AND GALAXIES USING MOLECULAR EMISSION: METHANOL AS A SIGNATURE OF THE LOW-MASS END OF THE IMF

    SciTech Connect

    Kristensen, Lars E.; Bergin, Edwin A.

    2015-07-10

    Most low-mass protostars form in clusters, in particular high-mass clusters; however, how low-mass stars form in high-mass clusters and what the mass distribution is are still open questions both in our own Galaxy and elsewhere. To access the population of forming embedded low-mass protostars observationally, we propose using molecular outflows as tracers. Because the outflow emission scales with mass, the effective contrast between low-mass protostars and their high-mass cousins is greatly lowered. In particular, maps of methanol emission at 338.4 GHz (J = 7{sub 0}–6{sub 0} A{sup +}) in low-mass clusters illustrate that this transition is an excellent probe of the low-mass population. We present here a model of a forming cluster where methanol emission is assigned to every embedded low-mass protostar. The resulting model image of methanol emission is compared to recent ALMA observations toward a high-mass cluster and the similarity is striking: the toy model reproduces observations to better than a factor of two and suggests that approximately 50% of the total flux originates in low-mass outflows. Future fine-tuning of the model will eventually make it a tool for interpreting the embedded low-mass population of distant regions within our own Galaxy and ultimately higher-redshift starburst galaxies, not just for methanol emission but also water and high-J CO.

  3. The Cluster Environment of High Mass Protostars

    NASA Astrophysics Data System (ADS)

    Moriarty, John C.; Smith, H. A.; Campbell, M. F.; Hora, J. L.; Marengo, M.; Sridharan, T. K.; Pillai, T.; Robitaille, T. P.; Fazio, G. G.; Molinari, S.

    2010-01-01

    We present images and some initial results from Spitzer IRAC and MIPS observations of 49 candidate high mass protostellar objects (HMPOs) and their surrounding environments. These candidate HMPOs are objects in the lists assembled by Sridharan et al (2002) and Molinari et al (1996) that were not covered by the GLIMPSE, GLIMPSEII and MIPSGAL surveys, with a few additions. Our sample has the advantage of longer exposure times than the GLIMPSE and MIPSGAL surveys. The images were reduced and photometry was performed using IRACproc (Schuster et al 2006). Color-color and color-magnitude criteria adopted from Gutermuth et al (2009), were used to identify candidate class0/I and classII protostars around each of the HMPO candidates. We present IRAS09131-4723 as an example of this analysis. It revealed 22 class0/I and 59 classII protostars distributed around IRAS 09131-4723. We plan to search the library of models presented by Robitaille et al (2007) for each class0/I/II candidate found, and use the parameters taken from the best fitting models to test the classifications obtained from the color-color analysis. We also plan to study the clustering of low mass protostars around the HMPOs. Gutermuth, R. A., et al, 2009 ApJS, 184, 18; Molinari, S. et al 1996 A&A 308, 573; Robitaille, T. P., et al, ApJS, 169, 328; Schuster M. T., Marengo, M., Patten, B. M. 2006, SPIE, 6270, 627020; Sridharan, T. K., et al, ApJ, 566, 931

  4. Waterfalls Around Protostars

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; van Dishoeck, E. F.; Schmalzl, M.; Kristensen, L. E.; Visser, R.; Hogerheijde, M. R.; Bruderer, S.

    2013-07-01

    Water is uniquely sensitive to motion of any kind within the protostellar environment due to its large Einstein A coefficient. As part of the 'Water in star-forming regions with Herschel' (WISH) survey, infall signatures were detected in the HIFI water spectra observed towards 5 Class 0/I protostars observed. The combination of observations of multiple water transitions and full 1-D non-LTE radiative transfer models of protostellar envelopes provides a self-consistent way to probe the physics and chemistry of infalling envelope material.

  5. Water and complex organic molecules in the warm inner regions of solar-type protostars

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Lykke, J. M.; Taquet, V.; van Dishoeck, E. F.; Vastel, C.; Wampfler, S. F.

    2015-12-01

    Water and complex organic molecules play an important role in the emergence of Life. They have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). In particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. Can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? By comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. We present recent results obtained with the Plateau de Bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar NGC 1333 IRAS2A.

  6. Stellar Properties of Embedded Protostars: Progress and Prospects

    NASA Technical Reports Server (NTRS)

    Greene, Thomas

    2006-01-01

    Until now, high extinctions have prevented direct observation of the central objects of self-embedded, accreting protostars. However, sensitive high dispersion spectrographs on large aperture telescopes have allowed us to begin studying the stellar astrophysical properties of dozens of embedded low mass protostars in the nearest regions of star formation. These high dispersion spectra allow, for the first time, direct measurements of their stellar effective temperatures, surface gravities, rotation velocities, radial velocities (and spectroscopic binarity), mass accretion properties, and mass outflow indicators. Comparisons of the stellar properties with evolutionary models also allow us to estimate masses and constrain ages. We find that these objects have masses similar to those of older, more evolved T Tauri stars, but protostars have higher mean rotation velocities and angular momenta. Most protostars indicate high mass accretion or outflow, but some in Taurus-Auriga appear to be relatively quiescent. These new results are testing, expanding, and refining the standard star formation paradigm, and we explore how to expand this work further.

  7. [Fe II] jets from intermediate-mass protostars in Carina

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan; Bally, John

    2016-12-01

    We present new HST/WFC3-IR narrow-band [Fe II] images of protostellar jets in the Carina Nebula. Combined with five previously published sources, we have a sample of 18 jets and two Herbig-Haro (HH) objects. All of the jets we targeted with Wide-Field Camera 3 (WFC3) show bright infrared [Fe II] emission, and a few Hα candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than Hα and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 μm/Hα flux ratio measured in the jets is ≳5 times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe+ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify for 13 jets. The remaining jets emerge from opaque globules that obscure emission from the protostar. In many respects, the HH jets in Carina look like a scaled-up version of the jets driven by low-mass protostars. Altogether, these observations suggest that [Fe II] emission is a reliable tracer of dense, irradiated jets driven by intermediate-mass protostars. We argue that highly collimated outflows are common to more massive protostars, and that they suggest the outflow physics inferred for low-mass stars formation scales up to at least ˜8 M⊙.

  8. Circumstellar dust: From protostars to planetary systems

    NASA Astrophysics Data System (ADS)

    Jayawardhana, Ray

    2000-11-01

    A combination of theoretical work and observational discoveries over the past three decades has led to significant advances in our understanding of the star and planet formation process. However, many important questions remain to be addressed, especially regarding the earliest phases of protostellar collapse and the transformation of circumstellar disks into planetary systems. In this thesis, I have undertaken a theoretical study of ``Class 0'' protostars and an observational investigation of the evolution of protoplanetary disks, diversity of planetary debris systems, and the kinship between dusty remnants and planets, using a new generation of infrared and sub- millimeter instruments. I present radiative transfer calculations of infalling envelopes surrounding Class 0 sources, compare them to the observed spectral energy distributions and radial intensity profiles, and derive mass infall rates. The rapid infall, probably inevitable given their dense environments, and the relatively flat inferred density distribution, perhaps due to contributions from external cloud material, lead us to suggest that many Class 0 sources could be the protostars of dense regions. It has been suggested that circumstellar disks evolve from massive, optically thick, actively accreting structures to low-mass, optically thin, passive remnants in about 10 Myr. That transition may mark the assembly of grains into planetesimals, or clearing of the disk by planets. I present mid infrared observation of the TW Hydrate Association, a recently identified nearby group of 10-Myr-old stars. The results suggest rapid evolution of inner disks as does our discovery of a spatially- resolved disk with a central cavity around the young A star HR 4796A. I also present the results of mid-infrared imaging of 11 other Vega-like stars, derive global properties of the dust disks, place constraints on their sizes, and discuss several interesting cases in detail. Finally, I report the detection of dust

  9. Tracing the origin of warm water emission through the stages of low-mass star formation

    NASA Astrophysics Data System (ADS)

    Vilhelm Persson, Magnus; Jorgensen, Jes K.; Coutens, Audrey; van Dishoeck, Ewine

    2015-08-01

    Water is a crucial molecule in the physics and chemistry of star- and planet formation, but its evolution from cold cores to disks is still poorly constrained. The gas-phase abundance of water varies between cold and warm regions up to a factor of 105 and this abundance variation makes water an excellent diagnostic of the physical structure in these sources.The origin of the warm water emission in deeply-embedded low-mass protostars is still debated, however. Current options include the innermost envelope (‘hot corino’), heated by the luminosity from the central protostar; a young disk heated by shocks related to ongoing accretion or the warm disk surface layers heated radiatively by the young star. Determining the location and kinematics of the warm water is important because it provides insights into whether water, and the locked up complex organics, actually moves from the outer envelope into the disk, and if so, whether it enters the disk mostly as gas or ice. Evolutionary models suggest that water and complex species enter the disk mostly as ice but this is so far unconfirmed observationally.Thus, in our collaboration we are undertaking a study of warm water in low-mass protostars. So far we have obtained interferometric maps of several isotopologues of water toward four deeply-embedded (i.e. Class 0) low-mass protostars with PdBI and ALMA. The detected water emission is compact toward the Class 0 sources, and a significant source of uncertainty in determining the abundances is the poorly constrained physical structure in the inner regions. Thus we try to constrain this physical structure by fitting simple disk models to the dust continuum visibilities that are left after subtracting a model of the spherical envelope. Furthermore we estimate upper limits to the warm water content toward the Class I protostars TMC-1A and L1527 from observations with PdBI.In this talk I will summarize our ongoing work in tracing the warm water emission through the various

  10. High Resolution Near-IR Spectroscopy of Protostars With Large Telescopes

    NASA Technical Reports Server (NTRS)

    Greene, Tom; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    It is now possible to measure absorption spectra of Class I protostars using D greater than or = 8m telescopes equipped with sensitive cryogenic IR spectrographs. Our latest high-resolution (R approx. 20,000) Keck data reveal that Class I protostars are indeed low-mass stars with dwarf-like features. However, they differ from T Tauri stars in that Class I protostars have much higher IR veilings (tau(sub k) greater than or = 1 - 3+) and they are rotating quickly, v sin i greater than 20 km/s. Interestingly, the vast majority of protostellar absorption spectra show stellar - not disk - absorption features. A preliminary H-R diagram suggests that protostellar photospheres may have different physical structures than T Tauri stars, perhaps due to their higher accretion rates.

  11. CARBON CHAINS AND METHANOL TOWARD EMBEDDED PROTOSTARS

    SciTech Connect

    Graninger, Dawn M.; Wilkins, Olivia H.; Öberg, Karin I.

    2016-03-10

    Large interstellar organic molecules are potential precursors of prebiotic molecules. Their formation pathways and chemical relationships with one another and simpler molecules are therefore of great interest. In this paper we address the relationships between two classes of large organic molecules, carbon chains and saturated complex organic molecules at the early stages of star formation through observations of C{sub 4}H and CH{sub 3}OH. We surveyed these molecules with the IRAM 30 m telescope toward 16 deeply embedded low-mass protostars selected from the Spitzer c2d ice survey. We find that CH{sub 3}OH and C{sub 4}H are positively correlated, indicating that these two classes of molecules can coexist during the embedded protostellar stage. The C{sub 4}H/CH{sub 3}OH gas abundance ratio tentatively correlates with the CH{sub 4}/CH{sub 3}OH ice abundance ratio in the same lines of sight. This relationship supports a scenario where carbon chain formation in protostellar envelopes begins with CH{sub 4} ice desorption.

  12. [Fe II] Emission Tracing Massive, Irradiated Jets from Intermediate-Mass Protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2013-07-01

    We present new spectroscopy and HST and ground-based AO imaging of five protostellar jets in the Carina nebula. Near-IR [Fe II] emission traces dense gas in the jet that is self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in Halpha emission from these jets, leading to densities and mass-loss rate estimates an order of magnitude higher than those derived from the Halpha emission measure. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (~2-8 Msun) protostars. For two of the sources, mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars, while the other two driving sources are more deeply embedded and require imaging at longer wavelengths with high spatial resolution to confirm their luminosity. Tangential velocities from new proper motion measurements exceed velocities typical for lower-luminosity sources (100-200 km/s). In addition, these outflows are highly collimated, with opening angles of only a few degrees, similar to low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the jets in Carina constitute a new view of collimated jets from intermediate-mass protostars that exists in a feedback dominated environment, and offer strong additional evidence that stars up to ~8 Msun form by the same accretion mechanisms as low-mass stars.

  13. No high-mass protostars in the silhouette young stellar object M17-SO1.

    PubMed

    Sako, Shigeyuki; Yamashita, Takuya; Kataza, Hirokazu; Miyata, Takashi; Okamoto, Yoshiko K; Honda, Mitsuhiko; Fujiyoshi, Takuya; Terada, Hiroshi; Kamazaki, Takeshi; Jiang, Zhibo; Hanawa, Tomoyuki; Onaka, Takashi

    2005-04-21

    The birth of very massive stars is not well understood, in contrast to the formation process of low-mass stars like our Sun. It is not even clear that massive stars can form as single entities; rather, they might form through the mergers of smaller ones born in tight groups. The recent claim of the discovery of a massive protostar in M17 (a nearby giant ionized region) forming through the same mechanism as low-mass stars has therefore generated considerable interest. Here we show that this protostar has an intermediate mass of only 2.5 to 8 solar masses (M(o), contrary to the earlier claim of 20M(o) (ref. 8). The surrounding circumstellar envelope contains only 0.09M(o) and a much more extended local molecular cloud has 4-9M(o).

  14. Monitoring the Far Infrared Variability of Deeply Embedded Protostars with SOFIA/HAWC

    NASA Astrophysics Data System (ADS)

    Johnstone, Doug

    2015-10-01

    Low-mass stars form via gravitational collapse of molecular cloud cores. The evolution of the mass accretion onto a forming protostar depends on the rate at which the interior of the core collapses, the significance of a circumstellar disk as a temporary mass reservoir, and the physics of how the gas is transported through the disk and accretes onto the central star. Despite a clear requirement for time dependency in the accretion rate onto deeply embedded protostars and a large number of theoretical mechanisms for powering variability, our understanding of both the timescale and amplitude of variability is almost entirely unconstrained. The bolometric luminosity of deeply embedded protostars is a direct proxy for the accretion luminosity, modified only by the addition of the stellar luminosity itself. For deeply embedded protostars, the spectral energy distribution peaks in the far infrared, near 100 microns, making this an ideal wavelength for long-term monitoring of accretion variability. We propose to use SOFIA/HAWC at 89 and 154 microns to monitor three star-forming fields (Cepheus, Perseus, and Serpens) as part of a long-term campaign dedicated to uncovering the observational signature of episodic accretion. These observations will aid in our understanding of how stars accumulate their final mass and are neceassry for discriminating between the various theoretical models of episodic accretion onto deeply embedded protostars.

  15. Powerful jets driven by intermediate-mass protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, N.

    2014-01-01

    The Carina nebula hosts the largest known population of powerful HH jets driven by intermediate-mass stars in a single region. These jets are externally irradiated by dozens of O-type stars in Carina that illuminate unshocked material in the jet, allowing for a more complete census of the mass-loss. Despite the strong incident ionizing radiation, portions of these jets remain neutral. Near-IR [Fe II] images reveal dense, neutral gas that was not seen in previous studies of Hα emission. We show that near-IR [Fe II] emitting gas must be self-shielded from Lyman continuum photons, regardless of its excitation mechanism (shocks, FUV radiation, or both). High densities are required for the survival of Fe+ amid the strong Lyman continuum luminosity from Tr14, raising estimates of the mass-loss rates by an order of magnitude. New proper motion measurements using Halpha images with a ~4.25 year baseline reveal tangential velocities of >200 km/s, in some cases exceeding velocities typical for jets from low-mass stars. In addition, these outflows are highly collimated, with opening angles of only a few degrees, similar to low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the irradiated jets in Carina constitute a new view of jets from intermediate-mass protostars that demonstrate that they are as collimated as their low-mass counterparts, but support higher densities and velocities, leading to higher mass-loss rates. This scaling of phenomena seen in low-mass star formation offers strong additional evidence that stars up to ~8 Msun form by the same accretion mechanism as low-mass stars.

  16. Constraining the Abundances of Complex Organics in the Inner Regions of Solar-type Protostars

    NASA Astrophysics Data System (ADS)

    Taquet, Vianney; López-Sepulcre, Ana; Ceccarelli, Cecilia; Neri, Roberto; Kahane, Claudine; Charnley, Steven B.

    2015-05-01

    The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected toward low-mass protostars, tend to be underpredicted by astrochemical models. This discrepancy might come from the large beam of the single-dish telescopes, encompassing several components of the studied protostar, commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol and several COMs toward the two low-mass protostars NGC 1333-IRAS 2A and -IRAS 4A with the Plateau de Bure interferometer at an angular resolution of 2″, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide toward low-mass protostars other than IRAS 16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowed us to accurately derive the source size of their emission and the COM column densities. The COM abundances with respect to methanol derived toward IRAS 2A and IRAS 4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COM abundance ratios do not vary significantly with the protostellar luminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-mass hot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methyl ether, suggesting that our understanding of their formation remains incomplete.

  17. CONSTRAINING THE ABUNDANCES OF COMPLEX ORGANICS IN THE INNER REGIONS OF SOLAR-TYPE PROTOSTARS

    SciTech Connect

    Taquet, Vianney; Charnley, Steven B.; López-Sepulcre, Ana; Ceccarelli, Cecilia; Kahane, Claudine; Neri, Roberto

    2015-05-10

    The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected toward low-mass protostars, tend to be underpredicted by astrochemical models. This discrepancy might come from the large beam of the single-dish telescopes, encompassing several components of the studied protostar, commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol and several COMs toward the two low-mass protostars NGC 1333-IRAS 2A and -IRAS 4A with the Plateau de Bure interferometer at an angular resolution of 2″, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide toward low-mass protostars other than IRAS 16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowed us to accurately derive the source size of their emission and the COM column densities. The COM abundances with respect to methanol derived toward IRAS 2A and IRAS 4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COM abundance ratios do not vary significantly with the protostellar luminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-mass hot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methyl ether, suggesting that our understanding of their formation remains incomplete.

  18. Chemistry in low-mass protostellar and protoplanetary regions

    PubMed Central

    van Dishoeck, Ewine F.

    2006-01-01

    When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are formed. Instrumentation to probe the chemistry in low-mass star-forming regions has only recently become available. The results of a systematic program to study the abundances in solar-mass protostellar and protoplanetary regions are presented. Surveys at submillimeter and infrared wavelengths reveal a rich chemistry, including simple and complex (organic) gases, ices, polycyclic aromatic hydrocarbons, and silicates. Each of these species traces different aspects of the physical and chemical state of the objects as they evolve from deeply embedded protostars to pre-main sequence stars with planet-forming disks. Quantitative information on temperatures, densities, and abundances is obtained through molecular excitation and radiative transfer models as well as from analysis of solid-state line profiles. The chemical characteristics are dominated by freeze-out in the coldest regions and ice evaporation in the warmer zones. In the surface layers of disks, UV radiation controls the chemistry. The importance of complementary laboratory experiments and calculations to obtain basic molecular data is emphasized. PMID:16894165

  19. Mapping Collapsing Cores in Scattered Light: HST NICMOS+WFC3 Imaging of Orion Protostars

    NASA Astrophysics Data System (ADS)

    Booker, Joseph J.; Megeath, Thomas

    2014-07-01

    A long standing question in the study of protostellar collapse is what halts the infall of a core onto a central protostar. Is the core eventually exhausted by infall, or does feedback from accretion-driven outflows disperse the core? Perhaps the best tracer of the impact of the outflow on the cores are the observed cavities carved by the outflows. We present a systematic study of near-infrared HST NICMOS+WFC3 1.6 micron images, mapping light scattered by dust grains in collapsing cores around low mass protostars with 80 AU resolution. These images are a component of HOPS, the Herschel Orion Protostar Survey, a multi-observatory survey designed to obtain 1-870 micron photometry, spectroscopy and imaging of a large sample of protostars in the Orion molecular clouds. Orion is home to half of the known protostars within 500 parsecs and is a largely unexplored ground for scattered-light studies of protostellar cores and disks. With 304 targets from the HOPS program imaged by the HST, we obtained a large sample of sources with resolved scattered light nebulae. The high spatial resolution allows us to determine properties of the protostars and collapsing cores that are not well constrained by the 1-870 micron spectral energy distributions. In particular, we map the profile of the outflow cavities for 25 sources by applying a variation of traditional edge detection techniques to the scattered light images and to radiative transfer models with known cavity geometries. From this, we estimate the fractional volumes of the collapsing cores dispersed by the outflows.

  20. Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin; Charnley, Steven; Buckle, Jane; Wash, Catherine; Millar, Tom

    2011-01-01

    From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed.

  1. The 0.8 mm Spectral Line Survey toward Low-Mass Protostellar Cores with ASTE

    NASA Astrophysics Data System (ADS)

    Watanabe, Y.; Sakai, N.; Lindberg, J.; Jørgensen, J.; Bisschop, S.; Yamamoto, S.

    2013-10-01

    We have conducted spectral line surveys in the 345 GHz band with Atacama Submillimeter Telescope Experiment (ASTE) 10 m dish toward two low mass class 0 protostars R CrA IRS7B and Serpens SMM4. For R CrA IRS7B, 16 molecular species and 16 isotopologues are identified. Strong emission of CN and CCH is observed, whereas complex organic molecules and long carbon-chain molecules are not detected. This result indicates that the hot corino activity as well as the WCCC activity is weak in R CrA IRS7B. Lindberg & Jørgensen (2012) suggested that UV radiation from the Herbig Be star R CrA significantly affects the chemical composition in R CrA IRS7B. Our results also support their conclusion. For Serpens SMM4, we identified 12 normal molecular species and 8 isotopologues. The chemical composition in Serpens SMM4 is similar to that found in hot corinos, although sulfur bearing species seem slightly deficient. These results illustrates the further chemical diversity in low-mass protostars.

  2. Characterizing the small scale structures in the earliest stages of low-mass star formation

    NASA Astrophysics Data System (ADS)

    Vilhelm Persson, Magnus; van Dishoeck, Ewine; Tobin, John; Harsono, Daniel; Jørgensen, Jes K.

    2015-08-01

    In deeply-embedded low-mass protostars, the density and temperature distribution in the inner few hundred AU’s are poorly constrained. In sources where the envelope is less massive, i.e. the Class I stage, disks with Keplerian rotation have been inferred using C18O lines. However, constraining the various disk characteristics turns out to be difficult even in this case. Continuum and molecular line observations of optically thin tracers at very high sensitivity and resolution are needed to constrain the density, temperature and kinematics. Ultimately the assumed structure affects the determination of molecular abundances.We are attempting to model high-resolution dust continuum radio-interferometric observations of a few deeply-embedded low-mass protostars with a power-law disk model embedded in a spherical envelope.We model the interferometric visibilities taken with either the Plateau de Bure Interferometer or the ALMA telescope, probing scales down to a few tens of AU in some cases. Given the assumptions, the study shows disk sizes in the deeply-embedded phase that could be slightly larger than typical found in the more evolved Class I sources. The fitting also highlights that models for the physical structure of the inner envelope, on 500-2000 AU scales, needs to be improved. With future high sensitivity observations, we could potentially also be able to constrain any vertical density and temperature structure. In this poster I will present the

  3. Tracing Massive Protostellar Jets from Intermediate-Mass Protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, A.

    2014-09-01

    We present new spectroscopy and imaging of four protostellar jets in the Carina nebula. Near-IR [Fe II] emission traces dense gas in the jet that is self-shielded from Lyman continuum photons from nearby O-type stars. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in the Halpha emission from these jets, leading to densities and mass-loss rate estimates an order of magnitude larger than those derived from the Halpha emission measure. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (around 2 - 8 solar masses) protostars. Velocities from new proper motion and spectroscopic measurements fall among the velocities typically measured in lower-luminosity sources (100 - 200 km/s). We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the jets in Carina constitute a new view of collimated jets from intermediate-mass protostars that exist in a feedback-dominated environment, and offer strong additional evidence that stars up to 8 solar masses form by the same accretion mechanisms as low-mass stars.

  4. Protostars and Stars in the Coronet Cluster: Age, Evolution, and Cluster Structure

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, Aurora; Henning, Thomas; Kainulainen, Jouni; Roccatagliata, Veronica

    2011-08-01

    We present new optical spectroscopy with the FLAMES spectrograph at the Very Large Telescope (VLT), near-IR imaging with VLT/HAWK-I, and 870 μm mapping with APEX/LABOCA of the Coronet cluster. The optical data allow us to estimate spectral types, extinction, and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in an H-R diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably ~0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50%-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks. Based on observations collected at the European Southern Observatory, Paranal, Chile (Proposal IDs: 081.C-0204(A), 083.C-0079(A), and 083.C-0079(B)).

  5. Kinematics of powerful jets from intermediate-mass protostars in the Carina nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2014-12-01

    We present measurements of proper motions and radial velocities of four powerful Herbig-Haro (HH) jets in the Carina nebula: HH 666, HH 901, HH 902, and HH 1066. Two epochs of Hubble Space Telescope imaging separated by a time baseline of ˜4.4 yr provide proper motions that allow us to measure the transverse velocities of the jets, while ground-based spectra sample their Doppler velocities. Together these yield full three-dimensional space velocities. Aside from HH 666, their identification as outflows was previously inferred only from morphology in images. Proper motions now show decisively that these objects are indeed jets, and confirm that the intermediate-mass protostars identified as the candidate driving sources for HH 666 and HH 1066 are indeed the origin of these outflows. The appearance of two new knots in the HH 1066 jet suggests recent (˜35 yr) changes in the accretion rate, underscoring the variable nature of accretion and outflow in the formation of intermediate-mass stars. In fact, kinematics and mass-ejection histories for all the jets suggest highly episodic mass loss, and point towards pronounced accretion fluctuations. Overall, we measure velocities similar to those found for low-mass protostars. However, the HH jets in Carina have higher densities and are more massive than their low-mass counterparts. Coarse estimates suggest that the heavy jets of intermediate-mass protostars can compete with or even exceed inject ˜10 or more times the cumulative momentum injection of lower mass protostars.

  6. LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Kryukova, E.; Megeath, S. T.; Allen, T. S.; Gutermuth, R. A.; Pipher, J.; Allen, L. E.; Myers, P. C.; Muzerolle, J.

    2012-08-15

    We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 {mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 {mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L{sub Sun} and show a tail extending toward luminosities above 100 L{sub Sun }. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L{sub Sun }. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity

  7. Extremely Low Mass: The Circumstellar Envelope of a Potential Proto-Brown Dwarf

    NASA Technical Reports Server (NTRS)

    Wiseman, Jennifer

    2011-01-01

    What is the environment for planet formation around extremely low mass stars? Is the environment around brown dwarfs and extremely low mass stars conducive and sufficiently massive for planet production? The determining conditions may be set very early in the process of the host object's formation. IRAS 16253-2429, the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated, very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet, indicating environmental disruption. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source to be one of the youngest and lowest mass sources in formation yet known, and discuss the ramifications for planet formation potential in this extremely low mass system.

  8. THIRTY NEW LOW-MASS SPECTROSCOPIC BINARIES

    SciTech Connect

    Shkolnik, Evgenya L.; Hebb, Leslie; Cameron, Andrew C.; Liu, Michael C.; Neill Reid, I. E-mail: Andrew.Cameron@st-and.ac.u E-mail: mliu@ifa.hawaii.ed

    2010-06-20

    As part of our search for young M dwarfs within 25 pc, we acquired high-resolution spectra of 185 low-mass stars compiled by the NStars project that have strong X-ray emission. By cross-correlating these spectra with radial velocity standard stars, we are sensitive to finding multi-lined spectroscopic binaries. We find a low-mass spectroscopic binary fraction of 16% consisting of 27 SB2s, 2 SB3s, and 1 SB4, increasing the number of known low-mass spectroscopic binaries (SBs) by 50% and proving that strong X-ray emission is an extremely efficient way to find M-dwarf SBs. WASP photometry of 23 of these systems revealed two low-mass eclipsing binaries (EBs), bringing the count of known M-dwarf EBs to 15. BD-22 5866, the ESB4, was fully described in 2008 by Shkolnik et al. and CCDM J04404+3127 B consists of two mid-M stars orbiting each other every 2.048 days. WASP also provided rotation periods for 12 systems, and in the cases where the synchronization time scales are short, we used P{sub rot} to determine the true orbital parameters. For those with no P{sub rot}, we used differential radial velocities to set upper limits on orbital periods and semimajor axes. More than half of our sample has near-equal-mass components (q > 0.8). This is expected since our sample is biased toward tight orbits where saturated X-ray emission is due to tidal spin-up rather than stellar youth. Increasing the samples of M-dwarf SBs and EBs is extremely valuable in setting constraints on current theories of stellar multiplicity and evolution scenarios for low-mass multiple systems.

  9. Calorimetry of low mass Pu239 items

    SciTech Connect

    Cremers, Teresa L; Sampson, Thomas E

    2010-01-01

    Calorimetric assay has the reputation of providing the highest precision and accuracy of all nondestructive assay measurements. Unfortunately, non-destructive assay practitioners and measurement consumers often extend, inappropriately, the high precision and accuracy of calorimetric assay to very low mass items. One purpose of this document is to present more realistic expectations for the random uncertainties associated with calorimetric assay for weapons grade plutonium items with masses of 200 grams or less.

  10. The origin of low mass stars.

    PubMed

    Wilking, B A

    1997-06-01

    Recent evidence indicates that most low mass stars in the Galaxy (< 5 M [symbol: see text]) form alongside massive stars in clusters embedded in giant molecular clouds. Once their parental gas is removed, the fate of these clusters is to disperse and blend into the field population of the galactic disk. The distribution of stellar masses in the solar neighborhood, called the Initial Mass Function, is discussed in the context of the origin of low mass stars. Arguments based on the production rate of field stars are presented that point to giant molecular clouds as the primary birth sites for low mass stars. The role of observations of molecular clouds at millimeter and infrared wavelengths in confirming this picture is reviewed. Millimeter-wave observations have revealed that molecular clouds consist of low-density gas interspersed with high-density cores. Near-infrared images of these clouds indicate that stars form preferentially in these cores, with the number of young stars roughly scaling with the mass of the core. Molecular-line and near-infrared observations which characterize star formation in the nearest giant molecular cloud complex in Orion are presented. The implications for the Sun forming in a cluster environment are briefly discussed.

  11. Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.; Lada, Charles J.; DeVincenzi, Donald L. (Technical Monitor)

    2002-01-01

    veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

  12. Unraveling the Evolution of Protostars in Diverse Environments: The Herschel Orion Protostar Survey

    NASA Astrophysics Data System (ADS)

    Megeath, S. Thomas; the Herschel Orion Protostar Survey Team

    2014-01-01

    The Herschel Orion Protostar Survey (HOPS), a 200 hour PACS imaging and spectroscopy OTKP, is the cornerstone of a large multi-observatory campaign combining Herschel data with observations from Spitzer,Hubble, APEX, and other facilities. HOPS has produced well sampled 1-870 micron SEDs of over 300 protostars in the Orion molecular clouds, the most extensive such survey of a single cloud complex to date, and has obtained PACS spectra of 36 protostars to observe line emission from CO, OH, and H2O. We will present the major HOPS discoveries that demonstrate Herschel's contributions to an emerging picture of protostellar evolution within the diverse environments of the Orion A & B molecular clouds. Among these, the HOPS team has discovered protostars undetected by Spitzer that appear to be the youngest protostars in Orion (Stutz et al. 2013). We have found that the luminosities of high-J CO lines are correlated with protostellar luminosities, but the excitation temperatures are not, indicating that these lines form in high-temperature gas within outflows (Manoj et al. 2013). We have also constructed and modeled the first 1-70 um SED of a protostellar FU Ori object before and after its outburst, finding an atypically low post-outburst luminosity (Fischer et al. 2012). Finally, we have identified systematic variations in the spacing and luminosity of protostars between the different environments found in Orion (Megeath, Stanke, in prep.). More generally, the HOPS team is now determining the fundamental protostellar properties (envelope mass and density, system luminosity, and outflow cavity geometry) of the 300 Orion protostars by a comparison of the SEDs to radiative transfer models. We will summarize the prospects of using these fundamental properties to construct a detailed sequence for the physical evolution of protostars as they dissipate their envelopes, accounting for the influence of the diverse environments found within Orion.

  13. OBSERVING SIMULATED PROTOSTARS WITH OUTFLOWS: HOW ACCURATE ARE PROTOSTELLAR PROPERTIES INFERRED FROM SEDs?

    SciTech Connect

    Offner, Stella S. R.; Robitaille, Thomas P.; Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.

    2012-07-10

    The properties of unresolved protostars and their local environment are frequently inferred from spectral energy distributions (SEDs) using radiative transfer modeling. In this paper, we use synthetic observations of realistic star formation simulations to evaluate the accuracy of properties inferred from fitting model SEDs to observations. We use ORION, an adaptive mesh refinement (AMR) three-dimensional gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud including the effects of protostellar outflows. To obtain the dust temperature distribution and SEDs of the forming protostars, we post-process the simulations using HYPERION, a state-of-the-art Monte Carlo radiative transfer code. We find that the ORION and HYPERION dust temperatures typically agree within a factor of two. We compare synthetic SEDs of embedded protostars for a range of evolutionary times, simulation resolutions, aperture sizes, and viewing angles. We demonstrate that complex, asymmetric gas morphology leads to a variety of classifications for individual objects as a function of viewing angle. We derive best-fit source parameters for each SED through comparison with a pre-computed grid of radiative transfer models. While the SED models correctly identify the evolutionary stage of the synthetic sources as embedded protostars, we show that the disk and stellar parameters can be very discrepant from the simulated values, which is expected since the disk and central source are obscured by the protostellar envelope. Parameters such as the stellar accretion rate, stellar mass, and disk mass show better agreement, but can still deviate significantly, and the agreement may in some cases be artificially good due to the limited range of parameters in the set of model SEDs. Lack of correlation between the model and simulation properties in many individual instances cautions against overinterpreting properties inferred from SEDs for unresolved protostellar

  14. Protostars at Low Extinction in Orion A

    NASA Astrophysics Data System (ADS)

    Lewis, John Arban; Lada, Charles J.

    2016-07-01

    In the list of young stellar objects (YSOs) compiled by Megeath et al. for the Orion A molecular cloud, only 44 out of 1208 sources found projected onto low extinction ({A}{{K}}\\lt 0.8 mag) gas are identified as protostars. These objects are puzzling because protostars are not typically expected to be associated with extended low extinction material. Here, we use high resolution extinction maps generated from Herschel data, optical/infrared and Spitzer Space Telescope photometry and spectroscopy of the low extinction protostellar candidate sources to determine if they are likely true protostellar sources or contaminants. Out of 44 candidate objects, we determine that 10 sources are likely protostars, with the rest being more evolved YSOs (18), galaxies (4), false detections of nebulosity and cloud edges (9), or real sources for which more data are required to ascertain their nature (3). We find none of the confirmed protostars to be associated with recognizable dense cores and we briefly discuss possible origins for these orphaned objects.

  15. A disk of dust and molecular gas around a high-mass protostar.

    PubMed

    Patel, Nimesh A; Curiel, Salvador; Sridharan, T K; Zhang, Qizhou; Hunter, Todd R; Ho, Paul T P; Torrelles, José M; Moran, James M; Gómez, José F; Anglada, Guillem

    2005-09-01

    The processes leading to the birth of low-mass stars such as our Sun have been well studied, but the formation of high-mass (over eight times the Sun's mass, M(o)) stars remains poorly understood. Recent studies suggest that high-mass stars may form through accretion of material from a circumstellar disk, in essentially the same way as low-mass stars form, rather than through the merging of several low-mass stars. There is as yet, however, no conclusive evidence. Here we report the presence of a flattened disk-like structure around a massive 15M(o) protostar in the Cepheus A region, based on observations of continuum emission from the dust and line emission from the molecular gas. The disk has a radius of about 330 astronomical units (Au) and a mass of 1 to 8 M(o). It is oriented perpendicular to, and spatially coincident with, the central embedded powerful bipolar radio jet, just as is the case with low-mass stars, from which we conclude that high-mass stars can form through accretion.

  16. Multi-Wavelength Views of Protostars in IC 1396

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site] Click on individual images below for larger view

    [figure removed for brevity, see original site]

    [figure removed for brevity, see original site]

    [figure removed for brevity, see original site]

    NASA's Spitzer Space Telescope has captured a glowing stellar nursery within a dark globule that is opaque at visible light. These new images pierce through the obscuration to reveal the birth of new protostars, or embryonic stars, and young stars never before seen.

    The Elephant's Trunk Nebula is an elongated dark globule within the emission nebula IC 1396 in the constellation of Cepheus. Located at a distance of 2,450 light-years, the globule is a condensation of dense gas that is barely surviving the strong ionizing radiation from a nearby massive star. The globule is being compressed by the surrounding ionized gas.

    The large composite image above is a product of combining data from the observatory's multiband imaging photometer and the infrared array camera. The thermal emission at 24 microns measured by the photometer (red) is combined with near-infrared emission from the camera at 3.6/4.5 microns (blue) and from 5.8/8.0 microns (green). The colors of the diffuse emission and filaments vary, and are a combination of molecular hydrogen (which tends to be green) and polycyclic aromatic hydrocarbon (brown) emissions.

    Within the globule, a half dozen newly discovered protostars, or embryonic stars, are easily discernible as the bright red-tinted objects, mostly along the southern rim of the globule. These were previously undetected at visible wavelengths due to obscuration by the thick cloud ('globule body') and by dust surrounding the newly forming stars. The newborn stars form in the dense gas because of compression by the wind and radiation from a nearby massive star (located outside the field of view to the left). The winds from this unseen star are also responsible for producing the

  17. Magnetometer Searches for Ultra Low Mass Fields

    NASA Astrophysics Data System (ADS)

    Romalis, Michael

    2017-01-01

    New spin interactions arise in a variety of extensions to the Standard Model. Well-known spin-dependent effects, such as permanent electric dipole moments and violations of Lorentz and CPT symmetries, have been searched for in many experiments. The existence of low-mass axion-like particles would also generate spin-dependent effects that can be searched for in similar experiments, but often with unique signatures. Since particles with spin also have a magnetic moment, such experiments are automatically sensitive to ordinary magnetic fields and one of the challenges is to eliminate such effects, using for example, two different spin species in a co-magnetometer arrangement. I will describe several past and on-going experiments using co-magnetometers based on nuclear spin-polarized noble gases. These experiments are used to search for both axion-like dark matter and for axion-mediated forces that are independent of dark matter.

  18. Olivier Chesneau's Work on Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Lagadec, E.

    2015-12-01

    During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.

  19. CFFF low mass flow DCW generator operation

    NASA Astrophysics Data System (ADS)

    Lineberry, J. T.; Galanga, F. L.; Frazier, J. W.

    1986-01-01

    A summary of testing of the low mass flow diagonal conducting sidewall MHD generator in the CFFF is given. These summaries include details of the powered generator tests conducted during the 1985 LMF4 test series. A presentation of experimental generator electrical data collected during these tests is included. The quality of these data is discussed and a review of representative data presentations is made as a means of identifying phenomena associated with coal-fired MHD generators. Unique characteristics of coal slag effects upon electrical performance are seen in the voltage profiles and power characteristics for the generator. Fundamental theoretical analyses of the generator are used to qualify the levels of generator performance that were demonstrated during testing. These analyses are directed at isolating possible sources that have caused performance deficiencies and anomalies seen in the test data.

  20. Energetic processes revealed by spectrally resolved high-J CO lines in low-mass star-forming regions with Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Yıldız, U. A.; van Dishoeck, E. F.; Kristensen, L. E.; Visser, R.; Herczeg, G.; van Kempen, T. A.; Jørgensen, J. K.; Hogerheijde, M. R.; Wish Team

    2011-11-01

    Herschel-HIFI observations of high-J lines (up to Ju = 10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars in NGC 1333. The observations show several energetic components including shocked and quiescent gas. Radiative transfer models are used to quantify the C18O envelope abundance which require a jump in the abundance at an evaporation temperature, Tev ~ 25 K, providing new direct evidence of a CO ice evaporation zone around protostars. The abundance in the outermost part of the envelope, X0, is within the canonical value of 2 × 10-4; however the inner abundance, Xin, is found around a factor of 3-5 lower than X0.

  1. Evidence for Cluster to Cluster Variations in Low-mass Stellar Rotational Evolution

    NASA Astrophysics Data System (ADS)

    Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M.

    2016-12-01

    The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar-disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star-disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport. For slow rotators, we confirm the need for star-disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.

  2. Current Advances in the Computational Simulation of the Formation of Low-Mass Stars

    SciTech Connect

    Klein, R I; Inutsuka, S; Padoan, P; Tomisaka, K

    2005-10-24

    Developing a theory of low-mass star formation ({approx} 0.1 to 3 M{sub {circle_dot}}) remains one of the most elusive and important goals of theoretical astrophysics. The star-formation process is the outcome of the complex dynamics of interstellar gas involving non-linear interactions of turbulence, gravity, magnetic field and radiation. The evolution of protostellar condensations, from the moment they are assembled by turbulent flows to the time they reach stellar densities, spans an enormous range of scales, resulting in a major computational challenge for simulations. Since the previous Protostars and Planets conference, dramatic advances in the development of new numerical algorithmic techniques have been successfully implemented on large scale parallel supercomputers. Among such techniques, Adaptive Mesh Refinement and Smooth Particle Hydrodynamics have provided frameworks to simulate the process of low-mass star formation with a very large dynamic range. It is now feasible to explore the turbulent fragmentation of molecular clouds and the gravitational collapse of cores into stars self-consistently within the same calculation. The increased sophistication of these powerful methods comes with substantial caveats associated with the use of the techniques and the interpretation of the numerical results. In this review, we examine what has been accomplished in the field and present a critique of both numerical methods and scientific results. We stress that computational simulations should obey the available observational constraints and demonstrate numerical convergence. Failing this, results of large scale simulations do not advance our understanding of low-mass star formation.

  3. Protostar formation in the early universe.

    PubMed

    Yoshida, Naoki; Omukai, Kazuyuki; Hernquist, Lars

    2008-08-01

    The nature of the first generation of stars in the universe remains largely unknown. Observations imply the existence of massive primordial stars early in the history of the universe, and the standard theory for the growth of cosmic structure predicts that structures grow hierarchically through gravitational instability. We have developed an ab initio computer simulation of the formation of primordial stars that follows the relevant atomic and molecular processes in a primordial gas in an expanding universe. The results show that primeval density fluctuations left over from the Big Bang can drive the formation of a tiny protostar with a mass 1% that of the Sun. The protostar is a seed for the subsequent formation of a massive primordial star.

  4. X-ray flares in protostars

    NASA Astrophysics Data System (ADS)

    Hayashi, M. R.; Shibata, K.; Matsumoto, R.

    1995-12-01

    Origin of X-ray flares in protostars and the formation of magnetohydrodynamical jets are studied by numerically simulating the interaction between the disk material and the dipole magnetic field of the central protostar.At the initial state, we assume that a thin Keplerian disk is threaded by the dipole magnetic fields of the central star. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. As the twist accumulates, magnetic loops expand and finally approach to the open field configuration. In the presence of resistivity, magnetic reconnection takes place in the current sheet developed along the expanding magnetic loops. Outgoing magnetic island and 'post flare loops' are formed as a result of the reconnection.This process can be regarded as a bifurcation to the lower energy state triggered by continuous helicity injection (e.g., Kusano 1995). The time scale of this flare is the order of the rotation period of the disk. The released magnetic energy (typically 10(35) erg in protostars) goes into the thermal energy of the plasma in the flaring loop and the thermal and kinetic energies of the ejected plasmoids. The maximum speed of the streamer is the order of the Keplerian rotation speed around the inner edge of the disk. High energy particles created by the reconnection by bremsstrahlung emission at the footpoints of the flaring loop. The length of the flaring loop is several times larger than the radius of the central star. The magnetic reconnection accompanying this mechanism can explain hard X-ray flares in protostars observed by ASCA (Koyama et al. 1995).

  5. The feeding and feedback of massive protostars

    NASA Astrophysics Data System (ADS)

    Smith, Michael

    2013-07-01

    A model for massive stars is constructed by piecing together evolutionary algorithms for the protostellar structure, the environment, the inflow and the radiation feedback. The framework requires the accretion rate from the clump to be specified. We investigate constant, decelerating and accelerating accretion rate scenarios and consider both hot and cold accretion, identified with spherical free-fall and disk accretion, respectively. We find that accelerated accretion is not favoured on the basis of the often-used diagnostic diagram which correlates the bolometric luminosity and clump mass. Instead, source counts as a function of the bolometric temperature can distinguish the accretion mode. Specifically, accelerated accretion yields a relatively high number of lowtemperatureob jects. On this basis, we demonstrate that evolutionary tracks to fit Herschel Space Telescope data require the generated stars to be three to four times less massive than in previous interpretations. Neither spherical nor disk accretion can explain the high radio luminosities of many protostars. Nevertheless, we discover a solution in which the extreme ultraviolet flux needed to explain the radio emission is produced if the accretion flow is via free-fall on to hot spots covering less than 20% of the surface area. Moreover, the protostar must be compact, and so has formed through cold accretion. This suggest that massive stars form via gas accretion through disks which, in the phase before the star bloats, download their mass via magnetic flux tubes on to the protostar.

  6. 30 Doradus: The Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Zinnecker, H.; Brandl, B.; Brandner, W.; Moneti, A.; Hunter, D.

    We have obtained HST/NICMOS H-band images of the central 1'x1' field around the R136 starburst cluster in the 30 Doradus HII region, in an attempt to reveal the presence (or absence) of a low-mass stellar population (M < 1 Mo). We will discuss the fascinating prospect of 30 Dor/R136 being a proto-globular cluster and a template starburst unit. At the time of writing, we are still working to determine which method and photometry package is best suited to our 0.15" NICMOS images, which are characterised by extreme crowding in the cluster center and a peculiar and slightly undersampled NICMOS PSF. The main difficulty with the PSF is identifying the many "dots" that appear outside the Airy ring as PSF features and not as faint stars. Prelimininary analysis suggests that the H-band luminosity function rises at least until H = 20 (2 Mo). We have detected numerous stars with 20.0 < H < 22.5 (the latter corresponding to 0.4 Mo) beyond about 7" from the cluster centre, but we have not yet determined the completeness in that magnitude range, and we are not yet in a position to make a statement about the shape of the H-band luminosity function there. We have combined our infrared data with the optical WFPC2 images of Hunter et al. (1995) to produce a VIH 3-colour image of the central 30" x 30" area. The result clearly shows unexpected patches of extinction, with one patch only about 5" from the cluster core.

  7. Detection of glycolaldehyde toward the solar-type protostar NGC 1333 IRAS2A

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Persson, M. V.; Jørgensen, J. K.; Wampfler, S. F.; Lykke, J. M.

    2015-04-01

    Glycolaldehyde is a key molecule in the formation of biologically relevant molecules such as ribose. We report its detection with the Plateau de Bure interferometer toward the Class 0 young stellar object NGC 1333 IRAS2A, which is only the second solar-type protostar for which this prebiotic molecule is detected. Local thermodynamic equilibrium analyses of glycolaldehyde, ethylene glycol (the reduced alcohol of glycolaldehyde), and methyl formate (the most abundant isomer of glycolaldehyde) were carried out. The relative abundance of ethylene glycol to glycolaldehyde is found to be ~5 - higher than in the Class 0 source IRAS 16293-2422 (~1), but similar to the lower limits derived in comets (≥3-6). The different ethylene glycol-to-glycolaldehyde ratios in the two protostars might be related to different CH3OH:CO compositions of the icy grain mantles. In particular, a more efficient hydrogenation on the grains in NGC 1333 IRAS2A would favor the formation of both methanol and ethylene glycol. In conclusion, it is possible that like NGC 1333 IRAS2A, other low-mass protostars show high ethylene glycol-to-glycolaldehyde abundance ratios. The cometary ratios might consequently be inherited from earlier stages of star formation if the young Sun experienced conditions similar to NGC 1333 IRAS2A. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Figures 3-4 and Table 1 are available in electronic form at http://www.aanda.org

  8. THE LUMINOSITIES OF PROTOSTARS IN THE SPITZER c2d AND GOULD BELT LEGACY CLOUDS

    SciTech Connect

    Dunham, Michael M.; Arce, Hector G.; Allen, Lori E.; Evans II, Neal J.; Harvey, Paul M.; Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Chapman, Nicholas L.; Cieza, Lucas A.; Gutermuth, Robert A.; Hatchell, Jennifer; Huard, Tracy L.; Miller, Jennifer F.; Kirk, Jason M.; Merin, Bruno; Peterson, Dawn E.; Spezzi, Loredana

    2013-04-15

    Motivated by the long-standing 'luminosity problem' in low-mass star formation whereby protostars are underluminous compared to theoretical expectations, we identify 230 protostars in 18 molecular clouds observed by two Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions, calculate L{sub bol} for each source, and study the protostellar luminosity distribution. This distribution extends over three orders of magnitude, from 0.01 L{sub Sun} to 69 L{sub Sun }, and has a mean and median of 4.3 L{sub Sun} and 1.3 L{sub Sun }, respectively. The distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (L{sub bol} {approx}< 0.5 L{sub Sun }) Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infrared and submillimeter (70 {mu}m <{lambda} < 850 {mu}m) and have L{sub bol} underestimated by factors of 2.5 on average, and up to factors of 8-10 in extreme cases. Correcting these underestimates for each source individually once additional data becomes available will likely increase both the mean and median of the sample by 35%-40%. We discuss and compare our results to several recent theoretical studies of protostellar luminosities and show that our new results do not invalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausible accretion scenario that can match observations, future attention is clearly needed. The better statistics provided by our increased data set should aid such future work.

  9. Microwave Spectroscopy of Complex Molecules Around the Young Protostar Chamaeleon MMS1

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin A.; Charnley, Steven B.; Wirstrom, Eva S.; Smith, Robert G.

    2011-01-01

    Observations are presented of emission lines from organic molecules at frequencies 30-100 GHz in the vicinity of the extremely young, chemically rich, very low-luminosity protostar and candidate first hydrostatic core Chamaeleon MMS1. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon-chains and methanol. Emission from the carbon-chain-bearing species peaks very near to the protostar; methanol peaks about 0.1 pc further away. The mean molecular hydrogen number density is calculated to be 10(exp 6) per cc. and the gas kinetic temperature is in the range 4-7 K. The abundances of long carbon chains (including C6H and HC7N) are very large -- similar to those found in the most carbon-chain-rich regions of the Galaxy, and indicative of a non-equilibrium carbon chemistry. The observed methanol and acetaldehyde abundances indicate active grain-surface chemistry and desorption processes. The carbon-chain anions C4H- and C6H- were not detected and the upper limit on the anion-to-neutral ratio for C4H- is less than 0.02% and for C6H-, less than 10%. These values are consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC3N and c-C3H2 were detected, with fractionation ratios of about 4%, and 22%, respectively. A low c-C3H2 ortho-to-para ratio was measured, which is consistent with a molecular hydrogen ortho-to-para ratio of close to zero and implies a relatively young chemical age (less than about 10(exp 5) yr) for the matter surrounding Cha-MMS1. These observations show that a high level of chemical complexity can be present in star-forming gas.

  10. Modeling Protostar Envelopes and Disks Seen With ALMA

    NASA Astrophysics Data System (ADS)

    Terebey, Susan; Flores-Rivera, Lizxandra; Willacy, Karen

    2017-01-01

    Thermal continuum emission from protostars comes from both the envelope and circumstellar disk. The dust emits on a variety of spatial scales, ranging from sub-arcseconds for disks to roughly 10 arcseconds for envelopes for nearby protostars. We present models of what ALMA should detect that incorporate a self-consistent collapse solution, radiative transfer, and realistic dust properties.

  11. Organic Chemistry of Low-Mass Star-Forming Cores. I. 7 mm Spectroscopy of Chamaeleon MMSl

    NASA Technical Reports Server (NTRS)

    Cordiner, Martn A.; Charnley, Steven B.; Wirtstroem, Eva S.; Smith, Robert G.

    2012-01-01

    Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 10(exp 6) / cubic cm and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a nonequilibrium carbon chemistry; C6H and HC7N column densities are 5.9(sup +2.9) (sub -1.3) x 10(exp 11) /cubic cm and 3.3 (sup +8.0)(sub -1.5) x 10(exp 12)/sq cm, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon chain anions C4H(-) and C6H(-), with anion-to-neutral ratios [C4H(-)]/[C4H] < 0.02% and [C6H(-l)]/[C6H] < 10%, consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC,3 and c-C3H2 were detected. The [DC3N]/[HC,N] ratio of approximately 4% is consistent with the value typically found in cold interstellar gas.

  12. Determining Protostar Masses: L1527 IRS in Taurus

    NASA Astrophysics Data System (ADS)

    Terebey, Susan; Isella, Andrea; De Vries, Christopher

    2013-07-01

    Protostar masses have been difficult to determine, in part due to the complex nature of protostar environments. We report on a pilot study to determine the mass of the L1527 protostar using CARMA interferometer data. The velocity channel maps are compared with a model that incorporates 1) LVG radiative transfer, 2) TSC collapse envelope and outflow cavity, and 3) a CARMA interferometer simulation. The models are able to reproduce observed C18O(2-1) channel maps quite well, and are sensitive to the gravity field of the infalling gas. The best-fit mass is 0.24 +/- 0.04 Mo for the L1527 protostar plus disk. The models indicate that line-width is a sensitive and robust indicator of mass. We conclude that this method of comparing millimeter interferometer data with infall models incorporating radiative transfer shows promise for determining a fundamental but poorly known quantity, the protostar mass.

  13. The formation of a massive protostar through the disk accretion of gas.

    PubMed

    Chini, Rolf; Hoffmeister, Vera; Kimeswenger, Stefan; Nielbock, Markus; Nürnberger, Dieter; Schmidtobreick, Linda; Sterzik, Michael

    2004-05-13

    The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars above ten solar masses through this mechanism, although some calculations have claimed that stars up to 40 solar masses can in principle be formed via accretion through a disk. Given this uncertainty and the fact that most massive stars are born in dense clusters, it was suggested that high-mass stars are the result of the runaway merging of intermediate-mass stars. Here we report observations that clearly show a massive star being born from a large rotating accretion disk. The protostar has already assembled about 20 solar masses, and the accretion process is still going on. The gas reservoir of the circumstellar disk contains at least 100 solar masses of additional gas, providing sufficient fuel for substantial further growth of the forming star.

  14. A substellar-mass protostar and its outflow of IRAS 15398–3359 revealed by subarcsecond-resolution observations of H{sub 2}CO and CCH

    SciTech Connect

    Oya, Yoko; Sakai, Nami; Watanabe, Yoshimasa; Yamamoto, Satoshi; Sakai, Takeshi; Hirota, Tomoya; Lindberg, Johan E.; Bisschop, Suzanne E.; Jørgensen, Jes K.; Van Dishoeck, Ewine F.

    2014-11-10

    Subarcsecond (0.''5) images of H{sub 2}CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398–3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about 20°, or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle and the mass of the protostar is estimated to be less than 0.09 M {sub ☉}. Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H{sub 2}CO emission associated with the protostar.

  15. A LOFAR Detection of the Low-mass Young Star T Tau at 149 MHz

    NASA Astrophysics Data System (ADS)

    Coughlan, Colm P.; Ainsworth, Rachael E.; Eislöffel, Jochen; Hoeft, Matthias; Drabent, Alexander; Scaife, Anna M. M.; Ray, Tom P.; Bell, Martin E.; Broderick, Jess W.; Corbel, Stéphane; Grießmeier, Jean-Mathias; van der Horst, Alexander J.; van Leeuwen, Joeri; Markoff, Sera; Pietka, Malgorzata; Stewart, Adam J.; Wijers, Ralph A. M. J.; Zarka, Philippe

    2017-01-01

    Radio observations of young stellar objects (YSOs) enable the study of ionized plasma outflows from young protostars via their free–free radiation. Previous studies of the low-mass young system T Tau have used radio observations to model the spectrum and estimate important physical properties of the associated ionized plasma (local electron density, ionized gas content, and emission measure). However, without an indication of the low-frequency turnover in the free–free spectrum, these properties remain difficult to constrain. This paper presents the detection of T Tau at 149 MHz with the Low Frequency Array (LOFAR)—the first time a YSO has been observed at such low frequencies. The recovered total flux indicates that the free–free spectrum may be turning over near 149 MHz. The spectral energy distribution is fitted and yields improved constraints on local electron density ((7.2+/- 2.1)× {10}3 cm‑3), ionized gas mass ((1.0+/- 1.8)× {10}-6 {M}ȯ ), and emission measure ((1.67+/- 0.14)× {10}5 pc cm‑6).

  16. Connecting diverse molecular cloud environments with nascent protostars in Orion

    NASA Astrophysics Data System (ADS)

    Stutz, Amelia M.; Megeath, S.; Fischer, W. J.; Ali, B.; Furlan, E.; Tobin, J. J.; Stanke, T.; Henning, T.; Krause, O.; Manoj, P.; Osorio, M.; Robitaille, T.; HOPS Team

    2014-01-01

    Understanding how the gas environment within molecular clouds influences the properties of protostars is a key step towards understanding the physical factors that control star formation. We report on an analysis of the connection between molecular cloud environment and protostellar properties using the Herschel Orion Protostar Survey (HOPS), a large multi-observatory survey of protostars in the Orion molecular clouds. HOPS has produced well sampled 1 um to 870 um SEDs of over 300 protostars in the Orion molecular clouds using images and spectra from 2MASS, Spitzer, Herschel and APEX. Furthermore, the combination of APEX 870 um continuum observations with the HOPS/PACS 160 um data over the same area allows for a determination of the temperatures and column densities in the often filamentary dense gas surrounding the Orion protostars. Based on these data, we link the protostellar properties with their environmental properties. Utilizing the diverse environments present within the Orion molecular clouds, we show how the luminosity and spacing of protostars in Orion depends on the local gas column density. Furthermore, we report an unusual concentration of the youngest known protostars (the Herschel identified PBRS, PACS Bright Red Sources) in the Orion B cloud, and we discuss possible reasons for this concentration.

  17. A new population of protostars discovered by Herschel

    NASA Astrophysics Data System (ADS)

    Stutz, A. M.; Tobin, J.; Fischer, W.; S. T. Megeath; Stanke, T.; Ali, B.; Henning, T.

    2012-03-01

    We present a newly discovered Herschel--detected class of very red protostars found in the Herschel Orion Protostar Survey (HOPS). In contrast to the known Orion protostars targeted with HOPS, the new sources are undetected or very faint in the Spitzer 24 μm imaging. A subset of these sources is redder than any of the known Orion Class 0 protostars, and appear similar in their 70 μm to 24 μm colors to the most extreme Class 0 objects known. These new Orion protostars are likely to be in a very early and short lived stage of protostellar evolution. As a sample of extremely red sources at a common distance, they represent an important new population of protostars. The majority of these reddest sources exhibit associated IRAC 4.5, and 5.8 μm extended emission that suggests the presence of an outflow, confirming their protostellar nature. In addition, many of these sources are located within classical filaments as traced by Spitzer absorption features and APEX 870 μm dust emission maps. Fits of the broad--band SEDs to radiative transfer models of protostars suggest that the extremely red 70 μm to 24 μm colors result from a combination of nearly edge--on viewing angles and high envelope infall rates. We analyze the properties of the filaments from which these sources form using sub--mm and IRAM 30 m N_2H^+ measurements. Finally, we present the initial results of a search for outflows using IRAM 30 m CO maps. As a population of cold protostars detected by Herschel but not Spitzer, the PBRS extend the Spitzer--identified sample to earlier stages of envelope evolution, allowing the most complete census yet of the Orion protostellar population.

  18. Untangling the protostars and jets in HH 900

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2013-02-01

    We propose to obtain high resolution (comparable to HST), narrowband [Fe II] images with GSAOI to disentangle the protostars and jets in HH 900. Recent H-alpha imaging of HH 900 reveals an unusually broad outflow emerging from a small ( 1"), dark globule in Trumpler 16. A bright H-alpha microjet along the western edge of HH 900 may be a second jet-protostar system that was ejected from the dark globule. Strong UV radiation from the many O stars in Trumpler 16 illuminates unshocked material in these jets, making it possible to estimate the jet mass-loss rates and infer the mass accretion history of the driving protostars. Two Spitzer-detected YSOs appear to lie within the globule, although with relatively coarse resolution (2"), Spitzer cannot resolve which protostar drives the jet. However, for HH jets with an associated Spitzer source, we have shown that IR [Fe II] emission traces the jet into the dark globule, connecting the H-alpha jet with the driving protostar. In addition, [Fe II] in these externally irradiated jets is excited in the dense, neutral jet core and may trace most of the mass in the outflow. We also propose to obtain narrowband H_2 images of HH 900 to see if extended H2 emission seen in ground-based images without AO correction corresponds to molecules entrained in the outflow. The associated Spitzer YSOs suggest that HH 900 samples the lower mass end of the jet-driving protostars detectable in Carina. Previous studies of [Fe II] in HH jets in Carina have focused on bright, highly collimated outflows likely driven by more massive, and more evolved protostars. Thus, HH 900 provides an important test of the behavior of lower mass jet driving protostars. These observation will be a chapter in P.I. M. Reiter's PhD thesis.

  19. Mapping dust in Orion protostars: from Herschel to APEX

    NASA Astrophysics Data System (ADS)

    Stanke, Thomas; Stutz, Amelia; Megeath, Thomas; HOPS Team

    2013-07-01

    HOPS (Herschel Orion Protostar Survey) is a 70 and 160mum Herschel PACS survey towards a sample of Spitzer identified protostar candidates in the Orion A and B giant molecular clouds. In this poster we give an overview of our efforts to obtain longer wavelength dust continuum maps, using the Laboca and Saboca cameras (870 and 350mum, respectively) at the APEX telescope, which provide maps at spatial resolutions well matched to the Herschel PACS data. The Laboca maps cover the entire field surveyed also by Herschel, providing a dust continuum measurement for all protostars observed by Herschel. The Saboca maps are restricted to smaller maps, mainly targeting PACS-bright protostar candidates, new protostar candidates not seen previously by Spitzer and identified from the Herschel maps, and also all bright cores found in the Laboca maps which do not have a protostellar association (i.e., starless cores). The data are used to provide long-wavelength submm photometry constraining the protostellar envelope masses. The 350mum Saboca data spatially resolve the emission from the outer envelope and are used to constrain their radial density distribution. Furthermore, combined with the Herschel data, we derive column density and temperature maps of the dense gas surrounding the protostars.

  20. Deuterium chemistry of dense gas in the vicinity of low-mass and massive star-forming regions

    NASA Astrophysics Data System (ADS)

    Awad, Zainab; Viti, Serena; Bayet, Estelle; Caselli, Paola

    2014-09-01

    The standard interstellar ratio of deuterium to hydrogen (D/H) atoms is ˜1.5 × 10-5. However, the deuterium fractionation is in fact found to be enhanced, to different degrees, in cold, dark cores, hot cores around massive star-forming regions, lukewarm cores, and warm cores (hereafter hot corinos) around low-mass star-forming regions. In this paper, we investigate the overall differences in the deuterium chemistry between hot cores and hot corinos. We have modelled the chemistry of dense gas around low-mass and massive star-forming regions using a gas-grain chemical model. We investigate the influence of varying the core density, the depletion efficiency of gaseous species on to dust grains, the collapse mode and the final mass of the protostar on the chemical evolution of star-forming regions. We find that the deuterium chemistry is, in general, most sensitive to variations of the depletion efficiency on to grain surfaces, in agreement with observations. In addition, the results showed that the chemistry is more sensitive to changes in the final density of the collapsing core in hot cores than in hot corinos. Finally, we find that ratios of deuterated sulphur bearing species in dense gas around hot cores and corinos may be good evolutionary indicators in a similar way as their non-deuterated counterparts.

  1. HIGH RESOLUTION H{alpha} IMAGES OF THE BINARY LOW-MASS PROPLYD LV 1 WITH THE MAGELLAN AO SYSTEM

    SciTech Connect

    Wu, Y.-L.; Close, L. M.; Males, J. R.; Follette, K.; Morzinski, K.; Kopon, D.; Rodigas, T. J.; Hinz, P.; Puglisi, A.; Esposito, S.; Pinna, E.; Riccardi, A.; Xompero, M.; Briguglio, R.

    2013-09-01

    We utilize the new Magellan adaptive optics system (MagAO) to image the binary proplyd LV 1 in the Orion Trapezium at H{alpha}. This is among the first AO results in visible wavelengths. The H{alpha} image clearly shows the ionization fronts, the interproplyd shell, and the cometary tails. Our astrometric measurements find no significant relative motion between components over {approx}18 yr, implying that LV 1 is a low-mass system. We also analyze Large Binocular Telescope AO observations, and find a point source which may be the embedded protostar's photosphere in the continuum. Converting the H magnitudes to mass, we show that the LV 1 binary may consist of one very-low-mass star with a likely brown dwarf secondary, or even plausibly a double brown dwarf. Finally, the magnetopause of the minor proplyd is estimated to have a radius of 110 AU, consistent with the location of the bow shock seen in H{alpha}.

  2. The Earliest Phases of Star Formation (EPoS): a Herschel key project. The thermal structure of low-mass molecular cloud cores

    NASA Astrophysics Data System (ADS)

    Launhardt, R.; Stutz, A. M.; Schmiedeke, A.; Henning, Th.; Krause, O.; Balog, Z.; Beuther, H.; Birkmann, S.; Hennemann, M.; Kainulainen, J.; Khanzadyan, T.; Linz, H.; Lippok, N.; Nielbock, M.; Pitann, J.; Ragan, S.; Risacher, C.; Schmalzl, M.; Shirley, Y. L.; Stecklum, B.; Steinacker, J.; Tackenberg, J.

    2013-03-01

    Context. The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. The instruments of the Herschel satellite provide us for the first time with both the spectral coverage and the spatial resolution that is needed to directly measure the dust temperature structure of nearby molecular cloud cores. Aims: With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, in particular of measuring their temperature structure, we initiated the guaranteed time key project (GTKP) "The Earliest Phases of Star Formation" (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, the Herschel and complementary ground-based observations, our analysis method, and the initial results of the survey. Methods: We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 μm and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. Results: We find that the thermal structure of all globules (mean mass 7 M⊙) is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K) with column densities of a few 1022 cm-2. The protostars embedded in some

  3. The origin of low-mass white dwarfs

    SciTech Connect

    Rebassa-Mansergas, A.; Schreiber, M. R.; Gaensicke, B. T.; Girven, J.; Gomez-Moran, A. Nebot

    2010-11-23

    We present white dwarf mass distributions of a large sample of post common-envelope binaries and wide white dwarf main sequence binaries and demonstrate that these distributions are statistically independent. While the former contains a much larger fraction of low-mass white dwarfs, the latter is similar to single white dwarf mass distributions. Taking into account observational biases we also show that the majority of low-mass white dwarfs are formed in close binaries.

  4. Direct Search for Low Mass Dark Matter Particles with CCDs

    DOE PAGES

    Barreto, J.; Cease, H.; Diehl, H. T.; ...

    2012-05-15

    A direct dark matter search is performed using fully-depleted high-resistivity CCD detectors. Due to their low electronic readout noise (RMS ~7 eV) these devices operate with a very low detection threshold of 40 eV, making the search for dark matter particles with low masses (~5 GeV) possible. The results of an engineering run performed in a shallow underground site are presented, demonstrating the potential of this technology in the low mass region.

  5. Very Low-Mass Stars and Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Rebolo, Rafael; Rosa Zapatero-Osorio, Maria

    2001-02-01

    Part I. Searches in Clusters, Stellar Associations and the Field: 1. Open clusters after HIPPARCOS J. S. Mermilliod; 2. Proper motions of very low mass stars and brown dwarfs in open clusters N. C. Hambly; 3. Parallaxes for brown dwarfs in clusters C. G. Tinney; 4. Very low mass stars and brown dwarfs in the Belt of Orion S. J. Wolk and F. M. Walter; 5. Photometric surveys in open clusters M. R. Zapatero Osorio; 6. The mass function of the Pleiades R. F. Jameson et al.; 7. Brown dwarfs and the low-mass initial mass function in young clusters K. L. Luhman; 8. Very low mass stars in globular clusters I. R. King and G. Piotto; 9. The DENIS very low mass star and brown dwarf results X. Delfosse and T. Forveille; 10. Preliminary results from the 2MASS core project J. Liebert et al.; Part II. Spectroscopic Properties, Fundamental Parameters and Modelling: 11. Properties of M dwarfs in clusters and the field S. L. Hawley et al.; 12. Spectroscopy of very low mass stars and brown dwarfs in young clusters E. L. Martin; 13. High resolution spectra of L type stars and brown dwarfs G. Basri et al.; 14. Modelling very low mass stars and brown dwarf atmospheres F. Allard; 15. Dust in very cool dwarfs T. Tsuji; 16. On the interpretation of the optical spectra of very cool dwarfs Ya. V. Pavlenko; 17. Absolute dimensions for M type dwarfs A. Gimenez; 18. Theory of very low mass stars and brown dwarfs I. Baraffe; Part III. Convection, Rotation and Acitivity: 19. Convection in low mass stars F. D'Antona; 20. Rotation law and magnetic field in M dwarf models G. Rudiger and M. Kuker; 21. Doppler imaging of cool dwarf stars K. G. Strassmeier; 22. X-ray Emission from cool dwarfs in clusters S. Randich; 23. X-ray variability for dM stars G. Micela and A. Marino; 24. The coronae of AD Leo and EV Lac S. Sciortino et al.; 25. Prospects of vuture X-ray missions for low mass stars and cluster stars R. Pallavicini.

  6. Flares and MHD Jets in Protostar

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Shibata, K.; Matsumoto, R.

    We present a magnetic reconnection model for hard X-ray emission and flare-like hard X-ray variabilities associated with protostars detected by ASCA. The energy released by protostellar flares is 102 - 105 times larger than solar flares. Moreover, the spectrum is harder. A new ingredient in protostellar flare is the existence of a protostellar disk which can twist the magnetic fields threading the protostellar disk. We carried out magnetohydrodynamic (MHD) simulations of the disk-star interaction. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. In the presence of resistivity, magnetic reconnection takes place in the current sheet formed inside the expanding loops. Hot, outgoing plasmoid and post flare loops are formed as a result of the reconnection. Numerical results are consistent with the observed plasma temperature (107 - 108K), the length of the flaring loop (1011-1012cm), the total energy of X-ray flares (~1035-36erg). Furthermore, along the opening magnetic loops, hot jet is ejected in bipolar directions with speed 200-400 km/s. The speed and mass flow rate of the jet is consistent with those of optical jets. Our model can explain both the X-ray flare-like variability and mass outflow in star forming region.

  7. Pulsed accretion in a variable protostar

    NASA Astrophysics Data System (ADS)

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-01

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 105 years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  8. Primordial stellar evolution - The protostar phase

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.; Palla, F.; Salpeter, E. E.

    1986-01-01

    The structure and evolution of a protostar forming from a cloud composed of pure hydrogen and helium gas are calculated. Using an accretion rate of 0.0044 solar mass/yr, the collapse of the cloud is followed numerically as a sequence of steady state accretion flows onto the hydrostatic core, which grows from an initial mass of 0.01 solar mass to 10.5 solar masses. The core is surrounded by an optically thick radiative precursor for most of its evolution. The core radius reaches 47 solar radii when the mass is 1 solar mass. For sufficiently massive cores, the deep interior contracts strongly, driving out a 'luminosity wave' which reaches the surface when the mass is 8 solar masses. This results in a large increase in core radius, the establishment of surface convection, and the disappearance of the radiative precursor. The dependence of core radius on the mass and accretion rate is analytically derived, and a new table or Rosseland mean opacities for metal-free gas is presented.

  9. METHYL CYANIDE OBSERVATIONS TOWARD MASSIVE PROTOSTARS

    SciTech Connect

    Rosero, V.; Hofner, P.; Kurtz, S.; Bieging, J.; Araya, E. D.

    2013-07-01

    We report the results of a survey in the CH{sub 3}CN J = 12 {yields} 11 transition toward a sample of massive proto-stellar candidates. The observations were carried out with the 10 m Submillimeter Telescope on Mount Graham, AZ. We detected this molecular line in 9 out of 21 observed sources. In six cases this is the first detection of this transition. We also obtained full beam sampled cross-scans for five sources which show that the lower K-components can be extended on the arcminute angular scale. The higher K-components, however, are always found to be compact with respect to our 36'' beam. A Boltzmann population diagram analysis of the central spectra indicates CH{sub 3}CN column densities of about 10{sup 14} cm{sup -2}, and rotational temperatures above 50 K, which confirms these sources as hot molecular cores. Independent fits to line velocity and width for the individual K-components resulted in the detection of an increasing blueshift with increasing line excitation for four sources. Comparison with mid-infrared (mid-IR) images from the SPITZER GLIMPSE/IRAC archive for six sources show that the CH{sub 3}CN emission is generally coincident with a bright mid-IR source. Our data clearly show that the CH{sub 3}CN J = 12 {yields} 11 transition is a good probe of the hot molecular gas near massive protostars, and provide the basis for future interferometric studies.

  10. Star Formation near Berkeley 59: Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (~2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, 12CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v LSR = -15 to -17 km s-1, which agrees with the velocity adopted for Berkeley 59 (-15.7 km s-1), while spectral energy distribution models yield an average interstellar extinction AV and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  11. Pulsed accretion in a variable protostar.

    PubMed

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-17

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 10(5) years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  12. The outburst of an embedded low-mass YSO in L1641

    NASA Astrophysics Data System (ADS)

    Caratti o Garatti, A.; Garcia Lopez, R.; Scholz, A.; Giannini, T.; Eislöffel, J.; Nisini, B.; Massi, F.; Antoniucci, S.; Ray, T. P.

    2011-02-01

    Context. Strong outbursts in very young and embedded protostars are rare and not yet fully understood. They are believed to originate from an increase in the mass accretion rate (dot{M}_acc) onto the source. Aims: We report the discovery of a strong outburst in a low-mass embedded young stellar object (YSO), namely 2MASS-J05424848-0816347 or [CTF93]216-2, as well as its photometric and spectroscopic follow-up. Methods: Using near- to mid-IR photometry and NIR low-resolution spectroscopy, we monitor the outburst, deriving its magnitude, duration, as well as the enhanced accretion luminosity and mass accretion rate. Results: [CTF93]216-2 increased in brightness by 4.6, 4.0, 3.8, and 1.9 mag in the J, H, Ks bands and at 24 μm, respectively, corresponding to an Lbol increase of 20 Lsun. Its early spectrum, probably taken soon after the outburst, displays a steep almost featureless continuum, with strong CO band heads and H2O broad-band absorption features, and Brγ line in emission. A later spectrum reveals more absorption features, allowing us to estimate Teff 3200 K, M_* 0.25 Msun, and dot{M}_acc 1.2 × 10-6 Msun yr-1. This makes it one of the lowest mass YSOs with a strong outburst so far discovered. Based on observations collected at the ESO/NTT (082.C-0264), at the REM telescope La Silla, Chile, and at the the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica).

  13. 2MASS J17112318-2724315: A DEEPLY EMBEDDED LOW-MASS PROTOSTELLAR SYSTEM IN THE B59 MOLECULAR CLOUD

    SciTech Connect

    Riaz, B.; Martin, E. L.; Bouy, H.; Tata, R.

    2009-08-01

    We present near-infrared observations of the low-mass deeply embedded Class 0/I system 2MASS J17112318-2724315 (2M171123) in the B59 molecular cloud. Bright scattered light nebulosity is observed toward this source in the K{sub s} images, that seems to trace the edges of an outflow cavity. We report the detection of a low-luminosity protostar 2M17112255-27243448 (2M17112255) that lies {approx}8'' ({approx}1000 AU) from 2M171123. This is a Class I system, as indicated by its 2-8 {mu}m slope and Infrared Array Camera colors, with an estimated internal luminosity of {approx}0.3 L{sub sun}. We estimate a mass of {approx}0.12-0.25 M{sub sun} for this source, at an age of 0.1-1 Myr. Also presented is detailed modeling of the 2M171123 system. The best-fit parameters indicate a large envelope density of the order of {approx}10{sup -13} g cm{sup -3}, and an intermediate inclination between 53 deg. and 59 deg. The observed K{sub s} -band variability for this system could be explained by slight variability in the mass infall rate between 2.5E-5 and 1.8E-5 M{sub sun} yr{sup -1}. The protostar 2M171123 exhibits a rarely observed absorption feature near 11.3 {mu}m within its 10 {mu}m silicate band. We find a strong correlation between the strength in this 11.3 {mu}m 'edge' and the H{sub 2}O-ice column density, indicating the origin of this feature in the thickness of the ice mantle over the silicate grains.

  14. The effect of episodic accretion on the phase transition of CO and CO2 in low-mass star formation

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Baraffe, Isabelle; Harries, Tim; Chabrier, Gilles

    2013-09-01

    We study the evaporation and condensation of CO and CO2 during the embedded stages of low-mass star formation by using numerical simulations. We focus on the effect of luminosity bursts, similar in magnitude to FUors and EXors, on the gas-phase abundance of CO and CO2 in the protostellar disk and infalling envelope. The evolution of a young protostar and its environment is followed based on hydrodynamical models using the thin-disk approximation, coupled with a stellar evolution code and phase transformations of CO and CO2. The accretion and associated luminosity bursts in our model are caused by disk gravitational fragmentation followed by quick migration of the fragments onto the forming protostar. We found that bursts with luminosity on the order of 100-200 L⊙ can evaporate CO ices in part of the envelope. The typical freeze-out time of the gas-phase CO onto dust grains in the envelope (a few kyr) is much longer than the burst duration (100-200 yr). This results in an increased abundance of the gas-phase CO in the envelope long after the system has returned into a quiescent stage. In contrast, luminosity bursts can evaporate CO2 ices only in the disk, where the freeze-out time of the gas-phase CO2 is comparable to the burst duration. We thus confirm that luminosity bursts can leave long-lasting traces in the abundance of gas-phase CO in the infalling envelope, enabling the detection of recent bursts as suggested by previous semi-analytical studies.

  15. ORGANIC CHEMISTRY OF LOW-MASS STAR-FORMING CORES. I. 7 mm SPECTROSCOPY OF CHAMAELEON MMS1

    SciTech Connect

    Cordiner, Martin A.; Charnley, Steven B.; Wirstroem, Eva S.; Smith, Robert G.

    2012-01-10

    Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 10{sup 6} cm{sup -3} and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a non-equilibrium carbon chemistry; C{sub 6}H and HC{sub 7}N column densities are 5.9{sup +2.9}{sub -1.3} Multiplication-Sign 10{sup 11} cm{sup -2} and 3.3{sup +8.0}{sub -1.5} Multiplication-Sign 10{sup 12} cm{sup -2}, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon-chain anions C{sub 4}H{sup -} and C{sub 6}H{sup -}, with anion-to-neutral ratios [C{sub 4}H{sup -}]/[C{sub 4}H] < 0.02% and [C{sub 6}H{sup -}]/[C{sub 6}H] < 10%, consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC{sub 3}N and c-C{sub 3}H{sub 2} were detected. The [DC{sub 3}N]/[HC{sub 3}N] ratio of approximately 4% is consistent with the value typically found in cold interstellar gas.

  16. Discovery of an outflow of the very low-mass star ISO 143

    NASA Astrophysics Data System (ADS)

    Joergens, V.; Kopytova, T.; Pohl, A.

    2012-12-01

    We discover that the very young very low-mass star ISO 143 (M5) is driving an outflow based on spectro-astrometry of forbidden [S II] emission lines at 6716 Å and 6731 Å observed in UVES/VLT spectra. This adds another object to the handful of brown dwarfs and very low-mass stars (M5-M8) for which an outflow has been confirmed and which show that the T Tauri phase continues at very low masses. We find the outflow of ISO 143 to be intrinsically asymmetric and the accretion disk to not obscure the outflow, as only the red outflow component is visible in the [S II] lines. ISO 143 is only the third T Tauri object showing a stronger red outflow component in spectro-astrometry, after RW Aur (G5) and ISO 217 (M6.25). We show here that, including ISO 143, two out of seven outflows confirmed in the very low-mass regime (M5-M8) are intrinsically asymmetric. We measure a spatial extension of the outflow in [S II] of up to 200-300 mas (about 30-50 AU) and velocities of up to 50-70 km s-1. We furthermore detect line emission of ISO 143 in Ca II (8498 Å), O I (8446 Å), He I (7065 Å), and weakly in [Fe II] (7155 Å). Based on a line profile analysis and decomposition we demonstrate that (i) the Ca II emission can be attributed to chromospheric activity, a variable wind, and the magnetospheric infall zone, (ii) the O I emission mainly to accretion-related processes but also a wind, and (iii) the He I emission to chromospheric or coronal activity. We estimate a mass outflow rate of ISO 143 of ~10-10 M⊙ yr-1 and a mass accretion rate in the range of ~10-8 to ~10-9 M⊙ yr-1. These values are consistent with those of other brown dwarfs and very low-mass stars. The derived Ṁout/Ṁacc ratio of 1-20% does not support previous findings of this number being very large (>40%) for very low-mass objects. Based on observations obtained at the Very Large Telescope of the European Southern Observatory at Paranal, Chile in program 080.C- 0904(A) 082.C-0023(A+B).

  17. FORMALDEHYDE AND METHANOL DEUTERATION IN PROTOSTARS: FOSSILS FROM A PAST FAST HIGH-DENSITY PRE-COLLAPSE PHASE

    SciTech Connect

    Taquet, V.; Ceccarelli, C.; Kahane, C.

    2012-03-20

    Extremely high deuteration of several molecules has been observed around low-mass protostars for a decade. Among them, formaldehyde and methanol present particularly high deuteration, with observations of abundant doubly and triply deuterated forms. Both species are thought to be mainly formed on interstellar grains during the low-temperature and dense pre-collapse phase by H and D atom additions on the iced CO. We present here a theoretical study of the formaldehyde and methanol deuteration obtained with our gas-grain model, GRAINOBLE. This model takes into account the multilayer nature of the mantle and explores the robustness of the results against the uncertainties of poorly constrained chemical and surface model parameters. The comparison of the model predictions with the observations leads to two major results: (1) the observed high deuteration is obtained during the last phase of the pre-collapse stage, when the density reaches {approx}5 Multiplication-Sign 10{sup 6} cm{sup -3}, and this phase is fast, lasting only several thousands years; and (2) D and H abstraction and substitution reactions are crucial in making up the observed deuteration ratios. This work shows the power of chemical composition as a tool to reconstruct the past history of protostars.

  18. Rotating Bullets from A Variable Protostar

    NASA Astrophysics Data System (ADS)

    Chen, Xuepeng; Arce, Héctor G.; Zhang, Qizhou; Launhardt, Ralf; Henning, Thomas

    2016-06-01

    We present Submillimeter Array (SMA) CO (2-1) observations toward the protostellar jet driven by SVS 13 A, a variable protostar in the NGC 1333 star-forming region. The SMA CO (2-1) images show an extremely high-velocity jet composed of a series of molecular “bullets.” Based on the SMA CO observations, we discover clear and large systematic velocity gradients, perpendicular to the jet axis, in the blueshifted and redshifted bullets. After discussing several alternative interpretations, such as twin-jets, jet precession, warped disk, and internal helical shock, we suggest that the systematic velocity gradients observed in the bullets result from the rotation of the SVS 13 A jet. From the SMA CO images, the measured rotation velocities are 11.7-13.7 km s-1 for the blueshifted bullet and 4.7 ± 0.5 km s-1 for the redshifted bullet. The estimated specific angular momenta of the two bullets are comparable to those of dense cores, about 10 times larger than those of protostellar envelopes, and about 20 times larger than those of circumstellar disks. If the velocity gradients are due to the rotation of the SVS 13 A jet, the significant amount of specific angular momenta of the bullets indicates that the rotation of jets/outflows is a key mechanism to resolve the so-called “angular momentum problem” in the field of star formation. The kinematics of the bullets suggests that the jet launching footprint on the disk has a radius of ˜7.2-7.7 au, which appears to support the extended disk-wind model. We note that further observations are needed to comprehensively understand the kinematics of the SVS 13 A jet, in order to confirm the rotation nature of the bullets.

  19. STAR FORMATION NEAR BERKELEY 59: EMBEDDED PROTOSTARS

    SciTech Connect

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (∼2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, {sup 12}CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v {sub LSR} = –15 to –17 km s{sup –1}, which agrees with the velocity adopted for Berkeley 59 (–15.7 km s{sup –1}), while spectral energy distribution models yield an average interstellar extinction A{sub V} and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  20. HST/WFC3 imaging of protostellar jets in Carina: [Fe II] emission tracing massive jets from intermediate-mass protostars

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2013-08-01

    We present narrow-band Wide Field Camera 3 (WFC3)-UVIS and WFC3-IR images of four externally irradiated protostellar jets in the Carina nebula: HH 666, HH 901, HH 902 and HH 1066. These massive jets are unusual because they are bathed in UV radiation from dozens of nearby O-type stars, but despite the strong incident ionizing radiation, portions of the jet remain neutral. Near-IR [Fe II] images reveal dense, neutral gas that was not seen in previous studies of Hα emission. We show that near-IR [Fe II] emitting gas must be self-shielded from Lyman continuum photons, regardless of its excitation mechanism (shocks, far-ultraviolet radiation or both). High densities are required for the survival of Fe+ amid the strong Lyman continuum luminosity from Tr14, raising estimates of the mass-loss rates by an order of magnitude. Higher jet mass-loss rates require higher accretion rates on to their driving protostars, implying that these jets are driven by intermediate-mass (˜2-8 M⊙) stars. Indeed, the IR driving sources of two of these outflows have luminosities that require intermediate-mass protostars (the other two are so deeply embedded that their luminosity is uncertain). All four of these HH jets are highly collimated, with opening angles of only a few degrees, similar to those observed in low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in wide-angle molecular outflows associated with intermediate- and high-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable in the harsh radiative environment of the Carina nebula. In more quiescent environments, this atomic core remains invisible, and outflows traced by shock-excited molecules in the outflow cavity give the impression that these outflows have a wider opening angle. Thus, the externally irradiated jets in Carina constitute a new view of collimated jets from intermediate-mass protostars and offer strong additional evidence

  1. Herschel/PACS far-IR spectral imaging of a jet from an intermediate mass protostar in the OMC-2 region

    NASA Astrophysics Data System (ADS)

    González-García, B.; Manoj, P.; Watson, D. M.; Vavrek, R.; Megeath, S. T.; Stutz, A. M.; Osorio, M.; Wyrowski, F.; Fischer, W.; Tobin, J. J.; Sánchez-Portal, M.; Diaz Rodriguez, A. K.; Wilson, T. L.

    2016-11-01

    We present the first detection of a jet in the far-IR [O I] lines from an intermediate mass protostar. This jet was detected in a Herschel/PACS spectral mapping study in the [O I] lines of OMC-2 FIR 3 and FIR 4, two of the most luminous protostars in Orion outside of the Orion Nebula. The spatial morphology of the fine structure line emission reveals the presence of an extended photodissociation region (PDR) and a narrow, but intense jet connecting the two protostars. The jet seen in [O I] emission is spatially aligned with the Spitzer/IRAC 4.5 μm jet and the CO (6-5) molecular outflow centered on FIR 3. The mass-loss rate derived from the total [O I] 63 μm line luminosity of the jet is 7.7 × 10-6M⊙ yr-1, more than an order of magnitude higher than that measured for typical low-mass class 0 protostars. The implied accretion luminosity is significantly higher than the observed bolometric luminosity of FIR 4, indicating that the [O I] jet is unlikely to be associated with FIR 4. We argue that the peak line emission seen toward FIR 4 originates in the terminal shock produced by the jet driven by FIR 3. The higher mass-loss rate that we find for FIR 3 is consistent with the idea that intermediate-mass protostars drive more powerful jets than their low-mass counterparts. Our results also call into question the nature of FIR 4. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.The final reduced Herschel data used in this paper (FITS) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/596/A26

  2. Low-Mass, Low-Power Hall Thruster System

    NASA Technical Reports Server (NTRS)

    Pote, Bruce

    2015-01-01

    NASA is developing an electric propulsion system capable of producing 20 mN thrust with input power up to 1,000 W and specific impulse ranging from 1,600 to 3,500 seconds. The key technical challenge is the target mass of 1 kg for the thruster and 2 kg for the power processing unit (PPU). In Phase I, Busek Company, Inc., developed an overall subsystem design for the thruster/cathode, PPU, and xenon feed system. This project demonstrated the feasibility of a low-mass power processing architecture that replaces four of the DC-DC converters of a typical PPU with a single multifunctional converter and a low-mass Hall thruster design employing permanent magnets. In Phase II, the team developed an engineering prototype model of its low-mass BHT-600 Hall thruster system, with the primary focus on the low-mass PPU and thruster. The goal was to develop an electric propulsion thruster with the appropriate specific impulse and propellant throughput to enable radioisotope electric propulsion (REP). This is important because REP offers the benefits of nuclear electric propulsion without the need for an excessively large spacecraft and power system.

  3. Luminosity functions for very low mass stars and brown dwarfs

    NASA Technical Reports Server (NTRS)

    Laughlin, Gregory; Bodenheimer, Peter

    1993-01-01

    A theoretical investigation of the luminosity function for low-mass objects to constrain the stellar initial mass function at the low-mass end is reported. The ways in which luminosity functions for low-mass stars are affected by star formation histories, brown dwarf and premain-sequence cooling rates and main-sequence mass luminosity relations, and the IMF are examined. Cooling rates and the mass-luminosity relation are determined through a new series of evolutionary calculations for very low mass stars and brown dwarfs in the range 0.05-0.50 solar mass. Model luminosity functions are constructed for specific comparison with the results of four recent observational surveys. The likelihood that the stellar mass function in the solar neighborhood is increasing at masses near the bottom of the main sequence and perhaps at lower masses is confirmed. In the most optimistic case, brown dwarfs contribute half of the local missing disk mass. The actual contribution is likely to be considerably less.

  4. HOT WATER IN THE INNER 100 AU OF THE CLASS 0 PROTOSTAR NGC 1333 IRAS2A

    SciTech Connect

    Visser, Ruud; Bergin, Edwin A.; Jorgensen, Jes K.; Kristensen, Lars E.; Van Dishoeck, Ewine F.

    2013-05-20

    Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of {approx}10{sup -4} relative to H{sub 2}. Observational evidence so far points at abundances of only a few 10{sup -6}. However, these values are based on spherical models, which are known from interferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier than expected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolved Herschel-HIFI spectra of the 3{sub 12}-3{sub 03} lines of H{sub 2}{sup 16}O and H{sub 2}{sup 18}O (1097 GHz, E{sub u}/k = 249 K) in the low-mass Class 0 protostar NGC 1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable to reproduce both the HIFI data and existing interferometric data on the H{sub 2}{sup 18}O 3{sub 13}-2{sub 20} line (203 GHz, E{sub u}/k = 204 K). Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. The mass of the hot core is estimated from the C{sup 18}O J = 9-8 and 10-9 lines. We derive a lower limit to the hot water abundance of 2 Multiplication-Sign 10{sup -5}, consistent with the theoretical predictions of {approx}10{sup -4}. The revised HDO/H{sub 2}O abundance ratio is 1 Multiplication-Sign 10{sup -3}, an order of magnitude lower than previously estimated.

  5. The low-mass star and sub-stellar populations of the 25 Orionis group

    NASA Astrophysics Data System (ADS)

    Downes, Juan José; Briceño, César; Mateu, Cecilia; Hernández, Jesús; Vivas, Anna Katherina; Calvet, Nuria; Hartmann, Lee; Petr-Gotzens, Monika G.; Allen, Lori

    2014-10-01

    We present the results of a survey of the low-mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA (Centro de Investigaciones de Astronomía `Francisco J. Duarte', Mérida, Venezuela) Deep Survey of Orion, near-IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low-resolution spectroscopy obtained with Hectospec at the MMT telescope, we selected 1246 photometric candidates to low-mass stars and brown dwarfs with estimated masses within 0.02 ≲ M/M⊙ ≲ 0.8 and spectroscopically confirmed a sample of 77 low-mass stars as new members of the cluster with a mean age of ˜7 Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices α3 = -1.73 ± 0.31 and α2 = 0.68 ± 0.41 in the mass ranges 0.03 ≤ M/M⊙ ≤ 0.08 and 0.08 ≤ M/M⊙ ≤ 0.5, respectively, or a Scalo lognormal function with coefficients m_c=0.21^{+0.02}_{-0.02} and σ = 0.36 ± 0.03 in the mass range 0.03 ≤ M/M⊙ ≤ 0.8. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the east-west elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low-mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low-mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged.

  6. ACCURATE LOW-MASS STELLAR MODELS OF KOI-126

    SciTech Connect

    Feiden, Gregory A.; Chaboyer, Brian; Dotter, Aaron

    2011-10-10

    The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the influence of physics currently not incorporated in standard stellar evolution models. We also predict apsidal motion constants for the two M dwarf companions. These values should be observationally determined to within 1% by the end of the Kepler mission.

  7. Mosquitoes survive raindrop collisions by virtue of their low mass

    PubMed Central

    Dickerson, Andrew K.; Shankles, Peter G.; Madhavan, Nihar M.; Hu, David L.

    2012-01-01

    In the study of insect flight, adaptations to complex flight conditions such as wind and rain are poorly understood. Mosquitoes thrive in areas of high humidity and rainfall, in which raindrops can weigh more than 50 times a mosquito. In this combined experimental and theoretical study, we here show that free-flying mosquitoes can survive the high-speed impact of falling raindrops. High-speed videography of those impacts reveals a mechanism for survival: A mosquito’s strong exoskeleton and low mass renders it impervious to falling drops. The mosquito’s low mass causes raindrops to lose little momentum upon impact and so impart correspondingly low forces to the mosquitoes. Our findings demonstrate that small fliers are robust to in-flight perturbations. PMID:22665779

  8. Concept for coring from a low-mass rover

    NASA Technical Reports Server (NTRS)

    Backes, Paul G.; Khatib, Oussama; Diaz-Calderon, Antonio; Warren, James; Collins, Curtis; Chang, Zensheu

    2006-01-01

    Future Mars missions, such as the Mars Sample Return (MSR) mission, may benefit from core sample acquisition from a low-mass rover where the rover cannot be assumed to be stationary during a coring operation. Manipulation from Mars rovers is currently done under the assumption that the rover acts as a stationary, stable platform for the arm. An MSR mission scenario with a low-mass rover has been developed and the technology needs have been investigated. Models for alternative types of coring tools and tool-environment interaction have been developed and input along with wheel-soil interaction models into the Stanford Simulation & Active Interfaces (SAI) simulation environment to enable simulation of coring operations from a rover. Coring tests using commercial coring tools indicate that the quality of the core is a critical criterion in the system design. Current results of the models, simulation, and coring tests are provided.

  9. Five New Low-Mass Eclipsing Binary Systems

    NASA Astrophysics Data System (ADS)

    Coughlin, Jeffrey L.; López-Morales, M.; Shaw, J. S.

    2006-12-01

    We present the discovery of five new low-mass eclipsing binaries with masses between 0.54 and 0.95 M⊙, their photometric light curves, and preliminary models. This is part of a continuing campaign to increase the available data on these interesting systems. Once radial-velocity curves are completed, physical parameters will be determined with an error of less than 2-3%, thus allowing for a rigorous examination of stellar models in the lower-main sequence. Our initial analysis seems to support the current findings that low-mass stars have greater radii than models predict, most likely due to the presence of strong magnetic fields. This work is funded by a partnership between the National Science Foundation (NSF AST-0552798) Research Experiences for Undergraduates (REU) and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs.

  10. Low-mass solitons from fractional charges in quantum chromodynamics

    NASA Astrophysics Data System (ADS)

    Balachandran, A. P.; Nair, V. P.; Panchapakesan, N.; Rajeev, S. G.

    1983-12-01

    Slansky, Goldman, and Shaw have proposed a model to account for the observation of fractionally charged states. We show that in this model, there are expected to be several low-mass solitons (four being in the mass range ~20-60 MeV) associated with the third homotopy group π3(SU(3)SO(3))=Z4, besides a low-mass (~30 MeV) Z2 monopole. Confirmation of these levels and hence of the model has important implications for Cabrera's results on the magnetic monopole. An efficient algorithm for the calculation of π3(GH) for a general Lie group G and a subgroup H is developed. It is pointed out that solitons associated with the third homotopy group are predicted by some grand-unified-theory scenarios.

  11. PROTOSTARS AND STARS IN THE CORONET CLUSTER: AGE, EVOLUTION, AND CLUSTER STRUCTURE

    SciTech Connect

    Sicilia-Aguilar, Aurora; Henning, Thomas; Kainulainen, Jouni; Roccatagliata, Veronica

    2011-08-01

    We present new optical spectroscopy with the FLAMES spectrograph at the Very Large Telescope (VLT), near-IR imaging with VLT/HAWK-I, and 870 {mu}m mapping with APEX/LABOCA of the Coronet cluster. The optical data allow us to estimate spectral types, extinction, and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in an H-R diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably {approx}0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50%-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks.

  12. A grid of one-dimensional low-mass star formation collapse models

    NASA Astrophysics Data System (ADS)

    Vaytet, N.; Haugbølle, T.

    2017-02-01

    Context. Numerical simulations of star formation are becoming ever more sophisticated, incorporating new physical processes in increasingly realistic set-ups. These models are being compared to the latest observations through state-of-the-art synthetic renderings that trace the different chemical species present in the protostellar systems. The chemical evolution of the interstellar and protostellar matter is very topical, with more and more chemical databases and reaction solvers available online to the community. Aims: The current study was developed to provide a database of relatively simple numerical simulations of protostellar collapse as a template library for observations of cores and very young protostars, and for researchers who wish to test their chemical modelling under dynamic astrophysical conditions. It was also designed to identify statistical trends that may appear when running many models of the formation of low-mass stars by varying the initial conditions. Methods: A large set of 143 calculations of the gravitational collapse of an isolated sphere of gas with uniform temperature and a Bonnor-Ebert-like density profile was undertaken using a 1D fully implicit Lagrangian radiation hydrodynamics code. The parameter space covered initial masses from 0.2 to 8 M⊙, temperatures of 5-30 K, and radii 3000 ≤ R0 ≤ 30 000 AU. Results: A spread due to differing initial conditions and optical depths, was found in the thermal evolutionary tracks of the runs. Within less than an order of magnitude, all first and second Larson cores had masses and radii essentially independent of the initial conditions. Radial profiles of the gas density, velocity, and temperature were found to vary much more outside of the first core than inside. The time elapsed between the formation of the first and second cores was found to strongly depend on the first core mass accretion rate, and no first core in our grid of models lived for longer than 2000 years before the onset of

  13. The different baryonic Tully-Fisher relations at low masses.

    PubMed

    Brook, Chris B; Santos-Santos, Isabel; Stinson, Greg

    2016-06-11

    We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity Vrot. We explore the BTFR when measuring Vrot at the flat part of the rotation curve, Vflat, at the extent of H i gas, Vlast, and using 20 per cent (W20) and 50 per cent (W50) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, [Formula: see text], within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using Vlast one obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring Vflat gives similar results as Vlast when galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low-mass galaxies if the cold gas extended far enough for Vrot to reach a maximum. W20 gives a similar slope as Vlast but with slightly lower values of Vrot for low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W50 bends away from these other relations towards low velocities at low masses. By contrast, [Formula: see text] bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach [Formula: see text]. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuring Vrot, and precise about the radius at which velocities are measured.

  14. Low mass lepton pair production at large transverse momentum

    NASA Astrophysics Data System (ADS)

    Qiu, Jianwei; Kang, Zhongbo; Vogelsang, Werner

    2008-10-01

    PHENIX collaboration has recently measured the transverse momentum distribution of lepton pair production at RHIC with the pair's invariant mass as low as 120 < Q < 300 MeV. We will show that the distribution of low mass lepton pair production at large transverse momentum QTQ can be systematically calculated in terms of the perturbative QCD factorization approach. All factorized short-distance parotnic hard parts are evaluated at a distance scale ˜1/QT, while all long-distance non-perturbative physics are factorized into the universal parton-to-lepton pair fragmentation functions. We introduce a model for the input lepton pair fragmentation functions at a scale μ˜ 1 GeV, which are then evolved perturbatively to scales relevant at RHIC. Using the evolved fragmentation functions, we calculate the transverse momentum distributions of low mass lepton pair production in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions. We demonstrate that the transverse momentum distribution of low mass lepton pairs is extremely sensitive to the shape of gluon distribution.

  15. Formation and composition of planets around very low mass stars

    NASA Astrophysics Data System (ADS)

    Alibert, Y.; Benz, W.

    2017-01-01

    Context. The recent detection of planets around very low mass stars raises the question of the formation, composition, and potential habitability of these objects. Aims: We use planetary system formation models to infer the properties, in particular their radius distribution and water content, of planets that may form around stars ten times less massive than the Sun. Methods: Our planetary system formation and composition models take into account the structure and evolution of the protoplanetary disk, the planetary mass growth by accretion of solids and gas, as well as planet-planet, planet-star, and planet-disk interactions. Results: We show that planets can form at small orbital period in orbit about low-mass stars. We show that the radius of the planets is peaked at about 1 R⊕ and that they are, in general, volatile rich especially if proto-planetary disks orbiting this type of stars are long lived. Conclusions: Close-in planets orbiting low-mass stars similar in terms of mass and radius to those recently detected can be formed within the framework of the core-accretion paradigm as modeled here. The properties of protoplanetary disks, and their correlation with the stellar type, are key to understand their composition.

  16. The first stars: A low-mass formation mode

    SciTech Connect

    Stacy, Athena; Bromm, Volker

    2014-04-10

    We perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as ∼1 AU, corresponding to gas densities of 10{sup 16} cm{sup –3}. Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1 M {sub ☉} to ∼5 M {sub ☉} by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.

  17. The First Stars: A Low-Mass Formation Mode

    NASA Technical Reports Server (NTRS)

    Stacy, Athena; Bromm, Volker

    2014-01-01

    We perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as approx. 1 AU, corresponding to gas densities of 10(exp 16)/cu cm. Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1Stellar Mass to approx. 5 Stellar Mass by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.

  18. The Low-mass Astrometric Binary LSR 1610-0040

    NASA Astrophysics Data System (ADS)

    Koren, Seth C.; Blake, Cullen H.; Dahn, Conard C.; Harris, Hugh C.

    2016-03-01

    Even though it was discovered more than a decade ago, LSR 1610-0040 remains an enigma. This object has a peculiar spectrum that exhibits some features typically found in L subdwarfs, and others common in the spectra of more massive M dwarf stars. It is also a binary system with a known astrometric orbital solution. Given the available data, it remains a challenge to reconcile the observed properties of the combined light of LSR 1610-0040AB with current theoretical models of low-mass stars and brown dwarfs. We present the results of a joint fit to both astrometric and radial velocity measurements of this unresolved, low-mass binary. We find that the photocentric orbit has a period P=633.0+/- 1.7 days, somewhat longer than previous results, eccentricity of e=0.42+/- 0.03, and we estimate that the semimajor axis of the orbit of the primary is {a}1≈ 0.32 {{AU}}, consistent with previous results. While a complete characterization of the system is limited by our small number of radial velocity measurements, we establish a likely primary mass range of 0.09-0.10 {M}⊙ from photometric and color-magnitude data. For a primary mass in this range, the secondary is constrained to be 0.06-0.075 {M}⊙ , making a negligible contribution to the total I-band luminosity. This effectively rules out the possibility of the secondary being a compact object such as an old, low-mass white dwarf. Based on our analysis, we predict a likely angular separation at apoapsis comparable to the resolution limits of current high-resolution imaging systems. Measuring the angular separation of the A and B components would finally enable a full, unambiguous solution for the masses of the components of this system.

  19. Low-mass materials and vertex detector systems

    SciTech Connect

    Cooper, William E.

    2014-01-01

    Physics requirements set the material budget and the precision and stability necessary in low-mass vertex detector systems. Operational considerations, along with physics requirements, set the operating environment to be provided and determine the heat to be removed. Representative materials for fulfilling those requirements are described and properties of the materials are tabulated. A figure of merit is proposed to aid in material selection. Multi-layer structures are examined as a method to allow material to be used effectively, thereby reducing material contributions. Lastly, comments are made on future directions to be considered in using present materials effectively and in developing new materials.

  20. Low-mass materials and vertex detector systems

    DOE PAGES

    Cooper, William E.

    2014-01-01

    Physics requirements set the material budget and the precision and stability necessary in low-mass vertex detector systems. Operational considerations, along with physics requirements, set the operating environment to be provided and determine the heat to be removed. Representative materials for fulfilling those requirements are described and properties of the materials are tabulated. A figure of merit is proposed to aid in material selection. Multi-layer structures are examined as a method to allow material to be used effectively, thereby reducing material contributions. Lastly, comments are made on future directions to be considered in using present materials effectively and in developing newmore » materials.« less

  1. Young stars of low mass in the Gum nebula

    NASA Technical Reports Server (NTRS)

    Graham, J. A.; Heyer, Mark H.

    1989-01-01

    Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun.

  2. Discovery of a protostar in the Large Magellanic Cloud

    NASA Technical Reports Server (NTRS)

    Gatley, I.; Becklin, E. E.; Hyland, A. R.; Jones, T. J.

    1981-01-01

    A near infrared search of the H II region/molecular cloud complex N159 in the Large Magellanic Cloud has revealed a very red (H-K = 2.1, K-L-prime = 2.7) compact object. The location, brightness, color and 2.1-2.4 micron spectrum of this source suggest that it is very young, and similar to the galactic infrared protostars. This is the first identification of an infrared protostar in an external galaxy. Its discovery provides direct evidence of current star formation in the Large Magellanic Cloud, and suggests that regions of star formation in external galaxies will appear similar to those in the Milky Way.

  3. Herschel Shines Light on the Episodic Evolutionary Sequence of Protostars

    NASA Astrophysics Data System (ADS)

    Green, Joel D.; DIGIT; FOOSH; COPS Teams

    2014-01-01

    New far-infrared and submillimeter spectroscopic capabilities, along with moderate spatial and spectral resolution, provide the opportunity to study the diversity of shocks, accretion processes, and compositions of the envelopes of developing protostellar objects in nearby molecular clouds. We present the "COPS" (CO in Protostars) sample; a statistical analysis of the full sample of 30 Class 0/I protostars from the "DIGIT" Key project using Herschel-PACS/SPIRE 50-700 micron spectroscopy. We consider the sample as a whole in characteristic spectral lines, using a standardized data reduction procedure for all targets, and analyze the differences in the continuum and gas over the full sample, presenting an overview of trends. We compare the sources in evolutionary state, envelope mass, and gas properties to more evolved sources from the"FOOSH'' (FUor) samples.

  4. New Low-Mass Members of Nearby Young Moving Groups

    NASA Astrophysics Data System (ADS)

    Schlieder, Joshua; Simon, Michal; Rice, Emily; Lepine, Sebastien

    2012-08-01

    We are now ready to expand our program to identify new low-mass members of nearby young moving groups (NYMGs) to stars of mass ≤0.3 M_⊙. This is important to: (1) complete the census of low-mass stars near the Sun, (2) provide high priority targets for disk and exoplanet studies by direct imaging, and (3) provide a well- characterized sample of nearby, young stars for detailed study of their physical and kinematic properties. Our proven technique starts with a proper motion selection algorithm, proceeds to vet the sample for indicators of youth, and requires as its last step the measurement of candidate member radial velocities (RVs). So far, we have measured more than 100 candidate RVs using CSHELL on the NASA-IRTF and PHOENIX on Gemini-South, yielding more than 50 likely new moving group members. Here we propose to continue our RV follow-up of candidate NYMG members using PHOENIX on the KPNO 4m. We aim to measure RVs and determine spectral types of 23 faint (V≥15, H≥9), late-type (≥M4) candidates of the (beta) Pic (10 Myrs), AB Dor (70 Myrs), Tuc/Hor (30 Myrs), and TW Hydrae (8 Myrs) moving groups.

  5. Angular momentum transport within evolved low-mass stars

    SciTech Connect

    Cantiello, Matteo; Bildsten, Lars; Paxton, Bill; Mankovich, Christopher; Christensen-Dalsgaard, Jørgen

    2014-06-10

    Asteroseismology of 1.0-2.0 M {sub ☉} red giants by the Kepler satellite has enabled the first definitive measurements of interior rotation in both first ascent red giant branch (RGB) stars and those on the helium burning clump. The inferred rotation rates are 10-30 days for the ≈0.2 M {sub ☉} He degenerate cores on the RGB and 30-100 days for the He burning core in a clump star. Using the Modules for Experiments in Stellar Evolution code, we calculate state-of-the-art stellar evolution models of low mass rotating stars from the zero-age main sequence to the cooling white dwarf (WD) stage. We include transport of angular momentum due to rotationally induced instabilities and circulations, as well as magnetic fields in radiative zones (generated by the Tayler-Spruit dynamo). We find that all models fail to predict core rotation as slow as observed on the RGB and during core He burning, implying that an unmodeled angular momentum transport process must be operating on the early RGB of low mass stars. Later evolution of the star from the He burning clump to the cooling WD phase appears to be at nearly constant core angular momentum. We also incorporate the adiabatic pulsation code, ADIPLS, to explicitly highlight this shortfall when applied to a specific Kepler asteroseismic target, KIC8366239.

  6. MASS-RADIUS RELATIONSHIPS FOR VERY LOW MASS GASEOUS PLANETS

    SciTech Connect

    Batygin, Konstantin; Stevenson, David J.

    2013-05-20

    Recently, the Kepler spacecraft has detected a sizable aggregate of objects, characterized by giant-planet-like radii and modest levels of stellar irradiation. With the exception of a handful of objects, the physical nature, and specifically the average densities, of these bodies remain unknown. Here, we propose that the detected giant planet radii may partially belong to planets somewhat less massive than Uranus and Neptune. Accordingly, in this work, we seek to identify a physically sound upper limit to planetary radii at low masses and moderate equilibrium temperatures. As a guiding example, we analyze the interior structure of the Neptune-mass planet Kepler-30d and show that it is acutely deficient in heavy elements, especially compared with its solar system counterparts. Subsequently, we perform numerical simulations of planetary thermal evolution and in agreement with previous studies, show that generally, 10-20 M{sub Circled-Plus }, multi-billion year old planets, composed of high density cores and extended H/He envelopes can have radii that firmly reside in the giant planet range. We subject our results to stability criteria based on extreme ultraviolet radiation, as well as Roche-lobe overflow driven mass-loss and construct mass-radius relationships for the considered objects. We conclude by discussing observational avenues that may be used to confirm or repudiate the existence of putative low mass, gas-dominated planets.

  7. Low mass galaxy clusters and galaxy morphology evolution

    NASA Astrophysics Data System (ADS)

    Nilo Castellón, J. L.; Órdenes, Y.; Ramos, F.; Alonso, M. V.; Cuevas, H.; García Lambas, D.; Ramírez, A.

    We present preliminary results about the galaxy morphology evolution in three low mass galaxy clusters: RX J0533.9-5809 ([VMF98]046, z 0.198), RX J1204.3-0350 ([VMF98]113, z 0.261) and RX J0533.8-5746 ([VMF98]045, z 0.295). Full photometric catalogues were created using SExtractor v2.8.0. Also, photometric redshifts (z phot ) were obtained for all the object classified as galaxies, using the ANNz code. Color-Magnitude Diagrams (CMD) were generated for those galaxies clas- sified as cluster members. Clear Red Cluster Sequences (RCS) with a me- dian slopes of -0.03 are observed for all the tree clusters. Based on the RCS best fit, a blue and a red population of galaxies were defined, observ- ing that the color distribution of the cluster [VMF98]045 is well fitted by a double Gaussian function (2 0.2), while the clusters [VMF98]046 and [VMF98]113 presents a third population between the blue and red peak dis- tributions. These preliminary results would show the existence of a possible transi- tion population between the blue and the red population in these low mass galaxy clusters at low redshifts.

  8. Constraining models of accretion outbursts in low-mass YSOs}

    NASA Astrophysics Data System (ADS)

    Ninan, J. P.; Ojha, D. K.; Ghosh, S. K.; Bhatt, B. C.

    Young low-mass stars, which are still undergoing accretion, have been found to undergo sudden outbursts in short period of time. They are believed to be due to sudden increase of typically ˜2 orders of magnitude in mass infall rate. Classically these objects are classified as FUors and EXors. FUors undergo long duration outbursts for several decades of typical magnitude δ m ˜ 4-5, while EXors undergo short duration outbursts for few months to years of typical magnitude δ m ˜ 2-3 and they might occur repeatedly. From the number count of FUors, it is estimated that every low-mass stars, on a minimum, undergo FUors kind of outburst in its early life. We present our study on three such rare outbursts in optical and near-infrared wavebands using long-term observations with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Observatory telescope. Using the current available models and the constrains on it, we can deduce to understand the physical process driving the outburst.

  9. Dynamical corotation torques on low-mass planets

    NASA Astrophysics Data System (ADS)

    Paardekooper, S.-J.

    2014-11-01

    We study torques on migrating low-mass planets in locally isothermal discs. Previous work on low-mass planets generally kept the planet on a fixed orbit, after which the torque on the planet was measured. In addition to these static torques, when the planet is allowed to migrate it experiences dynamical torques, which are proportional to the migration rate and whose sign depends on the background vortensity gradient. We show that in discs a few times more massive than the minimum-mass solar nebula, these dynamical torques can have a profound impact on planet migration. Inward migration can be slowed down significantly, and if static torques lead to outward migration, dynamical torques can take over, taking the planet beyond zero-torque lines set by saturation of the corotation torque in a runaway fashion. This means that the region in non-isothermal discs, where outward migration is possible, can be larger than what would be concluded from static torques alone.

  10. Low mass large aperture vacuum window development at CEBAF

    SciTech Connect

    Keppel, C.

    1995-04-01

    Large aperture low mass vacuum windows are being developed for the HMS (High Momentum Spectrometer) and SOS (Short Orbit Spectrometer) spectrometers in Hall C at CEBAF. Because multiple scattering degrades the performance of a spectrometer it is important that the volume be evacuated and that the entrance and exit windows be as low mass as possible. The material used for such windows must be thin and light enough so as to have minimum effect of the beam, and at the same time, be thick and strong enough to operate reliably and safely. To achieve these goals, composite vacuum windows have been constructed of a thin sheet of Mylar with a reinforcing fabric. Reinforcing fabrics such as Kevlar and Spectra are available with tensile strengths significantly greater than that of Mylar. A thin layer of Myler remains necessary since the fabrics cannot achieve any sort of vacuum seal. The design, fabrication, testing, and operating experience with such composite windows for the Hall C spectrometers will be discussed.

  11. Disk Masses of Class I Protostars in Taurus and Ophiuchus

    NASA Astrophysics Data System (ADS)

    Sheehan, Patrick; Eisner, Joshua A.

    2017-01-01

    Recent studies suggest that many protoplanetary disks around pre-main sequence stars with inferred ages of 1-5 Myr (known as Class II protostars) contain insufficient mass to form giant planets. This may be because by this stage much of the material in the disk has already grown into larger bodies, hiding the material from sight. To test this hypothesis, we have observed every protostar in the Taurus and Ophiuchus star forming regions identified as Class I in multiple independent surveys, whose young (< 1 Myr old) disks are more likely to represent the initial mass budget of protoplanetary disks. For my dissertation I have used detailed radiative transfer modeling of CARMA and ALMA millimeter images, broadband SEDs, and near-infrared scattered light images to determine the geometry of the circumstellar material and measure the mass of the disks around these protostars. By comparing the inferred disk mass distribution with results for the existing 1-5 Myr old disk sample, we constrain the initial mass budget for forming planets in protoplanetary disks. We find that the younger Class I disks are, on average, more massive than the older disk sample, but still may be shy of the necessary mass for forming planets. It may be that even by this early stage, planet formation is well underway.

  12. EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?

    SciTech Connect

    Baraffe, I.; Chabrier, G.; Gallardo, J. E-mail: chabrier@ens-lyon.fr

    2009-09-01

    We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T{sub eff}. The best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an {approx}10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T{sub eff}, as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young ({<=} a few Myr) clusters. Our results also show that the concept of a stellar birthline for low-mass objects has no valid support.

  13. Dust discs around low-mass main-sequence stars

    NASA Technical Reports Server (NTRS)

    Wolstencroft, R. D.; Walker, Helen J.

    1988-01-01

    The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit.

  14. Low-Mass Inflation Systems for Inflatable Structures

    NASA Technical Reports Server (NTRS)

    Thunnissen, Daniel P.; Webster, Mark S.; Engelbrecht, Carl S.

    1995-01-01

    The use of inflatable space structures has often been proposed for aerospace and planetary applications. Communication, power generation, and very-long-baseline interferometry are just three potential applications of inflatable technology. The success of inflatable structures depends on the development of an applications of inflatable technology. This paper describes two design studies performed to develop a low mass inflation system. The first study takes advantage of existing onboard propulsion gases to reduce the overall system mass. The second study assumes that there is no onboard propulsion system. Both studies employ advanced components developed for the Pluto fast flyby spacecraft to further reduce mass. The study examined four different types of systems: hydrazine, nitrogen and water, nitrogen, and xenon. This study shows that all of these systems can be built for a small space structure with masses lower than 0.5 kilograms.

  15. Formation of the low-mass solar nebula

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, T. V.; Khatuncev, I. V.; Konkina, T. V.

    1993-01-01

    We study an accretional stage of the formation and early evolution of the solar nebula with relatively small angular momentum. We investigate the evolution of the disk and its vertical structure, particularly the shock front between disk and infalling material. Calculations start at a moment when a low-mass star-like core surrounded by small embryo disk have been formed at the center of the presolar nebula and the bulk of mass remained in the envelope. The forming solar nebula is approximated as a thin viscous disk surrounded by accreting envelope. The distribution of temperature in the infalling envelope is determined by solving spherically symmetric equations of radiative transfer. As the energy source, we take into account all energy released within the centrifugal radius of the infalling matter. Other aspects of this study are discussed.

  16. Feedback in low-mass galaxies in the early Universe.

    PubMed

    Erb, Dawn K

    2015-07-09

    The formation, evolution and death of massive stars release large quantities of energy and momentum into the gas surrounding the sites of star formation. This process, generically termed 'feedback', inhibits further star formation either by removing gas from the galaxy, or by heating it to temperatures that are too high to form new stars. Observations reveal feedback in the form of galactic-scale outflows of gas in galaxies with high rates of star formation, especially in the early Universe. Feedback in faint, low-mass galaxies probably facilitated the escape of ionizing radiation from galaxies when the Universe was about 500 million years old, so that the hydrogen between galaxies changed from neutral to ionized-the last major phase transition in the Universe.

  17. Spectroscopic Study of Low Mass Members of NGC 2244

    NASA Astrophysics Data System (ADS)

    Alty, Michelle; Ybarra, Jason E.; Román-Zúñiga, Carlos G.; Lada, Elizabeth A.

    2017-01-01

    The results of a near-infrared spectroscopic study of low-mass stars in open cluster NGC 2244 are presented. JH spectra of the stars were obtained using the FLAMINGOS instrument at KPNO. To determine cluster membership, we used Spitzer Space Telescope mid-infrared photometry along with X-ray detections from the Chandra X-ray Observatory. The stars were spectral typed using absorption line ratios and spectral shapes. The stars were then plotted on an H-R diagram along with theoretical isochrones. We discuss these results in context of cluster evolution in the Rosette Molecular Complex. Work supported, in part, by the Dr. John W. Martin Summer Science Research Institute at Bridgewater College.

  18. Feedback in low-mass galaxies in the early Universe

    NASA Astrophysics Data System (ADS)

    Erb, Dawn K.

    2015-07-01

    The formation, evolution and death of massive stars release large quantities of energy and momentum into the gas surrounding the sites of star formation. This process, generically termed `feedback', inhibits further star formation either by removing gas from the galaxy, or by heating it to temperatures that are too high to form new stars. Observations reveal feedback in the form of galactic-scale outflows of gas in galaxies with high rates of star formation, especially in the early Universe. Feedback in faint, low-mass galaxies probably facilitated the escape of ionizing radiation from galaxies when the Universe was about 500 million years old, so that the hydrogen between galaxies changed from neutral to ionized--the last major phase transition in the Universe.

  19. DETECTION OF LOW-MASS-RATIO STELLAR BINARY SYSTEMS

    SciTech Connect

    Gullikson, Kevin; Dodson-Robinson, Sarah

    2013-01-01

    O- and B-type stars are often found in binary systems, but the low binary mass-ratio regime is relatively unexplored due to observational difficulties. Binary systems with low mass ratios may have formed through fragmentation of the circumstellar disk rather than molecular cloud core fragmentation. We describe a new technique sensitive to G- and K-type companions to early B stars, a mass ratio of roughly 0.1, using high-resolution, high signal-to-noise spectra. We apply this technique to a sample of archived VLT/CRIRES observations of nearby B stars in the CO bandhead near 2300 nm. While there are no unambiguous binary detections in our sample, we identify HIP 92855 and HIP 26713 as binary candidates warranting follow-up observations. We use our non-detections to determine upper limits to the frequency of FGK stars orbiting early B-type primaries.

  20. Fast migration of low-mass planets in radiative discs

    NASA Astrophysics Data System (ADS)

    Pierens, A.

    2015-12-01

    Low-mass planets are known to undergo Type I migration and this process must have played a key role during the evolution of planetary systems. Analytical formulae for the disc torque have been derived assuming that the planet evolves on a fixed circular orbit. However, recent work has shown that in isothermal discs, a migrating protoplanet may also experience dynamical corotation torques that scale with the planet drift rate. The aim of this study is to examine whether dynamical corotation torques can also affect the migration of low-mass planets in non-isothermal discs. We performed 2D radiative hydrodynamical simulations to examine the orbital evolution outcome of migrating protoplanets as a function of disc mass. We find that a protoplanet can enter a fast migration regime when it migrates in the direction set by the entropy-related horseshoe drag and when the Toomre stability parameter is less than a threshold value below which the horseshoe region contracts into a tadpole-like region. In that case, an underdense trapped region appears near the planet, with an entropy excess compared to the ambient disc. If the viscosity and thermal diffusivity are small enough so that the entropy excess is conserved during migration, the planet then experiences strong corotation torques arising from the material flowing across the planet orbit. During fast migration, we observe that a protoplanet can pass through the zero-torque line predicted by static torques. We also find that fast migration may help in disrupting the mean-motion resonances that are formed by convergent migration of embryos.

  1. Outflows in low-mass galaxies at z >1

    NASA Astrophysics Data System (ADS)

    Maseda, Michael V.; MUSE GTO Consortium

    2017-03-01

    Star formation histories of local dwarf galaxies, derived through resolved stellar populations, appear complex and varied. The general picture derived from hydrodynamical simulations is one of cold gas accretion and bursty star formation, followed by feedback from supernovae and winds that heat and eject the central gas reservoirs. This ejection halts star formation until the material cools and re-accretes, resulting in an episodic SFH, particularly at stellar masses below ~ 109 M⊙. Such feedback has often been cited as the driving force behind the observed slowly-rising rotation curves in local dwarfs, due to an under-density of dark matter compared to theoretical models, which is one of the primary challenges to LCDM cosmology. However, these events have not yet been directly observed at high-redshift. Recently, using HST imaging and grism spectroscopy, we have uncovered an abundant population of low-mass galaxies (M* < 109 M⊙) at z = 1 - 2 that are undergoing strong bursts of star formation, in agreement with the theoretical predictions. These Extreme Emission Line Galaxies, with high specific SFRs and shallow gravitational potential wells, are ideal places to test the theoretical prediction of strong feedback-driven outflows. Here we use deep MUSE spectroscopy to search these galaxies for signatures of outflowing material, namely kinematic offsets between absorption lines (in the restframe optical and UV), which trace cool gas, and the nebular emission lines, which define the systemic redshift of the galaxy. Although the EELGs are intrinsically very faint, stacked spectra reveal blueshifted velocity centroids for Fe II absorption, which is indicative of outflowing cold gas. This represents the first constraint on outflows in M* < 109 M⊙ galaxies at z = 1 - 2. These outflows should regulate the star formation histories of low-mass galaxies at early cosmic times and thus play a crucial role in galaxy growth and evolution.

  2. Low Mass Printable Devices for Energy Capture, Storage, and Use

    NASA Technical Reports Server (NTRS)

    Frazier, Donald O.; Singer, Christopher E.; Rogers, Jan R.; Schramm, Harry F.; Fabisinski, Leo L.; Lowenthal, Mark; Ray, William J.; Fuller, Kirk A.

    2010-01-01

    The energy-efficient, environmentally friendly technology that will be presented is the result of a Space Act Agreement between NthDegree Technologies Worldwide, Inc., and the National Aeronautics and Space Administration's (NASA's) Marshall Space Flight Center (MSFC). The work combines semiconductor and printing technologies to advance lightweight electronic and photonic devices having excellent potential for commercial and exploration applications. Device development involves three projects that relate to energy generation and consumption: (1) a low-mass efficient (low power, low heat emission) micro light-emitting diode (LED) area lighting device; (2) a low-mass omni-directional efficient photovoltaic (PV) device with significantly improved energy capture; and (3) a new approach to building super-capacitors. These three technologies, energy capture, storage, and usage (e.g., lighting), represent a systematic approach for building efficient local micro-grids that are commercially feasible; furthermore, these same technologies, appropriately replacing lighting with lightweight power generation, will be useful for enabling inner planetary missions using smaller launch vehicles and to facilitate surface operations during lunar and planetary surface missions. The PV device model is a two sphere, light trapped sheet approximately 2-mm thick. The model suggests a significant improvement over current thin film systems. For lighting applications, all three technology components are printable in-line by printing sequential layers on a standard screen or flexographic direct impact press using the three-dimensional printing technique (3DFM) patented by NthDegree. One primary contribution to this work in the near term by the MSFC is to test the robustness of prototype devices in the harsh environments that prevail in space and on the lunar surface. It is anticipated that this composite device, of which the lighting component has passed off-gassing testing, will function

  3. HIGH-PRECISION DYNAMICAL MASSES OF VERY LOW MASS BINARIES

    SciTech Connect

    Konopacky, Q. M.; Ghez, A. M.; McLean, I. S.; Barman, T. S.; Rice, E. L.; Bailey, J. I.; White, R. J.; Duchene, G. E-mail: ghez@astro.ucla.ed E-mail: barman@lowell.ed E-mail: white@chara.gsu.ed

    2010-03-10

    We present the results of a three year monitoring program of a sample of very low mass (VLM) field binaries using both astrometric and spectroscopic data obtained in conjunction with the laser guide star adaptive optics system on the W. M. Keck II 10 m telescope. Among the 24 systems studied, 15 have undergone sufficient orbital motion, allowing us to derive their relative orbital parameters and hence their total system mass. These measurements more than double the number of mass measurements for VLM objects, and include the most precise mass measurement to date (<2%). Among the 11 systems with both astrometric and spectroscopic measurements, six have sufficient radial velocity variations to allow us to obtain individual component masses. This is the first derivation of the component masses for five of these systems. Altogether, the orbital solutions of these low mass systems show a correlation between eccentricity and orbital period, consistent with their higher mass counterparts. In our primary analysis, we find that there are systematic discrepancies between our dynamical mass measurements and the predictions of theoretical evolutionary models (TUCSON and LYON) with both models either underpredicting or overpredicting the most precisely determined dynamical masses. These discrepancies are a function of spectral type, with late-M through mid-L systems tending to have their masses underpredicted, while one T-type system has its mass overpredicted. These discrepancies imply that either the temperatures predicted by evolutionary and atmosphere models are inconsistent for an object of a given mass, or the mass-radius relationship or cooling timescales predicted by the evolutionary models are incorrect. If these spectral-type trends are correct and hold into the planetary mass regime, the implication is that the masses of directly imaged extrasolar planets are overpredicted by the evolutionary models.

  4. Dynamical structure of the inner 100 AU of the deeply embedded protostar IRAS 16293–2422

    SciTech Connect

    Favre, Cécile; Field, David; Jørgensen, Jes K.; Brinch, Christian; Bisschop, Suzanne E.; Bourke, Tyler L.; Hogerheijde, Michiel R.; Frieswijk, Wilfred W. F.

    2014-07-20

    A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly formed stars, for example, to identify the presence of rotation and infall. IRAS 16293–2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.''46 × 0.''29, i.e., ∼55 × 35 AU) images of compact emission from the C{sup 17}O (3-2) and C{sup 34}S (7-6) transitions at 337 GHz (0.89 mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C{sup 17}O (3-2) and C{sup 34}S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS 16293A. Our combined eSMA and SMA observations show that the velocity field on the 50-400 AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293–2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.

  5. Change in the chemical composition of infalling gas forming a disk around a protostar.

    PubMed

    Sakai, Nami; Sakai, Takeshi; Hirota, Tomoya; Watanabe, Yoshimasa; Ceccarelli, Cecilia; Kahane, Claudine; Bottinelli, Sandrine; Caux, Emmanuel; Demyk, Karine; Vastel, Charlotte; Coutens, Audrey; Taquet, Vianney; Ohashi, Nagayoshi; Takakuwa, Shigehisa; Yen, Hsi-Wei; Aikawa, Yuri; Yamamoto, Satoshi

    2014-03-06

    IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.

  6. LEO P: AN UNQUENCHED VERY LOW-MASS GALAXY

    SciTech Connect

    McQuinn, Kristen B. W.; Skillman, Evan D.; Berg, Danielle; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.; Girardi, Léo

    2015-10-20

    Leo P is a low-luminosity dwarf galaxy discovered through the blind H i Arecibo Legacy Fast ALFA survey. The H i and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging with the Hubble Space Telescope to two magnitudes below the red clump in order to study the evolution of Leo P. We refine the distance measurement to Leo P to be 1.62 ± 0.15 Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ∼0.4 Mpc from Sextans B, the nearest galaxy in the NGC 3109 association of dwarf galaxies of which Leo P is clearly a member. The star responsible for ionizing the H ii region is most likely an O7V or O8V spectral type, with a stellar mass ≳25 M{sub ⊙}. The presence of this star provides observational evidence that massive stars at the upper end of the initial mass function are capable of being formed at star formation rates as low as ∼10{sup −5} M{sub ⊙} yr{sup −1}. The best-fitting star formation history (SFH) derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its SFH is subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that the local environment dominates the quenching of the Milky Way satellites.

  7. Leo P: An Unquenched Very Low-mass Galaxy

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Berg, Danielle; Giovanelli, Riccardo; Girardi, Léo; Haynes, Martha P.

    2015-10-01

    Leo P is a low-luminosity dwarf galaxy discovered through the blind H i Arecibo Legacy Fast ALFA survey. The H i and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging with the Hubble Space Telescope to two magnitudes below the red clump in order to study the evolution of Leo P. We refine the distance measurement to Leo P to be 1.62 ± 0.15 Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ˜0.4 Mpc from Sextans B, the nearest galaxy in the NGC 3109 association of dwarf galaxies of which Leo P is clearly a member. The star responsible for ionizing the H ii region is most likely an O7V or O8V spectral type, with a stellar mass ≳25 M⊙. The presence of this star provides observational evidence that massive stars at the upper end of the initial mass function are capable of being formed at star formation rates as low as ˜10-5 M⊙ yr-1. The best-fitting star formation history (SFH) derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its SFH is subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that the local environment dominates the quenching of the Milky Way satellites. Based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained from the

  8. Molecular outflows from protostars. Questions, options and facts.

    NASA Astrophysics Data System (ADS)

    Henriksen, R. N.

    In this discussion of molecular outflows the author isolates the basic theoretical questions, and discusses some of the model options in the light of a few decisive observational facts. In addition several new lines of theoretical argument are introduced regarding the behaviour of the protostar environment. These concern the global energy and momentum balance and the nature of the steady state that is compatible with a non-zero Poynting flux. Finally brief reference is made to a thorough study by Fiege and Henriksen, 1995 of the global model suggested in Henriksen and Valls-Gabaud, 1994.

  9. Bipolar Outflows Properties from Class 0/I protostars in Perseus

    NASA Astrophysics Data System (ADS)

    De La Rosa, Oscar A.; Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) Program

    2017-01-01

    The Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) program is a key project by the Submillimeter Array (SMA) telescope that is observing the 70 youngest protostars in the Perseus molecular cloud. From SMA CO(2-1) and continuum observations, we investigate correlations among the YSOs properties, including outflow opening angles, ages, luminosities, envelope masses, and temperatures. No discernable pattern between measured angle versus bolometric temperature was found, independent of the mass or luminosity. These results indicate that the evolutionary sequence is more chaotic than originally predicted in Arce & Sargent (2006).

  10. Low Mass Members in Nearby Young Moving Groups Revealed

    NASA Astrophysics Data System (ADS)

    Schlieder, Joshua; Simon, Michal; Rice, Emily; Lepine, Sebastien

    2010-08-01

    We are now ready to expand our program that identifies highly probable low-mass members of the nearby young moving groups (NYMGs) to stars of mass ~ 0.1 Msun. This is important 1) To provide high priority targets for exoplanet searches by direct imaging, 2) To complete the census of the membership in the NYMGs, and 3) To provide a well-characterized sample of nearby young stars for detailed study of their physical properties and multiplicity (the median distances of the (beta) Pic and AB Dor groups are ~ 35 pc with ages ~ 12 and 50 Myr respectively). Our proven technique starts with a proper motion selection algorithm, proceeds to vet the sample for indicators of youth, and requires as its last step the measurement of candidate member radial velocities (RVs). So far, we have obtained all RV measurements with the high resolution IR spectrometer at the NASA-IRTF and have reached the limits of its applicability. To identify probable new members in the south, and also those of the lowest mass, we need the sensitivity of PHOENIX at Gemini-S and NIRSPEC at Keck-II.

  11. Low-mass Visual Companions to Nearby G-dwarfs

    NASA Astrophysics Data System (ADS)

    Tokovinin, Andrei

    2011-02-01

    A complete census of wide visual companions to nearby G-dwarf stars can be achieved by selecting candidates from the Two Micron All Sky Survey (2MASS) Point-Source Catalog and checking their status by second-epoch imaging. Such data are obtained for 124 candidates with separations up to 20'', 47 of which are shown to be new physical low-mass stellar companions. A list of visual binaries with G-dwarf primaries is produced by combining newly found companions with historical data. Maximum likelihood analysis leads to a companion frequency of 0.13 ± 0.015 per decade of separation. The mass ratio is distributed almost uniformly, with a power-law index between -0.4 and 0. The remaining uncertainty in the index is related to modeling of the companion detection threshold in 2MASS. These findings are confirmed by an alternative analysis of wider companions in 2MASS, removing the contamination by background stars statistically. Extension of this work will lead to a complete detection of visual companions—a necessary step toward reaching unbiased multiplicity statistics over the full range of orbital periods and, eventually, understanding the origin of multiple systems.

  12. CHANDRA OBSERVATION OF POLARIS: CENSUS OF LOW-MASS COMPANIONS

    SciTech Connect

    Remage Evans, Nancy; Wolk, Scott J.; Karovska, Margarita; Spitzbart, Bradley; Guinan, Edward; Engle, Scott; Schlegel, Eric; Mason, Brian D.

    2010-05-15

    We have observed Cepheid Polaris ({alpha} UMi A: F7 Ib [Aa] + F6 V [Ab]) with Chandra ACIS-I for 10 ks. An X-ray source was found at the location of Polaris with log L{sub X} = 28.89 erg s{sup -1} (0.3-8 keV) and kT = 0.6 keV. A spectrum this soft could come from either the supergiant or the dwarf, as shown by comparable coronal stars. Two resolved low-mass visual companions, 'C' and 'D', are not physical members of the system based on the lack of X-rays (indicating an age older than the Cepheid) and inconsistent proper motions. Polaris B is not an X-ray source, consistent with its early F spectral type, and probably does not have a lower mass companion itself. A possible more distant member is identified, and an additional less plausible one. This provides a complete census of companions out to 0.1 pc covering a mass ratio range of an order of magnitude and a {Delta}V of nearly 15 mag.

  13. LOW-MASS VISUAL COMPANIONS TO NEARBY G-DWARFS

    SciTech Connect

    Tokovinin, Andrei

    2011-02-15

    A complete census of wide visual companions to nearby G-dwarf stars can be achieved by selecting candidates from the Two Micron All Sky Survey (2MASS) Point-Source Catalog and checking their status by second-epoch imaging. Such data are obtained for 124 candidates with separations up to 20'', 47 of which are shown to be new physical low-mass stellar companions. A list of visual binaries with G-dwarf primaries is produced by combining newly found companions with historical data. Maximum likelihood analysis leads to a companion frequency of 0.13 {+-} 0.015 per decade of separation. The mass ratio is distributed almost uniformly, with a power-law index between -0.4 and 0. The remaining uncertainty in the index is related to modeling of the companion detection threshold in 2MASS. These findings are confirmed by an alternative analysis of wider companions in 2MASS, removing the contamination by background stars statistically. Extension of this work will lead to a complete detection of visual companions-a necessary step toward reaching unbiased multiplicity statistics over the full range of orbital periods and, eventually, understanding the origin of multiple systems.

  14. A Unified Model of Low Mass X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Balucinska-Church, M.; Church, M.

    2014-07-01

    We present a unified physical model of Low Mass X-ray Binaries explaining the basic Atoll and Z-track types of source. In all LMXB with luminosity above 1-2.10^{37} erg/s, we have a new fundamental result that the temperature of the Comptonizing ADC corona equals that of the neutron star, i.e. there is thermal equilibrium. This equilibrium explains the properties of the basic Banana State of Atoll sources. Below this luminosity, equilibrium breaks down, T_ADC rising towards 100 keV by an unknown heating mechanism, explaining the Island State. Above 5.10^{37} erg/s flaring begins in the GX-Atolls which we show is unstable nuclear burning. Above 1.10^{38} erg/s, LMXB are seen as Z-track sources. Flaring in these and the GX-Atolls occurs when the mass accretion rate to the neutron star falls to the critical value for unstable nuclear burning on the star. Below 2.10^{37} erg/s, a different unstable burning: X-ray bursting, takes over. We show that the Normal Branch of the Z-track consists simply of increasing mass accretion rate, as is the Banana State in Atolls. In the Horizontal Branch, a measured, strongly increasing radiation pressure of the neutron star disrupts the inner disk launching the relativistic jets seen on this branch.

  15. DISCOVERY OF A LOW-MASS COMPANION AROUND HR 3549

    SciTech Connect

    Mawet, D.; David, T.; Bottom, M.; Hinkley, S.; Stapelfeldt, K.; Padgett, D.; Mennesson, B.; Serabyn, E.; Morales, F.; Kuhn, J.

    2015-10-01

    We report the discovery of a low-mass companion to HR 3549, an A0V star surrounded by a debris disk with a warm excess detected by WISE at 22 μm (10σ significance). We imaged HR 3549 B in the L band with NAOS-CONICA, the adaptive optics infrared camera of the Very Large Telescope, in January 2013 and confirmed its common proper motion in 2015 January. The companion is at a projected separation of ≃80 AU and position angle of ≃157°, so it is orbiting well beyond the warm disk inner edge of r > 10 AU. Our age estimate for this system corresponds to a companion mass in the range 15–80 M{sub J}, spanning the brown dwarf regime, and so HR 3549 B is another recent addition to the growing list of brown dwarf desert objects with extreme mass ratios. The simultaneous presence of a warm disk and a brown dwarf around HR 3549 provides interesting empirical constraints on models of the formation of substellar companions.

  16. 3D lumped LC resonators as low mass axion haloscopes

    NASA Astrophysics Data System (ADS)

    McAllister, Ben T.; Parker, Stephen R.; Tobar, Michael E.

    2016-08-01

    The axion is a hypothetical particle considered to be the most economical solution to the strong C P problem. It can also be formulated as a compelling component of dark matter. The haloscope, a leading axion detection scheme, relies on the conversion of galactic halo axions into real photons inside a resonant cavity structure in the presence of a static magnetic field, where the generated photon frequency corresponds to the mass of the axion. For maximum sensitivity it is key that the central frequency of the cavity mode structure coincides with the frequency of the generated photon. As the mass of the axion is unknown, it is necessary to perform searches over a wide range of frequencies. Currently there are substantial regions of the promising preinflationary low-mass axion range without any viable proposals for experimental searches. We show that three-dimensional resonant LC circuits with separated magnetic and electric fields, commonly known as reentrant cavities, can be sensitive dark matter haloscopes in this region, with frequencies inherently lower than those achievable in the equivalent size of empty resonant cavity. We calculate the sensitivity and accessible axion mass range of these experiments, designing geometries to exploit and maximize the separated magnetic and electric coupling of the axion to the cavity mode.

  17. Flare activity on low-mass eclipsing binary GJ 3236*

    NASA Astrophysics Data System (ADS)

    Šmelcer, L.; Wolf, M.; Kučáková, H.; Bílek, F.; Dubovský, P.; Hoňková, K.; Vraštil, J.

    2017-04-01

    We report the discovery of optical flares on the very low-mass red-dwarf eclipsing binary GJ 3236 and the results of our 2014-2016 photometric campaign. In total, this binary was monitored photometrically in all filters for about 900 h, which has revealed a flare rate of about 0.06 flares per hour. The amplitude of its flares is the largest among those detected in the V band (∼1.3 mag), R band (∼0.8 mag), I band (∼0.2 mag) and clear band (∼0.5 mag). The light curves of GJ 3236 were analysed and the statistics of detected flare events are presented. The energy released during individual flares was calculated as up to 2.4 × 1027 J and compared with other known active stars. The cumulative distribution of flare energies appears to follow a broken power law. The flare activity of this binary also plays an important role in the precise determination of its physical parameters and evolutionary status.

  18. The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). II. Multiplicity of Protostars in the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Tobin, John J.; Looney, Leslie W.; Li, Zhi-Yun; Chandler, Claire J.; Dunham, Michael M.; Segura-Cox, Dominique; Sadavoy, Sarah I.; Melis, Carl; Harris, Robert J.; Kratter, Kaitlin; Perez, Laura

    2016-02-01

    We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array survey at Ka-band (8 mm and 1 cm) and C-band (4 and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L⊙ and ˜33 L⊙, with a median of 0.7 L⊙. This multiplicity study is based on the Ka-band data, having a best resolution of ˜0.″065 (15 au) and separations out to ˜43″ (10,000 au) can be probed. The overall multiplicity fraction (MF) is found to be 0.40 ± 0.06 and the companion star fraction (CSF) is 0.71 ± 0.06. The MF and CSF of the Class 0 protostars are 0.57 ± 0.09 and 1.2 ± 0.2, and the MF and CSF of Class I protostars are both 0.23 ± 0.08. The distribution of companion separations appears bi-modal, with a peak at ˜75 au and another peak at ˜3000 au. Turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on <200 au scales. Toward three Class 0 sources we find companions separated by <30 au. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50-400 au) structures and may be candidates for ongoing disk fragmentation.

  19. THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD

    SciTech Connect

    Tobin, John J.; Harris, Robert J.; Looney, Leslie W.; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Perez, Laura; Dunham, Michael M.; Sadavoy, Sarah I.; Melis, Carl; Kratter, Kaitlin

    2016-02-10

    We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array survey at Ka-band (8 mm and 1 cm) and C-band (4 and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L{sub ⊙} and ∼33 L{sub ⊙}, with a median of 0.7 L{sub ⊙}. This multiplicity study is based on the Ka-band data, having a best resolution of ∼0.″065 (15 au) and separations out to ∼43″ (10,000 au) can be probed. The overall multiplicity fraction (MF) is found to be 0.40 ± 0.06 and the companion star fraction (CSF) is 0.71 ± 0.06. The MF and CSF of the Class 0 protostars are 0.57 ± 0.09 and 1.2 ± 0.2, and the MF and CSF of Class I protostars are both 0.23 ± 0.08. The distribution of companion separations appears bi-modal, with a peak at ∼75 au and another peak at ∼3000 au. Turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on <200 au scales. Toward three Class 0 sources we find companions separated by <30 au. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50–400 au) structures and may be candidates for ongoing disk fragmentation.

  20. Radio variability survey of very low luminosity protostars

    SciTech Connect

    Choi, Minho; Kang, Miju; Lee, Jeong-Eun

    2014-07-01

    Ten very low luminosity objects were observed multiple times in the 8.5 GHz continuum in search of protostellar magnetic activities. A radio outburst of IRAM 04191+1522 IRS was detected, and the variability timescale was about 20 days or shorter. The results of this survey and archival observations suggest that IRAM 04191+1522 IRS is in active states about half the time. Archival data show that L1014 IRS and L1148 IRS were detectable previously and suggest that at least 20%-30% of very low luminosity protostars are radio variables. Considering the variability timescale and flux level of IRAM 04191+1522 IRS and the previous detection of the circular polarization of L1014 IRS, the radio outbursts of these protostars are probably caused by magnetic flares. However, IRAM 04191+1522 IRS is too young and small to develop an internal convective dynamo. If the detected radio emission is indeed coming from magnetic flares, the discovery implies that the flares may be caused by the fossil magnetic fields of interstellar origin.

  1. HOPS 383: AN OUTBURSTING CLASS 0 PROTOSTAR IN ORION

    SciTech Connect

    Safron, Emily J.; Megeath, S. Thomas; Booker, Joseph; Fischer, William J.; Furlan, Elise; Rebull, Luisa M.; Stutz, Amelia M.; Stanke, Thomas; Billot, Nicolas; Tobin, John J.; Ali, Babar; Allen, Lori E.; Watson, Dan M.; Wilson, T. L.

    2015-02-10

    We report the dramatic mid-infrared brightening between 2004 and 2006 of Herschel Orion Protostar Survey (HOPS) 383, a deeply embedded protostar adjacent to NGC 1977 in Orion. By 2008, the source became a factor of 35 brighter at 24 μm with a brightness increase also apparent at 4.5 μm. The outburst is also detected in the submillimeter by comparing APEX/SABOCA to SCUBA data, and a scattered-light nebula appeared in NEWFIRM K{sub s} imaging. The post-outburst spectral energy distribution indicates a Class 0 source with a dense envelope and a luminosity between 6 and 14 L{sub ⊙}. Post-outburst time-series mid- and far-infrared photometry show no long-term fading and variability at the 18% level between 2009 and 2012. HOPS 383 is the first outbursting Class 0 object discovered, pointing to the importance of episodic accretion at early stages in the star formation process. Its dramatic rise and lack of fading over a 6 year period hint that it may be similar to FU Ori outbursts, although the luminosity appears to be significantly smaller than the canonical luminosities of such objects.

  2. Rotational Velocities of Individual Components in Very Low Mass Binaries

    NASA Astrophysics Data System (ADS)

    Konopacky, Q. M.; Ghez, A. M.; Fabrycky, D. C.; Macintosh, B. A.; White, R. J.; Barman, T. S.; Rice, E. L.; Hallinan, G.; Duchêne, G.

    2012-05-01

    We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s-1), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349-25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes lsim3.5 AU, have component v sin i values that differ by greater than 3σ. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A-BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A-Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349-25AB and 2MASS 0746+20AB, are also known radio sources.

  3. Model Atmospheres From Very Low Mass Stars to Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Allard, F.; Homeier, D.; Freytag, B.

    2011-12-01

    Since the discovery of brown dwarfs in 1994, and the discovery of dust cloud formation in the latest Very Low Mass Stars (VLMs) and Brown Dwarfs (BDs) in 1996, the most important challenge in modeling their atmospheres as become the understanding of cloud formation and advective mixing. For this purpose, we have developed radiation hydrodynamic 2D model atmosphere simulations to study the formation of forsterite dust in presence of advection, condensation, and sedimentation across the M-L-T VLMs to BDs sequence (Teff = 2800 K to 900 K, Freytag et al. 2010). We discovered the formation of gravity waves as a driving mechanism for the formation of clouds in these atmospheres, and derived a rule for the velocity field versus atmospheric depth and Teff, which is relatively insensitive to gravity. This rule has been used in the construction of the new model atmosphere grid, BT-Settl, to determine the micro-turbulence velocity, the diffusion coefficient, and the advective mixing of molecules as a function of depth. This new model grid of atmospheres and synthetic spectra has been computed for 100,000 K > Teff > 400 K, 5.5 > logg > -0.5, and [M/H]= +0.5 to -1.5, and the reference solar abundances of Asplund et al. (2009). We found that the new solar abundances allow an improved (close to perfect) reproduction of the photometric and spectroscopic VLMs properties, and, for the first time, a smooth transition between stellar and substellar regimes -- unlike the transition between the NextGen models from Hauschildt et al. 1999a,b, and the AMES-Dusty models from Allard et al. 2001. In the BDs regime, the BT-Settl models propose an improved explanation for the M-L-T spectral transition. In this paper, we therefore present the new BT-Settl model atmosphere grid, which explains the entire transition from the stellar to planetary mass regimes.

  4. Low Mass Stellar Companions to Nearby A and B Stars

    NASA Astrophysics Data System (ADS)

    Gullikson, Kevin; Kraus, Adam L.

    2015-01-01

    Recent discoveries of planets orbiting retired A-stars on close orbits and young A-stars on very wide orbits have renewed interest in the properties of nearby intermediate-mass stars. Especially interesting are the young stars, because directly-imaged planets orbiting them may be bright enough for characterization (e.g. HR 8799, Beta Pictoris, etc). However, intermediate-mass stars and especially young intermediate mass stars are part of multiple systems more often than not. Close stellar companions may affect the formation and orbital evolution of any planets, and the properties of the companions can help constrain the binary formation mechanism. The mass ratio distribution of a population of stars, especially if it is significantly different from the distribution for wide companions, is helpful to distinguish companions that were born in or affected by the circumprimary disk from those which formed through fragmentation of the molecular core. We have conducted a spectroscopic survey of 400 nearby A- and B-type stars, aimed at detecting stellar companions as late as M4 for all orbital separations <100 AU. We have searched for companions to the stars by cross-correlating the spectra against model templates for F-M type stars; a significant peak in the cross-correlation function indicates a detection. Our cross-correlation technique can detect low-mass companions with orbits that are too wide to detect with radial velocity monitoring and too small to detect with imaging techniques, making it complementary to work already done. We present initial results from our survey and present the distribution of mass ratios for inner companions.

  5. Tidal Alignment of Exoplanets Around Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Penev, Kaloyan; Jackson, Brian K.

    2014-06-01

    Using the Rossiter-McLaughlin effect, the projected spin-orbit angle for many exoplanetary systems has now been measured. Thanks to this rapidly increasing sample it is becoming clear that stars with surface convective zones appear to be well aligned while those without span a wide range of inclinations. The explanation proposed (Winn et al 2010) is that perhaps only the convective zones align with the planet, while the cores remain misaligned. This explanation suffers from two problems however: the core-envelope coupling in low mass stars appears to be strong enough to prevent long-lived differential rotation and even if only the convective zone is aligned, the planet generally does not survive for long after that. Since tides due to a planet on a misaligned orbit have a component at the rotational frequency of the star, and for an aligned planet the only frequency is the difference between the generally fast planet and the slowly rotating star, it is conceivable that misaligned systems are subject to much enhanced dissipation, acting for example on resonantly excited inertial waves in the star. However, Rogers & Lin (2013) point out that under inertial mode dissipation, in addition to aligned orbits one would expect a pile-up on polar and/or exactly counter-rotating orbits. We propose that the extra equilibrium solutions disappear if one includes in the evolution the fact that stars evolve and shed angular momentum throughout their lifetime. We have built a model including all those effects and will show results exploring this explanation.

  6. ROTATIONAL VELOCITIES OF INDIVIDUAL COMPONENTS IN VERY LOW MASS BINARIES

    SciTech Connect

    Konopacky, Q. M.; Macintosh, B. A.; Ghez, A. M.; Fabrycky, D. C.; White, R. J.; Barman, T. S.; Rice, E. L.; Hallinan, G.; Duchene, G. E-mail: konopacky@di.utoronto.ca E-mail: fabrycky@ucolick.org E-mail: barman@lowell.edu E-mail: gh@astro.caltech.edu

    2012-05-01

    We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s{sup -1}), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349-25B and HD 130948C, are rotating at {approx}30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes {approx}<3.5 AU, have component v sin i values that differ by greater than 3{sigma}. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A-BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A-Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349-25AB and 2MASS 0746+20AB, are also known radio sources.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  8. Molecular jets driven by high-mass protostars: a detailed study of the IRAS 20126+4104 jet

    NASA Astrophysics Data System (ADS)

    Caratti o Garatti, A.; Froebrich, D.; Eislöffel, J.; Giannini, T.; Nisini, B.

    2008-07-01

    Context: Protostellar jets from intermediate- and high-mass protostars provide an excellent opportunity to understand the mechanisms responsible for intermediate- and high-mass star-formation. A crucial question is if they are scaled-up versions of their low-mass counterparts. Such high-mass jets are relatively rare and, usually, they are distant and highly embedded in their parental clouds. The IRAS 20126+4104 molecular jet, driven by a 10^4 L⊙ protostar, represents a suitable target to investigate. Aims: We present here an extensive analysis of this protostellar jet, deriving the kinematical, dynamical, and physical conditions of the H2 gas along the flow. Methods: The jet was investigated by means of near-IR H2 and [Fe II] narrow-band imaging, high-resolution spectroscopy of the 1-0 S(1) line (2.12 μm), NIR (0.9-2.5 μm) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200 μm). Results: The flow shows a complex morphology. In addition to the large-scale jet precession presented in previous studies, we detect a small-scale wiggling close to the source, which may indicate the presence of a multiple system. The peak radial velocities of the H2 knots range from -42 to -14 km s-1 in the blue lobe, and from -8 to 47 km s-1 in the red lobe. The low-resolution spectra are rich in H2 emission, and relatively faint [Fe II] (NIR), [O I] and [C II] (FIR) emission is observed in the region close to the source. A warm H2 gas component has an average excitation temperature that ranges between 2000 K and 2500 K. Additionally, the ISO-SWS spectrum reveals a cold component (520 K) that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated L_H2 of the jet is 8.2 ± 0.7 L⊙, suggesting that IRAS 20126+4104 has a significantly increased accretion rate compared to low-mass YSOs. This is also supported by the derived mass flux rate from the H2 lines (dot{M}_out(H2)˜ 7.5× 10-4 M

  9. Near and far infrared observations of protostars and dark clouds

    NASA Astrophysics Data System (ADS)

    Suters, Mark Gerard

    1992-11-01

    Far infrared point source and extended emission data from the Infrared Astronomical Satellite (IRAS) survey are used to investigate the properties of star formation in the regions of high galactic latitude dark cloud complexes. The properties of individual sources are examined using near infrared spectroscopy and broad band spectral energy distributions. The IRAS signature of star formation is derived by comparing the far infrared colors of a sample of protostars with those of other common far infrared objects. The quality of the IRAS data is ignored for the purposes of this investigation. The criteria developed for identifying protostars from the IRAS Point Source Catalog discriminates against most non-protostellar objects, with the exception of galaxies and HII regions. Objects identified as protostellar according to other criteria are also likely to be identified by the criteria developed. Extended emission data in the far infrared is used to estimate the column density and temperature of several dark cloud complexes, and the optical extinction in the same regions is estimated with the Guide Star Catalog. Temperature and column density share an inverse relationship cloud cores are characterized by column densities above 1024 hydrogen atoms m-2 and temperatures around 20 K, while the inter cloud medium has column densities below 1023 atoms m-2 and temperatures above 50 K. The column density, as measured by IRAS, and the optical extinction appear to be related up to values of around 1025 atoms m-2 and 5 magnitudes respectively but the IRAS detectors appear insensitive to material at higher densities than these. Near infrared spectra of a variety of objects chosen for their youth, including IRAS sources which satisfy the protostar criteria, are investigated. These spectra are categorized into three distinct groups of increasing youth: (1) T Tauri-like spectra, with flat H and K band continua, lacking both Br-gamma emission and CO absorption; (2) FU Orilike spectra

  10. The Discovery of Extremely Young Protostars in Orion with Herschel and APEX

    NASA Astrophysics Data System (ADS)

    Stutz, Amelia; Tobin, John; Stanke, Thomas; Megeath, Tom; Fischer, Will; Robitaille, Thomas; Henning, Thomas; Ali, Babar; Di Francesco, James; Furlan, Elise; Osorio, Mayra; HOPS Team

    2013-07-01

    We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using 24 um - 870 um imaging obtained with the Spitzer, Herschel, and APEX telescopes as part of the Herschel Orion Protostar Survey (HOPS). We find a sample of 15 new extremely red protostar candidates that can reliably identified as protostars (Stutz et al., 2013). Taking the previously known sample of 300 Spitzer protostars and the new sample of 15 Herschel identified protostars together, we find 18 extremely red protostars (i.e., log λFλ70 / λFλ24 > 1.65). These are the reddest protostars known in Orion and we name them "PACS Bright Red sources", or PBRS. Our analysis reveals that the PBRs sample is composed of Class 0 like sources with very red spectral energy distributions (SEDs; Tbol < 45 K) and large sub-millimeter fluxes (Lsmm/Lbol > 0.6%). Modified blackbody fits to the SEDs provide lower limits to the envelope masses of 0.2 Msun - 2 Msun and luminosities of 0.7 Lsun - 10 Lsun. Based on these properties, and a comparison of the SEDs with radiative transfer models of protostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typical envelope densities and possibly high mass infall rates. We estimate the ages of the PBRs to be between 5000 and 25000 years. We find that the fraction of PBRS is more than 5 times higher in the Orion B cloud than in Orion A; this may be due to differences in the star formation histories or in the star forming environment.

  11. Coronal Activity in Low-Mass Pre-Main Sequence Stars: NGC 2264

    NASA Technical Reports Server (NTRS)

    Tebbe, H. J.; Patten, B. M.

    2000-01-01

    We present the preliminary results of an analysis of ROSAT images in the region of the populous young (age approx. 3 Myr) star-forming region NGC 2264. The cluster was imaged with the ROSAT HRI in two sets of pointings -- one set near the central region of the cluster, centered on the star LW Mon, and the other set in the southern part of the cluster, centered near the star V428 Mon, just south of the Cone Nebula. In total 113 unique X-ray sources have been identified in the ROSAT images with signal-to-noise ratios greater than 3. The limiting luminosities (log Lx(ergs/sec)) for 3-sigma detections are estimated to be 30.18, 30.23, and 30.08 for the northern field, southern field, and overlap region between the two fields respectively. Extensive optical photometry, classification spectroscopy, and proper motions, obtained from recent ground-based surveys of this region, were used to identify the most likely optical counterpart to each X-ray source. Although most of our X-ray selected sample appears to be associated with NGC 2264 members, we find that the vast majority of the cluster membership was undetected in the ROSAT HRI survey. The X-ray cumulative luminosity function for solar-mass stars in NGC 2264 shows that most of the low-mass members probably have X-ray luminosities similar to those seen for the X-ray brightest members of older clusters such as IC 2391/IC 2602 (age approx. 50 Myr) and the Pleiades (age approx. 100 Myr). This research was funded in part by the SAO Summer Intern Program and NASA grant NAG5-8120.

  12. Terrestrial planets and water delivery around low-mass stars

    NASA Astrophysics Data System (ADS)

    Dugaro, A.; de Elía, G. C.; Brunini, A.; Guilera, O. M.

    2016-11-01

    Context. Theoretical and observational studies suggest that protoplanetary disks with a wide range of masses could be found around low-mass stars. Aims: We analyze planetary formation processes in systems without gas giants around M3- and M0-type stars of 0.29 M⊙ and 0.5 M⊙, respectively. In particular, we assume disks with masses of 5% and 10% of the mass of the star. Our study focuses on the formation of terrestrial-like planets and water delivery in the habitable zone (HZ). Methods: First, we use a semi-analytical model to describe the evolution of embryos and planetesimals during the gaseous phase. Then, a N-body code is used to analyze the last giant impact phase after the gas dissipation. Results: For M3-type stars, five planets with different properties are formed in the HZ. These planets have masses of 0.072 M⊕, 0.13 M⊕ (two of them), and 1.03 M⊕, and have water contents of 5.9%, 16.7%, 28.6%, and 60.6% by mass, respectively. Then, the fifth planet formed in the HZ is a dry world with 0.138 M⊕. For M0-type stars, four planets are produced in the HZ with masses of 0.28 M⊕, 0.51 M⊕, 0.72 M⊕, and 1.42 M⊕, and they have water contents of 26.7%, 45.8%, 68%, and 50.5% by mass, respectively. Conclusions: M3- and M0-type stars represent targets of interest for the search of exoplanets in the HZ. In fact, the Mars-mass planets formed around M3-type stars could maintain habitable conditions in their early histories. Thus, the search for candidates around young M3-type stars could lead to the detection of planets analogous to early Mars. Moreover, Earth-mass planets should also be discovered around M3-type stars and, sub- and super-Earths should be detected around M0-type stars. Such planets are very interesting since they could maintain habitable conditions for very long.

  13. Atmospheric circulations of terrestrial planets orbiting low mass stars

    NASA Astrophysics Data System (ADS)

    Edson, Adam Robert

    Atmospheres of planets orbiting low mass stars have properties unlike those typically studied by climatologists. One of the most glaring differences is that the rotation is "trapped" for planets orbiting within the habitable zone of the star. This lack of a typical "day" changes these planets' dynamics. Previous work includes that of Gareth Williams and Manoj Joshi. Joshi discussed planets with 10-day orbits only. Williams focused on planets with differing rotation rates, but still rotating relative to their star. Here, tidally locked planets with a variety of orbital periods ranging from 1 to 100 days are discussed. The GENESIS model is used to simulate these planets, and the data are analyzed for waves, energy fluxes, and habitability. The major components of the energy fluxes are the mean meridional circulation (i.e., the Hadley cell) and stationary eddies in the form of a wave number 1 stationary Rossby wave. A transition point in the atmospheric circulation is identified for orbital periods between 100 hours and 101 hours for dry planets. For the wet planets, the transition occurs near 96-hour rotation period. This transition occurs when the Rossby radius of deformation approaches the planet's radius and is associated with the increasing importance of the wave number two stationary eddy as the Rossby radius approaches the planetary radius. The most habitable dry planet is found to be the 2400-hour orbiter. For the wet planets, the 24-hour rotator is most habitable. The most habitable wet planet is the 24-hour rotator, with the least habitable wet planet being the 2400-hour rotator. The difference in the rotation period of the most habitable planets between the dry planets and the wet planets is caused by the availability of water vapor as a greenhouse gas, the added heat transport through sea ice movement, and the larger heat capacity for the wet planets. When realistic planets are modeled, the habitable surface area and average surface temperature is

  14. The low-mass companion of GQ Lup

    NASA Astrophysics Data System (ADS)

    Guenther, E. W.; Neuhäuser, R.; Wuchterl, G.; Mugrauer, M.; Bedalov, A.; Hauschildt, P. H.

    2005-12-01

    Using NACO on the VLT in the imaging mode we have detected an object at a distance of only 0.7 arcsec from GQ Lup. The object turns out to be co-moving. We have taken two K-band spectra with a resolution of \\lambda / \\Delta \\lambda=700. In here, we analyze the spectra in detail. We show that the shape of spectrum is not spoiled by differences in the Strehl ratio in the blue and in the red part, as well as differential refraction. We reanalyze the spectra and derive the spectral type of the companion using classical methods. We find that the object has a spectral type between M9V and L4V, which corresponds to a T_eff between 1600 and 2500 K. Using GAIA-dusty models, we find that the spectral type derivation is robust against different log(g)-values. The T_eff derived from the models is again in the range between 1800 and 2400 K. While the models reproduce nicely the general shape of the spectrum, the 12CO lines in the spectrum have about half the depth as those in the model. We speculate that this difference might be caused by veiling, like in other objects of similar age, and spectral class. We also find that the absolute brightness of the companion matches that of other low-mass free-floating objects of similar age and spectral type. A comparison with the objects in USco observed by Mohanty et al. (\\cite{mohanty04b}) shows that the companion of GQ Lup has a lower mass than any of these, as it is of later spectral type, and younger. The same is as true, for the companion of AB Pic. To have a first estimate of the mass of the object we compare the derived T_eff and luminosity with those calculated from evolutionary tracks. We also point out that future instruments, like NAHUAL, will finally allow us to derive the masses of such objects more precisely.

  15. Miniature Low-Mass Drill Actuated by Flextensional Piezo Stack

    NASA Technical Reports Server (NTRS)

    Sherrit, Stewart; Badescu, Mircea; Bar-Cohen, Yoseph

    2010-01-01

    characteristics of low mass, small size, low power, and low axial loads for sampling.

  16. Atmospheres of Quiescent Low-Mass Neutron Stars

    NASA Astrophysics Data System (ADS)

    Karpov, Platon; Medin, Zachary; Calder, Alan; Lattimer, James M.

    2016-01-01

    Observations of the neutron stars in quiescent low-mass X-ray binaries are important for determining their masses and radii which can lead to powerful constraints on the dense matter nuclear equation of state. The interpretation of these sources is complex and their spectra differ appreciably from blackbodies. Further progress hinges on reducing the uncertainties stemming from models of neutron star atmospheres. We present a suite of low-temperature neutron star atmospheres of different chemical compositions (pure H and He). Our models are constructed over a range of temperatures [log(T/1 K)=5.3, 5.6, 5.9, 6.2, 6.5] and surface gravities [log(g/1 cm/s2)=14.0, 14.2, 14.4, 14.6]. We generated model atmospheres using zcode - a radiation transfer code developed at Los Alamos National Laboratory. In order to facilitate analytic studies, we developed three-parameter fits to our models, and also compared them to diluted blackbodies in the energy range of 0.4-5 keV (CXO/MGE). From the latter, we extract color-correction factors (fc), which represent the shift of the spectra as compared to a blackbody with the same effective temperature. These diluted blackbodies are also useful for studies of photspheric expansion X-ray bursts. We provide a comparison of our models to previous calculations using the McGill Planar Hydrogen Atmosphere Code (McPHAC). These results enhance our ability to interpret thermal emission from neutron stars and to constrain the mass-radius relationship of these exotic objects.This research was supported in part by the U.S. Department of Energy under grant DE-FG02-87ER40317 and by resources at the Institute for Advanced Computational Science at Stony Brook University. This research was carried out in part under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory and supported by Contract No. DE-AC52-06NA25396.

  17. A Search for Close, Low-Mass Companions to Nearby A and B stars

    NASA Astrophysics Data System (ADS)

    Gullikson, Kevin; Kraus, Adam

    2014-02-01

    A stars have become high-priority targets for direct-imaging planet searches following the recent discoveries of planets orbiting e.g. HR 8799 and (beta) Pictoris. Close stellar companions to these stars can affect the formation and orbital evolution of any planets, and so a census of the multiplicity properties of nearby intermediate mass stars is needed. To this end, we propose to observe a sample of southern main sequence A- and B-type stars with high signal-to-noise ratio, high- resolution spectroscopy, in order to search for close low-mass companions. We will cross-correlate the spectra we observe against model spectra for F- to M-type secondary stars; a detected companion will appear as a peak in the cross-correlation function. The cross- correlation method is sensitive to mass-ratios q≡ M_s/M_p ≳ 0.06-0.15, and to orbital separations less then a few tens of AU. We will use the binary population we reveal to measure the mass-ratio distribution for intermediate mass stars, which can help distinguish between companions formed through disk fragmentation and molecular core fragmentation.

  18. No Evidence for Multiple Stellar Populations in the Low-mass Galactic Globular Cluster E 3

    NASA Astrophysics Data System (ADS)

    Salinas, Ricardo; Strader, Jay

    2015-08-01

    Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M˜ 1.4× {10}4 {M}⊙ ) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found. Based on observations obtained at the Southern Astrophysical Research (SOAR) Telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  20. The c2d Spitzer Spectroscopic Survey of Ices Around Low-mass Young Stellar Objects. IV. NH3 and CH3OH

    NASA Astrophysics Data System (ADS)

    Bottinelli, Sandrine; Boogert, A. C. Adwin; Bouwman, Jordy; Beckwith, Martha; van Dishoeck, Ewine F.; Öberg, Karin I.; Pontoppidan, Klaus M.; Linnartz, Harold; Blake, Geoffrey A.; Evans, Neal J., II; Lahuis, Fred

    2010-08-01

    NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the ~8-10 μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9 μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 ν2 umbrella mode and derive abundances with respect to water between ~2% and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the ν4 C-O stretch mode of this molecule at ~9.7 μm in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 μm data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of nitrogen is locked up in known

  1. Driven and decaying turbulence simulations of low–mass star formation: From clumps to cores to protostars

    SciTech Connect

    Offner, Stella S. R.; Klein, Richard I.; McKee, Christopher F.

    2008-10-20

    Molecular clouds are observed to be turbulent, but the origin of this turbulence is not well understood. As a result, there are two different approaches to simulating molecular clouds, one in which the turbulence is allowed to decay after it is initialized, and one in which it is driven. We use the adaptive mesh refinement (AMR) code, Orion, to perform high-resolution simulations of molecular cloud cores and protostars in environments with both driven and decaying turbulence. We include self-gravity, use a barotropic equation of state, and represent regions exceeding the maximum grid resolution with sink particles. We analyze the properties of bound cores such as size, shape, line width, and rotational energy, and we find reasonable agreement with observation. At high resolution the different rates of core accretion in the two cases have a significant effect on protostellar system development. Clumps forming in a decaying turbulence environment produce high-multiplicity protostellar systems with Toomre Q unstable disks that exhibit characteristics of the competitive accretion model for star formation. In contrast, cores forming in the context of continuously driven turbulence and virial equilibrium form smaller protostellar systems with fewer low-mass members. Furthermore, our simulations of driven and decaying turbulence show some statistically significant differences, particularly in the production of brown dwarfs and core rotation, but the uncertainties are large enough that we are not able to conclude whether observations favor one or the other.

  2. Driven and decaying turbulence simulations of low–mass star formation: From clumps to cores to protostars

    DOE PAGES

    Offner, Stella S. R.; Klein, Richard I.; McKee, Christopher F.

    2008-10-20

    Molecular clouds are observed to be turbulent, but the origin of this turbulence is not well understood. As a result, there are two different approaches to simulating molecular clouds, one in which the turbulence is allowed to decay after it is initialized, and one in which it is driven. We use the adaptive mesh refinement (AMR) code, Orion, to perform high-resolution simulations of molecular cloud cores and protostars in environments with both driven and decaying turbulence. We include self-gravity, use a barotropic equation of state, and represent regions exceeding the maximum grid resolution with sink particles. We analyze the propertiesmore » of bound cores such as size, shape, line width, and rotational energy, and we find reasonable agreement with observation. At high resolution the different rates of core accretion in the two cases have a significant effect on protostellar system development. Clumps forming in a decaying turbulence environment produce high-multiplicity protostellar systems with Toomre Q unstable disks that exhibit characteristics of the competitive accretion model for star formation. In contrast, cores forming in the context of continuously driven turbulence and virial equilibrium form smaller protostellar systems with fewer low-mass members. Furthermore, our simulations of driven and decaying turbulence show some statistically significant differences, particularly in the production of brown dwarfs and core rotation, but the uncertainties are large enough that we are not able to conclude whether observations favor one or the other.« less

  3. Disk and Envelope Structure in Class 0 Protostars. I. The Resolved Massive Disk in Serpens Firs 1

    NASA Astrophysics Data System (ADS)

    Enoch, Melissa L.; Corder, Stuartt; Dunham, Michael M.; Duchêne, Gaspard

    2009-12-01

    We present the first results of a program to characterize the disk and envelope structure of typical Class 0 protostars in nearby low-mass star-forming regions. We use Spitzer Infrared Spectrograph (IRS) mid-infrared spectra, high-resolution Combined Array for Research in Millimeter-wave Astronomy (CARMA) 230 GHz continuum imaging, and two-dimensional radiative transfer models to constrain the envelope structure, as well as the size and mass of the circumprotostellar disk in Serpens FIRS 1. The primary envelope parameters (centrifugal radius, outer radius, outflow opening angle, and inclination) are well constrained by the spectral energy distribution (SED), including Spitzer IRAC and MIPS photometry, IRS spectra, and 1.1 mm Bolocam photometry. These together with the excellent uv-coverage (4.5-500 kλ) of multiple antenna configurations with CARMA allow for a robust separation of the envelope and a resolved disk. The SED of Serpens FIRS 1 is best fit by an envelope with the density profile of a rotating, collapsing spheroid with an inner (centrifugal) radius of approximately 600 AU, and the millimeter data by a large resolved disk with Mdisk ~ 1.0 M sun and Rdisk ~ 300 AU. These results suggest that large, massive disks can be present early in the main accretion phase. Results for the larger, unbiased sample of Class 0 sources in the Perseus, Serpens, and Ophiuchus molecular clouds are needed to determine if relatively massive disks are typical in the Class 0 stage.

  4. A Cluster of Class 0 Protostars in Serpens

    NASA Astrophysics Data System (ADS)

    Barsony, M.

    1997-01-01

    We present new 12, 25, 60, and 100 micron HIRES-processed IRAS images of the nearby Serpens star-forming cloud core at FWHM resolutions of ~ 30"-10'. We use HIRES-processed point-source models of the IRAS emission to derive new flux values and flux upper limits for all the protostellar candidates in the Serpens core. Our fluxes (and flux upper limits) determine the spectral energy distributions (SED's) necessary to derive the dust temperature, circumstellar mass, bolometric luminosity, and evolutionary status of each protostellar candidate. Remarkably, we find that all five sources: FIRS1, SMM4, S68N, SMM2, and SMM3 studied by Hurt, Barsony & Wootten (1996) share the defining characteristics of Class 0 protostars, the short-lived (a few X 10^4 yr) earliest observable protostellar stage (Andre, Ward-Thompson & Barsony 1993, Barsony 1994).

  5. DETECTION OF A MAGNETIZED DISK AROUND A VERY YOUNG PROTOSTAR

    SciTech Connect

    Rao, Ramprasad; Girart, Josep M.; Lai, Shih-Ping; Marrone, Daniel P. E-mail: girart@ice.cat

    2014-01-01

    We present subarcsecond resolution polarimetric observations of the 878 μm thermal dust continuum emission obtained with the Submillimeter Array toward the IRAS 16293–2422 protostellar binary system. We report the detection of linearly polarized dust emission arising from the circumstellar disk associated with the IRAS 16293–2422 B protostar. The fractional polarization of ≅ 1.4% is only slightly lower than that expected from theoretical calculations in such disks. The magnetic field structure on the plane of the sky derived from the dust polarization suggests a complex magnetic field geometry in the disk, possibly associated with a rotating disk that is wrapping the field lines as expected from the simulations. The polarization around IRAS 16293–2422 A at subarcsecond angular resolution is only marginally detected.

  6. APEX-CHAMP+ high-J CO observations of low-mass young stellar objects. III. NGC 1333 IRAS 4A/4B envelope, outflow, and ultraviolet heating

    NASA Astrophysics Data System (ADS)

    Yıldız, Umut A.; Kristensen, Lars E.; van Dishoeck, Ewine F.; Belloche, Arnaud; van Kempen, Tim A.; Hogerheijde, Michiel R.; Güsten, Rolf; van der Marel, Nienke

    2012-06-01

    Context. The NGC 1333 IRAS 4A and IRAS 4B sources are among the most well-studied Stage 0 low-mass protostars, which drive prominent bipolar outflows. Spectrally resolved molecular emission lines provide crucial information about the physical and chemical structure of the circumstellar material as well as the dynamics of the different components. Most studies have so far concentrated on the colder parts (T ≤ 30 K) of these regions. Aims: The aim is to characterize the warmer parts of the protostellar envelope using the new generation of submillimeter instruments. This will allow us to quantify the feedback of the protostars on their surroundings in terms of shocks, ultraviolet (UV) heating, photodissociation, and outflow dispersal. Methods: The dual frequency 2 × 7 pixel 650/850 GHz array receiver CHAMP+ mounted on APEX was used to obtain a fully sampled, large-scale ~4' × 4' map at 9″ resolution of the IRAS 4A/4B region in the 12CO J = 6-5 line. Smaller maps were observed in the 13CO 6-5 and [C i] J = 2-1 lines. In addition, a fully sampled 12CO J = 3-2 map made with HARP-B on the JCMT is presented and deep isotopolog observations are obtained at selected outflow positions to constrain the optical depth. Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs, from J = 1-0 up to 10-9 (Eu/k ≈ 300 K), are collected at the source positions and used to construct velocity-resolved CO ladders and rotational diagrams. Radiative-transfer models of the dust and lines are used to determine the temperatures and masses of the outflowing and photon-heated gas and infer the CO abundance structure. Results: Broad CO emission-line profiles trace entrained shocked gas along the outflow walls, which have an average temperature of ~100 K. At other positions surrounding the outflow and the protostar, the 6-5 line profiles are narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the UV heated gas distribution for the first time. The

  7. Intense accretion and mass loss of a very low mass young stellar object

    NASA Astrophysics Data System (ADS)

    Fernández, M.; Comerón, F.

    2001-12-01

    We present visible and near-infrared photometry and spectroscopy of LS-RCrA 1, a faint, very late-type object (M 6.5-M 7) seen in the direction of the R Coronae Australis star forming complex. While its emission spectrum shows prominent features of accretion and mass loss typical of young stellar objects, its underlying continuum and photometric properties are puzzling when trying to derive a mass and age based on pre-main sequence evolutionary tracks: the object appears to be far too faint for a young member of the R Coronae Australis complex of its spectral type. We speculate that this may be due to either its evolution along pre-main sequence tracks being substantially altered by the intense accretion, or to a combination of partial blocking and scattering of the light of the object by a nearly edge-on circumstellar disk. The rich emission line spectrum superimposed on the stellar continuum is well explained by an intense accretion process: the Halpha , CaII infrared triplet, and HeI 6678 lines show equivalent widths typical of very active classical T Tauri stars. The near-infrared observations show anomalously weak spectral features and no significant excess emission in the K band, which we tentatively interpret as indicating line filling due to emission in a magnetic accretion funnel flow. At the same time, numerous, strong forbidden optical lines ([OI], [NII] and [SII]) and H2 emission at 2.12 mu m suggest that the object is simultaneously undergoing mass loss, providing another example that shows that mass loss and accretion are closely related processes. Such an intense accretion and mass loss activity is observed for the first time in a young stellar object in the transition region between low mass stars and brown dwarfs, and provides a valuable observational test on the effects of accretion on the evolution of objects with such low masses. Based on observations collected at the European Southern Observatory in La Silla and Cerro Paranal (Chile), in

  8. APEX-CHAMP+ high-J CO observations of low-mass young stellar objects. IV. Mechanical and radiative feedback

    NASA Astrophysics Data System (ADS)

    Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Hogerheijde, M. R.; Karska, A.; Belloche, A.; Endo, A.; Frieswijk, W.; Güsten, R.; van Kempen, T. A.; Leurini, S.; Nagy, Z.; Pérez-Beaupuits, J. P.; Risacher, C.; van der Marel, N.; van Weeren, R. J.; Wyrowski, F.

    2015-04-01

    Context. During the embedded stage of star formation, bipolar molecular outflows and UV radiation from the protostar are important feedback processes. Both processes reflect the accretion onto the forming star and affect subsequent collapse or fragmentation of the cloud. Aims: Our aim is to quantify the feedback, mechanical and radiative, for a large sample of low-mass sources in a consistent manner. The outflow activity is compared to radiative feedback in the form of UV heating by the accreting protostar to search for correlations and evolutionary trends. Methods: Large-scale maps of 26 young stellar objects, which are part of the Herschel WISH key program are obtained using the CHAMP+ instrument on the Atacama Pathfinder EXperiment (12CO and 13CO 6-5; Eup ~ 100 K), and the HARP-B instrument on the James Clerk Maxwell Telescope (12CO and 13CO 3-2; Eup ~ 30 K). The maps have high spatial resolution, particularly the CO 6-5 maps taken with a 9″ beam, resolving the morphology of the outflows. The maps are used to determine outflow parameters and the results are compared with higher-J CO lines obtained with Herschel. Envelope models are used to quantify the amount of UV-heated gas and its temperature from 13CO 6-5 observations. Results: All sources in our sample show outflow activity, with the spatial extent decreasing from the Class 0 to the Class I stage. Consistent with previous studies, the outflow force, FCO, is larger for Class 0 sources than for Class I sources, even if their luminosities are comparable. The outflowing gas typically extends to much greater distances than the power-law envelope and therefore influences the surrounding cloud material directly. Comparison of the CO 6-5 results with HIFI H2O and PACS high-J CO lines, both tracing currently shocked gas, shows that the two components are linked, even though the transitions do not probe the same gas. The link does not extend down to CO 3-2. The conclusion is that CO 6-5 depends on the shock

  9. 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 λ6708 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

  10. A HERSCHEL AND APEX CENSUS OF THE REDDEST SOURCES IN ORION: SEARCHING FOR THE YOUNGEST PROTOSTARS

    SciTech Connect

    Stutz, Amelia M.; Robitaille, Thomas; Henning, Thomas; Krause, Oliver; Tobin, John J.; Stanke, Thomas; Megeath, S. Thomas; Fischer, William J.; Ali, Babar; Furlan, Elise; Hartmann, Lee; Osorio, Mayra; Wilson, Thomas L.; Allen, Lori; Manoj, P.

    2013-04-10

    We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using data obtained with the PACS instrument on board the Herschel Space Observatory and the LABOCA and SABOCA instruments on APEX as part of the Herschel Orion Protostar Survey (HOPS). A total of 55 new protostar candidates are detected at 70 {mu}m and 160 {mu}m that are either too faint (m{sub 24} > 7 mag) to be reliably classified as protostars or undetected in the Spitzer/MIPS 24 {mu}m band. We find that the 11 reddest protostar candidates with log {lambda}F{sub {lambda}}70/{lambda}F{sub {lambda}}24 > 1.65 are free of contamination and can thus be reliably explained as protostars. The remaining 44 sources have less extreme 70/24 colors, fainter 70 {mu}m fluxes, and higher levels of contamination. Taking the previously known sample of Spitzer protostars and the new sample together, we find 18 sources that have log {lambda}F{sub {lambda}}70/{lambda}F{sub {lambda}}24 > 1.65; we name these sources 'PACS Bright Red sources', or PBRs. Our analysis reveals that the PBR sample is composed of Class 0 like sources characterized by very red spectral energy distributions (SEDs; T{sub bol} < 45 K) and large values of sub-millimeter fluxes (L{sub smm}/L{sub bol} > 0.6%). Modified blackbody fits to the SEDs provide lower limits to the envelope masses of 0.2-2 M{sub Sun} and luminosities of 0.7-10 L{sub Sun }. Based on these properties, and a comparison of the SEDs with radiative transfer models of protostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typical envelope densities and hence, high mass infall rates.

  11. HST 1.6μm Imaging Survey of Orion Protostars

    NASA Astrophysics Data System (ADS)

    Booker, Joseph J.; Megeath, S. Thomas; Fischer, William J.; Kounkel, Marina; Poteet, Charles A.; Furlan, Elise; Stutz, Amelia Marie; Puravankara, Manoj; Tobin, John J.; Nagy, Zsofia; Watson, Dan M.; Herschel Orion Protostar Survey

    2017-01-01

    We present near-infrared 1.6μm HST NICMOS and/or WFC3 images of 244 protostars in the Orion A & B molecular clouds, the largest sample of protostars imaged in a single cloud complex to date. These protostars are part of the Herschel Orion Protostar Survey (HOPS), a multi-observatory program which obtained 1-870μm photometry, spectroscopy, imaging of 319 protostars in the Orion clouds. The HST images resolve structures illuminated in scattered light from the central protostar, including disks, cavities, and shadows cast in envelopes by disks, with better than 100 AU spatial resolution. We classify all the protostars into five morphological classes: non-detections, point sources, bipolar cavities, unipolar cavities and irregular sources. Sixteen of the bipolar sources show disks in absorption, revealing a minimum spatial extent of the disks. The resolved cavities allow us to directly measure the clearing of the envelopes by bipolar outflows. We map cavities for 30 of these sources by applying a custom edge detection technique to both the scattered light images and radiative transfer models with known cavity geometries. We constrain the shape of the cavities and estimate the fractional volumes of the collapsing cores dispersed by the outflows. Contrary to previous results, we do not find evidence that outflow cavities grow in volume as protostars evolve from Class 0 to flat spectrum sources. These results indicate that feedback by outflow clearing is not the primary agent for dissipating envelopes and halting accretion, and cannot explain the 30-40% star formation efficiency estimated for molecular cores.

  12. Searching for Correlations with the HCO+ 4-3 Molecular Spectra of Protostars

    NASA Astrophysics Data System (ADS)

    Acikgoz, Ogulcan; Basturk, Seda

    The assignment is based on HCO+ J=4-3 spectral line molecular observations of protostars from the James Clerk Maxwell Telescope, which has the 15 m diameter dish and located in Mauna Kea, Hawaii, USA. Data of 20 protostars are taken from the public LOMASS database and analyzed. We looked for correlations between a few observational quantities. We thank Dr Umut Yildiz (NASA/JPL-Caltech) for providing data and his comments and support to our research project.

  13. The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

    NASA Astrophysics Data System (ADS)

    Furlan, E.; Fischer, W. J.; Ali, B.; Stutz, A. M.; Stanke, T.; Tobin, J. J.; Megeath, S. T.; Osorio, M.; Hartmann, L.; Calvet, N.; Poteet, C. A.; Booker, J.; Manoj, P.; Watson, D. M.; Allen, L.

    2016-05-01

    We present key results from the Herschel Orion Protostar Survey: spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2-870 μm and sample the peak of the protostellar envelope emission at ˜100 μm. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.

  14. Constraining the disk masses of the class I binary protostar GV Tau

    SciTech Connect

    Sheehan, Patrick D.; Eisner, Josh A.

    2014-08-10

    We present new spatially resolved 1.3 mm imaging with CARMA of the GV Tau system. GV Tau is a Class I binary protostar system in the Taurus Molecular Cloud, the components of which are separated by 1.''2. Each protostar is surrounded by a protoplanetary disk, and the pair may be surrounded by a circumbinary envelope. We analyze the data using detailed radiative transfer modeling of the system. We create synthetic protostar model spectra, images, and visibilities and compare them with CARMA 1.3 mm visibilities, a Hubble Space Telescope near-infrared scattered light image, and broadband spectral energy distributions from the literature to study the disk masses and geometries of the GV Tau disks. We show that the protoplanetary disks around GV Tau fall near the lower end of estimates of the Minimum Mass Solar Nebula, and may have just enough mass to form giant planets. When added to the sample of Class I protostars from Eisner, we confirm that Class I protostars are on average more massive than their Class II counterparts. This suggests that substantial dust grain processing occurs between the Class I and Class II stages, and may help to explain why the Class II protostars do not appear to have, on average, enough mass in their disks to form giant planets.

  15. A Search for Low Mass Stars and Substellar Companions and A Study of Circumbinary Gas and Dust Disks

    NASA Astrophysics Data System (ADS)

    Rodriguez, David R.

    2011-01-01

    We have searched for nearby low-mass stars and brown dwarfs and have studied the planet-forming environment of binary stars. We have carried out a search for young, low-mass stars in nearby stellar associations using X-ray and UV source catalogs. We discovered a new technique to identify 10-100 Myr-old low-mass stars within 100 pc of the Earth using GALEX-optical/near-IR data. We present candidate young stars found by applying this new method in the 10 Myr old TW Hydrae and Scorpius-Centaurus associations. In addition, we have searched for the coolest brown dwarf class: Y-dwarfs, expected to appear at temperatures <500 K. Using wide-field near infrared imaging with ground (CTIO, Palomar, KPNO) and space (Spitzer, AKARI) observatories, we have looked for companions to nearby, old (2 Gyr or older), high proper motion white dwarfs. We present results for Southern Hemisphere white dwarfs. Additionally, we have characterized how likely planet formation occurs in binary star systems. While 20% of planets have been discovered around one member of a binary system, these binaries have semi-major axes larger than 20 AU. We have performed an AO and spectroscopic search for binary stars among a sample of known debris disk stars, which allows us to indirectly study planet formation and evolution in binary systems. As a case study, we examined the gas and dust present in the circumbinary disk around V4046 Sagittarii, a 2.4-day spectroscopic binary. Our results demonstrate it is unlikely that planets can form in binaries with stellar semi-major axes of 10s of AU. This research has been funded by a NASA ADA grant to UCLA and RIT.

  16. c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines

    NASA Astrophysics Data System (ADS)

    Lahuis, F.; van Dishoeck, E. F.; Jørgensen, J. K.; Blake, G. A.; Evans, N. J.

    2010-09-01

    Context. A survey of mid-infrared gas-phase emission lines of H2, H2O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer “Cores to Disks” (c2d) legacy program. Aims: The environment of embedded protostars is complex both in its physical structure (envelopes, outflows, jets, protostellar disks) and the physical processes (accretion, irradiation by UV and/or X-rays, excitation through slow and fast shocks) which take place. The mid-IR spectral range hosts a suite of diagnostic lines which can distinguish them. A key point is to spatially resolve the emission in the Spitzer-IRS spectra to separate extended PDR and shock emission from compact source emission associated with the circumstellar disk and jets. Methods: An optimal extraction method is used to separate both spatially unresolved (compact, up to a few hundred AU) and spatially resolved (extended, thousand AU or more) emission from the IRS spectra. The results are compared with the c2d disk sample and literature PDR and shock models to address the physical nature of the sources. Results: Both compact and extended emission features are observed. Warm (T_ex few hundred K) H2, observed through the pure rotational H2 S(0), S(1) and S(2) lines, and [S i] 25 μm emission is observed primarily in the extended component. [S i] is observed uniquely toward truly embedded sources and not toward disks. On the other hand hot (T_ex ⪆ 700 K) H2, observed primarily through the S(4) line, and [Ne ii] emission is seen mostly in the spatially unresolved component. [Fe ii] and [Si ii] lines are observed in both spatial components. Hot H2O emission is found in the spatially unresolved component of some sources. Conclusions: The observed emission on ≥1000 AU scales is characteristic of PDR emission and likely originates in the outflow cavities in the remnant envelope created by the stellar wind and jets from the embedded

  17. Intermediate to low-mass stellar content of Westerlund 1

    NASA Astrophysics Data System (ADS)

    Brandner, W.; Clark, J. S.; Stolte, A.; Waters, R.; Negueruela, I.; Goodwin, S. P.

    2008-01-01

    We have analysed near-infrared NTT/SofI observations of the starburst cluster Westerlund 1, which is among the most massive young clusters in the Milky Way. A comparison of colour-magnitude diagrams with theoretical main-sequence and pre-main sequence evolutionary tracks yields improved extinction and distance estimates of AKs = 1.13 ± 0.03 mag and d = 3.55 ± 0.17 kpc (DM = 12.75 ± 0.10 mag). The pre-main sequence population is best fit by a Palla & Stahler isochrone for an age of 3.2 Myr, while the main sequence population is in agreement with a cluster age of 3 to 5 Myr. An analysis of the structural parameters of the cluster yields that the half-mass radius of the cluster population increases towards lower mass, indicative of the presence of mass segregation. The cluster is clearly elongated with an eccentricity of 0.20 for stars with masses between 10 and 32 M_⊙, and 0.15 for stars with masses in the range 3 to 10 M_⊙. We derive the slope of the stellar mass function for stars with masses between 3.4 and 27 M_⊙. In an annulus with radii between 0.75 and 1.5 pc from the cluster centre, we obtain a slope of Γ = -1.3. Closer in, the mass function of Westerlund 1 is shallower with Γ = -0.6. The extrapolation of the mass function for stars with masses from 0.08 to 120 M_⊙ yields an initial total stellar mass of ≈52 000 M_⊙, and a present-day mass of 20 000 to 45 000 M_⊙ (about 10 times the stellar mass of the Orion nebula cluster, and 2 to 4 times the mass of the NGC 3603 young cluster), indicating that Westerlund 1 is the most massive starburst cluster identified to date in the Milky Way. Based on observations collected at the European Southern Observatory, La Silla, Chile, and retrieved from the ESO archive (Prog ID 67.C-0514).

  18. Probing the CO and methanol snow lines in young protostars. Results from the CALYPSO IRAM-PdBI survey

    NASA Astrophysics Data System (ADS)

    Anderl, S.; Maret, S.; Cabrit, S.; Belloche, A.; Maury, A. J.; André, Ph.; Codella, C.; Bacmann, A.; Bontemps, S.; Podio, L.; Gueth, F.; Bergin, E.

    2016-06-01

    Context. So-called snow lines, indicating regions where abundant volatiles freeze out onto the surface of dust grains, play an important role for planet growth and bulk composition in protoplanetary disks. They can already be observed in the envelopes of the much younger, low-mass Class 0 protostars, which are still in their early phase of heavy accretion. Aims: We aim to use the information on the sublimation regions of different kinds of ices to understand the chemistry of the envelope, its temperature and density structure, and the history of the accretion process. This information is crucial to get the full picture of the early protostellar collapse and the subsequent evolution of young protostars. Methods: As part of the CALYPSO IRAM Large Program, we have obtained observations of C18O, N2H+, and CH3OH towards nearby Class 0 protostars with the IRAM Plateau de Bure interferometer at sub-arcsecond resolution. For four of these sources, we have modeled the emission using a chemical code coupled with a radiative transfer module. Results: We observe an anti-correlation of C18O and N2H+ in NGC 1333-IRAS4A, NGC 1333-IRAS4B, L1157, and L1448C, with N2H+ forming a ring (perturbed by the outflow) around the centrally peaked C18O emission. This emission morphology, which is due to N2H+ being chemically destroyed by CO, reveals the CO and N2 ice sublimation regions in these protostellar envelopes with unprecedented resolution. We also observe compact methanol emission towards three of the sources. Based on our chemical model and assuming temperature and density profiles from the literature, we find that for all four sources the CO snow line appears further inwards than expected from the binding energy of pure CO ices (~855 K). The emission regions of models and observations match for a higher value of the CO binding energy of 1200 K, corresponding to a dust temperature of ~24 K at the CO snow line. The binding energy for N2 ices is modeled at 1000 K, also higher than for

  19. Water in low-mass star-forming regions with Herschel. The link between water gas and ice in protostellar envelopes

    NASA Astrophysics Data System (ADS)

    Schmalzl, M.; Visser, R.; Walsh, C.; Albertsson, T.; van Dishoeck, E. F.; Kristensen, L. E.; Mottram, J. C.

    2014-12-01

    Aims: Our aim is to determine the critical parameters in water chemistry and the contribution of water to the oxygen budget by observing and modelling water gas and ice for a sample of eleven low-mass protostars, for which both forms of water have been observed. Methods: A simplified chemistry network, which is benchmarked against more sophisticated chemical networks, is developed that includes the necessary ingredients to determine the water vapour and ice abundance profiles in the cold, outer envelope in which the temperature increases towards the protostar. Comparing the results from this chemical network to observations of water emission lines and previously published water ice column densities, allows us to probe the influence of various agents (e.g., far-ultraviolet (FUV) field, initial abundances, timescales, and kinematics). Results: The observed water ice abundances with respect to hydrogen nuclei in our sample are 30-80 ppm, and therefore contain only 10-30% of the volatile oxygen budget of 320 ppm. The keys to reproduce this result are a low initial water ice abundance after the pre-collapse phase together with the fact that atomic oxygen cannot freeze-out and form water ice in regions with Tdust ≳ 15 K. This requires short prestellar core lifetimes ≲0.1 Myr. The water vapour profile is shaped through the interplay of FUV photodesorption, photodissociation, and freeze-out. The water vapour line profiles are an invaluable tracer for the FUV photon flux and envelope kinematics. Conclusions: The finding that only a fraction of the oxygen budget is locked in water ice can be explained either by a short pre-collapse time of ≲0.1 Myr at densities of nH ~ 104 cm-3, or by some other process that resets the initial water ice abundance for the post-collapse phase. A key for the understanding of the water ice abundance is the binding energy of atomic oxygen on ice. Herschel is an ESA space observatory with science instruments provided by European

  20. The Survey of HI in Extremely Low-mass Dwarfs: A Multi-Wavelength Perspective on Low-Mass Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Cannon, John M.; McNichols, Andrew; Teich, Yaron; Adams, Elizabeth A.; Giovanelli, Riccardo; Haynes, Martha P.; McQuinn, Kristen B.; Salzer, John Joseph; Skillman, Evan D.; Dolphin, Andrew E.; Elson, Edward C.; Haurberg, Nathalie C.; Huang, Shan; Janowiecki, Steven; Jozsa, Gyula; Leisman, Luke; Ott, Juergen; Papastergis, Emmanouil; Rhode, Katherine L.; Saintonge, Amelie; Van Sistine, Angela; Warren, Steven R.

    2017-01-01

    The “Survey of HI in Extremely Low-mass Dwarfs” (SHIELD) is a multiwavelength study of local volume low-mass galaxies drawn from the Arecibo Legacy Fast ALFA (ALFALFA) catalog. HST/Spitzer joint program GO-12658 revealed the stellar populations of the first 12 SHIELD galaxies (Cannon et al. 2011), allowing accurate distance measurements (McQuinn et al. 2014) and detailed studies of the patterns of recent star formation in each galaxy (McQuinn et al. 2015). These HST and Spitzer images are a critical interpretive benchmark for ground-based optical imaging and spectroscopy (Haurberg et al. 2015), as well as for sensitive VLA HI spectral line imaging of the SHIELD galaxies (McNichols et al. 2016; Teich et al. 2016). These results have furthered our understanding of the evolution of galaxies in a mass regime that was previously only sparsely populated. With the low-redshift ALFALFA catalog now complete, the scope of the SHIELD program has been expanded to include all 82 galaxies that meet distance, line width, and HI flux criteria for being gas-rich, low-mass galaxies. In HST program 13750, images of 18 more SHIELD galaxies have again set the physical scales for supporting HI spectral line imaging with both the VLA and the WSRT (Gordon et al. 2016). Taken as a whole, the ongoing SHIELD program is one of the most comprehensive multiwavelength studies of the physical properties of low-mass galaxies outside of the Local Group.

  1. Reflected infrared spectrum of a massive protostar in Orion.

    PubMed

    Morino, J I; Yamashita, T; Hasegawa, T; Nakano, T

    1998-05-28

    The infrared source IRc2 in the star-forming region Orion-KL is generally believed to contain a massive and very young star. Its nature and evolutionary status, however, are difficult to determine because it is hidden from direct view by a dense disklike envelope of gas and dust. Here we report observations of infrared radiation (at a wavelength of about 2 microm) that has escaped the surrounding dust in the polar direction, perpendicular to the plane of the disk, and then been reflected towards us by dust farther away from the star. The reflected spectrum contains absorption lines of neutral metallic atoms and carbon monoxide, which we interpret as indicating a source temperature of about 4,500 K. But, given the luminosity of the source, its radius must be at least 300 solar radii-too large to be attained with the modest gas-accretion rates in existing theories of massive-star formation. Whether the infrared radiation is coming from the protostar itself or the self-luminous accretion disk around it, the accretion rate must be around (5-15) x 10(-3) solar masses per year, at least two orders of magnitude greater than is commonly assumed in models of star formation.

  2. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    SciTech Connect

    Spalding, Christopher; Batygin, Konstantin; Adams, Fred C. E-mail: kbatygin@gps.caltech.edu

    2014-12-20

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function.

  3. IRAS 23385+6053: AN Example of Candidate Massive Protostar

    NASA Astrophysics Data System (ADS)

    Fontani, Francesco; Cesaroni, Riccardo; Testi, Leonardo; Walmsley, Malcolm

    We present the results of a multi-line study towards the source IRAS 23385+6053 performed with the IRAM-30m telescope the Plateau de Bure Interferometer and the Very Large Array. We have obtained single-dish and interferometric maps in various transitions of the C18O C17O CH3CCH and NH3 molecular species. Our results confirm the findings of Molinari et al. (1998b) namely that IRAS 23385 a luminous (and therefore massive) source (L ~ 1.6 x 104 solar luminosities) is a good candidate high-mass class 0 object precursor of an ultracompact HII region. The source is approximately made out of two components: a compact molecular ~2 arcsec core with temperature of ~40 K and an H2 volume density of the order of 107 cm-3 and a more extended clump (~15 arcsec) with an average kinetic temperature of ~15 K and H2 volume density of the order of 105 cm-3. The core temperature is much smaller than typical temperatures found in hot molecular cores around massive ZAMS stars. This result supports the idea that IRAS 23385 is a massive protostar in a pre-ZAMS evolutionary stage still accreting material from its parental molecular cloud and deriving most of its luminosity from the release of gravitational energy.

  4. Recent Advances in the Theoretical Modeling of Pulsating Low-mass He-core White Dwarfs

    NASA Astrophysics Data System (ADS)

    Córsico, A. H.; Althaus, L. G.; Calcaferro, L. M.; Serenelli, A. M.; Kepler, S. O.; Jeffery, C. S.

    2017-03-01

    Many extremely low-mass (ELM) white-dwarf (WD) stars are currently being found in the field of the Milky Way. Some of these stars exhibit long-period nonradial g-mode pulsations, and constitute the class of ELMV pulsating WDs. In addition, several low-mass pre-WDs, which could be precursors of ELM WDs, have been observed to show short-period photometric variations likely due to nonradial p modes and radial modes. They could constitute a new class of pulsating low-mass pre-WD stars, the pre-ELMV stars. Here, we present the recent results of a thorough theoretical study of the nonadiabatic pulsation properties of low-mass He-core WDs and pre-WDs on the basis of fully evolutionary models representative of these stars.

  5. The naked T Tauri stars - The low-mass pre-main sequence unveiled

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.

    1987-01-01

    The search for low-mass premain-sequence (PMS) stars associated with X-ray sources in regions of star formation is discussed. The survey to date has revealed at least 30 low-mass PMS stars in the Tau-Aur region, and a comparable number in Oph. These stars are the naked T Tau stars, unveiled versions of the well-known classical T Tau stars. The properties of these newly discovered PMS stars and their relation to the classical T Tau stars are discussed, and it is concluded that the naked T Tau stars are the true low-mass PMS stars, and that the observable characteristics defining the classical T Tau stars are due to the interaction of an underlying, fairly normal star with a dominant circumstellar environment. The impact the naked T Tau stars are likely to have on models of the PMS evolution of low-mass stars is considered.

  6. ON THE SIMULTANEOUS EVOLUTION OF MASSIVE PROTOSTARS AND THEIR HOST CORES

    SciTech Connect

    Kuiper, R.; Yorke, H. W. E-mail: Harold.W.Yorke@jpl.nasa.gov

    2013-07-20

    Studies of the evolution of massive protostars and the evolution of their host molecular cloud cores are commonly treated as separate problems. However, interdependencies between the two can be significant. Here, we study the simultaneous evolution of massive protostars and their host molecular cores using a multi-dimensional radiation hydrodynamics code that incorporates the effects of the thermal pressure and radiative acceleration feedback of the centrally forming protostar. The evolution of the massive protostar is computed simultaneously using the stellar evolution code STELLAR, modified to include the effects of variable accretion. The interdependencies are studied in three different collapse scenarios. For comparison, stellar evolutionary tracks at constant accretion rates and the evolution of the host cores using pre-computed stellar evolutionary tracks are computed. The resulting interdependencies of the protostellar evolution and the evolution of the environment are extremely diverse and depend on the order of events, in particular the time of circumstellar accretion disk formation with respect to the onset of the bloating phase of the star. Feedback mechanisms affect the instantaneous accretion rate and the protostar's radius, temperature, and luminosity on timescales t {<=} 5 kyr, corresponding to the accretion timescale and Kelvin-Helmholtz contraction timescale, respectively. Nevertheless, it is possible to approximate the overall protostellar evolution in many cases by pre-computed stellar evolutionary tracks assuming appropriate constant average accretion rates.

  7. Radiative Feedback from Primordial Protostars and Final Mass of the First Stars

    NASA Technical Reports Server (NTRS)

    Hosokawa, Takashi; Omukai, Kazuyuki; Yoshida, Naoki; Yorke, Harold W.

    2012-01-01

    In this contribution, we review our efforts toward understanding the typical mass-scale of primordial stars. Our direct numerical simulations show that, in both of Population III.1 and III.2 cases, strong UV stellar radiative feedback terminatesmass accretion onto a protostar.AnHII region formed around the protostar very dynamically expands throughout the gas accreting envelope, which cuts off the gas supply to a circumstellar disk. The disk is exposed to the stellar UV radiation and loses its mass by photoevaporation. The derived final masses are 43 Stellar Mass and 17 Stellar Mass in our fiducial Population III.1 and III.2 cases. Much more massive stars should form in other exceptional conditions. In atomic-cooling halos where H2 molecules are dissociated, for instance, a protostar grows via very rapid mass accretion with the rates M* approx. 0.1 - 1 Stellar Mass/yr. Our newstellar evolution calculations show that the protostar significantly inflates and never contracts to reach the ZAMS stage in this case. Such the "supergiant protostars" have very low UV luminosity, which results in weak radiative feedback against the accretion flow. In the early universe, supermassive stars formed through this process might provide massive seeds of supermassive black holes.

  8. On the nature of the deeply embedded protostar OMC-2 FIR 4

    SciTech Connect

    Furlan, E.; Megeath, S. T.; Fischer, W. J.; Osorio, M.; Stutz, A. M.; Ali, B.; Manoj, P.; Adams, J. D.; Tobin, J. J.

    2014-05-01

    We use mid-infrared to submillimeter data from the Spitzer, Herschel, and Atacama Pathfinder Experiment telescopes to study the bright submillimeter source OMC-2 FIR 4. We find a point source at 8, 24, and 70 μm, and a compact, but extended source at 160, 350, and 870 μm. The peak of the emission from 8 to 70 μm, attributed to the protostar associated with FIR 4, is displaced relative to the peak of the extended emission; the latter represents the large molecular core the protostar is embedded within. We determine that the protostar has a bolometric luminosity of 37 L {sub ☉}, although including more extended emission surrounding the point source raises this value to 86 L {sub ☉}. Radiative transfer models of the protostellar system fit the observed spectral energy distribution well and yield a total luminosity of most likely less than 100 L {sub ☉}. Our models suggest that the bolometric luminosity of the protostar could be as low as 12-14 L {sub ☉}, while the luminosity of the colder (∼20 K) extended core could be around 100 L {sub ☉}, with a mass of about 27 M {sub ☉}. Our derived luminosities for the protostar OMC-2 FIR 4 are in direct contradiction with previous claims of a total luminosity of 1000 L {sub ☉}. Furthermore, we find evidence from far-infrared molecular spectra and 3.6 cm emission that FIR 4 drives an outflow. The final stellar mass the protostar will ultimately achieve is uncertain due to its association with the large reservoir of mass found in the cold core.

  9. The Influence of Environment on the Chemical Evolution in Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    Liu, Yiqing; Ho, Luis C.; Peng, Eric

    2016-10-01

    The mean alpha-to-iron abundance ratio ([α/Fe]) of galaxies is sensitive to the chemical evolution processes at early time, and it is an indicator of star formation timescale ({τ }{SF}). Although the physical reason remains ambiguous, there is a tight relation between [α/Fe] and stellar velocity dispersion (σ) among massive early-type galaxies (ETGs). However, no work has shown convincing results as to how this relation behaves at low masses. We assemble 15 data sets from the literature and build a large sample that includes 192 nearby low-mass (18\\lt σ \\lt 80 km s-1) ETGs. We find that the [α/Fe]-σ relation generally holds for low-mass ETGs, except in extreme environments. Specifically, in normal galaxy cluster environments, the [α/Fe]-σ relation and its intrinsic scatter are, within uncertainties, similar for low-mass and high-mass ETGs. However, in the most massive relaxed galaxy cluster in our sample, the zero point of the relation is higher and the intrinsic scatter is significantly larger. By contrast, in galaxy groups the zero point of the relation offsets in the opposite direction, again with substantial intrinsic scatter. The elevated [α/Fe] of low-mass ETGs in the densest environments suggests that their star formation was quenched earlier. For the low-mass ETGs in the lowest-density environments, we suggest that their more extended star formation histories suppressed their average [α/Fe]. The large scatter in [α/Fe] may reflect stochasticity in the chemical evolution of low-mass galaxies.

  10. A triple protostar system formed via fragmentation of a gravitationally unstable disk.

    PubMed

    Tobin, John J; Kratter, Kaitlin M; Persson, Magnus V; Looney, Leslie W; Dunham, Michael M; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J; Sadavoy, Sarah I; Harris, Robert J; Melis, Carl; Pérez, Laura M

    2016-10-27

    Binary and multiple star systems are a frequent outcome of the star formation process and as a result almost half of all stars with masses similar to that of the Sun have at least one companion star. Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large-scale fragmentation of turbulent gas cores and filaments or smaller-scale fragmentation of a massive protostellar disk due to gravitational instability. Observational evidence for turbulent fragmentation on scales of more than 1,000 astronomical units has recently emerged. Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems. The triple protostar system L1448 IRS3B is an ideal system with which to search for evidence of disk fragmentation as it is in an early phase of the star formation process, it is likely to be less than 150,000 years old and all of the protostars in the system are separated by less than 200 astronomical units. Here we report observations of dust and molecular gas emission that reveal a disk with a spiral structure surrounding the three protostars. Two protostars near the centre of the disk are separated by 61 astronomical units and a tertiary protostar is coincident with a spiral arm in the outer disk at a separation of 183 astronomical units. The inferred mass of the central pair of protostellar objects is approximately one solar mass, while the disk surrounding the three protostars has a total mass of around 0.30 solar masses. The tertiary protostar itself has a minimum mass of about 0.085 solar masses. We demonstrate that the disk around L1448 IRS3B appears susceptible to disk fragmentation at radii between 150 and 320 astronomical units, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability

  11. Feedback from deeply embedded low- and high-mass protostars. Surveying hot molecular gas with Herschel.

    NASA Astrophysics Data System (ADS)

    Karska, Agata

    2014-09-01

    Protostars interact violently with their natal cocoons within dense molecular clouds. Characterizing this feedback is key to understanding the efficiency of the star formation process and the chemical processing of material that will be available for planet formation. In this thesis, the imprints of physical processes on molecular gas are analyzed using state-of-the-art far-infrared spectroscopy from Herschel / PACS. Interpretation of the origin of far-infrared line emission allows us to quantify the physical conditions and the role of shocks and ultraviolet radiation during the 'kindergarten years' of low- and high-mass protostars.

  12. A triple protostar system formed via fragmentation of a gravitationally unstable disk

    NASA Astrophysics Data System (ADS)

    Tobin, John J.; Kratter, Kaitlin M.; Persson, Magnus V.; Looney, Leslie W.; Dunham, Michael M.; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Sadavoy, Sarah I.; Harris, Robert J.; Melis, Carl; Pérez, Laura M.

    2016-10-01

    Binary and multiple star systems are a frequent outcome of the star formation process and as a result almost half of all stars with masses similar to that of the Sun have at least one companion star. Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large-scale fragmentation of turbulent gas cores and filaments or smaller-scale fragmentation of a massive protostellar disk due to gravitational instability. Observational evidence for turbulent fragmentation on scales of more than 1,000 astronomical units has recently emerged. Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems. The triple protostar system L1448 IRS3B is an ideal system with which to search for evidence of disk fragmentation as it is in an early phase of the star formation process, it is likely to be less than 150,000 years old and all of the protostars in the system are separated by less than 200 astronomical units. Here we report observations of dust and molecular gas emission that reveal a disk with a spiral structure surrounding the three protostars. Two protostars near the centre of the disk are separated by 61 astronomical units and a tertiary protostar is coincident with a spiral arm in the outer disk at a separation of 183 astronomical units. The inferred mass of the central pair of protostellar objects is approximately one solar mass, while the disk surrounding the three protostars has a total mass of around 0.30 solar masses. The tertiary protostar itself has a minimum mass of about 0.085 solar masses. We demonstrate that the disk around L1448 IRS3B appears susceptible to disk fragmentation at radii between 150 and 320 astronomical units, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability

  13. Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES): A Catalog of Very Wide, Low-mass Pairs

    NASA Astrophysics Data System (ADS)

    Dhital, Saurav; West, Andrew A.; Stassun, Keivan G.; Bochanski, John J.

    2010-06-01

    We present the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES), a catalog of 1342 very-wide (projected separation gsim500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from astrometry, photometry, and proper motions in the Sloan Digital Sky Survey. A Monte Carlo-based Galactic model is constructed to assess the probability of chance alignment for each pair; only pairs with a probability of chance alignment <=0.05 are included in the catalog. The overall fidelity of the catalog is expected to be 98.35%. The selection algorithm is purposely exclusive to ensure that the resulting catalog is efficient for follow-up studies of low-mass pairs. The SLoWPoKES catalog is the largest sample of wide, low-mass pairs to date and is intended as an ongoing community resource for detailed study of bona fide systems. Here, we summarize the general characteristics of the SLoWPoKES sample and present preliminary results describing the properties of wide, low-mass pairs. While the majority of the identified pairs are disk dwarfs, there are 70 halo subdwarf (SD) pairs and 21 white dwarf-disk dwarf pairs, as well as four triples. Most SLoWPoKES pairs violate the previously defined empirical limits for maximum angular separation or binding energies. However, they are well within the theoretical limits and should prove very useful in putting firm constraints on the maximum size of binary systems and on different formation scenarios. We find a lower limit to the wide binary frequency (WBF) for the mid-K to mid-M spectral types that constitute our sample to be 1.1%. This frequency decreases as a function of Galactic height, indicating a time evolution of the WBF. In addition, the semi-major axes of the SLoWPoKES systems exhibit a distinctly bimodal distribution, with a break at separations around 0.1 pc that is also manifested in the system binding energy. Compared with theoretical predictions for the disruption of

  14. Very low-luminosity Class I/Flat outflow sources in sigma Orionis: Clues to alternative formation mechanisms for very low-mass stars

    NASA Astrophysics Data System (ADS)

    Riaz, Basmah; Whelan, E.; Thompson, M.; Vorobyov, E.; Lodieu, N.

    2015-01-01

    We present an optical through sub-millimetre multi-wavelength study of two very low-luminosity Class I/Flat systems, Mayrit 1701117 and Mayrit 1082188, in the sigma Orionis cluster. We performed moderate resolution (R 1000) optical ( 0.4-0.9mu) spectroscopy with the TWIN spectrograph at the Calar Alto 3.5-m telescope. The spectra for both sources show prominent emission in accretion- and outflow-associated lines. The mean accretion rate measured from multiple line diagnostics is 6.4x10^{-10} Msun/yr for Mayrit 1701117, and 2.5x10^{-10} Msun/yr for Mayrit 1082188. The outflow mass loss rates for the two systems are similar and estimated to be 1x10^{-9} Msun/yr. The activity rates are within the range observed for low-mass Class I protostars. We obtained sub-millimetre continuum observations with the Submillimetre Common-User Bolometer Array (SCUBA-2) bolometer at the James Clerk Maxwell Telescope. Both objects are detected at a >5-sigma level in the SCUBA-2 850mu band. The bolometric luminosity of the targets as measured from the observed spectral energy distribution over 0.8-850mu is 0.18+/-0.04 Lsun for Mayrit 1701117, and 0.16+/-0.03 Lsun for Mayrit 1082188, and is in the very low-mass range. The total dust+gas mass derived from sub-millimetre fluxes is 36 M_Jup and 22 M_Jup for Mayrit 1701117 and Mayrit 1082188, respectively. There is the possibility that some of the envelope material might be dissipated by the strong outflows driven by these sources, resulting in a final mass of the system close to or below the sub-stellar limit. Given the membership of these objects in a relatively evolved cluster of 3 Myr of age, we consider an alternate formation mechanism in the context of the `hybrid' model of disk fragmentation, followed by ejection of a gaseous clump.

  15. A systematic study of magnetic braking in low-mass binaries

    NASA Technical Reports Server (NTRS)

    Verbunt, F.; Rappaport, S.; Joss, P. C.

    1985-01-01

    A short summary is given of Rappaport et al. (1983) which described results of extending a simplified stellar evolution code covering the evolution of low-mass compact binaries. Magnetic braking is probably an important process in the evolution of such binaries (such as cataclysmic variables and low-mass X-ray sources). The initial simplified code describes the mass-losing star as an n = 3/2 polytrope and was developed to study the evolution of binaries with a secondary of low mass (between 0.01 and 0.4 solar mass) when the angular momentum losses are due to gravitational radiation. In the extended code, a composite polytrope model is used for the secondary, wherein the structure of the radiative core is described by an n = 3 polytrope and the convective envelope by an n = 3/2 polytrope.

  16. Herschel photometry of disks around low-mass stars in the R CrA cloud

    SciTech Connect

    Harvey, Paul M.; Henning, Thomas; Liu, Yao; Wolf, Sebastian E-mail: nje@astro.as.utexas.edu E-mail: yliu@pmo.ac.cn E-mail: yliu@pmo.ac.cn

    2014-11-01

    We report photometric results from a subset of a Herschel-PACS program to observe cool dust in disks around low-mass stars as a complement to our earlier program to measure far-infrared emission from brown dwarfs. In this latest study we observed five low-mass objects in the nearby R Corona Australis region and detected at least three at 70 μm. Using a Monte Carlo radiative transfer code we have investigated the disk masses and geometry based on detailed spectral energy distribution (SED) modeling, and we compare these new results to those from our earlier larger sample of brown dwarfs. In particular, our SED analysis for these five objects shows again that disk geometries of brown dwarfs or low-mass stars are generally similar to their higher mass counterparts like T Tauri disks, but the range of disk mass extends to well below the value found in T Tauri stars.

  17. CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Bell, Eric F.; Koo, David C.; Faber, Sandra M.; Lu, Yu

    2017-01-01

    We use a simple method to investigate the environmental quenching of low-mass galaxies beyond the local universe. Essentially all local low-mass quenched galaxies are believed to live in massive dark matter halos and hence close to the massive central galaxies. We use CANDELS data to test up to which redshift and stellar mass is this statement still true. By investigating whether or not this quenched dwarf--massive central galaxy connection, a manifestation of environmental quenching, exists, we only need a statistically representative, rather than complete, sample of low-mass galaxies. Such a sample enables extending environment studies of low-mass galaxies up to z=2. For each detected quenched low-mass galaxy, we measure the projected distance (θmin) to its nearest massive neighbor (stellar mass > 10^{10.5} solar mass) within a projected volume. In a given redshift and stellar mass bin, we compare the distribution of the projected distances (θmin) of quenched galaxies to that of star-forming galaxies. At z<˜1 and stellar mass between 10^{8} and 10^{10} solar masses, the θmin distributions of quenched galaxies are significantly different from and skewed toward lower values than those of star-forming galaxies, thereby demonstrating that quenching is strongly related to low-mass galaxy distances to massive central galaxies. Such a difference between the two populations disappears at z>1.2. This transition around z=1 places a constraint on the environmental quenching timescale (T_Q). We find that T_Q gradually increases from 4 Gyr at 10^{8.5} solar mass to 6 Gyr at 10^{10.5} solar mass. Our method provides a uniform way to measure T_Q over 2 dex of satellite stellar masses.

  18. Occurrence rate of low-mass planets around nearby M dwarfs

    NASA Astrophysics Data System (ADS)

    Jones, Hugh

    2015-08-01

    We re-analyse archival radial velocities of nearby M dwarfs to constrain low-amplitude Keplerian signals. We apply a variety of signal detection criteria and photometric monitoring to assess the number of planet candidates in the sample. We use the estimated detection probability function to calculate the occurrence rate of low-mass planets around nearby M dwarfs. Our results indicate that M dwarfs are hosts to an abundance of low-mass planets and the occurrence rate of planets less massive than 10 Earth masses is of the order of one planet per star and that planets are common in the stellar habitable zones of M dwarfs.

  19. Mass-Radius Relationships for Low-Mass Planets: From Iron Planets to Water Planets

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2007-01-01

    Transit observations, and radial velocity measurements, have begun to populate the mass radius diagram for extrasolar planets; fubture astrometric measurements and direct images promise more mass and radius information. Clearly, the bulk density of a planet indicates something about a planet s composition--but what? I will attempt to answer this question in general for low-mass planets (low-mass planets obey a kind of universal mass-radius relationship: an expansion whose first term is M approx. R(sup 3).

  20. The Diversity of Low-mass Exoplanets Characterized via Transit Timing

    NASA Astrophysics Data System (ADS)

    Jontof-Hutter, Daniel; Ford, Eric B.; Rowe, Jason F.; Lissauer, Jack. J.; Fabrycky, Daniel C.

    2016-10-01

    Transit timing variations (TTV) in multi-transiting systems enables precise characterizations of low-mass planets and their orbits. The range of orbital periods and incident fluxes with detailed TTV constraints complements the radial velocity sample for low-mass planets, pushing exoplanet characterization to the regime sub-Earth size planets and out to Mercury-like distances. This has revealed an astonishing diversity in the density of super-Earth mass planets. We summarize these and other contributions to exoplanet science from TTVs.

  1. A Triple Protostar System in L1448 IRS3B Formed via Fragmentation of a Gravitationally Unstable Disk

    NASA Astrophysics Data System (ADS)

    Tobin, John J.; Kratter, Kaitlin M.; Persson, Magnus; Looney, Leslie; Dunham, Michael; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Sadavoy, Sarah; Harris, Robert J.; Melis, Carl; Perez, Laura M.

    2017-01-01

    Binary and multiple star systems are a frequent outcome of the star formation process; most stars form as part of a binary/multiple protostar system. A possible pathway to the formation of close (< 500 AU) binary/multiple star systems is fragmentation of a massive protostellar disk due to gravitational instability. We observed the triple protostar system L1448 IRS3B with ALMA at 1.3 mm in dust continuum and molecular lines to determine if this triple protostar system, where all companions are separated by < 200 AU, is likely to have formed via disk fragmentation. From the dust continuum emission, we find a massive, 0.39 solar mass disk surrounding the three protostars with spiral structure. The disk is centered on two protostars that are separated by 61 AU and the third protostar is located in the outer disk at 183 AU. The tertiary companion is coincident with a spiral arm, and it is the brightest source of emission in the disk, surrounded by ~0.09 solar masses of disk material. Molecular line observations from 13CO and C18O confirm that the kinematic center of mass is coincident with the two central protostars and that the disk is consistent with being in Keplerian rotation; the combined mass of the two close protostars is ~1 solar mass. We demonstrate that the disk around L1448 IRS3B remains marginally unstable at radii between 150~AU and 320~AU, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning the companion stars.

  2. Organic Chemistry of Southern Sources: Microwave Spectroscopy of Cha-MMS1 and IRAS 15194-5115

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin; Charnley, Steven

    2011-01-01

    We report new spectra of molecule-rich sources in the southern hemisphere obtained using the 22-meter Mopra telescope. Spectra and maps are presented of organic molecules detected between 30 and 50 GHz in the young Class 0 protostar Chamaeleon MMS-1. The large abundances of polyynes, cyanopolyynes and methanol may be indicative of a warm carbon chemistry in the dense gas surrounding this protostar. Spectra are also presented from a 78-96 GHz scan of the carbon-rich AGB star IRAS 15194-5115, including new detections of HC5N, CCS and C13CH.

  3. In Search of the Youngest Protostars: IRAS HIRES Results in the Serpens Cloud Core

    NASA Astrophysics Data System (ADS)

    Hurt, R. L.; Barsony, M.

    1995-12-01

    Protostars which have yet to accrete the bulk of their initial main sequence mass from their infall envelopes, dubbed ``Class 0'' (Andre, Ward-Thompson, & Barsony 1993), represent the youngest (a few x 10(4) yr) protostellar sources. The defining observational characteristics for Class 0 protostars include a high ratio of mm/submm to bolometric luminosity, the presence of molecular outflows, invisibility shortward of 10 mu m, and spectral energy distributions (SEDs) resembling modified blackbodies with T <= 30 K. Since Class 0 SEDs peak at ~ 100--200 mu m, far-infrared (FIR) data are required to produce SEDs for these sources. The nearby Serpens star-forming cloud core is a region of great interest for Class 0 protostar searches. Millimeter continuum maps of the central 6(') x 5(') reveal at least five cold dust continuum peaks which lack NIR counterparts (Casali, Eiroa, & Duncan 1993). A recent multi-transition H_2CO study of these millimeter continuum sources (FIRS1, SMM2, SMM3, SMM4, & S68N) confirms the presence of central heating sources and substantial masses of circumstellar gas in these objects, suggesting that they could all be Class 0 protostars (Hurt, Barsony & Wooten 1996). We present new 12, 25, 60, & 100 mu m HIRES processed IRAS images of the Serpens cloud core at FWHM resolutions of ~ 30('') --1(') . Such resolutions are necessary to help identify the individual contributions from the closely spaced sources. We use HIRES-processed point source models of the IRAS emission to determine new flux values and flux upper limits for all the protostellar candidates in the Serpens core. From the resulting SEDs we derive the dust temperature, circumstellar mass, bolometric luminosity, and evolutionary status of each protostellar candidate. Remarkably, we find all five millimeter continuum sources to share the defining characteristics of Class 0 protostars, potentially making the Serpens core the densest known collection of such objects.

  4. CHARACTERIZING THE YOUNGEST HERSCHEL-DETECTED PROTOSTARS. I. ENVELOPE STRUCTURE REVEALED BY CARMA DUST CONTINUUM OBSERVATIONS

    SciTech Connect

    Tobin, John J.; Stutz, Amelia M.; Henning, Thomas; Ragan, Sarah E.; Megeath, S. Thomas; Fischer, William J.; Ali, Babar; Stanke, Thomas; Manoj, P.; Calvet, Nuria; Hartmann, Lee

    2015-01-10

    We present Combined Array for Research in Millimeter-wave Astronomy 2.9 mm dust continuum emission observations of a sample of 14 Herschel-detected Class 0 protostars in the Orion A and B molecular clouds, drawn from the PACS Bright Red Sources (PBRS) sample. These objects are characterized by very red 24-70 μm colors and prominent submillimeter emission, suggesting that they are very young Class 0 protostars embedded in dense envelopes. We detect all of the PBRS in 2.9 mm continuum emission and emission from four protostars and one starless core in the fields toward the PBRS; we also report one new PBRS source. The ratio of 2.9 mm luminosity to bolometric luminosity is higher by a factor of ∼5 on average, compared to other well-studied protostars in the Perseus and Ophiuchus clouds. The 2.9 mm visibility amplitudes for 6 of the 14 PBRS are very flat as a function of uv distance, with more than 50% of the source emission arising from radii <1500 AU. These flat visibility amplitudes are most consistent with spherically symmetric envelope density profiles with ρ ∝ R {sup –2.5}. Alternatively, there could be a massive unresolved structure like a disk or a high-density inner envelope departing from a smooth power law. The large amount of mass on scales <1500 AU (implying high average central densities) leads us to suggest that that the PBRS with flat visibility amplitude profiles are the youngest PBRS and may be undergoing a brief phase of high mass infall/accretion and are possibly among the youngest Class 0 protostars. The PBRS with more rapidly declining visibility amplitudes still have large envelope masses, but could be slightly more evolved.

  5. VLA Ammonia Observations of IRAS 16253-2429: A Very Young and Low Mass Protostellar System

    NASA Technical Reports Server (NTRS)

    Wiseman, Jennifer J.

    2011-01-01

    IRAS l6253-2429. the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source as possibly one of the youngest and lowest mass sources in formation yet known.

  6. ROSAT Observations of Low Mass Disk Galaxies: No Evidence of Baryonic Blow Out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James

    1994-01-01

    To test the hypothesis that galctic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT PSPC observations of three such galaxies.

  7. Relativistic Astrophysics in Black Hole and Low-Mass Neutron Star X-ray Binaries

    NASA Technical Reports Server (NTRS)

    2000-01-01

    During the five-year period, our study of "Relativistic Astrophysics in Black Hole and Low-Mass Neutron Star X-ray Binaries" has been focused on the following aspects: observations, data analysis, Monte-Carlo simulations, numerical calculations, and theoretical modeling. Most of the results of our study have been published in refereed journals and conference presentations.

  8. Collision safety of a hard-shell low-mass vehicle.

    PubMed

    Kaeser, R; Walz, F H; Brunner, A

    1994-06-01

    Low-mass vehicles and in particular low-mass electric vehicles as produced today in very small quantities are in general not designed for crashworthiness in collisions. Particular problems of compact low-mass cars are: reduced length of the car front, low mass compared to other vehicles, and heavy batteries in the case of an electric car. With the intention of studying design improvements, three frontal crash tests were run last year: the first one with a commercial, lightweight electric car; the second with a reinforced version of the same car; and the last one with a car based on a different structural design with a "hard-shell" car body. Crash tests showed that the latter solution made better use of the small zone available for continuous energy absorption. The paper discusses further the problem of frontal collisions between vehicles of different weight and, in particular, the side collision. A side-collision test was run with the hard-shell vehicle following the ECE lateral-impact test procedure at 50 km/h and led to results for the EuroSID1-dummy well below current injury tolerance criteria.

  9. Collision safety of a hard-shell low-mass vehicle

    SciTech Connect

    Kaeser, R.; Walz, F.H.; Brunner, A.

    1994-06-01

    Low-mass vehicles and in particular low-mass electric vehicles as produced today in very small quantities are in general not designed for crashworthiness in collisions. Particular problems of compact low-mass cars are: reduced length of the car front, low mass compared to other vehicles, and heavy batteries in the case of an electric car. With the intention of studying design improvements, three frontal crash tests were run last year: the first one with a commercial, lightweight electric car; the second with a reinforced version of the same car; and the last one with a car based on a different structural design with a `hard-shell` car body. Crash tests showed that the latter solution made better use of the small zone available for continuous energy absorption. The paper discusses further the problem of frontal collisions between vehicles of different weight and, in particular, the side collision. A side-collision test was run with the hard-shell vehicle following the ECE lateral-impact test procedure at 50 km/h and led to results for the EuroSIDI-dummy well below current injury tolerance criteria.

  10. A SPITZER SEARCH FOR SUBSTELLAR COMPANIONS TO LOW-MASS WHITE DWARFS

    SciTech Connect

    Kilic, Mukremin; Brown, Warren R.; McLeod, B.

    2010-01-01

    The formation scenarios for single low-mass (M < 0.45 M{sub sun}) white dwarfs (WDs) include enhanced mass loss from a metal-rich progenitor star or a common envelope phase of a solar-like star with a close-in massive planet or a brown dwarf. Both scenarios suggest that low-mass WDs may have planets. Here, we present a Spitzer IRAC search for substellar and planetary mass companions to 14 low-mass WDs. One of our targets, HS 1653+7753, displays near- and mid-infrared flux excess. However, follow-up MMT observations show that this excess is due to a nearby resolved source, which is mostly likely a background object. Another target, PG 2257+162, shows flux excess compatible with a late-type stellar companion. We do not detect substellar companions to any of the remaining targets. In addition, eight of these stars do not show any radial velocity variations, ruling out stellar mass companions including other WDs. We conclude that a significant fraction of the low-mass WDs in our sample do not have stellar or massive brown dwarf companions.

  11. LOW-MASS ACTIVE GALACTIC NUCLEI WITH RAPID X-RAY VARIABILITY

    SciTech Connect

    Ho, Luis C.; Kim, Minjin

    2016-04-10

    We present a detailed study of the optical spectroscopic properties of 12 active galactic nuclei (AGNs) with candidate low-mass black holes (BHs) selected by Kamizasa et al. through rapid X-ray variability. The high-quality, echellette Magellan spectra reveal broad Hα emission in all the sources, allowing us to estimate robust virial BH masses and Eddington ratios for this unique sample. We confirm that the sample contains low-mass BHs accreting at high rates: the median M{sub BH} = 1.2 × 10{sup 6} M{sub ⊙} and median L{sub bol}/L{sub Edd} = 0.44. The sample follows the M{sub BH}–σ{sub *} relation, within the considerable scatter typical of pseudobulges, the probable hosts of these low-mass AGNs. Various lines of evidence suggest that ongoing star formation is prevalent in these systems. We propose a new strategy to estimate star formation rates in AGNs hosted by low-mass, low-metallicity galaxies, based on modification of an existing method using the strength of [O ii] λ3727, [O iii] λ5007, and X-rays.

  12. Using K2 to Investigate Planetary Systems Orbiting Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Dressing, Courtney D.; Newton, Elisabeth R.; Charbonneau, David; Schlieder, Joshua E.; K2 CHAI Consortium

    2016-10-01

    The NASA K2 mission is using the repurposed Kepler spacecraft to search for transiting planets in multiple fields along the ecliptic plane. Unlike the original Kepler mission, which stared at a single region of the sky for four years, K2 observes each field for a much shorter timespan of roughly 80 days. While planets in the habitable zones of Sun-like stars would be unlikely to transit even once during an 80-day interval, planets in the habitable zones of faint low-mass stars have much shorter orbital periods and may even transit multiple times during a single K2 campaign. Accordingly, M and K dwarfs are frequently nominated as K2 Guest Observer targets and K2 has already observed significantly more low-mass stars than the original Kepler mission. While the K2 data are therefore an enticing resource for studying the properties and frequency of planetary systems orbiting low-mass stars, many K2 target stars are not well-characterized and some candidate low-mass stars are actually giants or reddened Sun-like stars. We are improving the characterization of K2 planetary systems orbiting low-mass stars by using SpeX on the NASA Infrared Telescope Facility and TripleSpec on the 200-inch Hale Telescope at Palomar Observatory to acquire near-infrared spectra of K2 target stars. We then employ empirically-based relations to determine the temperatures, radii, luminosities, and metallicities of K2 planet candidate host stars. Refining the stellar parameters allows us to identify astrophysical false positives and better constrain the radii and insolation flux environments of bona fide transiting planets. I will present our resulting catalog of stellar properties and discuss the prospects for using K2 data to investigate whether planet occurrence rates for mid-M dwarfs are similar to those for early-M and late-K dwarfs.

  13. Companions and Environments of Low-Mass Stars: From Star-Forming Regions to the Field

    NASA Astrophysics Data System (ADS)

    Ward-Duong, Kimberly; Patience, Jenny; De Rosa, Robert J.; Bulger, Joanna; Rajan, Abhijith; Goodwin, Simon; Parker, Richard J.; McCarthy, Donald W.; Kulesa, Craig; van der Plas, Gerrit; Menard, Francois; Pinte, Christophe; Jackson, Alan Patrick; Bryden, Geoffrey; Turner, Neal J.; Harvey, Paul M.; Hales, Antonio

    2017-01-01

    We present results from two studies probing the multiplicity and environmental properties of low-mass stars: (1) The MinMs (M-dwarfs in Multiples) Survey, a large, volume-limited survey of 245 field M-dwarfs within 15 pc, and (2) the TBOSS (Taurus Boundary of Stellar/Substellar) Survey, an ongoing study of disk properties for the lowest-mass members within the Taurus star-forming region. The MinMs Survey provides new measurements of the companion star fraction, separation distribution, and mass ratio distribution for the nearest K7-M6 dwarfs, utilizing a combination of high-resolution adaptive optics imaging and digitized widefield archival plates to cover an unprecedented separation range of ~1-10,000 AU. Within these data, we also identify companions below the stellar/brown dwarf boundary, enabling characterization of the substellar companion population to low-mass field stars. For the much younger population in Taurus, we present results from ALMA Band 7 continuum observations of low-mass stellar and substellar Class II objects, spanning spectral types from M4-M7.75. The sub-millimeter detections of these disks provide key estimates of the dust mass in small grains, which is then assessed within the context of region age, environment, and viability for planet formation. This young population also includes a number of interesting young binary systems. Covering both young (1-2 Myr) and old (>5 Gyr) populations of low-mass stars, the results from these studies provide benchmark measurements on the population statistics of low-mass field stars, and on the early protoplanetary environments of their younger M-star counterparts.

  14. Feedback of atomic jets from embedded protostars in NGC 1333

    NASA Astrophysics Data System (ADS)

    Dionatos, Odysseas; Güdel, Manuel

    2017-01-01

    Context. The feedback of star formation to the parent cloud is conventionally examined through the study of molecular outflows. Little is known, however, about the effect that atomic ejecta tracing fast shocks can have on small scales or on global cloud properties. Aims: Our immediate objective is to study the morphology of protostellar ejecta through far-infrared atomic lines, compare them to other outflow tracers, and associate them with their driving sources. The main goal is to study the feedback from atomic jet emission that is excited by fast shocks on the parent cloud material, and examine the relative importance of atomic jets as regulators of the star formation process. Methods: We employed [O i] and [C ii] line maps of the NGC 1333 star-forming region observed with Herschel/PACS. We studied the detailed morphology and velocity distribution of the [O i] line using channel and line-centroid maps. We derived the momentum, energy, and mass flux for all the bipolar outflows traced by [O i] line emission. We compared the [O i] morphology to CO and H2 emission, and its dynamical and kinematic properties to the emission corresponding to CO outflows. Results: We find that the line-centroid maps can trace velocity structures down to 5 km s-1 which is a factor of 20 beyond the nominal velocity resolution reached by Herschel/PACS. These maps reveal an unprecedented degree of details that significantly assist in the association and characterization of outflows. We associate most of the [O i] emission with ejecta from embedded protostars. The spatial distribution of the [O i] emission closely follows the CO emission pattern and strongly correlates to the spatial distribution of the H2 emission, with the latter indicating excitation in shocks. The [O i] momentum accounts for only 1% of the momentum carried by the large-scale CO outflows. The energy released in shocks, however, corresponds to 50-100% of the energy carried away by outflows. Mass-flux estimates of the

  15. Very Low Mass Stellar and Substellar Companions to Solar-like Stars from MARVELS. IV. A Candidate Brown Dwarf or Low-mass Stellar Companion to HIP 67526

    NASA Astrophysics Data System (ADS)

    Jiang, Peng; Ge, Jian; Cargile, Phillip; Crepp, Justin R.; De Lee, Nathan; Porto de Mello, Gustavo F.; Esposito, Massimiliano; Ferreira, Letícia D.; Femenia, Bruno; Fleming, Scott W.; Gaudi, B. Scott; Ghezzi, Luan; González Hernández, Jonay I.; Hebb, Leslie; Lee, Brian L.; Ma, Bo; Stassun, Keivan G.; Wang, Ji; Wisniewski, John P.; Agol, Eric; Bizyaev, Dmitry; Brewington, Howard; Chang, Liang; Nicolaci da Costa, Luiz; Eastman, Jason D.; Ebelke, Garrett; Gary, Bruce; Kane, Stephen R.; Li, Rui; Liu, Jian; Mahadevan, Suvrath; Maia, Marcio A. G.; Malanushenko, Viktor; Malanushenko, Elena; Muna, Demitri; Nguyen, Duy Cuong; Ogando, Ricardo L. C.; Oravetz, Audrey; Oravetz, Daniel; Pan, Kaike; Pepper, Joshua; Paegert, Martin; Allende Prieto, Carlos; Rebolo, Rafael; Santiago, Basilio X.; Schneider, Donald P.; Shelden Bradley, Alaina C.; Sivarani, Thirupathi; Snedden, Stephanie; van Eyken, J. C.; Wan, Xiaoke; Weaver, Benjamin A.; Zhao, Bo

    2013-09-01

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695^{+0.0188}_{-0.0187} days, an eccentricity of 0.4375 ± 0.0040, and a semi-amplitude of 2948.14^{+16.65}_{-16.55} m s-1. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T eff = 6004 ± 34 K, a surface gravity log g (cgs) =4.55 ± 0.17, and a metallicity [Fe/H] =+0.04 ± 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 ± 0.09 M ⊙ and 0.92 ± 0.19 R ⊙. The minimum mass of MARVELS-5b is 65.0 ± 2.9M Jup, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 ± 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M ⊙ at a separation larger than 40 AU.

  16. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    SciTech Connect

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji; Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G.; Crepp, Justin R.; Porto de Mello, Gustavo F.; Ferreira, Leticia D.; Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I.; Ghezzi, Luan; Wisniewski, John P.; Agol, Eric; and others

    2013-09-15

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

  17. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotsky, Richard (Technical Monitor)

    2004-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was observed on September of 2002. Data analysis for both observation has been completed: an investigation of the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure. A study of behavior of the emission features as a function of binary orbit shows modulated behavior in one of the systems. A paper on "High-resolution observations of low-mass X-ray binaries" is near completion. The paper includes observations with the Chandra HETG that are not yet completed.

  18. Radius constraints from high-speed photometry of 20 low-mass white dwarf binaries

    SciTech Connect

    Hermes, J. J.; Brown, Warren R.; Kilic, Mukremin; Gianninas, A.; Chote, Paul; Sullivan, D. J.; Winget, D. E.; Bell, Keaton J.; Falcon, R. E.; Winget, K. I.; Harrold, Samuel T.; Montgomery, M. H.; Mason, Paul A.

    2014-09-01

    We carry out high-speed photometry on 20 of the shortest-period, detached white dwarf binaries known and discover systems with eclipses, ellipsoidal variations (due to tidal deformations of the visible white dwarf), and Doppler beaming. All of the binaries contain low-mass white dwarfs with orbital periods of less than four hr. Our observations identify the first eight tidally distorted white dwarfs, four of which are reported for the first time here. We use these observations to place empirical constraints on the mass-radius relationship for extremely low-mass (≤0.30 M {sub ☉}) white dwarfs. We also detect Doppler beaming in several of these binaries, which confirms their high-amplitude radial-velocity variability. All of these systems are strong sources of gravitational radiation, and long-term monitoring of those that display ellipsoidal variations can be used to detect spin-up of the tidal bulge due to orbital decay.

  19. Infrared and optical studies of the Chamaeleon II and Lupus low-mass star forming regions .

    NASA Astrophysics Data System (ADS)

    Spezzi, L.; Alcalá, J. M.; Chapman, N.; Covino, E.; Evans, N. J., II; Frasca, A.; Gandolfi, D.; Huard, T. L.; Oliveira, I.; Jørgensen, J. K.; Merín, B.; Stapelfeldt, K. R.

    The Spitzer Legacy survey ``From Molecular Cores to Planet-forming Disks'' \\citep[c2d][]{Eva03} provided infrared observations of sources that span the evolutionary sequence from molecular cores to proto-planetary disks, encompassing a wide range of star-forming environments. These overall observations allowed to study crucial steps in the formation of stars and planets with unprecedented sensitivity. We present some results from the Spitzer observations and complementary data in the low-mass star forming regions in Chamaeleon II and Lupus. We focus, in particular, on the star-formation history and activity of these clouds, the low-mass end of their IMF and the envelope/disk properties of their young populations.

  20. Can transport peak explain the low-mass enhancement of dileptons at RHIC?

    NASA Astrophysics Data System (ADS)

    Akamatsu, Y.; Hamagaki, H.; Hatsuda, T.; Hirano, T.

    2011-12-01

    We propose a novel relation between the low-mass enhancement of dielectrons observed at PHENIX and transport coefficients of QGP such as the charge diffusion constant D and the relaxation time τJ. We parameterize the transport peak in the spectral function using the second-order relativistic dissipative hydrodynamics by Israel and Stewart. Combining the spectral function and the full (3+1)-dimensional hydrodynamical evolution with the lattice EoS, theoretical dielectron spectra and the experimental data are compared. Detailed analysis suggests that the low-mass dilepton enhancement originates mainly from the high-temperature QGP phase where there is a large electric charge fluctuation as obtained from lattice QCD simulations.

  1. MINERVA: A Dedicated Observatory for Detection of Nearby Low-Mass Exoplanets

    NASA Astrophysics Data System (ADS)

    McCrady, Nate; Johnson, John; Wright, Jason; Wittenmyer, Robert A.; Blake, Cullen; Swift, Jonathan; Eastman, Jason D.; Plavchan, Peter; Riddle, Reed L.; Muirhead, Philip Steven; Bottom, Michael; Zhao, Ming; Beatty, Thomas G.

    2015-01-01

    Detection of low-mass planets around GKM stars requires sub-meter-per-second radial velocity precision. Stellar noise sources (starspots, oscillations, and granulation) necessitate high cadence observations. MINERVA is a dedicated observatory for velocimetric detection of low mass exoplanets orbiting nearby stars. Our array of four robotic 0.7-meter PlaneWave telescopes feeds a purpose-built, temperature-stabilized, iodine cell spectrometer from Callaghan Innovation. We will monitor bright, sun-like stars within 100 pc every clear night from Whipple Observatory on Mt Hopkins, Arizona. Each telescope is also equipped with an Andor CCD for followup photometry and education use. Commissioning is underway on the site and science observations will begin in early 2015.

  2. The seismic properties of low-mass He-core white dwarf stars

    NASA Astrophysics Data System (ADS)

    Córsico, A. H.; Romero, A. D.; Althaus, L. G.; Hermes, J. J.

    2012-11-01

    Context. In recent years, many low-mass (≲ 0.45 M⊙) white dwarf stars expected to harbor He cores have been detected in the field of the Milky Way and in several galactic globular and open clusters. Until recently, no objects of this kind showed pulsations. This situation has changed recently with the exciting discovery of SDSS J184037.78+642312.3, the first pulsating low-mass white dwarf star. Aims: Motivated by this extremely important finding, and in view of the very valuable asteroseismological potential of these objects, we present here a detailed pulsational study applied to low-mass He-core white dwarfs with masses ranging from 0.17 to 0.46 M⊙, based on full evolutionary models representative of these objects. This study is aimed to provide a theoretical basis from which to interpret future observations of variable low-mass white dwarfs. Methods: The background stellar models on which our pulsational analysis was carried out were derived by taking into account the complete evolutionary history of the progenitor stars, with special emphasis on the diffusion processes acting during the white dwarf cooling phase. We computed nonradial g-modes to assess the dependence of the pulsational properties of these objects with stellar parameters such as the stellar mass and the effective temperature, and also with element diffusion processes. We also performed a g- and p-mode pulsational stability analysis on our models and found well-defined blue edges of the instability domain, where these stars should start to exhibit pulsations. Results: We found substantial differences in the seismic properties of white dwarfs with M∗ ≳ 0.20 M⊙ and the extremely low-mass (ELM) white dwarfs (M∗ ≲ 0.20 M⊙). Specifically, g-mode pulsation modes in ELM white dwarfs mainly probe the core regions and are not dramatically affected by mode-trapping effects by the He/H interface, whereas the opposite is true for more massive He-core white dwarfs. We found that element

  3. THE ROTATING OUTFLOW, ENVELOPE, AND DISK OF THE CLASS-0/I PROTOSTAR [BHB2007] no. 11 IN THE PIPE NEBULA

    SciTech Connect

    Hara, C.; Shimajiri, Y.; Kurono, Y.; Saigo, K.; Nakamura, F.; Saito, M.; Kawabe, R.; Tsukagoshi, T.; Wilner, David

    2013-07-10

    We present the results of observations toward a low-mass Class-0/I protostar [BHB2007] no. 11 (B59 no. 11) in the nearby (d = 130 pc) star-forming region Barnard 59 (B59), in the Pipe Nebula. We utilize the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope ({approx}22'' resolution), focusing on the CO(3-2), HCO{sup +}, H{sup 13}CO{sup +}(4-3), and 1.1 mm dust-continuum emission transitions. We also show Submillimeter Array (SMA) data with {approx}5'' resolution in {sup 12}CO, {sup 13}CO, C{sup 18}O(2-1), and 1.3 mm dust-continuum emission. From ASTE CO(3-2) observations, we found that B59 no. 11 is blowing a collimated outflow whose axis lies almost on the plane of the sky. The outflow traces well a cavity-like structure seen in the 1.1 mm dust-continuum emission. The results of SMA {sup 13}CO and C{sup 18}O(2-1) observations have revealed that a compact and elongated structure of dense gas is associated with B59 no. 11; the structure is oriented perpendicular to the outflow axis. There is a compact dust condensation with a size of 350 Multiplication-Sign 180 AU seen in the SMA 1.3 mm continuum map, and the direction of its major axis is almost the same as that of the dense gas elongation. The distributions of {sup 13}CO and C{sup 18}O emission also show velocity gradients along their major axes, which are thought to arise from the envelope/disk rotation. From detailed analysis of the SMA data, we infer that B59 no. 11 is surrounded by a Keplerian disk with a radius of less than 350 AU. In addition, the SMA CO(2-1) image shows a velocity gradient in the outflow in the same direction as that of the dense gas rotation. We suggest that this velocity gradient indicates rotation in the outflow.

  4. Caustic waves in galaxy disks produced in collisions with low mass companions

    NASA Technical Reports Server (NTRS)

    Struck-Marcell, Curtis

    1990-01-01

    The author lists a few reasons for studying collisions with relatively low mass companions, specifically those that are less than about one third of the mass of the target galaxy. The primary effect of such collisions on a target galaxy with a 'cold' disk component is the generation of waves in the disk. The focus here is on the purely stellar waves in such disks. The example of a ring galaxy case is examined.

  5. The low-mass X-ray binary LMC X-2

    SciTech Connect

    Crampton, D.; Hutchings, J.B.; Cowley, A.P.; Schmidtke, P.C.; Thompson, I.B. Arizona State Univ., Tempe Mount Wilson and Las Campanas Observatories, Pasadena, CA )

    1990-06-01

    Spectroscopic and photometric observations of LMC X-2 reveal the source to be an X-ray binary with a relatively long orbital period, probably 12.5 days. It appears to be a partially eclipsing system. It is one of a small subclass of low-mass X-ray binaries with longer orbital periods and higher X-ray luminosity than average, which contain a compact object accreting material from an evolving giant companion. 26 refs.

  6. Low-mass, high-rate cylindrical MWPC's for the MEGA experiment

    SciTech Connect

    Mischke, R.E.; Armijo, V.; Black, J.K.; Bolton, R.D.; Carius, S.; Cooper, M.D.; Espinoza, C.; Hart, G.W.; Hogan, G.E.; Piilonen, L.E.; Sandoval, J.; Schilling, S.; Sena, J.; Stanislaus, S.; Suazo, G.; Szymanski, J.J.; Whitehouse, D.A.; Wilkinson, C.A. ); Fisk, R.; Koetke, D.D.; Manweiler, R.W. ); Jui, C. )

    1990-01-01

    The construction of MWPCs for the MEGA experiment at LAMPF are described. The chambers are cylindrical, low mass (3 {times} 10{sup {minus}4} radiation lengths), and are designed to operate at high rates (3 {times} 10{sup 4} /mm{sup 2}/s). Several novel construction techniques have been developed and custom electronics have been designed to help achieve the required performance, which corresponds to that needed at high luminosity colliders. 4 refs., 3 figs.

  7. Age-dating Low-Mass Star-Forming Galaxies at intermediate redshifts

    NASA Astrophysics Data System (ADS)

    Gallego, Jesus; Rodriguez-Muñoz, Lucía; Pacifici, Camilla; Tresse, Laurence; Charlot, Stéphane; Gil de Paz, Armando; Barro, Guillermo; Gomez-Guijarro, Carlos; Villar, Víctor

    2015-08-01

    Dwarf galaxies play a key role in galaxy formation and evolution: (1) hierarchical models predict that low-mass systems merged to form massive galaxies (building block paradigm; Dekel & Silk 1986); (2) dwarf systems might have been responsible for the reionization of the Universe (Wyithe & Loeb 2006); (3) theoretical models are particularly sensitive to the density of low-mass systems at diferent redshifts (Mamon et al. 2011), being one of the key science cases for the future E-ELT (Evans et al. 2013). While the history of low-mass dark matter halos is relatively well understood, the formation history of dwarf galaxies is still poorly reproduced by the models due to the distinct evolution of baryonic and dark matter.We present physical properties and constraints on the star formation histories (SFHs) of a sample of low-mass Star-Forming Galaxies (LMSFGs; 7.3 < log M∗/Mo < 8.0, at 0.3 < zspec < 0.9) selected by photometric stellar mass and apparent magnitude. The SFHs were obtained through the analysis of their spectral energy distributions using a novel approach (Pacifici et al. 2012) that (1) consistently combines photometric (HST and ground-based multi-broadband) and spectroscopic (equivalent widths of emission lines from VLT and GTC spectroscopy) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time.The median SFH of our LMSFGs appears to form 90% of the median stellar mass inferred for the sample in the ˜0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for dwarf SFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for a slightly more massive secondary sample 8.0 < log M∗/Mo < 9.1).

  8. THE SURVEY OF H I IN EXTREMELY LOW-MASS DWARFS (SHIELD)

    SciTech Connect

    Cannon, John M.; Engstrom, Eric; Allan, John; Erny, Grace; Fliss, Palmer; Smith, AnnaLeigh

    2011-09-20

    We present first results from the Survey of H I in Extremely Low-mass Dwarfs (SHIELD), a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas contents and dynamics of galaxies with H I masses in the 10{sup 6}-10{sup 7} M{sub sun} range detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We describe the survey motivation and concept demonstration using Very Large Array imaging of six low-mass galaxies detected in early ALFALFA data products. We then describe the primary scientific goals of SHIELD and present preliminary EVLA and WIYN 3.5 m imaging of the 12 SHIELD galaxies. With only a few exceptions, the neutral gas distributions of these extremely low-mass galaxies are centrally concentrated. In only one system have we detected H I column densities higher than 10{sup 21} cm{sup -2}. Despite this, the stellar populations of all of these systems are dominated by blue stars. Further, we find ongoing star formation as traced by H{alpha} emission in 10 of the 11 galaxies with H{alpha} imaging obtained to date. Taken together these results suggest that extremely low-mass galaxies are forming stars in conditions different from those found in more massive systems. While detailed dynamical analysis requires the completion of data acquisition, the most well-resolved system is amenable to meaningful position-velocity analysis. For AGC 749237, we find well-ordered rotation of 30 km s{sup -1} at {approx}40'' distance from the dynamical center. At the adopted distance of 3.2 Mpc, this implies the presence of a {approx}>1 x 10{sup 8} M{sub sun} dark matter halo and a baryon fraction {approx}<0.1.

  9. UNVEILING A POPULATION OF GALAXIES HARBORING LOW-MASS BLACK HOLES WITH X-RAYS

    SciTech Connect

    Schramm, M.; Silverman, J. D.; Greene, J. E.; Brandt, W. N.; Luo, B.; Xue, Y. Q.; Capak, P.; Kakazu, Y.; Kartaltepe, J.; Mainieri, V.

    2013-08-20

    We report the discovery of three low-mass black hole (BH) candidates residing in the centers of low-mass galaxies at z < 0.3 in the Chandra Deep Field-South Survey. These BHs are initially identified as candidate active galactic nuclei based on their X-ray emission in deep Chandra observations. Multi-wavelength observations are used to strengthen our claim that such emission is powered by an accreting supermassive BH. While the X-ray luminosities are low at L{sub X} {approx} 10{sup 40} erg s{sup -1} (and variable in one case), we argue that they are unlikely to be attributed to star formation based on H{alpha} or UV fluxes. Optical spectroscopy from Keck and the VLT allows us to (1) measure accurate redshifts, (2) confirm their low stellar host mass, (3) investigate the source(s) of photo-ionization, and (4) estimate extinction. With stellar masses of M{sub *} < 3 Multiplication-Sign 10{sup 9} M{sub Sun} determined from Hubble Space Telescope/Advanced Camera for Surveys imaging, the host galaxies are among the lowest mass systems known to host actively accreting BHs. We estimate BH masses M{sub BH} {approx} 2 Multiplication-Sign 10{sup 5} M{sub Sun} based on scaling relations between BH mass and host properties for more luminous systems. In one case, a broad component of the H{alpha} emission-line profile is detected, thus providing a virial mass estimate. BHs in such low-mass galaxies are of considerable interest as the low-redshift analogs to the seeds of the most massive BHs at high redshift which have remained largely elusive to date. Our study highlights the power of deep X-ray surveys to uncover such low-mass systems.

  10. Supernova enrichment of planetary systems in low-mass star clusters

    NASA Astrophysics Data System (ADS)

    Nicholson, Rhana B.; Parker, Richard J.

    2017-02-01

    The presence and abundance of short-lived radioisotopes 26Al and 60Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters (>1000 M⊙) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of ˜1 pc. We investigate whether low-mass (50-200 M⊙) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse N-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience SN enrichment than in high-mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first SN even in clusters with relatively low (100 stars pc-3) initial densities. However, because of the high number of low-mass clusters containing one or two massive stars, the absolute number of enriched stars is the same, if not higher than for more populous clusters. Our results show that direct enrichment of protoplanetary discs from SNe occurs as frequently in low-mass clusters containing one or two massive stars (>20 M⊙) as in more populous star clusters (1000 M⊙). This relaxes the constraints on the direct enrichment scenario and therefore the birth environment of the Solar system.

  11. Physical Properties of the Narrow-line Region of Low-mass Active Galaxies

    NASA Astrophysics Data System (ADS)

    Ludwig, Randi R.; Greene, Jenny E.; Barth, Aaron J.; Ho, Luis C.

    2012-09-01

    We present spectroscopic observations of 27 active galactic nuclei (AGNs) with some of the lowest black hole (BH) masses known. We use the high spectral resolution and small aperture of our Keck data, taken with the Echellette Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these low-mass BHs. We investigate their emission-line properties and compare them with those of AGNs with higher-mass BHs. While we are unable to determine absolute metallicities, some of our objects plausibly represent examples of the low-metallicity AGNs described by Groves et al., based on their [N II]/Hα ratios and their consistency with the Kewley & Ellison mass-metallicity relation. We find tentative evidence for steeper far-UV spectral slopes in lower-mass systems. Overall, NLR emission lines in these low-mass AGNs exhibit trends similar to those seen in AGNs with higher-mass BHs, such as increasing blueshifts and broadening with increasing ionization potential. Additionally, we see evidence of an intermediate-line region whose intensity correlates with L/L Edd, as seen in higher-mass AGNs. We highlight the interesting trend that, at least in these low-mass AGNs, the [O III] equivalent width (EW) is highest in symmetric NLR lines with no blue wing. This trend of increasing [O III] EW with line symmetry could be explained by a high covering factor of lower-ionization gas in the NLR. In general, low-mass AGNs preserve many well-known trends in the structure of the NLR, while exhibiting steeper ionizing continuum slopes and somewhat lower gas-phase metallicities.

  12. High Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. 1; Ices and Infalling Gas in the Disk of L1489 IRS

    NASA Technical Reports Server (NTRS)

    Boogert, A. C. A.; Hogerheijde, M. R.; Blake, G. A.

    2001-01-01

    We explore the infrared M band (4.7 micron) spectrum of the class I protostar L1489 IRS in the Taurus Molecular Cloud. This is the highest resolution wide coverage spectrum at this wavelength of a low mass protostar observed to date (R =25,000; (Delta)v =12 km s(exp -1). A large number of narrow absorption lines of gas phase (12)CO, (13)CO, and C(sup 18)O are detected, as well as a prominent band of solid (12)CO. The gas phase (12)CO lines have red shifted absorption wings (up to 100 km s(exp -1)), which likely originate from warm disk material falling toward the central object. Both the isotopes and the extent of the (12)CO line wings are successfully fitted with a contracting disk model of this evolutionary transitional object. This shows that the inward motions seen in millimeter wave emission lines continue to within approx. 0.1 AU from the star. The amount of high velocity infalling gas is however overestimated by this model, suggesting that only part of the disk is infalling, e.g. a hot surface layer or hot gas in magnetic field tubes. The colder parts of the disk are traced by the prominent CO ice band. The band profile results from CO in 'polar' ices (CO mixed with H2O), and CO in 'apolar' ices. At the high spectral resolution, the 'apolar' component is, for the first time, resolved into two distinct components, likely due to pure CO and CO mixed with CO2, O2 and/or N2. The ices have probably experienced thermal processing in the upper disk layer traced by our pencil absorption beam: much of the volatile 'apolar' ices has evaporated, the depletion factor of CO onto grains is remarkably low (approx. 7%), and the CO2 traced in the CO band profile was possibly formed energetically. This study shows that high spectral resolution 4.7 micron observations provide important and unique information on the dynamics and structure of protostellar disks and the origin and evolution of ices in these disks.

  13. Complex organic molecules during low-mass star formation: Pilot survey results

    SciTech Connect

    Öberg, Karin I.; Graninger, Dawn; Lauck, Trish

    2014-06-10

    Complex organic molecules (COMs) are known to be abundant toward some low-mass young stellar objects (YSOs), but how these detections relate to typical COM abundance are not yet understood. We aim to constrain the frequency distribution of COMs during low-mass star formation, beginning with this pilot survey of COM lines toward six embedded YSOs using the IRAM 30 m Telescope. The sample was selected from the Spitzer c2d ice sample and covers a range of ice abundances. We detect multiple COMs, including CH{sub 3}CN, toward two of the YSOs, and tentatively toward a third. Abundances with respect to CH{sub 3}OH vary between 0.7% and 10%. This sample is combined with previous COM observations and upper limits to obtain a frequency distributions of CH{sub 3}CN, HCOOCH{sub 3}, CH{sub 3}OCH{sub 3}, and CH{sub 3}CHO. We find that for all molecules more than 50% of the sample have detections or upper limits of 1%-10% with respect to CH{sub 3}OH. Moderate abundances of COMs thus appear common during the early stages of low-mass star formation. A larger sample is required, however, to quantify the COM distributions, as well as to constrain the origins of observed variations across the sample.

  14. Large {sigma} Channel Low-Mass Enhancement in Exclusively Measured Double Pionic Fusion to 3He

    SciTech Connect

    Bashkanov, M.; Skorodko, T.; Clement, H.; Khakimova, O.; Kren, F.; Wagner, G. J.

    2006-07-11

    The pd {yields} 3He {pi}0{pi}0 and pd {yields} 3He {pi}+{pi}- reactions have been measured exclusively at CELSIUS using the WASA 4{pi} detector with pellet target system. For the double-pionic fusion to 3He data have been taken at Tp = 0.893 GeV, where the maximum of the socalled ABC effect is expected. A very large low-mass enhancement is observed in the {pi}0{pi}0 invariant mass spectrum M{pi}0{pi}0, whereas only a moderate low-mass enhancement is seen in M{pi}+{pi}- raising thus the question of isospin invariance in this region. With both channels summed up the data agree well to previous inclusive measurements regarding the low-mass enhancement. However, they do not exhibit the high-mass enhancement seen in the inclusive measurements and predicted by theoretical calculations based on a {delta}{delta} process, which produces a double-hump structure in the M{pi}{pi} spectra.

  15. Securing the Extremely Low-Densities of Low-Mass Planets Characterized by Transit Timing Variations

    NASA Astrophysics Data System (ADS)

    Ford, Eric B.

    2015-12-01

    Transit timing variations (TTVs) provide an excellent tool to characterize the masses and orbits of dozens of small planets, including many at orbital periods beyond the reach of both Doppler surveys and photoevaporation-induced atmospheric loss. Dynamical modeling of these systems has identified low-mass planets with surprisingly large radii and low densities (e.g., Kepler-79d, Jontof-Hutter et al. 2014; Kepler-51, Masuda 2014; Kepler-87c, Ofir et al. 2014). Additional low-density, low-mass planets will likely become public before ESS III (Jontof-Hutter et al. in prep). Collectively, these results suggest that very low density planets with masses of 2-6 MEarth are not uncommon in compact multiple planet systems. Some astronomers have questioned whether there could be an alternative interpretation of the TTV observations. Indeed, extraordinary claims require extraordinary evidence. While the physics of TTVs is rock solid, the statistical analysis of Kepler observations can be challenging, due to the complex interactions between model parameters and high-dimensional parameter spaces that must be explored. We summarize recent advances in computational statistics that enable robust characterization of planetary systems using TTVs. We present updated analyses of a few particularly interesting systems and discuss the implications for the robustness of extremely low densities for low-mass planets. Such planets pose an interesting challenge for planet formation theory and are motivating detailed theoretical studies (e.g., Lee & Chiang 2015 and associated ESS III abstracts).

  16. The ELM Survey. VII. Orbital Properties of Low-Mass White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Gianninas, A.; Kilic, Mukremin; Kenyon, Scott J.; Allende Prieto, Carlos

    2016-02-01

    We present the discovery of 15 extremely low-mass (5\\lt {log}g\\lt 7) white dwarf (WD) candidates, 9 of which are in ultra-compact double-degenerate binaries. Our targeted extremely low-mass Survey sample now includes 76 binaries. The sample has a lognormal distribution of orbital periods with a median period of 5.4 hr. The velocity amplitudes imply that the binary companions have a normal distribution of mass with 0.76 M⊙ mean and 0.25 M⊙ dispersion. Thus extremely low-mass WDs are found in binaries with a typical mass ratio of 1:4. Statistically speaking, 95% of the WD binaries have a total mass below the Chandrasekhar mass, and thus are not type Ia supernova progenitors. Yet half of the observed binaries will merge in less than 6 Gyr due to gravitational wave radiation; probable outcomes include single massive WDs and stable mass transfer AM CVn binaries. Based on observations obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona.

  17. KOI-126: a triply eclipsing hierarchical triple with two low-mass stars.

    PubMed

    Carter, Joshua A; Fabrycky, Daniel C; Ragozzine, Darin; Holman, Matthew J; Quinn, Samuel N; Latham, David W; Buchhave, Lars A; Van Cleve, Jeffrey; Cochran, William D; Cote, Miles T; Endl, Michael; Ford, Eric B; Haas, Michael R; Jenkins, Jon M; Koch, David G; Li, Jie; Lissauer, Jack J; MacQueen, Phillip J; Middour, Christopher K; Orosz, Jerome A; Rowe, Jason F; Steffen, Jason H; Welsh, William F

    2011-02-04

    The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses M(B) = 0.2413 ± 0.0030 solar mass (M(⊙)), M(C) = 0.2127 ± 0.0026 M(⊙); radii R(B) = 0.2543 ± 0.0014 solar radius (R(⊙)), R(C) = 0.2318 ± 0.0013 R(⊙); orbital period P(1) = 1.76713 ± 0.00019 days] on an eccentric orbit about a third star (mass M(A) = 1.347 ± 0.032 M(⊙); radius R(A) = 2.0254 ± 0.0098 R(⊙); period of orbit around the low-mass binary P(2) = 33.9214 ± 0.0013 days; eccentricity of that orbit e(2) = 0.3043 ± 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models.

  18. The Interstellar Medium and Star Formation of Nearby, Low-Mass Galaxies

    NASA Astrophysics Data System (ADS)

    Warren, Steven Ray

    This thesis presents four different studies of the interstellar medium (ISM) and stellar content of ˜40 nearby (D ≲ 4 Mpc), low-mass galaxies. We aim to address two fundamental questions: "How do stellar processes effect the ISM in low-mass galaxies?" and "What are the local gas conditions which lead to molecular cloud formation?". Much of the data presented here come from our survey the "Very Large Array - Advanced Camera for Surveys Nearby Galaxy Survey Treasury" (VLA-ANGST). VLA-ANGST is a targeted atomic hydrogen (H I) emission line survey directed towards 35 low-mass galaxies selected from the ANGST Hubble Space Telescope (HST) galaxy sample of the nearby universe. The VLA-ANGST project is the largest survey of its kind, demanding nearly 600 hours of VLA observing time. This unprecedented amount of observing time gives us data which has long lasting legacy value for its wealth of high resolution and high sensitivity information on the H I gas content and dynamics in a large sample of nearby, low-mass galaxies. H I data from the VLA-ANGST project will be used to explore the interactions between the gas and stellar content as well as trace the underlying dark matter distribution. Combining the H I and HST data with other tracers of recent star formation (e.g., emission processes from far ultraviolet star light, dust in the infrared, and carbon monoxide in the submillimeter) provides a comprehensive census of each galaxy, useful for understanding their evolution. We investigate the role of multiple generations of star formation in the formation of large, kiloparsec scale cavities observed in the global H I distributions of five nearby, low mass galaxies. The small gravitational potential wells of some low-mass galaxies allow the outflow of energy from stellar

  19. The outburst and nature of young eruptive low mass stars in dark clouds

    NASA Astrophysics Data System (ADS)

    Ninan, J. P.; Ojha, D. K.; Bhatt, B. C.; Mallick, K. K.; Tej, A.; Sahu, D. K.; Ghosh, S. K.; Mohan, V.

    The FU Orionis (FUor) or EX Orionis (EXor) phenomenon has attracted increasing attention in recent years and is now accepted as a crucial element in the early evolution of low-mass stars. FUor and EXor eruptions of young stellar objects (YSOs) are caused by strongly enhanced accretion from the surrounding disk. FUors display optical outbursts of ˜ 4 mag or more and last for several decades, whereas EXors show smaller outbursts (Δm ˜ 2 - 3 mag) that last from a few months to a few years and may occur repeatedly. Therefore, FUor/EXor eruptions represent a rare but very important phenomenon in early stellar evolution, during which a young low-mass YSO brightens by up to several optical magnitudes. Hence, long-term observations of this class of eruptive variables are important to design theoretical models of low-mass star formation. In this paper, we present recent results from our long-term monitoring observations of three rare types of eruptive young variables with the 2-m Himalayan Chandra Telescope (HCT) and the 2-m IUCAA Girawali Observatory (IGO) telescope.

  20. Investigating the Processes Driving Low-Mass Galaxy Evolution with Gas Metallicities of Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Ly, Chun; Malkan, Matthew; Nagao, Tohru; Hayashi, Masao; Kashikawa, Nobunari; Shimasaku, Kazuhiro; Motohara, Kentaro

    2013-02-01

    There appears to be a ``fundamental" relationship that links the stellar masses, star-formation rates (SFRs), and gas metallicities of local galaxies. It has been used to constrain the major processes in galaxy evolution. However, it is unclear whether (1) this observed relation holds at earlier cosmic time, and (2) if it applies to low-mass galaxies and/or those with relatively higher specific SFRs (sSFRs). We request follow-up Hectospec spectroscopy %and DEIMOS spectroscopy to obtain gas metallicity measurements in key unexplored domains of galaxy parameter space. We will target Ntarget low-mass high equivalent width (EW) emission-line galaxies at zrange in the Subaru Deep Field (SDF). This sample is a factor of almost 4 larger than the existing data for galaxies with similar redshifts, SFRs and stellar masses. The SDF is ideal for such a survey because of its unique multi-wavelength imaging data that allow us to (1) identify a much higher surface density of high-EW star-forming galaxies over a wide redshift range than in any other survey, and (2) determine stellar masses and SFRs for individual galaxies. With the largest spectroscopic sample of low mass and/or high sSFR galaxies, we will determine the relationships between metallicity, stellar mass, and SFRs for dwarf galaxies. We will examine if the same galaxy evolution processes in massive galaxies also hold for lower mass galaxies over the past six billion years.

  1. Candidate Very-Low-Mass Companions to Nearby Stars Found in the WISE Survey

    NASA Astrophysics Data System (ADS)

    Mennen, Anne; Dutcher, D.; Lepine, S.; Faherty, J.

    2012-01-01

    We report the identification in the Wide-Field Survey Explorer (WISE) preliminary release of 36 probable very-low-mass companions to nearby stars from the SUPERBLINK proper motion catalogue. We examined all WISE sources within one arcminute of a subset of 156,000 SUPERBLINK stars with proper motions between 0.040 and 0.015 seconds of arc per year, photometric distances within 100 parsecs, and positions at least seven degrees from the galactic plane. Using proper motions calculated by comparing the WISE positions of the sources to those of their counterparts in the 2MASS Catalogue, we identified all WISE sources sharing a common proper motion with the SUPERBLINK star. We eliminated all sources detected in the Palomar Sky Survey blue plates, keeping only those red enough to be low-mass or brown dwarf companions. We used WISE and 2MASS colors to select only objects consistent with being M, L, or T dwarfs, leaving only 36 likely companions. Based on their color and assumed distances, we estimate the 36 low-mass companions to be either late M or early L dwarfs. Follow-up spectroscopic observations will be required for confirmation and formal spectral classification of the companions. We acknowledge the American Museum of Natural History and the National Science Foundation for their support.

  2. Evolutionary implications of the new triple-α nuclear reaction rate for low mass stars

    NASA Astrophysics Data System (ADS)

    Dotter, A.; Paxton, B.

    2009-12-01

    Context: Ogata et al. (2009, Progr. Theor. Phys., 122, 1055) presented a theoretical determination of the ^4He(αα,γ)12C, or triple-α, nuclear reaction rate. Their rate differs from the NACRE rate by many orders of magnitude at temperatures relevant for low mass stars. Aims: We explore the evolutionary implications of adopting the OKK triple-α reaction rate in low mass stars and compare the results with those obtained using the NACRE rate. Methods: The triple-α reaction rates are compared by following the evolution of stellar models at 1 and 1.5 M⊙ with Z = 0.0002 and Z = 0.02. Results: Results show that the OKK rate has severe consequences for the late stages of stellar evolution in low mass stars. Most notable is the shortening-or disappearance-of the red giant phase. Conclusions: The OKK triple-α reaction rate is incompatible with observations of extended red giant branches and He burning stars in old stellar systems.

  3. 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.

  4. Pathways towards Neptune-mass Planets around Very Low-mass Stars

    NASA Astrophysics Data System (ADS)

    Dreizler, S.; Bean, J.; Seifahrt, A.; Hartman, H.; Nilsson, H.; Wiedemann, G.; Reiners, A.; Henry, T. J.

    2010-10-01

    Radial velocities measured from near-infrared spectra are a potentially powerful tool to search for planets around low-mass stars. The radial velocity precision routinely obtained in the visible can, however, not be achieved in the NIR with existing techniques. In this paper, we describe a method for measuring high-precision radial velocities of a sample of the lowest-mass M dwarfs using CRIRES on the VLT. Our project makes use of a gas cell filled with ammonia to calibrate the instrument response similar to the iodine cell technique that has been used so successfully in the visible. Tests of the method based on the analysis of hundreds of spectra obtained for late M dwarfs over six months demonstrate that precisions of ˜5 m s-1 are obtainable over long timescales, and precisions better than 3 m s-1 can be obtained over timescales up to a week. This allows to search for low-mass planets, i.e., Neptune-mass or even Super-Earth planets around very low-mass stars or sub-stellar objects.

  5. RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I

    SciTech Connect

    Reiners, Ansgar; Mohanty, Subhanjoy

    2012-02-10

    Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behavior of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars and field saturation at longer periods in very low mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.

  6. SHIELD II: AGC 198507 - An Extremely Rare Low-Mass Galaxy Interaction?

    NASA Astrophysics Data System (ADS)

    Nikolina Borg Stevens, Karin; Cannon, John M.; McNichols, Andrew; McQuinn, Kristen B.; Teich, Yaron; SHIELD II Team

    2016-01-01

    The "Survey of HI in Extremely Low-mass Dwarfs II" ("SHIELD II") is a multiwavelength, legacy-class observational campaign that is facilitating the study of both internal and global evolutionary processes in low-mass dwarf galaxies discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. New HST imaging of one of these sample galaxies, AGC 198507, has revealed it to be a very rare interacting system; to our knowledge this is one of only a few known interactions in this extreme mass range. WSRT imaging indicates that the bulk of the HI is associated with the more luminous AGC 198507, while low surface brightness gas extends toward and coincides with the less luminous companion, which is separated by roughly 1.5 kpc from AGC 198507. Here we present new VLA B configuration HI imaging that allows us to localize the HI gas, to examine the rotational dynamics of AGC 198507, and to study the nature of star formation in this unique low-mass interacting system.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College, and by NASA through grant GO-13750 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

  7. SHIELD: EVLA HI Spectral Line Observations of Low-mass Dwarfs

    NASA Astrophysics Data System (ADS)

    Miazzo, Masao; Ruvolo, Elizabeth; Cannon, John M.; McNichols, Andrew; Teich, Yaron; Adams, Elizabeth A.; Giovanelli, Riccardo; Haynes, Martha P.; McQuinn, Kristen B.; Salzer, John Joseph; Skillman, Evan D.; Dolphin, Andrew E.; Elson, Edward C.; Haurberg, Nathalie C.; Huang, Shan; Janowiecki, Steven; Jozsa, Gyula; Leisman, Luke; Ott, Juergen; Papastergis, Emmanouil; Rhode, Katherine L.; Saintonge, Amelie; Van Sistine, Angela; Warren, Steven R.

    2017-01-01

    The “Survey of HI in Extremely Low-mass Dwarfs” (SHIELD) is a multiwavelength study of local volume low-mass galaxies. Using the now-complete Arecibo Legacy Fast ALFA (ALFALFA) source catalog, 82 systems are identified that meet distance, line width, and HI flux criteria for being gas-rich, low-mass galaxies. These systems harbor neutral gas reservoirs smaller than 3x10^7 M_sun, thus populating the faint end of the HI mass function with statistical confidence for the first time. Here we present new Karl G. Jansky Very Large Array D-configuration HI spectral line observations of 32 previously unobserved galaxies. These low angular resolution (~40" beam) images localize the HI gas; with a few exceptions, the HI gas is co-spatial with the optical centers of the galaxies. These images provide the first glimpse of the neutral interstellar medium in these systems.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College.

  8. The coronal temperatures of low-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.; Güdel, M.

    2015-06-01

    Aims: We study the X-ray emission of low-mass main-sequence stars to derive a reliable general scaling law between coronal temperature and the level of X-ray activity. Methods: We collect ROSAT measurements of hardness ratios and X-ray luminosities for a large sample of stars to derive which stellar X-ray emission parameter is most closely correlated with coronal temperature. We calculate average coronal temperatures for a sample of 24 low-mass main-sequence stars with measured emission measure distributions (EMDs) collected from the literature. These EMDs are based on high-resolution X-ray spectra measured by XMM-Newton and Chandra. Results: We confirm that there is one universal scaling relation between coronal average temperature and surface X-ray flux, FX, that applies to all low-mass main-sequence stars. We find that coronal temperature is related to FX by T̅cor = 0.11 FX0.26, where T̅cor is in MK and FX is in erg s-1 cm-2.

  9. 3D MODEL ATMOSPHERES FOR EXTREMELY LOW-MASS WHITE DWARFS

    SciTech Connect

    Tremblay, P.-E.; Gianninas, A.; Kilic, M.; Ludwig, H.-G.; Steffen, M.; Freytag, B.; Hermes, J. J.

    2015-08-20

    We present an extended grid of mean three-dimensional (3D) spectra for low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD radiation-hydrodynamics 3D simulations covering T{sub eff} = 6000–11,500 K and log g = 5–6.5 (g in cm s{sup −2}) to derive analytical functions to convert spectroscopically determined 1D temperatures and surface gravities to 3D atmospheric parameters. Along with the previously published 3D models, the 1D to 3D corrections are now available for essentially all known convective DA WDs (i.e., log g = 5–9). For low-mass WDs, the correction in temperature is relatively small (a few percent at the most), but the surface gravities measured from the 3D models are lower by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the discrepancies seen in the radius and mass measurements for relatively cool ELM WDs in eclipsing double WD and WD + millisecond pulsar binary systems. We also use the 3D corrections to revise the boundaries of the ZZ Ceti instability strip, including the recently found ELM pulsators.

  10. Two protostar candidates in the bright-rimmed dark cloud LDN 1206

    NASA Technical Reports Server (NTRS)

    Ressler, Michael E.; Shure, Mark

    1991-01-01

    The discovery of several near IR objects associated with two IRAS point sources in the LDN 1206 region is reported. IRAS 22272 + 6358A is probably a 'protostar' which is seen only in scattered light at near-IR wavelengths because of heavy obscuration by an almost edge-on circumstellar disk. In contrast, IRAS 22272 + 6358B is directly visible at these wavelengths and is perhaps an object which lies between protostars and T-Tauri stars in its evolution. Both direct and polarimetric K-band images of the region are presented, as well as spectral energy distributions constructed from J, H, K, L, L-prime, and M data and published far-IR and mm data.

  11. Expected water line spectrum of the protostar OMC2-FIR4

    NASA Astrophysics Data System (ADS)

    Crimier, N.; Ceccarelli, C.; Lefloch, B.; Faure, A.

    2007-12-01

    We present the expected water line spectrum of the protostar OMC2-FIR4. Dust continuum maps obtained at 350, 450 and 850 μm have been used to constrain the density and dust temperature profiles of the FIR4 envelope. We then compute the gas temperature. Since previous studies (Jorgensen et al. 2005) have suggested the presence of a strong external illuminating FUV field, we considered this possibility in addition to the standard IS FUV illumination case. Specifically, we computed the water line spectrum for both G0=1 and G0=1000 case and for different water abundances. We show that the two spectra are very different and their observation will therefore allow us to constrain water abundance in the protostar envelope and discriminate between the two possibilities, G0=1 and G0=1000.

  12. VizieR Online Data Catalog: The Herschel Orion Protostar Survey (HOPS): SEDs (Furlan+, 2016)

    NASA Astrophysics Data System (ADS)

    Furlan, E.; Fischer, W. J.; Ali, B.; Stutz, A. M.; Stanke, T.; Tobin, J. J.; Megeath, S. T.; Osorio, M.; Hartmann, L.; Calvet, N.; Poteet, C. A.; Booker, J.; Manoj, P.; Watson, D. M.; Allen, L.

    2016-06-01

    To summarize, starting from a sample of 410 Herschel Orion Protostar Survey (HOPS) targets (see section 2), but excluding likely contaminants and objects not observed or detected by PACS, there are 330 remaining objects that have Spitzer and Herschel data and are considered protostars (based on their Spitzer classification from Megeath et al. 2012, J/AJ/144/192). They form the sample studied in this work. In order to construct SEDs for our sample of 330 YSOs, we combined our own Herschel/PACS observations (see Proposal KPOTtmegeath2) with data from the literature and existing catalogs (see section 3.1). To extend the SEDs into the submillimeter, most of the YSOs were also observed in the continuum at 350 and 870um with the Atacama Pathfinder Experiment (APEX) telescope (Stutz et al. 2013, J/ApJ/767/36). (5 data files).

  13. The Herschel Orion Protostar Survey: Constraining Protostellar Models with Mid-Infrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Furlan, Elise; HOPS Team

    2013-01-01

    During the protostellar stage of star formation, a young star is surrounded by a large infalling envelope of dust and gas; the material falls onto a circumstellar disk and is eventually accreted by the central star. The dust in the disk and envelope emits prominently at mid- to far-infrared wavelengths; at 10 micron, absorption by small silicate grains causes a broad absorption feature. By modeling the near- to far-IR spectral energy distributions (SEDs) of protostars, properties of their disks and envelopes can be derived; in particular, mid-IR spectroscopy reveals the detailed emission around the silicate absorption feature and thus provides additional constraints for the models. Here we present results from modeling a sample of protostars in the Orion star-forming region that were observed as part of the Herschel Orion Protostar Survey (HOPS). These protostars represent a subsample of HOPS; they have Spitzer/IRS spectra, which cover the mid-IR SED from 5 to 35 micron, and photometry in the near-IR (2MASS), mid-IR (Spitzer/IRAC and MIPS), and far-IR (Herschel/PACS). We show the importance of adding Spitzer/IRS spectra with appropriate weights in determining the best fit to the SED from a large grid of protostellar models. The 10 micron silicate absorption feature and the mid- to far-IR SED slope provide key constraints for the inclination angle of the object and its envelope density, with a deep absorption feature and steep SED slope for the most embedded and highly inclined objects. We show a few examples that illustrate our SED fitting method and present preliminary results from our fits.

  14. Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. I. Adiabatic properties

    NASA Astrophysics Data System (ADS)

    Córsico, A. H.; Althaus, L. G.

    2014-09-01

    Context. Many low-mass white dwarfs with masses M∗/M⊙ ≲ 0.45, including the so-called extremely low-mass white dwarfs (M∗/M⊙ ≲ 0.20 - 0.25), have recently been discovered in the field of our Galaxy through dedicated photometric surveys. The subsequent discovery of pulsations in some of them has opened the unprecedented opportunity of probing the internal structure of these ancient stars. Aims: We present a detailed adiabatic pulsational study of these stars based on full evolutionary sequences derived from binary star evolution computations. The main aim of this study is to provide a detailed theoretical basis of reference for interpreting present and future observations of variable low-mass white dwarfs. Methods: Our pulsational analysis is based on a new set of He-core white-dwarf models with masses ranging from 0.1554 to 0.4352 M⊙ derived by computing the non-conservative evolution of a binary system consisting of an initially 1 M⊙ ZAMS star and a 1.4 M⊙ neutron star. We computed adiabatic radial (ℓ = 0) and non-radial (ℓ = 1,2) p and g modes to assess the dependence of the pulsational properties of these objects on stellar parameters such as the stellar mass and the effective temperature, as well as the effects of element diffusion. Results: We found that for white dwarf models with masses below ~ 0.18 M⊙, g modes mainly probe the core regions and p modes the envelope, therefore pulsations offer the opportunity of constraining both the core and envelope chemical structure of these stars via asteroseismology. For models with M∗ ≳ 0.18 M⊙, on the other hand, g modes are very sensitive to the He/H compositional gradient and therefore can be used as a diagnostic tool for constraining the H envelope thickness. Because both types of objects have not only very distinct evolutionary histories (according to whether the progenitor stars have experienced CNO-flashes or not), but also have strongly different pulsation properties, we propose to

  15. Hazardous Early Days In (and Beyond) the Habitable Zones Around Ultra-Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Kastner, Joel

    Although a majority of stars in the solar neighborhood are of mid- to late-M type, the magnetically-induced coronal (X-ray) and chromospheric (UV, H-alpha) activity of such stars remain essentially unexplored for the important age range 10-100 Myr. Such information on high-energy processes associated with young M stars would provide much-needed constraints on models of the effects of stellar irradiation on the physics and chemistry of planet-forming disks and newborn planets. In addition, X-ray and UV observations of ultra-low-mass young stars can serve to probe the (presently ill-defined) spectral type boundary that determines which very low-mass objects will eventually become M stars -- as opposed to brown dwarfs (BDs) -- following their pre-main sequence evolutionary stages. Via ADAP support, we have developed the GALEX Nearby Young Star Search (GALNYSS), a search method that combines GALEX, 2MASS, WISE and proper motion catalog information to identify nearby, young, lowmass stars. We have applied this method to identify ~2000 candidate young (10-100 Myr), low-mass (M-type) stars within 150 pc. These GALNYSS-identified young star candidates are distributed over the entire GALEX-covered sky, and their spectral types peak in the M3-4 range; followup optical spectroscopic work is ongoing (Rodriguez et al. 2013, ApJ, 774, 101). We now propose an ADA program to determine the X-ray properties of representative stars among these GALNYSS candidates, so as to confirm their youth and investigate the early evolution of coronal activity near the low-mass star/BD boundary and the effects of such activity on planet formation. Specifically, we will exploit the presence in the HEASARC archives of XMM-Newton and (to a lesser extent) Chandra X-ray Observatory data for a few dozen GALNYSS candidates that have been observed serendipitously by one or both of these space observatories. The proposed ADA program will yield the full reduction and analysis of these as-yet unexplored data

  16. Testing low-mass stellar models with M-dwarf eclipsing binaries from SDSS Stripe 82

    NASA Astrophysics Data System (ADS)

    Bhatti, Waqas A.

    Large astronomical surveys such as the Sloan Digital Sky Survey (SDSS) have revolutionized ensemble studies of stellar populations in the Galaxy. Modern and upcoming synoptic surveys extend this concept to the time-domain, by covering large areas of the sky to a faint magnitude limit, and at observing cadences optimized for a large range in variability. In this thesis, we explore methods of efficiently analyzing a large synoptic survey dataset and its application to stellar astronomy, specifically focusing on the discovery and characterization of low-mass star eclipsing binaries. Eclipsing binaries (EBs) provide direct measurements of the absolute masses and radii of the component stars. Recent observations of EBs composed of low-mass stars (< 0.7 M⊙ ) indicate that the measured radii of the component stars are systematically 10-15% larger than those predicted by stellar models. Tidally induced magnetic fields that arise in these close binaries may be responsible for this discrepancy. The small number of fully characterized low-mass EBs, however, makes any hypothesis for this discrepancy difficult to verify. These objects are difficult to detect because of the intrinsic faintness of low-mass stars, in addition to the already low probability of favorable orbital alignment for eclipse observation. Fortunately, both of these problems can be overcome by a large-area and deep time-domain survey. We describe a search for periodic variables carried out using multi-band timeseries photometry from SDSS Stripe 82 focused on identifying a large sample of EBs to help resolve this issue. We outline the construction of our light-curve catalog and the methodology for extracting variable point sources. We discuss the classification of the ˜1100 periodic variables found in these data, and the subsequent discovery of ˜211 EB candidates with securely determined periods. For ˜90 EBs with suitable light-curves, we fit binary models and estimate parameters for the binary components

  17. Low-Mass Pre-Main-Sequence Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios A.

    2012-09-01

    The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre-main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore- and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the

  18. Hydroxyl (OH) Emission from the Intermediate-mass Protostar LDN 1641N MM1

    NASA Astrophysics Data System (ADS)

    Burkhardt, Andrew; Bergin, E. A.; Visser, R.; Manoj, P.; Fischer, W. J.; Tobin, J. J.; HOPS Team

    2013-01-01

    The hydroxyl (OH) radical is an important molecule for the formation and destruction of water during protostellar evolution. The ultimate aim of this work is to determine the OH column density and compare it to that of water to explore the chemistry of oxygen in shocked gas near protostars. We present an analysis of hydroxyl emission from 60 to 200 micron within a intermediate-mass embedded protostar (LDN 1641N MM1/HOPS-182) located in the Orion Molecular Cloud. These data were obtained as part of the Herschel Orion Protostar Survey (HOPS) (Manoj et al 2012) using the PACS instrument (Poglitsch, 2010) onboard the Herschel Space Observatory (Pilbratt et al, 2010). We detect 16 rotational transitions of OH, covering energies up to 600 K above the ground state. The emission probably originates on scales of a few 100 AU in shocked gas associated with the bipolar outflow. The OH lines are a sensitive probe of the physical properties of the emitting gas (density, temperature), as well as for the far-infrared radiation field close to the central star (Wampfler et al, 2012). We will present the results of our excitation analysis using the large-velocity gradient code RADEX (Van der Tak et al, 2007).

  19. Searching for coronal radio emission from protostars using very-long-baseline interferometry

    NASA Astrophysics Data System (ADS)

    Forbrich, J.; Massi, M.; Ros, E.; Brunthaler, A.; Menten, K. M.

    2007-07-01

    Aims:In order to directly study the role of magnetic fields in the immediate vicinity of protostars, we use Very-Long-Baseline Interferometry (VLBI), aiming at the detection of non-thermal centimetric radio emission. This is technically the only possibility to study coronal emission at sub-AU resolution. Methods: We performed VLBI observations of the four nearby protostars HL Tau, LDN 1551 IRS5, EC 95, and YLW 15 in order to look for compact non-thermal centimetric radio emission. For maximum sensitivity, we used the High Sensitivity Array (HSA) where possible, involving the Very Long Baseline Array (VLBA), the phased Very Large Array (VLA), as well as the Arecibo, Green Bank, and Effelsberg radio telescopes. Results: While all four protostars were detected in VLA-only data, only one source (YLW 15 VLA 2) was detected in the VLBI data. The possibility of non-detections due to free-free absorption, possibly depending on source geometry, is considered.

  20. Multiple Monopolar Outflows Driven by Massive Protostars in IRAS 18162-2048

    NASA Astrophysics Data System (ADS)

    Fernández-López, M.; Girart, J. M.; Curiel, S.; Zapata, L. A.; Fonfría, J. P.; Qiu, K.

    2013-11-01

    In this article, we present Combined Array for Research in Millimeter-wave Astronomy (CARMA) 3.5 mm observations and SubMillimeter Array (SMA) 870 μm observations toward the high-mass star-forming region IRAS 18162-2048, which is the core of the HH 80/81/80N system. Molecular emission from HCN, HCO+, and SiO traces two molecular outflows (the so-called northeast and northwest outflows). These outflows have their origin in a region close to the position of MM2, a millimeter source known to harbor two protostars. For the first time we estimate the physical characteristics of these molecular outflows, which are similar to those of 103-5 × 103 L ⊙ protostars, and suggest that MM2 harbors high-mass protostars. High-angular resolution CO observations show an additional outflow due southeast. Also for the first time, we identify its driving source, MM2(E), and see evidence of precession. All three outflows have a monopolar appearance, but we link the NW and SE lobes, and explain their asymmetric shape as being a consequence of possible deflection.

  1. Multiple monopolar outflows driven by massive protostars in IRAS 18162-2048

    SciTech Connect

    Fernández-López, M.; Girart, J. M.; Curiel, S.; Fonfría, J. P.; Zapata, L. A.; Qiu, K. E-mail: girart@ieec.cat

    2013-11-20

    In this article, we present Combined Array for Research in Millimeter-wave Astronomy (CARMA) 3.5 mm observations and SubMillimeter Array (SMA) 870 μm observations toward the high-mass star-forming region IRAS 18162-2048, which is the core of the HH 80/81/80N system. Molecular emission from HCN, HCO{sup +}, and SiO traces two molecular outflows (the so-called northeast and northwest outflows). These outflows have their origin in a region close to the position of MM2, a millimeter source known to harbor two protostars. For the first time we estimate the physical characteristics of these molecular outflows, which are similar to those of 10{sup 3}-5 × 10{sup 3} L {sub ☉} protostars, and suggest that MM2 harbors high-mass protostars. High-angular resolution CO observations show an additional outflow due southeast. Also for the first time, we identify its driving source, MM2(E), and see evidence of precession. All three outflows have a monopolar appearance, but we link the NW and SE lobes, and explain their asymmetric shape as being a consequence of possible deflection.

  2. Low-Mass Field Stars with Infrared Excesses: Potential Signatures of Planetary Collisions

    NASA Astrophysics Data System (ADS)

    West, Andrew

    This proposed study will investigate the occurrence of mid-infrared (MIR) excesses—found in WISE data—in low-mass field stars. These MIR excesses are interpreted as dust reprocessed star-light, occurring when terrestrial planetary bodies collide. These systems serve as an important signatures of terrestrial planet formation and evolution (or destruction). This proposal builds off the results of a pilot study (Theissen & West 2014) conducted using WISE, 2MASS, and SDSS observations. This study used MIR observations from WISE to identify 175 spectroscopically confirmed low-mass stars exhibiting excess MIR flux over expected stellar photospheric levels. Theissen & West (2014) investigated other explanations for stars exhibiting excess MIR flux. Accounting for any possible contaminants, 175 stars were found with MIR excesses, and a low probability of MIR excesses being attributable to a contaminating source. Through investigation of the disk luminosities and approximate stellar ages estimated from spectroscopic tracers, it was determined the most likely cause of the excess MIR flux is a large abundance of circumstellar material, likely caused by collisions between planetary bodies. The pilot study was limited by its small sample size (175 stars) and incompleteness due to the SDSS spectroscopic target selection. Our proposed study will use a photometrically selected sample to create a more complete and statistically significant sample of low-mass stars exhibiting MIR excesses. The first objective of this proposal will be to construct a photometric catalog of low-mass stars, combining WISE, 2MASS, and SDSS photometry. To differentiate stars from other point-like sources of similar color (e.g. red galaxies), we will use proper motions. The large time baselines between WISE, 2MASS, and SDSS observations (~9-12 years) allow us to compute reliable proper motions for millions of photometric low-mass stars contained within the combined WISE+2MASS+SDSS dataset (estimated to

  3. HIERARCHICAL FRAGMENTATION AND JET-LIKE OUTFLOWS IN IRDC G28.34+0.06: A GROWING MASSIVE PROTOSTAR CLUSTER

    SciTech Connect

    Wang Ke; Wu Yuefang; Zhang Huawei; Zhang Qizhou E-mail: qzhang@cfa.harvard.edu

    2011-07-01

    We present Submillimeter Array (SMA) {lambda} = 0.88 mm observations of an infrared dark cloud G28.34+0.06. Located in the quiescent southern part of the G28.34 cloud, the region of interest is a massive (>10{sup 3} M{sub sun}) molecular clump P1 with a luminosity of {approx}10{sup 3} L{sub sun}, where our previous SMA observations at 1.3 mm have revealed a string of five dust cores of 22-64 M{sub sun} along the 1 pc IR-dark filament. The cores are well aligned at a position angle (P.A.) of 48 deg. and regularly spaced at an average projected separation of 0.16 pc. The new high-resolution, high-sensitivity 0.88 mm image further resolves the five cores into 10 compact condensations of 1.4-10.6 M{sub sun}, with sizes of a few thousand AU. The spatial structure at clump ({approx}1 pc) and core ({approx}0.1 pc) scales indicates a hierarchical fragmentation. While the clump fragmentation is consistent with a cylindrical collapse, the observed fragment masses are much larger than the expected thermal Jeans masses. All the cores are driving CO (3-2) outflows up to 38 km s{sup -1}, the majority of which are bipolar, jet-like outflows. The moderate luminosity of the P1 clump sets a limit on the mass of protostars of 3-7 M{sub sun}. Because of the large reservoir of dense molecular gas in the immediate medium and ongoing accretion as evident by the jet-like outflows, we speculate that P1 will grow and eventually form a massive star cluster. This study provides a first glimpse of massive, clustered star formation that currently undergoes through an intermediate-mass stage.

  4. The origin of the warm gas in the low-mass L1448 outflow

    NASA Astrophysics Data System (ADS)

    Eisloeffel, Jochen

    2013-10-01

    For our understanding of the outflows from young stellar objects it is crucial to know the origin and the kinematics of the warm and dense CO gas (n(H2) = 10^5 - 10^6 cm^-3 and T_kin = 300 - 1000 K) that has a key role in the dynamics and energetics of these flows. This gas has first been observed at the outflow base by ISO, whose poor spatial and spectral resolution, however, prevented one from locating its region of emission. We propose here to observe the CO(16-15), (13-12), and (11-10) lines in the outflow driven by the young and heavily embedded Class 0 protostar L1448-mm with GREAT. Together with available ground-based and Herschel observations of lower-J CO transitions we will be able to test whether the warm gas results from the highly-collimated fast 'primary' jet, or it is due to shocks created at the interface between the highly-collimated atomic jet and the cold entrained outflow.

  5. Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7

    NASA Astrophysics Data System (ADS)

    Dressing, Courtney D.; Newton, Elisabeth R.; Schlieder, Joshua E.; Charbonneau, David; Knutson, Heather A.; Vanderburg, Andrew; Sinukoff, Evan

    2017-02-01

    We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1–7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3–M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 {R}ȯ (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.

  6. CFHTLenS: weak lensing calibrated scaling relations for low-mass clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Kettula, K.; Giodini, S.; van Uitert, E.; Hoekstra, H.; Finoguenov, A.; Lerchster, M.; Erben, T.; Heymans, C.; Hildebrandt, H.; Kitching, T. D.; Mahdavi, A.; Mellier, Y.; Miller, L.; Mirkazemi, M.; Van Waerbeke, L.; Coupon, J.; Egami, E.; Fu, L.; Hudson, M. J.; Kneib, J. P.; Kuijken, K.; McCracken, H. J.; Pereira, M. J.; Rowe, B.; Schrabback, T.; Tanaka, M.; Velander, M.

    2015-08-01

    We present weak lensing and X-ray analysis of 12 low-mass clusters from the Canada-France-Hawaii Telescope Lensing Survey and XMM-CFHTLS surveys. We combine these systems with high-mass systems from Canadian Cluster Comparison Project and low-mass systems from Cosmic Evolution Survey to obtain a sample of 70 systems, spanning over two orders of magnitude in mass. We measure core-excised LX-TX, M-LX and M-TX scaling relations and include corrections for observational biases. By providing fully bias-corrected relations, we give the current limitations for LX and TX as cluster mass proxies. We demonstrate that TX benefits from a significantly lower intrinsic scatter at fixed mass than LX. By studying the residuals of the bias-corrected relations, we show for the first time using weak lensing masses that galaxy groups seem more luminous and warmer for their mass than clusters. This implies a steepening of the M-LX and M-TX relations at low masses. We verify the inferred steepening using a different high-mass sample from the literature and show that variance between samples is the dominant effect leading to discrepant scaling relations. We divide our sample into subsamples of merging and relaxed systems, and find that mergers may have enhanced scatter in lensing measurements, most likely due to stronger triaxiality and more substructure. For the LX-TX relation, which is unaffected by lensing measurements, we find the opposite trend in scatter. We also explore the effects of X-ray cross-calibration and find that Chandra calibration leads to flatter LX-TX and M-TX relations than XMM-Newton.

  7. LOW-MASS ECLIPSING BINARIES IN THE INITIAL KEPLER DATA RELEASE

    SciTech Connect

    Coughlin, J. L.; Harrison, T. E.; Ule, N.; Lopez-Morales, M.; Hoffman, D. I.

    2011-03-15

    We identify 231 objects in the newly released Cycle 0 data set from the Kepler Mission as double-eclipse, detached eclipsing binary systems with T{sub eff} < 5500 K and orbital periods shorter than {approx}32 days. We model each light curve using the JKTEBOP code with a genetic algorithm to obtain precise values for each system. We identify 95 new systems with both components below 1.0 M{sub sun} and eclipses of at least 0.1 mag, suitable for ground-based follow-up. Of these, 14 have periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29 have periods greater than 10.0 days. This new sample of main-sequence, low-mass, double-eclipse, detached eclipsing binary candidates more than doubles the number of previously known systems and extends the sample into the completely heretofore unexplored P > 10.0 day period regime. We find preliminary evidence from these systems that the radii of low-mass stars in binary systems decrease with period. This supports the theory that binary spin-up is the primary cause of inflated radii in low-mass binary systems, although a full analysis of each system with radial-velocity and multi-color light curves is needed to fully explore this hypothesis. Also, we present seven new transiting planet candidates that do not appear among the list of 706 candidates recently released by the Kepler team, or in the Kepler False Positive Catalog, along with several other new and interesting systems. We also present novel techniques for the identification, period analysis, and modeling of eclipsing binaries.

  8. MASSIVE: A Bayesian analysis of giant planet populations around low-mass stars

    NASA Astrophysics Data System (ADS)

    Lannier, J.; Delorme, P.; Lagrange, A. M.; Borgniet, S.; Rameau, J.; Schlieder, J. E.; Gagné, J.; Bonavita, M. A.; Malo, L.; Chauvin, G.; Bonnefoy, M.; Girard, J. H.

    2016-12-01

    Context. Direct imaging has led to the discovery of several giant planet and brown dwarf companions. These imaged companions populate a mass, separation and age domain (mass >1 MJup, orbits > 5 AU, age < 1 Gyr) quite distinct from the one occupied by exoplanets discovered by the radial velocity or transit methods. This distinction could indicate that different formation mechanisms are at play. Aims: We aim at investigating correlations between the host star's mass and the presence of wide-orbit giant planets, and at providing new observational constraints on planetary formation models. Methods: We observed 58 young and nearby M-type dwarfs in L'-band with the VLT/NaCo instrument and used angular differential imaging algorithms to optimize the sensitivity to planetary-mass companions and to derive the best detection limits. We estimate the probability of detecting a planet as a function of its mass and physical separation around each target. We conduct a Bayesian analysis to determine the frequency of substellar companions orbiting low-mass stars, using a homogenous sub-sample of 54 stars. Results: We derive a frequency of for companions with masses in the range of 2-80 MJup, and % for planetary mass companions (2-14 MJup), at physical separations of 8 to 400 AU for both cases. Comparing our results with a previous survey targeting more massive stars, we find evidence that substellar companions more massive than 1 MJup with a low mass ratio Q with respect to their host star (Q < 1%), are less frequent around low-mass stars. This may represent observational evidence that the frequency of imaged wide-orbit substellar companions is correlated with stellar mass, corroborating theoretical expectations. Contrarily, we show statistical evidence that intermediate-mass ratio (1% < Q < 5%) companion with masses >2 MJup might be independent from the mass of the host star.

  9. CHARACTERIZING THE STAR FORMATION OF THE LOW-MASS SHIELD GALAXIES FROM HUBBLE SPACE TELESCOPE IMAGING

    SciTech Connect

    McQuinn, Kristen B. W.; Skillman, Evan D.; Simones, Jacob E.; Cannon, John M.; Dolphin, Andrew E.; Haynes, Martha P.; Giovanelli, Riccardo; Salzer, John J.; Adams, Elizabeth A. K.; Elson, Ed C.; Ott, Jürgen

    2015-03-20

    The Survey of Hi in Extremely Low-mass Dwarfs is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies that populate the faint end of the galaxy luminosity function. The galaxies were selected from the first ∼10% of the Hi Arecibo Legacy Fast ALFA survey based on their low Hi mass and low baryonic mass. Here, we measure the star formation properties from optically resolved stellar populations for 12 galaxies using a color–magnitude diagram fitting technique. We derive lifetime average star formation rates (SFRs), recent SFRs, stellar masses, and gas fractions. Overall, the recent SFRs are comparable to the lifetime SFRs with mean birthrate parameter of 1.4, with a surprisingly narrow standard deviation of 0.7. Two galaxies are classified as dwarf transition galaxies (dTrans). These dTrans systems have star formation and gas properties consistent with the rest of the sample, in agreement with previous results that some dTrans galaxies may simply be low-luminosity dwarf irregulars. We do not find a correlation between the recent star formation activity and the distance to the nearest neighboring galaxy, suggesting that the star formation process is not driven by gravitational interactions, but regulated internally. Further, we find a broadening in the star formation and gas properties (i.e., specific SFRs, stellar masses, and gas fractions) compared to the generally tight correlation found in more massive galaxies. Overall, the star formation and gas properties indicate these very low-mass galaxies host a fluctuating, non-deterministic, and inefficient star formation process.

  10. THEORETICAL LIMITS ON MAGNETIC FIELD STRENGTHS IN LOW-MASS STARS

    SciTech Connect

    Browning, Matthew K.; Weber, Maria A.; Chabrier, Gilles; Massey, Angela P.

    2016-02-20

    Observations have suggested that some low-mass stars have larger radii than predicted by 1D structure models. Some theoretical models have invoked very strong interior magnetic fields (of order 1 MG or more) as a possible cause of such large radii. Whether fields of that strength could in principle be generated by dynamo action in these objects is unclear, and we do not address the matter directly. Instead, we examine whether such fields could remain in the interior of a low-mass object for a significant amount of time, and whether they would have any other obvious signatures. First, we estimate the timescales for the loss of strong fields by magnetic buoyancy instabilities. We consider a range of field strengths and simple morphologies, including both idealized flux tubes and smooth layers of field. We confirm some of our analytical estimates using thin flux tube magnetohydrodynamic simulations of the rise of buoyant fields in a fully convective M-dwarf. Separately, we consider the Ohmic dissipation of such fields. We find that dissipation provides a complementary constraint to buoyancy: while small-scale, fibril fields might be regenerated faster than they rise, the dissipative heating associated with such fields would in some cases greatly exceed the luminosity of the star. We show how these constraints combine to yield limits on the internal field strength and morphology in low-mass stars. In particular, we find that for stars of 0.3 solar masses, no fields in flux tubes stronger than about 800 kG are simultaneously consistent with both constraints.

  11. Search for light curve modulations among Kepler candidates. Three very low-mass transiting companions

    NASA Astrophysics Data System (ADS)

    Lillo-Box, J.; Ribas, A.; Barrado, D.; Merín, B.; Bouy, H.

    2016-07-01

    Context. Light curve modulations in the sample of Kepler planet candidates allows the disentangling of the nature of the transiting object by photometrically measuring its mass. This is possible by detecting the effects of the gravitational pull of the companion (ellipsoidal modulations) and in some cases, the photometric imprints of the Doppler effect when observing in a broad band (Doppler beaming). Aims: We aim to photometrically unveil the nature of some transiting objects showing clear light curve modulations in the phase-folded Kepler light curve. Methods: We selected a subsample among the large crop of Kepler objects of interest (KOIs) based on their chances to show detectable light curve modulations, i.e., close (a< 12 R⋆) and large (in terms of radius, according to their transit signal) candidates. We modeled their phase-folded light curves with consistent equations for the three effects, namely, reflection, ellipsoidal and beaming (known as REB modulations). Results: We provide detailed general equations for the fit of the REB modulations for the case of eccentric orbits. These equations are accurate to the photometric precisions achievable by current and forthcoming instruments and space missions. By using this mathematical apparatus, we find three close-in very low-mass companions (two of them in the brown dwarf mass domain) orbiting main-sequence stars (KOI-554, KOI-1074, and KOI-3728), and reject the planetary nature of the transiting objects (thus classifying them as false positives). In contrast, the detection of the REB modulations and transit/eclipse signal allows the measurement of their mass and radius that can provide important constraints for modeling their interiors since just a few cases of low-mass eclipsing binaries are known. Additionally, these new systems can help to constrain the similarities in the formation process of the more massive and close-in planets (hot Jupiters), brown dwarfs, and very low-mass companions.

  12. The History of Low-Mass Star Formation in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Preibisch, Thomas; Zinnecker, Hans

    1999-05-01

    We use a large sample of about 100 low-mass pre-main-sequence (PMS) stars in the Upper Scorpius OB association to explore the star formation history and the initial mass function of this association. Upper Scorpius is an ideal target for such a study, because the star formation process there is finished. The PMS stars have recently been found in a spatially unbiased wide-field survey of X-ray-selected stars in a 160 deg^2 area, covering the Upper Scorpius association nearly completely. Following the optical characterization of these PMS stars, we present a new HR diagram for this association. We perform a detailed analysis of the HR diagram, taking proper account of the uncertainties and the effects of unresolved binaries, and derive ages and masses for the PMS stars. We find that the low-mass PMS stars have a mean age of about 5 Myr and show no evidence for a large age dispersion. This agrees very well with the age of 5-6 Myr previously found for the massive stars and shows that low-mass and high-mass stars are coeval and cospatial and thus have formed together. We conclude that the star formation process in Upper Scorpius was probably triggered by the shock wave of a supernova explosion in the nearby Upper Centaurus-Lupus association. After a short burst of very high star formation activity, which lasted only for a few Myr, star formation in Upper Scorpius was halted, probably by the strong winds and the ionizing radiation of the numerous massive stars that dispersed the molecular cloud.

  13. Optical Spectroscopy of Low-Mass Stars and Brown Dwarfs in Orion

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

    Using multi-object optical spectroscopy from the AAT and Gemini-North, 35 low-mass stars and brown dwarfs in the Trapezium Cluster in Orion have been classified both by comparison with other previously classified young, low-mass sources in the Chamaeleon I star-forming region and by the use of spectral indices: narrowband indices which measure the strength of various highly temperature-sensitive molecular lines. The objects are all very likely cluster members, by analysis of the strength of the gravity-sensitive Na doublet, which is much weaker than in dwarfs for these very young objects. The spectral types obtained have been converted to effective temperatures using the temperature scale of Luhman et al. (2003b), which is intermediate between dwarf and giant scales and hence suitable for young pre-main sequence objects. In combination with the dereddened H band luminosities obtained from the photometry of Lucas & Roche (2000), the objects have been placed on an H-R diagram overlaid with the theoretical isochrones of Baraffe et al. (1998). The low-mass stars and the higher mass substellar objects are found to be clustered around the 1 Myr isochrone, while the lower mass substellar objects are located well above this isochrone, probably due to selection effects. The average age of 1 Myr for the majority of the objects is in agreement with other age estimates for the region, but the lack of any objects older than 5 Myr is in contrast to the results of Slesnick et al. (2004) which show in addition an older population at 10 Myr. Assuming coevality of the sources and an average age of 1 Myr, the masses of the objects have been estimated and 18 of the objects are found to have substellar masses.

  14. The atomic and molecular content of disks around very low-mass stars and brown dwarfs

    SciTech Connect

    Pascucci, I.; Herczeg, G.; Carr, J. S.; Bruderer, S.

    2013-12-20

    There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne{sup +}, H{sub 2}, CO{sub 2}, and tentative detections of H{sub 2}O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (≥5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H{sub 2} S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C{sub 2}H{sub 2}/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H{sub 2}O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H{sub 2}O lines trace warm ≥600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs.

  15. Evolution of Low-mass X-Ray Binaries: The Effect of Donor Evaporation

    NASA Astrophysics Data System (ADS)

    Jia, Kun; Li, Xiang-Dong

    2016-10-01

    Millisecond pulsars (MSPs) are thought to originate from low-mass X-ray binaries (LMXBs). The discovery of eclipsing radio MSPs, including redbacks and black widows, indicates that evaporation of the donor star by the MSP’s irradiation takes place during the LMXB evolution. In this work, we investigate the effect of donor evaporation on the secular evolution of LMXBs, considering different evaporation efficiencies and related angular momentum loss. We find that for widening LMXBs, the donor star leaves a less massive white dwarf than without evaporation; for contracting systems, evaporation can speed up the evolution, resulting in dynamically unstable mass transfer and possibly the formation of isolated MSPs.

  16. VizieR Online Data Catalog: Low-mass helium white dwarfs evolutionary models (Istrate+, 2016)

    NASA Astrophysics Data System (ADS)

    Istrate, A.; Marchant, P.; Tauris, T. M.; Langer, N.; Stancliffe, R. J.; Grassitelli, L.

    2016-07-01

    Evolutionary models of low-mass helium white dwarfs including element diffusion and rotational mixing. The WDs are produced considering binary evolution through the LMXB channel, with final WDs masses between ~0.16-~0.44. The models are computed using MESA, for different metallicities: Z=0.02, 0.01, 0.001 and 0.0002. For each metallicity, the models are divided in three categories: (1) basic (no diffusion nor rotation are considered) (2) diffusion (element diffusion is considered) (3) rotation+diffusion (both element diffusion and rotational mixing are considered) (4 data files).

  17. Resolving the low-mass content of Westerlund 1 using MCAO

    NASA Astrophysics Data System (ADS)

    Andersen, M.; Neichel, B.; Bernard, A.; Garrel, V.

    2015-12-01

    We present deep Ks band Gemini GeMS/GSAOI observations of Westerlund 1, the most massive young Galactic star cluster known. The high spatial resolution combined with a relatively stable point spread function across a large field of view provide unique possibilities to resolve the low-mass content of the cluster. We show that the clean point spread function is crucial in handling the source detection in this crowded field suffering extremely high contrast from the brightest hypergiants in the cluster to faint brown dwarfs.

  18. No evidence for a low-mass black hole in Swift J1753.5-0127

    NASA Astrophysics Data System (ADS)

    Shaw, A. W.; Charles, P. A.; Casares, J.; Hernández Santisteban, J. V.

    2016-12-01

    We present high-resolution, time-resolved optical spectroscopy of the black hole X-ray transient Swift J1753.5-0127. Our optical spectra do not show features that we can associate with the companion star. However we do observe broad, double-peaked emission lines, typical of an accretion disc. We show that the mass of the compact object is likely >7.4 ± 1.2 M⊙, much higher than previous suggestions of a low-mass (<5 M⊙) black hole.

  19. Creation by stellar ablation of the low-mass companion to pulsar 1829 - 10

    NASA Technical Reports Server (NTRS)

    Krolik, Julian H.

    1991-01-01

    It is argued that the low-mass companion of PSR1829 - 10 began its life as a star and has been ablated down to its present mass by absorbing a portion of the pulsar's spindown energy. Similar phenomena have already been seen in two other binary pulsars, PSR1957 + 20 and PSR1744 + 24A. The final mass of the remnant is determined by the interplay between decreasing spindown luminosity, recession of the companion from the pulsar as a result of its mass loss, and most important, shrinkage of the companion due to convective cooling of its interior.

  20. Neutron star formation in theoretical supernovae. Low mass stars and white dwarfs

    SciTech Connect

    Nomoto, K.

    1986-01-01

    The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. The conditions for which neutron stars form from accretion-induced collapse of white dwarfs in clsoe binary systems is also examined.

  1. Selection effects on the orbital period distribution of Low Mass X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Arur, Kavitha; Maccarone, Tom

    2017-01-01

    Observations show a lack of Low Mass Black Hole Binaries with orbital periods below 4 hours. While it is known that Black Hole Binaries (BHBs) tend to have lower peak luminosities in outburst compared to their Neutron Star counterparts, it is unclear if selection effects can account for the difference in the numbers. Studying the effect of these selection biases is important for binary population studies. Here we report on the implications for the inferred orbital period distribution of these BHBs after a simulation that accounts for extinction of the optical counterpart, absorption of X-ray counts and detectability of the outburst.

  2. 2MASS J05162881+2607387: A New Low-mass Double-lined Eclipsing Binary

    NASA Astrophysics Data System (ADS)

    Bayless, Amanda J.; Orosz, Jerome A.

    2006-11-01

    We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a double-lined eclipsing binary with nearly identical low-mass components. The spectroscopic elements derived from 18 spectra obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope during the fall of 2005 are K1=88.45+/-0.48 and K2=90.43+/-0.60 km s-1, resulting in a mass ratio of q=K1/K2=0.978+/-0.018 and minimum masses of M1sin3i=0.775+/-0.016 Msolar and M2sin3i=0.759+/-0.012 Msolar, respectively. We have extensive differential photometry of J0516 obtained over several nights between 2004 January and March (epoch 1) and between 2004 October and 2005 January plus 2006 January (epoch 2) using the 1 m telescope at the Mount Laguna Observatory. The source was roughly 0.1 mag brighter in all three bandpasses during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1 show considerable out-of-eclipse variability, presumably due to bright spots on one or both stars. In contrast, the phased light curves from epoch 2 show little out-of-eclipse variability. The light curves from epoch 2 and the radial velocity curves were analyzed using our ELC code with updated model atmospheres for low-mass stars. We find the following: M1=0.787+/-0.012 Msolar, R1=0.788+/-0.015 Rsolar, M2=0.770+/-0.009 Msolar, and R2=0.817+/-0.010 Rsolar. The stars in J0516 have radii that are significantly larger than model predictions for their masses, similar to what is seen in a handful of other well-studied low-mass double-lined eclipsing binaries. We compiled all recent mass and radius determinations from low-mass binaries and determine an empirical mass-radius relation of the form R(Rsolar)=0.0324+0.9343M(Msolar)+0.0374M2(Msolar). Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg

  3. Review of LHC experimental results on low mass bosons in multi Higgs models

    NASA Astrophysics Data System (ADS)

    Aggleton, R.; Barducci, D.; Bomark, N.-E.; Moretti, S.; Shepherd-Themistocleous, C.

    2017-02-01

    A variety of searches have been performed at the LHC using Run I data, looking for decays of the discovered Higgs boson, h 125, decaying to a pair of low mass bosons, with mass in the range 2{m}_{μ }-{m}_{h_{125}}/2˜eq 62 GeV. We summarise the most pertinent ones, and look at how their limits affect a variety of supersymmetric and non-supersymmetric models which can give rise to such light bosons: the 2HDM (Types I and II), the NMSSM, and the nMSSM.

  4. A Deep HRI Survey of Low-Mass PMS Stars in NGC 2264

    NASA Technical Reports Server (NTRS)

    Patten, Brian

    1999-01-01

    Brian Patten is the Principal Investigator of the NASA ADP project 'A Deep HRI Survey of Low-Mass PMS Stars in NGC 2264'. This project was funded to support primarily the data reduction and analysis for new ROSAT data to be acquired in ROSAT AO8. For AO8 we were awarded two deep (100 ks) exposures with the ROSAT HRI instrument of a rotation and proper-motion selected sample of young (3 Myr - 15 Myr), low-mass, PMS stars in the populous star-forming region NGC 2264. These X-ray data were to be combined with an extensive rotation database for members of this cluster to allow us, for the first time, to probe the early evolution of magnetic dynamo activity for both fully convective stars and those stars found lower on the Hayashi tracks which have developed radiative cores. This database would have been used to study the interrelationship between coronal activity level, interior structure, and rotation rate as a function of mass and age.in the PMS and to define empirical constraints for theoretical models of angular momentum and magnetic dynamo evolution.

  5. Under pressure: quenching star formation in low-mass satellite galaxies via stripping

    NASA Astrophysics Data System (ADS)

    Fillingham, Sean P.; Cooper, Michael C.; Pace, Andrew B.; Boylan-Kolchin, Michael; Bullock, James S.; Garrison-Kimmel, Shea; Wheeler, Coral

    2016-12-01

    Recent studies of galaxies in the local Universe, including those in the Local Group, find that the efficiency of environmental (or satellite) quenching increases dramatically at satellite stellar masses below ˜108 M⊙. This suggest a physical scale where quenching transitions from a slow `starvation' mode to a rapid `stripping' mode at low masses. We investigate the plausibility of this scenario using observed H I surface density profiles for a sample of 66 nearby galaxies as inputs to analytic calculations of ram-pressure and turbulent viscous stripping. Across a broad range of host properties, we find that stripping becomes increasingly effective at M* ≲ 108 - 9 M⊙, reproducing the critical mass scale observed. However, for canonical values of the circumgalactic medium density (nhalo < 10-3.5 cm-3), we find that stripping is not fully effective; infalling satellites are, on average, stripped of only ≲ 40-60 per cent of their cold gas reservoir, which is insufficient to match observations. By including a host halo gas distribution that is clumpy and therefore contains regions of higher density, we are able to reproduce the observed H I gas fractions (and thus the high quenched fraction and short quenching time-scale) of Local Group satellites, suggesting that a host halo with clumpy gas may be crucial for quenching low-mass systems in Local Group-like (and more massive) host haloes.

  6. A RADIO SEARCH FOR PULSAR COMPANIONS TO SLOAN DIGITAL SKY SURVEY LOW-MASS WHITE DWARFS

    SciTech Connect

    Agueeros, Marcel A.; Camilo, Fernando; Silvestri, Nicole M.; Anderson, Scott F.; Kleinman, S. J.; Liebert, James W.

    2009-05-20

    We have conducted a search for pulsar companions to 15 low-mass white dwarfs (LMWDs; M <0.4 M {sub sun}) at 820 MHz with the NRAO Green Bank Telescope (GBT). These LMWDs were spectroscopically identified in the Sloan Digital Sky Survey (SDSS), and do not show the photometric excess or spectroscopic signature associated with a companion in their discovery data. However, LMWDs are believed to evolve in binary systems and to have either a more massive white dwarf (WD) or a neutron star (NS) as a companion. Indeed, evolutionary models of low-mass X-ray binaries, the precursors of millisecond pulsars (MSPs), produce significant numbers of LMWDs, suggesting that the SDSS LMWDs may have NS companions. No convincing pulsar signal is detected in our data. This is consistent with the findings of van Leeuwen et al., who conducted a GBT search for radio pulsations at 340 MHz from unseen companions to eight SDSS WDs (five are still considered LMWDs; the three others are now classified as 'ordinary' WDs). We discuss the constraints our nondetections place on the probability P {sub MSP} that the companion to a given LMWD is a radio pulsar in the context of the luminosity and acceleration limits of our search; we find that P {sub MSP} < 10{sup +4} {sub -2}%.

  7. Substellar companions in low-mass eclipsing binaries. NSVS 01286630, NSVS 02502726, and NSVS 07453183

    NASA Astrophysics Data System (ADS)

    Wolf, M.; Zasche, P.; Kučáková, H.; Vraštil, J.; Hornoch, K.; Šmelcer, L.; Bílek, F.; Pilarčík, L.; Chrastina, M.

    2016-03-01

    Aims: As part of our long-term observational project we aim to measure very precise mid-eclipse times for low-mass eclipsing binaries, which are needed to accurately determine their period changes. Over two hundred new precise times of minimum light recorded with CCD were obtained for three eclipsing binaries with short orbital periods: NSVS 01286630 (P = 0.38°), NSVS 02502726 (0.56°), and NSVS 07453183 (0.37°). Methods: O-C diagrams of studied stars were analysed using all reliable timings, and new parameters of the light-time effect were obtained. Results: We derived for the first time or improved the very short orbital periods of third bodies of between one and seven years for all measured low-mass systems. We calculated that the lowest masses of the third components are between those of red and brown dwarfs. The multiplicity of these systems also plays an important role in the precise determination of their physical parameters. This research is part of an ongoing collaboration between professional astronomers and the Czech Astronomical Society, Variable Star and Exoplanet Section.

  8. ROSAT observations of quiescent low mass disk galaxies: No evidence of baryonic blow out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James; Schombert, James M.

    1994-01-01

    To test the hypothesis that galactic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT Position Sensitive Proportional Counter (PSPC) observations of three such galaxies. The sensitivity of the PSPC to the presence of an extended, approximately 0.15 KEV halo of 10(exp 9) solar mass of gas, is quite high for the exposure times we used. We failed to detect this halo in all three cases and the observed x-ray luminosity of the galaxy is two orders of magnitude less than the hypothetical case in which the mass of gas that has been expelled by previous generations of star formation is equal to the stellar mass of the galaxy itself. This limit is much less than the actual mass of cold gas in these galaxies. Thus, we were unable to verify directly the presence of significant galactic winds in these three galaxies either because they are not operative, because their halos are not sufficiently massive to aid in the retention of this gas, or because the amount of injected gas is just a small percentage of the cold disk gas. If the latter reason is emblematic of low mass galaxies then we would not expect the detection of halos. We also report here the serendipitous detection of Abell 1560, a distance class 7 cluster of unknown redshift.

  9. Extended main sequence turn-offs in low mass intermediate-age clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Bastian, Nate

    2016-05-01

    We present an imaging analysis of four low mass stellar clusters (≲5000 M⊙) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1-2 Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters - more than 5 times less massive than the eMSTO clusters previously studied - suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older clusters (~2 Gyr) is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their colour magnitude diagrams should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO. Full Table 2, and Tables 3-5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A50

  10. DISCOVERY OF A BRIGHT, EXTREMELY LOW MASS WHITE DWARF IN A CLOSE DOUBLE DEGENERATE SYSTEM

    SciTech Connect

    Vennes, S.; Kawka, A.; Nemeth, P.; Thorstensen, J. R.; Skinner, J. N.; Pigulski, A.; Steslicki, M.; Kolaczkowski, Z.; Srodka, P.

    2011-08-10

    We report the discovery of a bright (V {approx} 13.7), extremely low mass white dwarf in a close double degenerate system. We originally selected GALEX J171708.5+675712 for spectroscopic follow-up among a group of white dwarf candidates in an ultraviolet-optical reduced proper-motion diagram. The new white dwarf has a mass of 0.18 M{sub sun} and is the primary component of a close double degenerate system (P = 0.246137 days, K{sub 1} = 288 km s{sup -1}) comprising a fainter white dwarf secondary with M{sub 2} {approx} 0.9 M{sub sun}. Light curves phased with the orbital ephemeris show evidence of relativistic beaming and weaker ellipsoidal variations. The light curves also reveal secondary eclipses (depth {approx}8 mmag) while the primary eclipses appear partially compensated by the secondary gravitational deflection and are below detection limits. Photospheric abundance measurements show a nearly solar composition of Si, Ca, and Fe (0.1-1 sun), while the normal kinematics suggest a relatively recent formation history. Close binary evolutionary scenarios suggest that extremely low mass white dwarfs form via a common-envelope phase and possible Roche lobe overflow.

  11. Abundance ratios of red giants in low-mass ultra-faint dwarf spheroidal galaxies

    NASA Astrophysics Data System (ADS)

    François, P.; Monaco, L.; Bonifacio, P.; Moni Bidin, C.; Geisler, D.; Sbordone, L.

    2016-04-01

    Context. Low-mass dwarf spheroidal galaxies are key objects for our understanding of the chemical evolution of the pristine Universe and the Local Group of galaxies. Abundance ratios in stars of these objects can be used to better understand their star formation and chemical evolution. Aims: We report on the analysis of a sample of 11 stars belonging to five different ultra-faint dwarf spheroidal galaxies (UfDSph) that is based on X-Shooter spectra obtained at the VLT. Methods: Medium-resolution spectra have been used to determine the detailed chemical composition of their atmosphere. We performed a standard 1D LTE analysis to compute the abundances. Results: Considering all the stars as representative of the same population of low-mass galaxies, we found that the [α/Fe] ratios vs.s [Fe/H] decreases as the metallicity of the star increases in a way similar to that which is found for the population of stars that belong to dwarf spheroidal galaxies. The main difference is that the solar [α/Fe] is reached at a much lower metallicity for the UfDSph than for the dwarf spheroidal galaxies. We report for the first time the abundance of strontium in CVn II. The star we analyzed in this galaxy has a very high [Sr/Fe] and a very low upper limit of barium which makes it a star with an exceptionally high [Sr/Ba] ratio.

  12. THE FREQUENCY OF LOW-MASS EXOPLANETS. III. TOWARD {eta}{sub +} AT SHORT PERIODS

    SciTech Connect

    Wittenmyer, Robert A.; Tinney, C. G.; Bailey, J.; Horner, J.; Butler, R. P.; O'Toole, Simon J.; Jones, H. R. A.; Carter, B. D.

    2011-09-01

    Determining the occurrence rate of 'super-Earth' planets (m sin i < 10 M{sub +}) is a critically important step on the path toward determining the frequency of Earth-like planets ({eta}{sub +}), and hence the uniqueness of our solar system. Current radial-velocity surveys, achieving precisions of 1 m s{sup -1}, are now able to detect super-Earths and provide meaningful estimates of their occurrence rate. We present an analysis of 67 solar-type stars from the Anglo-Australian Planet Search specifically targeted for very high precision observations. When corrected for incompleteness, we find that the planet occurrence rate increases sharply with decreasing planetary mass. Our results are consistent with those from other surveys: in periods shorter than 50 days, we find that 3.0% of stars host a giant (msin i > 100 M{sub +}) planet, and that 17.4% of stars host a planet with msin i < 10 M{sub +}. The preponderance of low-mass planets in short-period orbits is in conflict with formation simulations in which the majority of super-Earths reside at larger orbital distances. This work gives a hint as to the size of {eta}{sub +}, but to make meaningful predictions on the frequency of terrestrial planets in longer, potentially habitable orbits, low-mass terrestrial planet searches at periods of 100-200 days must be made an urgent priority for ground-based Doppler planet searches in the years ahead.

  13. ALMA and VLA Observations: Evidence for Ongoing Low-mass Star Formation near Sgr A*

    NASA Astrophysics Data System (ADS)

    Yusef-Zadeh, F.; Cotton, W.; Wardle, M.; Royster, M. J.; Kunneriath, D.; Roberts, D. A.; Wootten, A.; Schödel, R.

    2017-01-01

    Using the VLA, we recently detected a large number of protoplanetary disk (proplyd) candidates lying within a couple of light years of the massive black hole Sgr A*. The bow-shock appearance of proplyd candidates point toward the young massive stars located near Sgr A*. Similar to Orion proplyds, the strong UV radiation from the cluster of massive stars at the Galactic center is expected to photoevaporate and photoionize the circumstellar disks around young, low mass stars, thus allowing detection of the ionized outflows from the photoionized layer surrounding cool and dense gaseous disks. To confirm this picture, ALMA observations detect millimeter emission at 226 GHz from five proplyd candidates that had been detected at 44 and 34 GHz with the VLA. We present the derived disk masses for four sources as a function of the assumed dust temperature. The mass of protoplanetary disks from cool dust emission ranges between 0.03 - 0.05 M⊙. These estimates are consistent with the disk masses found in star forming sites in the Galaxy. These measurements show the presence of on-going star formation with the implication that gas clouds can survive near Sgr A* and the relative importance of high vs low-mass star formation in the strong tidal and radiation fields of the Galactic center.

  14. Hard X-ray Flux from Low-Mass Stars in the Cygnus OB2 Association

    NASA Astrophysics Data System (ADS)

    Caramazza, M.; Drake, J. J.; Micela, G.; Flaccomio, E.

    2009-05-01

    We investigate the X-ray emission in the 20-40 keV band expected from the flaring low-mass stellar population in Cygnus OB2 assuming that the observed soft X-ray emission is due to a superposition of flares and that the ratio of hard X-ray to soft X-ray emission is described by a scaling found for solar flares by Isola and co-workers. We estimate a low-mass stellar hard X-ray flux in the 20-40 keV band in the range ~7×1031-7×1033 erg/s and speculate the limit of this values. Hard X-ray emission could lie at a level not much below the current observed flux upper limits for Cygnus OB2. Simbol-X, with its broad energy band (10-100 keV) and its sensitivity should be able to detect this emission and would provide insights into the hard X-ray production of flares on pre-main sequence stars.

  15. Speeding up low-mass planetary microlensing simulations and modeling: The caustic region of influence

    SciTech Connect

    Penny, Matthew T.

    2014-08-01

    Extensive simulations of planetary microlensing are necessary both before and after a survey is conducted: before to design and optimize the survey and after to understand its detection efficiency. The major bottleneck in such computations is the computation of light curves. However, for low-mass planets, most of these computations are wasteful, as most light curves do not contain detectable planetary signatures. In this paper, I develop a parameterization of the binary microlens that is conducive to avoiding light curve computations. I empirically find analytic expressions describing the limits of the parameter space that contain the vast majority of low-mass planet detections. Through a large-scale simulation, I measure the (in)completeness of the parameterization and the speed-up it is possible to achieve. For Earth-mass planets in a wide range of orbits, it is possible to speed up simulations by a factor of ∼30-125 (depending on the survey's annual duty-cycle) at the cost of missing ∼1% of detections (which is actually a smaller loss than for the arbitrary parameter limits typically applied in microlensing simulations). The benefits of the parameterization probably outweigh the costs for planets below 100 M{sub ⊕}. For planets at the sensitivity limit of AFTA-WFIRST, simulation speed-ups of a factor ∼1000 or more are possible.

  16. DECam Survey for Substellar and Low-mass Stellar Members of Sco-Cen

    NASA Astrophysics Data System (ADS)

    Mamajek, Eric E.; Moolekamp, Fred; James, David; Luhman, Kevin; Pecaut, Mark; Metchev, Stanimir A.; Denbo, Sara; Bell, Cameron P. M.

    2017-01-01

    We present the results of a DECam imaging survey for low-mass stellar and substellar objects in the nearby Sco-Cen OB association. The DECam survey was taken in izY bands in 2013 and 2015 and covered $\\sim$87 deg$^2$ in the two nearest and oldest subgroups, Upper Cen-Lup ($\\sim$142 pc) and Lower Cen-Cru ($\\sim$118 pc; both with mean ages $\\sim$16 Myr). Using color-magnitude and proper motion selection, we identify 391 candidate Sco-Cen members with masses ranging from near the D-burning limit of $\\sim$13 M$_{Jup}$, through the H-burning limit, up to $\\sim$0.4 M$_\\odot$. Our initial spectroscopic follow-up with the ARCoIRIS and COSMOS spectrographs for 19 objects have yielded young M dwarfs showing signatures of low surface-gravity. Our survey yields the first constraints on the substellar and low-mass initial mass function and disk fraction in the two oldest Sco-Cen subgroups, and will yield a large sample of young, low-surface gravity M and L-type objects of constrained age, distance, and chemical composition. We acknowledge support from NSF award AST-1313029 and the REU Site in Physics and Astrophysics at the University of Rochester supported by NSF award PHY-1156339.

  17. In Search Of Tiny Giants: Finding Supermassive Black Holes In Low Mass Galaxies

    NASA Astrophysics Data System (ADS)

    Tanner Berger, Dillon; Satyapal, Shobita; Abel, Nick; Blecha, Laura; Mushotzky, Richard; Reynolds, Christopher

    2017-01-01

    Most, if not all, massive galaxies have a central supermassive black hole (SMBH) with a mass of up to 1 billion times the mass of the Sun. While the properties of SMBHs and their host galaxies have been well-studied in massive galaxies, very few SMBHs have been found in galaxies with low masses and those with small bulges. This is a significant deficiency since the study of this population allows us to gain an understanding of merger-free pathways to black hole growth, and to gain insight into the origin and growth efficiency of SMBH seeds, thought to have formed at high redshift. Most studies aimed at finding SMBHs have been conducted using optical spectroscopic studies, where active SMBHs (active galactic nuclei or AGNs) display distinctive optical emission lines indicative of accreting SMBHs. However, in low mass galaxies, the SMBHs will likely be less massive. As the black hole masses decreases, the Schwartzchild radius of the black hole decreases, and in response, the temperature of the surrounding accretion disk increases. The shape of the ionizing radiation field therefore changes with black hole mass, potentially affecting the optical spectroscopic signatures generally associated with AGNs. In this work, we investigate the effect of black hole mass on the emission line spectrum from AGNs.

  18. Direct evidence of hierarchical assembly at low masses from isolated dwarf galaxy groups

    NASA Astrophysics Data System (ADS)

    Stierwalt, S.; Liss, S. E.; Johnson, K. E.; Patton, D. R.; Privon, G. C.; Besla, G.; Kallivayalil, N.; Putman, M.

    2017-01-01

    The demographics of dwarf galaxy populations have long been in tension with predictions from the Λ cold dark matter (ΛCDM) paradigm 1-4 . If primordial density fluctuations were scale-free as predicted, dwarf galaxies should themselves host dark-matter subhaloes 5 , the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as sate­llites of more massive galaxies 6-9 , and there is observational 10 and theoretical 11 evidence to suggest that these satellites at redshift z = 0 were captured by the massive host halo as a group. However, the evolution of dwarf galaxies is highly susceptible to environment 12-14 , making these satellite groups imperfect probes of ΛCDM in the low-mass regime. Here we report one of the clearest examples yet of hierarchical structure formation at low masses: using deep multi-wavelength data, we identify seven isolated, spectroscopically confirmed groups of only dwarf galaxies. Each group hosts three to five known members, has a baryonic mass of ~4.4 × 109 to 2 × 1010 solar masses (M ⊙), and requires a mass-to-light ratio of <100 to be gravitationally bound. Such groups are predicted to be rare theoretically and found to be rare observationally at the current epoch, and thus provide a unique window into the possible formation mechanism of more massive, isolated galaxies.

  19. A substantial population of low-mass stars in luminous elliptical galaxies.

    PubMed

    van Dokkum, Pieter G; Conroy, Charlie

    2010-12-16

    The stellar initial mass function (IMF) describes the mass distribution of stars at the time of their formation and is of fundamental importance for many areas of astrophysics. The IMF is reasonably well constrained in the disk of the Milky Way but we have very little direct information on the form of the IMF in other galaxies and at earlier cosmic epochs. Here we report observations of the Na (I) doublet and the Wing-Ford molecular FeH band in the spectra of elliptical galaxies. These lines are strong in stars with masses less than 0.3M(⊙) (where M(⊙) is the mass of the Sun) and are weak or absent in all other types of stars. We unambiguously detect both signatures, consistent with previous studies that were based on data of lower signal-to-noise ratio. The direct detection of the light of low-mass stars implies that they are very abundant in elliptical galaxies, making up over 80% of the total number of stars and contributing more than 60% of the total stellar mass. We infer that the IMF in massive star-forming galaxies in the early Universe produced many more low-mass stars than the IMF in the Milky Way disk, and was probably slightly steeper than the Salpeter form in the mass range 0.1M(⊙) to 1M(⊙).

  20. GAP OPENING BY EXTREMELY LOW-MASS PLANETS IN A VISCOUS DISK

    SciTech Connect

    Duffell, Paul C.; MacFadyen, Andrew I. E-mail: macfadyen@nyu.edu

    2013-05-20

    By numerically integrating the compressible Navier-Stokes equations in two dimensions, we calculate the criterion for gap formation by a very low mass (q {approx} 10{sup -4}) protoplanet on a fixed orbit in a thin viscous disk. In contrast with some previously proposed gap-opening criteria, we find that a planet can open a gap even if the Hill radius is smaller than the disk scale height. Moreover, in the low-viscosity limit, we find no minimum mass necessary to open a gap for a planet held on a fixed orbit. In particular, a Neptune-mass planet will open a gap in a minimum mass solar nebula with suitably low viscosity ({alpha} {approx}< 10{sup -4}). We find that the mass threshold scales as the square root of viscosity in the low mass regime. This is because the gap width for critical planet masses in this regime is a fixed multiple of the scale height, not of the Hill radius of the planet.

  1. Identification and Follow-Up Observations of Low-Mass Eclipsing Binaries from Kepler

    NASA Astrophysics Data System (ADS)

    Coughlin, Jeffrey; Lopez-Morales, M.; Marzoa, R. I.; Harrison, T.; Ule, N.; Hoffman, D.

    2011-01-01

    An outstanding problem in Astronomy for the past 15+ years has been that the radii of low-mass, (M < 1.0 M⊙), main-sequence stars in eclipsing binary systems are consistently about 15% larger than predicted by theoretical models. The main cause is hypothesized to be rapid rotation due to binary spin-up, as all but one of the currently known systems have P < 3.0 days. We present 100+ new low-mass, main-sequence, double-lined eclipsing binaries (LMMS DDEBs) from both our Kepler Guest Observer Program, as well as the initial Kepler public data release. We identify over 25 new systems with P > 10 days, extending the sample of LMMS DDEBs into this completely heretofore unexplored period range. We present the initial results of our intensive observing campaign to obtain ground-based radial-velocity and multi-color photometry follow-up of these long-period systems, in order to determine precise masses and radii. We thank all the hard-working members of the Kepler team, and acknowledge support from the Kepler Guest Observer Program, the New Mexico Space Grant Consortium, and a NSF Graduate Research Fellowship.

  2. Steep-Spectrum Radio Emission from the Low-Mass Active Galactic Nucleus GH 10

    NASA Astrophysics Data System (ADS)

    Wrobel, J. M.; Greene, J. E.; Ho, L. C.; Ulvestad, J. S.

    2008-10-01

    GH 10 is a broad-lined active galactic nucleus (AGN) energized by a black hole of mass 800,000 M⊙. It was the only object detected by Greene et al. in their Very Large Array (VLA) survey of 19 low-mass AGNs discovered by Greene & Ho. New VLA imaging at 1.4, 4.9, and 8.5 GHz reveals that GH 10's emission has an extent of less than 320 pc, has an optically thin synchrotron spectrum with a spectral index α = - 0.76 +/- 0.05 (Sν propto ν+ α), is less than 11% linearly polarized, and is steady—although poorly sampled—on timescales of weeks and years. Circumnuclear star formation cannot dominate the radio emission, because the high inferred star formation rate, 18 M⊙ yr-1, is inconsistent with the rate of less than 2 M⊙ yr-1 derived from narrow Hα and [O II] λ3727 emission. Instead, the radio emission must be mainly energized by the low-mass black hole. GH 10's radio properties match those of the steep-spectrum cores of Palomar Seyfert galaxies, suggesting that, like those galaxies, the emission is outflow-driven. Because GH 10 is radiating close to its Eddington limit, it may be a local analog of the starting conditions, or seeds, for supermassive black holes. Future imaging of GH 10 at higher linear resolution thus offers an opportunity to study the relative roles of radiative versus kinetic feedback during black hole growth.

  3. ORBITAL MIGRATION OF LOW-MASS PLANETS IN EVOLUTIONARY RADIATIVE MODELS: AVOIDING CATASTROPHIC INFALL

    SciTech Connect

    Lyra, Wladimir; Mac Low, Mordecai-Mark; Paardekooper, Sijme-Jan E-mail: mordecai@amnh.or

    2010-06-01

    Outward migration of low-mass planets has recently been shown to be a possibility in non-barotropic disks. We examine the consequences of this result in evolutionary models of protoplanetary disks. Planet migration occurs toward equilibrium radii with zero torque. These radii themselves migrate inwards because of viscous accretion and photoevaporation. We show that as the surface density and temperature fall the planet orbital migration and disk depletion timescales eventually become comparable, with the precise timing depending on the mass of the planet. When this occurs, the planet decouples from the equilibrium radius. At this time, however, the gas surface density is already too low to drive substantial further migration. A higher mass planet, of 10 M {sub +}, can open a gap during the late evolution of the disk, and stops migrating. Low-mass planets, with 1 or 0.1 M {sub +}, released beyond 1 AU in our models avoid migrating into the star. Our results provide support for the reduced migration rates adopted in recent planet population synthesis models.

  4. On the effects of Cosmions upon the structure and evolution of very low mass stars

    NASA Technical Reports Server (NTRS)

    Deluca, E. E.; Griest, K.; Rosner, R.; Wang, J.

    1989-01-01

    A number of recent studies have suggested that cosmions, or WIMPS, may play an important role in the energetics of the solar interior; in particular, it has been argued that these hypothetical particles may transport sufficient energy within the nuclear-burning solar core so as to depress the solar core temperature to the point of resolving the solar neutrino problem. Solutions to the solar neutrino problem have proven themselves to be quite nonunique, so that it is of some interest whether the cosmion solution can be tested in some independent manner. It is argued that if cosmions solve the solar neutrino problem, then they must also play an important role in the evolution of low mass main sequence stars; and, second, that if they do so, then a simple (long mean free path) model for the interaction of cosmions with baryons leads to changes in the structure of the nuclear-burning core which may be in principal observable. Such changes include suppression of a fully-convective core in very low mass main sequence stars; and a possible thermal runaway in the core of the nuclear burning region. Some of these changes may be directly observable, and hence may provide independent constraints on the properties of the cosmions required to solve the solar neutrino problem, perhaps even ruling them out.

  5. Investigating the low-mass slope and possible turnover in the LMC IMF

    NASA Astrophysics Data System (ADS)

    Gennaro, Mario

    2014-10-01

    We propose to derive the Initial Mass Function (IMF) of the field population of the Large Magellanic Cloud (LMC) down to 0.2 solar masses, probing the mass regime where the characteristic IMF turnover is observed in our Galaxy. The power of the HST, using the WFC3 IR channel, is necessary to obtain photometric mass estimates for the faint, cool, dwarf stars with masses below the expected IMF turnover point. Only by probing the IMF down to such masses, it will be possible to clearly distinguish between a bottom-heavy or bottom-light IMF in the LMC. Recent studies, using the deepest available observations for the Small Magellanic Cloud, cannot find clear evidence of a turnover in the IMF for this galaxy, suggesting a bottom-heavy IMF in contrast to the Milky Way. A similar study of the LMC is needed to confirm a possible dependence of the low-mass IMF with galactic environment. Studies of giant ellipticals have recently challenged the picture of a universal IMF, and suggest an enviromental dependence of the IMF, with the most massive galaxies having a larger fraction of low mass stars and no IMF turnover. A study of possible IMF variations from resolved stellar populations in nearby galaxies is of great importance in sheding light on this issue. Our simple approach, using direct evidence from basic star counts, is much less prone to systematic errors with respect to studies of more distant objects which have to rely on the observations of integrated properties.

  6. Formation of millisecond pulsars with low-mass helium white dwarf companions in very compact binaries

    SciTech Connect

    Jia, Kun; Li, X.-D.

    2014-08-20

    Binary millisecond pulsars (BMSPs) are thought to have evolved from low-mass X-ray binaries (LMXBs). If the mass transfer in LMXBs is driven by nuclear evolution of the donor star, the final orbital period is predicted to be well correlated with the mass of the white dwarf (WD), which is the degenerate He core of the donor. Here we show that this relation can be extended to very small WD mass (∼0.14-0.17 M {sub ☉}) and narrow orbital period (about a few hours), depending mainly on the metallicities of the donor stars. There is also discontinuity in the relation, which is due to the temporary contraction of the donor when the H-burning shell crosses the hydrogen discontinuity. BMSPs with low-mass He WD companions in very compact binaries can be accounted for if the progenitor binary experienced very late Case A mass transfer. The WD companion of PSR J1738+0333 is likely to evolve from a Pop II star. For PSR J0348+0432, to explain its extreme compact orbit in the Roche-lobe-decoupling phase, even lower metallicity (Z = 0.0001) is required.

  7. FORMATION OF MILLISECOND PULSARS FROM INTERMEDIATE- AND LOW-MASS X-RAY BINARIES

    SciTech Connect

    Shao Yong; Li Xiangdong

    2012-09-01

    We present a systematic study of the evolution of intermediate- and low-mass X-ray binaries consisting of an accreting neutron star of mass 1.0-1.8 M{sub Sun} and a donor star of mass 1.0-6.0 M{sub Sun }. In our calculations we take into account physical processes such as unstable disk accretion, radio ejection, bump-induced detachment, and outflow from the L{sub 2} point. Comparing the calculated results with the observations of binary radio pulsars, we report the following results. (1) The allowed parameter space for forming binary pulsars in the initial orbital period-donor mass plane increases with increasing neutron star mass. This may help explain why some millisecond pulsars with orbital periods longer than {approx}60 days seem to have less massive white dwarfs than expected. Alternatively, some of these wide binary pulsars may be formed through mass transfer driven by planet/brown-dwarf-involved common envelope evolution. (2) Some of the pulsars in compact binaries might have evolved from intermediate-mass X-ray binaries with anomalous magnetic braking. (3) The equilibrium spin periods of neutron stars in low-mass X-ray binaries are in general shorter than the observed spin periods of binary pulsars by more than one order of magnitude, suggesting that either the simple equilibrium spin model does not apply or there are other mechanisms/processes spinning down the neutron stars.

  8. SHIELD: The Star Formation Law in Extremely Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    Teich, Yaron; McNichols, Andrew; Cannon, John M.; SHIELD Team

    2016-01-01

    The "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD) is a multiwavelength, legacy-class observational study of 12 low-mass dwarf galaxies discovered in Arecibo Legacy Fast ALFA (ALFALFA) survey data products. Here we analyze the relationships between HI and star formation in these systems using multi-configuration, high spatial (~300 pc) and spectral (0.82 - 2.46 km s-1 ch-1) resolution HI observations from the Karl G. Jansky Very Large Array, Hα imaging from the WIYN 3.5m telescope, and archival GALEX far-ultraviolet imaging. We compare the locations and intensities of star formation with the properties of the neutral ISM. We quantify the degree of local co-spatiality between star forming regions and regions of high HI column densities using the Kennicutt-Schmidt (K-S) relation. The values of the K-S index N vary considerably from system to system; because no single galaxy is representative of the sample, we instead focus on the narratives of the individual galaxies and their complex distribution of gaseous and stellar components. At the extremely faint end of the HI mass function, these systems are dominated by stochastic fluctuations in their interstellar media, which governs whether or not they show signs of recent star formation.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College.

  9. A pulsation search among young brown dwarfs and very-low-mass stars

    SciTech Connect

    Cody, Ann Marie; Hillenbrand, Lynne A.

    2014-12-01

    In 2005, Palla and Baraffe proposed that brown dwarfs (BDs) and very-low-mass stars (VLMSs; < 0.1 solar masses) may be unstable to radial oscillations during the pre-main-sequence deuterium burning phase. With associated periods of one to four hours, this potentially new class of pulsation offers unprecedented opportunities to probe the interiors and evolution of low-mass objects in the 1-15 million year age range. Following up on reports of short-period variability in young clusters, we designed a high-cadence photometric monitoring campaign to search for deuterium-burning pulsation among a sample of 348 BDs and VLMSs in the four young clusters σ Orionis, Chamaeleon I, IC 348, and Upper Scorpius. In the resulting light curves we achieved sensitivity to periodic signals of amplitude several millimagnitudes, on timescales from 15 minutes to two weeks. Despite the exquisite data quality, we failed to detect any periodicities below seven hours. We conclude that D-burning pulsations are not able to grow to observable amplitudes in the early pre-main sequence. In spite of the nondetection, we did uncover a rich set of variability behavior—both periodic and aperiodic—on day to week timescales. We present new compilations of variable sources from our sample, as well as three new candidate cluster members in Chamaeleon I.

  10. Physical Properties Of The NLR In Low-mass Active Galaxies

    NASA Astrophysics Data System (ADS)

    Ludwig, Randi R.; Greene, J. E.; Barth, A. J.; Ho, L. C.

    2012-01-01

    We present high-resolution spectroscopic observations of 27 active galactic nuclei (AGN) with black hole masses M_BH < 2 × 10^6 M⊙. We investigate their narrow emission line properties and compare them with those of AGN with higher mass black holes. While we are unable to determine absolute metallicities, these low-luminosity objects plausibly represent AGN with sub-solar metallicities, based on their [N II]/Hα ratios and their consistency with the Kewley et al. (2008) mass-metallicity relation. We find that these low-mass AGN have UV continuum slopes similar to those of more massive AGN based on their He II/Hβ ratio, similar blueshifts and broadening in their narrow lines with respect to ionization potential, and we see evidence of an intermediate line region whose intensity correlates with L/L_Edd in these objects. In contrast to higher-mass AGN, we find that the low-mass AGN have selectively high narrow line EWs when [O III] shows no blue wing, which could be explained by a high covering factor of lower ionization gas in the narrow-line region of objects with symmetric emission lines.

  11. POTENTIAL GAMMA-RAY EMISSIONS FROM LOW-MASS X-RAY BINARY JETS

    SciTech Connect

    Zhang, Jian-Fu; Gu, Wei-Min; Liu, Tong; Xue, Li; Lu, Ju-Fu E-mail: guwm@xmu.edu.cn

    2015-06-20

    By proposing a pure leptonic radiation model, we study the potential gamma-ray emissions from the jets of low-mass X-ray binaries. In this model, the relativistic electrons that are accelerated in the jets are responsible for radiative outputs. Nevertheless, jet dynamics are dominated by magnetic and proton–matter kinetic energies. The model involves all kinds of related radiative processes and considers the evolution of relativistic electrons along the jet by numerically solving the kinetic equation. Numerical results show that the spectral energy distributions can extend up to TeV bands, in which synchrotron radiation and synchrotron self-Compton scattering are dominant components. As an example, we apply the model to the low-mass X-ray binary GX 339–4. The results not only can reproduce the currently available observations from GX 339–4, but also predict detectable radiation at GeV and TeV bands by the Fermi and CTA telescopes. Future observations with Fermi and CTA can be used to test our model, which could be employed to distinguish the origin of X-ray emissions.

  12. Waterfalls around protostars. Infall motions towards Class 0/I envelopes as probed by water

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; van Dishoeck, E. F.; Schmalzl, M.; Kristensen, L. E.; Visser, R.; Hogerheijde, M. R.; Bruderer, S.

    2013-10-01

    Context. For stars to form, material must fall inwards from core scales through the envelope towards the central protostar. While theories of how this takes place have been around for some time, the velocity profile around protostars is poorly constrained. The combination of observations in multiple transitions of a tracer which is sensitive to kinematics and radiative transfer modelling of those lines has the potential to break this deadlock. Aims: Seven protostars observed with the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory as part of the "Water in star-forming regions with Herschel" (WISH) survey show infall signatures in water line observations. We aim to constrain the infall velocity and the radii over which infall is taking place within the protostellar envelopes of these sources. We will also use these data to constrain the chemistry of cold water. Methods: We use 1-D non-LTE ratran radiative transfer models of the observed water lines to constrain the infall velocity and chemistry in the protostellar envelopes of six Class 0 protostars and one Class I source. We assume a free-fall velocity profile and, having found the best fit, vary the radii over which infall takes place. Results: In the well-studied Class 0 protostar NGC 1333-IRAS4A we find that our observations probe infall over the whole envelope to which our observations are sensitive (r ≳ 1000 AU). For L1527, L1157, BHR71 and IRAS 15398 infall takes place on core to envelope scales (i.e. ~10 000-3000 AU). In Serpens-SMM4 and GSS30 the inverse P-Cygni profiles seen in the ground-state lines are more likely due to larger-scale motions or foreground clouds. Models including a simple consideration of the chemistry are consistent with the observations, while using step abundance profiles are not. The non-detection of excited water in the inner envelope in six out of seven protostars is further evidence that water must be heavily depleted from the gas

  13. THE SPITZER c2d SURVEY OF NEARBY DENSE CORES. VI. THE PROTOSTARS OF LYNDS DARK NEBULA 1221

    SciTech Connect

    Young, Chadwick H.; Young, Kaisa E.; Popa, Victor; Bourke, Tyler L.; Dunham, Michael M.; Evans, Neal J.; Joergensen, Jes K.; Shirley, Yancy L.; De Vries, Christopher; Claussen, Mark J.

    2009-09-01

    Observations of Lynds Dark Nebula 1221 from the Spitzer Space Telescope are presented. These data show three candidate protostars toward L1221, only two of which were previously known. The infrared observations also show signatures of outflowing material, an interpretation which is also supported by radio observations with the Very Large Array. In addition, molecular line maps from the Five College Radio Astronomy Observatory are shown. One-dimensional dust continuum modeling of two of these protostars, IRS1 and IRS3, is described. These models show two distinctly different protostars forming in very similar environments. IRS1 shows a higher luminosity and a larger inner radius of the envelope than IRS3. The disparity could be caused by a difference in age or mass, orientation of outflow cavities, or the impact of a binary in the IRS1 core.

  14. A Low-Power Low-Mass Dual-Polarization Sensitive Submillimeter-Wave Radiometer/Spectrometer

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, G.; Reck, T.; Jung-Kubiak, C.; Gonzalez-Ovejero, D.; Lee, C.; Alonso-Del Pino, M.

    2016-10-01

    Applying CMOS components and silicon micromachining technology that enable low-mass and highly integrated receivers, we are developing a state-of-the-art submillimeter wavelength radiometer/spectrometer instrument for planetary orbiter missions.

  15. The Puzzling Atmospheres of Low-mass Stars, Brown Dwarfs and Exoplanets Revealed by the Discovery Channel Telescope

    NASA Astrophysics Data System (ADS)

    Muirhead, Philip Steven; Croll, Bryce; Dalba, Paul A.; Veyette, Mark; Han, Eunkyu; Kesseli, Aurora; Healy, Brian

    2017-01-01

    The Large Monolithic Imager (LMI) on the Discovery Channel Telescope (DCT) enables high-precision photometry with a scriptable interface and rapid cycling between photometric bands, all while guiding off-axis. Using LMI, scientists at Boston University have undertaken a number of investigations into low-mass stars, brown dwarfs and extrasolar planets. We will report on recent results from these investigations, including (1) measurements of transiting asteroids orbiting a white dwarf, (2) refined ephemerides for long-period transiting exoplanets, (3) investigations revealing biases in space-based exoplanet light curves, (4) investigations of the nature of activity in low-mass stars and brown dwarfs and (5) investigations of low-mass eclipsing binary stars. We will also propose future studies of low-mass stars, brown dwarfs and exoplanets using current and future DCT instrumentation.

  16. The Herschel Orion Protostar Survey: Constraining Protostellar Models with Near- to Far-Infrared Observations

    NASA Astrophysics Data System (ADS)

    Furlan, Elise; Ali, Babar; Fischer, Will; Tobin, John; Stutz, Amy; Megeath, Tom; Allen, Lori; HOPS Team

    2013-07-01

    During the protostellar stage of star formation, a young star is surrounded by a large infalling envelope of dust and gas; the material falls onto a circumstellar disk and is eventually accreted by the central star. The dust in the disk and envelope emits prominently at mid- to far-infrared wavelengths; at 10 micron, absorption by small silicate grains typically causes a broad absorption feature. By modeling the near- to far-IR spectral energy distributions (SEDs) of protostars, properties of their disks and envelopes can be derived. As part of the Herschel Orion Protostar Survey (HOPS; PI: S. T. Megeath), we have observed a large sample of protostars in the Orion star-forming complex at 70 and 160 micron with the PACS instrument on the Herschel Space Observatory. For most objects, we also have photometry in the near-IR (2MASS), mid-IR (Spitzer/ IRAC and MIPS), at 100 micron (PACS data from the Gould Belt Survey), sub-mm (APEX/SABOCA and LABOCA), and mid-infrared spectra (Spitzer/IRS). For the interpretation of the SEDs, we have constructed a large grid of protostellar models using a Monte Carlo radiative transfer code. Here we present our SED fitting techniques to determine the best-fit model for each object. We show the importance of including IRS spectra with appropriate weights, in addition to the constraints provided by the PACS measurements, which probe the peak of the SED. The 10 micron silicate absorption feature and the mid- to far-IR SED slope provide key constraints for the inclination angle of the object and its envelope density, with a deep absorption feature and steep SED slope for the most embedded and highly inclined objects. We show a few examples that illustrate our SED fitting method and present some preliminary results from our fits.

  17. A MASSIVE PROTOSTAR FORMING BY ORDERED COLLAPSE OF A DENSE, MASSIVE CORE

    SciTech Connect

    Zhang, Yichen; Tan, Jonathan C.; Telesco, Charles; De Buizer, James M.; Sandell, Goeran; Shuping, Ralph; Beltran, Maria T.; Churchwell, Ed; Whitney, Barbara; McKee, Christopher F.; Staff, Jan E.

    2013-04-10

    We present 30 and 40 {mu}m imaging of the massive protostar G35.20-0.74 with SOFIA-FORCAST. The high surface density of the natal core around the protostar leads to high extinction, even at these relatively long wavelengths, causing the observed flux to be dominated by that emerging from the near-facing outflow cavity. However, emission from the far-facing cavity is still clearly detected. We combine these results with fluxes from the near-infrared to mm to construct a spectral energy distribution (SED). For isotropic emission the bolometric luminosity would be 3.3 Multiplication-Sign 10{sup 4} L{sub Sun }. We perform radiative transfer modeling of a protostar forming by ordered, symmetric collapse from a massive core bounded by a clump with high-mass surface density, {Sigma}{sub cl}. To fit the SED requires protostellar masses {approx}20-34 M{sub Sun} depending on the outflow cavity opening angle (35 Degree-Sign -50 Degree-Sign ), and {Sigma}{sub cl} {approx} 0.4-1 g cm{sup -2}. After accounting for the foreground extinction and the flashlight effect, the true bolometric luminosity is {approx}(0.7-2.2) Multiplication-Sign 10{sup 5} L{sub Sun }. One of these models also has excellent agreement with the observed intensity profiles along the outflow axis at 10, 18, 31, and 37 {mu}m. Overall our results support a model of massive star formation involving the relatively ordered, symmetric collapse of a massive, dense core and the launching bipolar outflows that clear low-density cavities. Thus a unified model may apply for the formation of both low- and high-mass stars.

  18. PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

    SciTech Connect

    Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed; Shkolnik, Evgenya L.; Flagg, Laura; Liu, Michael C.; Howard, Andrew W.; Aller, Kimberly M.; Best, William M. J.; Kotson, Michael C.; Baranec, Christoph; Schlieder, Joshua E.; Mann, Andrew W.; Dupuy, Trent J.; Hinkley, Sasha; Crepp, Justin R.; Johnson, John Asher; Weinberger, Alycia J.; Allers, Katelyn N.; Herczeg, Gregory J.; and others

    2015-06-10

    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 M{sub Jup}) 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 M{sub Jup}) 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 λ6708 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

  19. On the formation of low-mass black holes in massive binary stars

    SciTech Connect

    Brown, G.E.; Weingartner, J.C.; Wijers, R.A. |

    1996-05-01

    Recently, Brown & Bethe suggested that most stars with main-sequence mass in the range of {approximately}18{minus}30 {ital M}{sub {circle_dot}} explode, returning matter to the Galaxy, and then go into low-mass ({ge}1.5 {ital M}{sub {circle_dot}}) black holes. Even more massive main-sequence stars would chiefly go into high-mass ({approximately}10 {ital M}{sub {circle_dot}}) black holes. The Brown-Bethe estimates gave {approximately}5{times}10{sup 8} low-mass black holes in the Galaxy. We here address why none of these have been seen, with the possible exception of the compact objects in SN 1987A and 4U 1700-37. Our main point is that the primary star in a binary loses its hydrogen envelope by transfer of matter to the secondary and loss into space, and the resulting {open_quote}{open_quote}naked{close_quote}{close_quote} helium star evolves differently than a helium core, which is at least initially covered by the hydrogen envelope in a massive main-sequence star. We show that primary stars in binaries can end up as neutron stars even if their initial mass substantially exceeds the mass limit for neutron star formation from single stars ({approximately}18 {ital M}{sub {circle_dot}}). An example is 4U 1223{endash}62, in which we suggest that the initial primary mass exceeded 35 {ital M}{sub {circle_dot}}, yet X-ray pulsations show a neutron star to be present. We also discuss some individual systems and argue that 4U 1700{endash}37, the only example of a well-studied high-mass X-ray binary that does not pulse, could well contain a low-mass black hole. The statistical composition of the X-ray binary population is consistent with our scenario, but due to the paucity of systems it is consistent with more traditional models as well. {copyright} {ital 1996 The American Astronomical Society.}

  20. Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

    NASA Astrophysics Data System (ADS)

    Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

    2016-03-01

    Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

  1. OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Chung, S.-J.; Zhu, W.; Udalski, A.; Lee, C.-U.; Ryu, Y.-H.; Jung, Y. K.; Shin, I.-G.; Yee, J. C.; Hwang, K.-H.; Gould, A.; and; Albrow, M.; Cha, S.-M.; Han, C.; Kim, D.-J.; Kim, H.-W.; Kim, S.-L.; Kim, Y.-H.; Lee, Y.; Park, B.-G.; Pogge, R. W.; The KMTNet Collaboration; Poleski, R.; Mróz, P.; Pietrukowicz, P.; Skowron, J.; Szymański, M. K.; Soszyński, I.; Kozłowski, S.; Ulaczyk, K.; Pawlak, M.; The OGLE Collaboration; Beichman, C.; Bryden, G.; Calchi Novati, S.; Carey, S.; Fausnaugh, M.; Gaudi, B. S.; Henderson, Calen B.; Shvartzvald, Y.; Wibking, B.; The Spitzer Team

    2017-04-01

    We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are due to the passage of the lens close to or directly over the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a mass 0.10+/- 0.02 {M}ȯ or a brown dwarf with a mass 55+/- 9 {M}J, which are located at {D}{LS}=0.80+/- 0.19 {kpc} and {D}{LS}=0.54+/- 0.08 {kpc}, respectively, where {D}{LS} is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe ({{Δ }}{χ }2=0.3). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for ρ, the angular size of the source in units of the angular Einstein ring radius. Because the ρ degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically ∼ 1 {{day}}-1, we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this ρ degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is {μ }{rel}=9.0+/- 1.9 {mas} {{yr}}-1, while for the brown dwarf it is 5.5+/- 0.5 {mas} {{yr}}-1. Hence, the degeneracy can be resolved within ∼ 10 {years} from direct-lens imaging by using next-generation instruments with high spatial resolution.

  2. Kepler’s Low-Mass, Low Density Planets Characterized via Transit Timing

    NASA Astrophysics Data System (ADS)

    Jontof-Hutter, Daniel; Ford, Eric B.; Lissauer, Jack; Rowe, Jason; Fabrycky, Daniel

    2015-08-01

    The Kepler mission has revealed an abundance of planets in a regime of mass and size that is absent from the Solar System. This includes systems of high multiplicity within 1 AU, where low-mass volatile-rich planets have been observed in compact orbital configurations, as have smaller, rocky planets. The existing sample of characterized planets on the mass-radius diagram shows no abrupt transition from rocky planets to those that must be volatile-rich, but characteristic trends are beginning to emerge. More precise characterizations of planets by mass, radius, and incident flux are revealing fundamental properties of a common class of exoplanets.There is a small sample of low mass exoplanets with known masses and radii, whose radii are known from transit depths, and whose masses are determined from radial velocity spectroscopy (RV). In the super-Earth mass range, detectability limits this sample to planets that have short orbital periods, and high incident fluxes.In the absence of mass determinations via RV observations, transit timing variations (TTVs) offer a chance to probe perturbations between planets that pass close to one another or are near resonance, and hence dynamical fits to observed transit times can be used to measure planetary masses and orbital parameters. Such modeling with Kepler data probes planetary masses over orbital periods ranging from ~5-200 days, complementing the sample of RV detections, but also with some overlap.In addition, dynamical fits to observed TTVs can tightly constrain the orbital eccentricity vectors in select cases, which can, alongside the transit light curve, tightly constrain the density and radius of the host star, and hence reduce the uncertainty on planetary radius.TTV studies have revealed a class of low-mass, low-density objects with a substantial mass fraction in the form of a voluminous H-rich atmosphere. We will present new precise planetary mass characterizations from TTVs. We find that super-Earth mass planets

  3. Low-mass spectroscopic binaries in the Hyades: a candidate brown dwarf companion

    NASA Astrophysics Data System (ADS)

    Reid, I. Neill; Mahoney, S.

    2000-08-01

    We have used the HIRES echelle spectrograph on the Keck I telescope to obtain high-resolution spectroscopy of 51 late-type M dwarfs in the Hyades cluster. Cross-correlating the calibrated data against spectra of white dwarfs allows us to determine heliocentric velocities with an accuracy of +/-0.3kms-1. 27 stars were observed at two epochs in 1997; two stars, RHy 42 and RHy 403, are confirmed spectroscopic binaries. RHy 42 is a double-lined, equal-mass system; RHy 403 is a single-lined, short-period binary, P~1.275d. RHy 403A has an absolute magnitude of MI=10.85, consistent with a mass of 0.15Msolar. The systemic mass function has a value M2sin(i)]3/(M1+M2)2 =0.0085, which, combined with the non-detection of a secondary peak in the cross-correlation function, implies 0.095>M2>0.07Msolar, and the strong possibility that the companion is the first Hyades brown dwarf to be identified. Unfortunately, the maximum expected angular separation in the system is only ~0.25mas. Five other low-mass Hyads are identified as possible spectroscopic binaries, based either on repeat observations or on a comparison between the observed radial velocity and the value expected for Hyades cluster members. Combined with HST imaging data, we infer a binary fraction between 23 and 30per cent. All of the stars are chromospherically active. RHy 281 was caught in mid-flare and, based on that detection, we estimate a flaring frequency of ~2.5per cent for low-mass Hyades stars. Nine stars have rotational velocities, vsin(i), exceeding 20kms-1, and most of the sample have detectable rotation. We examine the H&alpha emission characteristics of low-mass cluster members, and show that there is no evidence for a correlation with rotation.

  4. PHYSICAL PROPERTIES OF THE LOW-MASS ECLIPSING BINARY NSVS 02502726

    SciTech Connect

    Lee, Jae Woo; Youn, Jae-Hyuck; Kim, Seung-Lee; Lee, Chung-Uk E-mail: jhyoon@kasi.re.kr E-mail: leecu@kasi.re.kr

    2013-01-01

    NSVS 02502726 has been known as a double-lined, detached eclipsing binary that consists of two low-mass stars. We obtained BVRI photometric follow-up observations in 2009 and 2011 to measure improved physical properties of the binary star. Each set of light curves, including the 2008 data given by Cakirli et al., was simultaneously analyzed with the previously published radial velocity curves using the Wilson-Devinney binary code. The conspicuous seasonal light variations of the system are satisfactorily modeled by a two-spot model with one starspot on each component and by changes of the spot parameters with time. Based on 23 eclipse timings calculated from the synthetic model and one ephemeris epoch, an orbital period study of NSVS 02502726 reveals that the period has experienced a continuous decrease of -5.9 Multiplication-Sign 10{sup -7} day yr{sup -1} or a sinusoidal variation with a period and semi-amplitude of 2.51 yr and 0.0011 days, respectively. The timing variations could be interpreted as either the light-travel-time effect due to the presence of an unseen third body, or as the combination of this effect and angular momentum loss via magnetic stellar wind braking. Individual masses and radii of both components are determined to be M{sub 1} = 0.689 {+-} 0.016 M{sub Sun }, M{sub 2} = 0.341 {+-} 0.009 M{sub Sun }, R{sub 1} = 0.707 {+-} 0.007 R{sub Sun }, and R{sub 2} = 0.657 {+-} 0.008 R{sub Sun }. The results are very different from those of Cakirli et al. with the primary's radius (0.674 {+-} 0.006 R{sub Sun }) smaller the secondary's (0.763 {+-} 0.007 R{sub Sun }). We compared the physical parameters presented in this paper with current low-mass stellar models and found that the measured values of the primary star are best fitted to a 79 Myr isochrone. The primary is in good agreement with the empirical mass-radius relation from low-mass binaries, but the secondary is oversized by about 85%.

  5. SMA OBSERVATIONS OF CLASS 0 PROTOSTARS: A HIGH ANGULAR RESOLUTION SURVEY OF PROTOSTELLAR BINARY SYSTEMS

    SciTech Connect

    Chen Xuepeng; Arce, Hector G.; Dunham, Michael M.; Zhang Qizhou; Bourke, Tyler L.; Launhardt, Ralf; Henning, Thomas; Jorgensen, Jes K.; Lee, Chin-Fei; Foster, Jonathan B.; Pineda, Jaime E. E-mail: xuepeng.chen@yale.edu

    2013-05-10

    We present high angular resolution 1.3 mm and 850 {mu}m dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.''5, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 AU to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64 {+-} 0.08 and 0.91 {+-} 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I young stellar objects, and approximately three (for MF) and four (for CSF) times larger than the values found among main-sequence stars, with a similar range of separations. Furthermore, the observed fraction of high-order multiple systems to binary systems in Class 0 protostars (0.50 {+-} 0.09) is also larger than the fractions found in Class I young stellar objects (0.31 {+-} 0.07) and main-sequence stars ({<=}0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a general trend in which CSF increases with decreasing companion separation. We find that 67% {+-} 8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation, based on this work and

  6. The origin of single low-mass WDs: another problem that consequential angular momentum loss in CVs might solve

    NASA Astrophysics Data System (ADS)

    Zorotovic, M.; Schreiber, M. R.

    2017-03-01

    Low-mass helium-core white dwarfs (WDs) with masses below 0.5 M_{⊙} are known to be formed in binary star systems but unexpectedly, a significant fraction of them seems to be single. On the other hand, in cataclysmic variables (CVs), a large number of low-mass WD primary stars is predicted but not observed. We recently showed that the latter problem can be solved if consequential angular momentum loss causes especially CVs with low-mass WDs to merge and form single stars. Here we simulate the population of single WDs resulting from single-star evolution and from binary star mergers taking into account these new merging CVs. We show that according to the revised model of CV evolution, merging CVs might be the dominant channel leading to the formation of low-mass single WDs and that the predicted relative numbers are consistent with observations. This can be interpreted as further evidence for the revised model of CV evolution we recently suggested. This model includes consequential angular momentum loss that increases with decreasing WD mass and might not only explain the absence of low-mass WD primaries in CVs but also the existence of single low-mass WDs.

  7. A Deep X-Ray Survey of Low Mass PMS Stars in NGC 2264

    NASA Technical Reports Server (NTRS)

    Patten, Brian M.; Mushotzky, Richard (Technical Monitor)

    2001-01-01

    We have proposed to make a deep X-ray survey of a rotation- and proper-motion selected sample of young (3-15 Myr old), low-mass, pre-main sequence (PMS) stars in the populous star-forming region NGC 2264. These X-ray Multimirror Mission (XMM) data will be combined with an extensive set of rotation data for members of this cluster to allow us, for the first time, to probe the early evolution of magnetic dynamo activity for both fully convective stars and those stars found lower on their Hayashi tracks, which are developing radiative cores. We will use these data to study the interrelationship between rotation, interior structure, and coronal activity as a function of mass and age in the PMS and to define empirical constraints for theoretical models of angular momentum/dynamo evolution.

  8. Constraints on Low-mass WIMP Signals from the Cryogenic Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Leman, Steven W.; CDMS Collaboration

    2011-09-01

    Two different, previously released, Cryogenic Dark Matter Search (CDMS) data sets have been reanalyzed to improve sensitivity to low-mass Weakly Interacting Massive Particle (WIMP) signals. The first data set was obtained from 2001 to 2002 at the shallow-depth Stanford Underground Facility (SUF) with four germanium and two silicon detectors. The second data set utilized eight germanium detectors at the deep Soudan Underground Laboratory from 2006 to 2008. The SUF data excludes parameter space between 3 and 4 GeV / c2 while the Soudan result excludes parameter space favored by the DAMA / LIBRA and CoGeNT data as light WIMP signals at the >90% confidence level. Expected performance of new detectors with an interleaved charge readout, also being commissioned at Soudan, will also be discussed.

  9. Spitzer Spectroscopy of Low-Mass Dwarfs - Clouds and Chemistry at the Bottom of the IMF

    NASA Technical Reports Server (NTRS)

    Roellig, Thomas L.

    2006-01-01

    Brown dwarfs and low-mass stars show evidence of complicated atmospheres, including a variety of molecular species and clouds. Infrared observations are one of the best probes of the physics of these objects, but up until recently these observations have been limited in studies from ground-based telescopes by atmospheric absorption and insufficient sensitivity. With the launch of the Spitzer Space Telescope with its Infrared Spectrograph (IRS) instrument we now have the capability to undertake a systematic study of the atmospheric structure and chemistry in these cool objects. The IRS Dim Suns team has compiled spectra from objects ranging from M1 dwarfs with effective temperatures 3,800K of down to T8 dwarfs with effective temperatures of 700. This talk will present these results and discuss their implications for our understanding of cool dwarf atmospheric physics and structure.

  10. LP 400-22, A Very Low Mass and High-Velocity White Dwarf

    NASA Technical Reports Server (NTRS)

    Kawka, Adela; Vennes, Stephane; Oswalt, Terry D.; Smith, J. Allyn; Silvestri, Nicole M.

    2006-01-01

    We report the identification of LP 400-22 (WD 2234+222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080+/-140 K and a surface gravity of log g = 6.32 +/-0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 M,. The tangential velocity of this white dwarf is 414+/-43 km/s, making it one of the fastest moving white dwarfs known. We discuss probable evolutionary scenarios for this remarkable object.

  11. Observations of Deuterated Species toward Low-Mass Prestellar and Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Sakai, N.; Watanabe, Y.; Sakai, T.; Hirota, T.; Yamamoto, S.

    2013-10-01

    We have conducted observations of the ground-state transition lines (J = 1-0) of the fundamental deuterated species DCO+, DNC, DCN, CCD and N2D+ as well as those of H13CO+, HN13C, H13CN, CCH and N2H+ with the Nobeyama 45 m telescope. The target sources are the cold starless cores, TMC-1 and Lupus-1A, and the low-mass star forming cores, L1527 and IRAS15398-3359. The excitation temperatures derived from intensities of resolved hyperfine components are systematically different between DNC and HN13C. On the other hand, the excitation temperatures of DCN and H13CN are comparable to each other. Although the origin of these results is puzzling, the present result indicates that accurate evaluation of the excitation temperature is essential for deriving deuterium fractionation ratios accurately.

  12. Sigma observations of the low mass X-ray binaries of the galactic bulge

    NASA Technical Reports Server (NTRS)

    Goldwurm, A.; Denis, M.; Paul, J.; Faisse, S.; Roques, J. P.; Bouchet, L.; Vedrenne, G.; Mandrou, P.; Sunyaev, R.; Churazov, E.

    1995-01-01

    The soft gamma-ray telescope (35-1300 keV) SIGMA aboard the high energy GRANAT space observatory has been monitoring the Galactic Bulge region for more than 2000 h of effective time since March 1990. In the resulting average 35-75 keV image we detected ten sources at a level of greater than 5 standard deviations, 6 of which can be identified with low mass X-ray binaries (LMXB). Among them, one is the 1993 X-ray nova in Ophiuchus (GRS 1726-249), one is an X-ray pulsar (GX 1+4), two are associated with X-ray bursters (GX 354-0 and A 1742-294) and two with bursting X-ray binaries in the globular clusters Terzan 2 and Terzan 1. Their spectral and long term variability behavior as measured by SIGMMA are presented and discussed.

  13. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion. Revised

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotzky, Richard (Technical Monitor)

    2001-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. observation of one of the two objects has taken place and the data were received in late November. The second object is yet to be observed. Over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  14. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    Vrtilek, Saeqa Dil; Mushotzky, Richard F. (Technical Monitor)

    2002-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was not observed until September of 2002. Data analysis for the new observation is underway. over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  15. Evolution of the Spin Periods of Neutron Stars in Low-mass X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Xu, X. T.; Zhu, Z. L.

    2016-11-01

    We present numerical analysis of the spin evolution of the neutron stars in low-mass X-ray binaries, trying to explain the discrepancy in the spin period distribution between observations of millisecond pulsars and theoretical results. In our calculations, we take account of possible effect of radiation pressure, and irradiation-induced instability on the structure of the disk, and the evolution of the mass transfer rate, respectively. We report the following results: (1) Radiation pressure leads to a slight increase of the spin periods, and irradiation-induced mass transfer cycles can shorten the spin-down phase of evolution. (2) The calculated results in the model combining radiation pressure and irradiation-induced mass transfer cycles show that accretion is strongly limited by radiation pressure in high mass transfer phase. (3) The accreted mass and the critical fastness parameter can affect the number of systems in equilibrium state.

  16. Improved limits on interactions of low-mass spin-0 dark matter from atomic clock spectroscopy

    NASA Astrophysics Data System (ADS)

    Stadnik, Y. V.; Flambaum, V. V.

    2016-08-01

    Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently oscillating classical field ϕ =ϕ0cos(mϕt ) , can induce oscillating variations in the fundamental constants through their interactions with the standard model sector. We calculate the effects of such possible interactions, which may include the linear interaction of ϕ with the Higgs boson, on atomic and molecular transitions. Using recent atomic clock spectroscopy measurements, we derive limits on the linear interaction of ϕ with the Higgs boson, as well as its quadratic interactions with the photon and light quarks. For the linear interaction of ϕ with the Higgs boson, our derived limits improve on existing constraints by up to 2-3 orders of magnitude.

  17. A Large Hubble Space Telescope Survey of Low-Mass Exoplanets

    NASA Astrophysics Data System (ADS)

    Benneke, Björn; Crossfield, Ian; Knutson, Heather; Lothringer, Joshua; McCullough, Peter R.; Dragomir, Diana; Morley, Caroline; Kempton, Eliza

    2016-10-01

    The discovery of short-period planets with masses and radii between Earth and Neptune was one of the biggest surprises in the brief history of exoplanet science. From the Kepler mission, we know that these "super-Earths" or "sub-Neptunes" orbit at least 40% of stars, likely representing the most common outcome of planet formation. Despite this ubiquity, we know little about their typical compositions and formation histories. In this talk, we will shed new light on these worlds by presenting the multiple the main results from our 124-orbit HST transit spectroscopy survey to probe the chemical compositions of low-mass exoplanets. We will report on multiple molecular detections. Our unprecedented HST survey provides the first comprehensive look at this intriguing new class of planets by covering seven planets ranging from 1 Neptune mass and temperatures close to 2000K to a 1 Earth-mass planet near the habitable zone of its host star.

  18. Results from beam tests of MEGA's low-mass, high-rate cylindrical MWPCs

    SciTech Connect

    Stanislaus, S.; Armijo, V.; Black, J.K.; Bolton, R.D.; Carius, S.; Cooper, M.D.; Espinoza, C.; Hart, G.; Hogan, G.; Gonzales, A.; Mischke, R.E.; Piilonen, L.E.; Sandoval, J.; Schilling, S.; Sena, J.; Suazo, G.; Szymanski, J.J.; Whitehouse, D.A.; Wilkinson, C.A. ); Fisk, R.; Koetke, D.D.; Manweiler, R.W. ); Jui, C.C. (Stanford Univ., CA

    1991-01-01

    One of the leading experimental projects at LAMPF has been the MEGA experiment. This is an experiment to search for the rare decay {mu} {yields} e{gamma} with a sensitivity of 10{sup {minus}13}. A prime component of this project has been the design and construction of high-rate, low mass MWPCs for the tracking of positrons from muon decay. With rate capabilities of 2 {times} 10{sup 4} e{sup +}/mm{sup 2}/s and a thickness of 3 {times} 10{sup {minus}4} radiation lengths, these chambers are state-of-the-art cylindrical MWPCs. Cylindrical chambers of this size (0.9 m{sup 2}) and thinness have never been previously constructed. The MEGA project at LAMPF has recently succeeded in building chambers with these necessary performance characteristics as demonstrated by data taken from muon decays, cosmic rays, and sources.

  19. A prototype detector for the CRESST-III low-mass dark matter search

    NASA Astrophysics Data System (ADS)

    Strauss, R.; Angloher, G.; Bauer, P.; Defay, X.; Erb, A.; Feilitzsch, F. v.; Iachellini, N. Ferreiro; Hampf, R.; Hauff, D.; Kiefer, M.; Lanfranchi, J.-C.; Langenkämper, A.; Mondragon, E.; Münster, A.; Oppenheimer, C.; Petricca, F.; Potzel, W.; Pröbst, F.; Reindl, F.; Rothe, J.; Schönert, S.; Seidel, W.; Steiger, H.; Stodolsky, L.; Tanzke, A.; Thi, H. H. Trinh; Ulrich, A.; Wawoczny, S.; Willers, M.; Wüstrich, M.; Zöller, A.

    2017-02-01

    The CRESST-III experiment which is dedicated to low-mass dark matter search uses scintillating CaWO4 crystals operated as cryogenic particle detectors. Background discrimination is achieved by exploiting the scintillating light signal of CaWO4 and by a novel active detector holder presented in this paper. In a test setup above ground, a nuclear-recoil energy threshold of Eth =(190.6 ± 5.2) eV is reached with a 24 g prototype detector, which corresponds to an estimated threshold of ∼50 eV when being operated in the low-noise CRESST cryostat. This is the lowest threshold reported for direct dark matter searches. For CRESST-III phase 1, ten such detector modules were installed in the cryostat which have the potential to improve significantly the sensitivity to scatterings of dark matter particles with masses down to ∼0.1 GeV/c2.

  20. Stellar and Circumstellar Properties of Low-Mass, Young, Subarcsecond Binaries

    NASA Astrophysics Data System (ADS)

    Bruhns, Sara; Prato, L. A.

    2014-01-01

    We present a study of the stellar and circumstellar characteristics of close (< 1''), young (< 2 to 3 Myr), low-mass (<1 solar mass) binary stars in the Taurus star forming region. Low-resolution (R ~ 2000) spectra were taken in the K-band using adaptive optics to separate the observations for each component and identify the individual spectral types, extinction, and K-band excess. Combining these data with stellar luminosities allows us to estimate the stellar masses and ages. We also measured equivalent widths of the hydrogen Brackett gamma line in order to estimate the strength of gas accretion. We obtained spectra for six binary systems with separations from 1'' down to 0.3''. In the CZ Tau binary we found that the fainter secondary star spectrum appears to be of earlier spectral type than the primary; we speculate on the origin of this inversion.

  1. Theoretical spectra of nonmagnetized low-mass X-ray binaries

    NASA Technical Reports Server (NTRS)

    Czerny, Bozena; Czerny, Michal; Grindlay, Jonathan E.

    1986-01-01

    Theoretical X-ray spectra of low-mass X-ray binaries with negligible magnetic fields are presented. The geometry of the X-ray emitting region, the energetic efficiency of the accretion in the disk and in the boundary layer which leads to a relation between the disk and the boundary layer luminosities, and the irradiation of the disk by the boundary layer are studied. The model of the radiation spectrum emerging from the neutron star and the innermost part of the disk is presented. The relativistic and Doppler effects and their influence on the spectrum as a function of inclination angle are discussed. A simple method for comparing the spectrum model with observations by studying the hardness ratio is given, and the results for three X-ray sources in globular clusters observed by the Einstein satellite are presented. The range of applicability of the spectrum models is also discussed.

  2. Models of very-low-mass stars, brown dwarfs and exoplanets.

    PubMed

    Allard, F; Homeier, D; Freytag, B

    2012-06-13

    Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets.

  3. Low Mass-Damping Vortex-Induced Vibrations of a Single Cylinder at Moderate Reynolds Number.

    PubMed

    Jus, Y; Longatte, E; Chassaing, J-C; Sagaut, P

    2014-10-01

    The feasibility and accuracy of large eddy simulation is investigated for the case of three-dimensional unsteady flows past an elastically mounted cylinder at moderate Reynolds number. Although these flow problems are unconfined, complex wake flow patterns may be observed depending on the elastic properties of the structure. An iterative procedure is used to solve the structural dynamic equation to be coupled with the Navier-Stokes system formulated in a pseudo-Eulerian way. A moving mesh method is involved to deform the computational domain according to the motion of the fluid structure interface. Numerical simulations of vortex-induced vibrations are performed for a freely vibrating cylinder at Reynolds number 3900 in the subcritical regime under two low mass-damping conditions. A detailed physical analysis is provided for a wide range of reduced velocities, and the typical three-branch response of the amplitude behavior usually reported in the experiments is exhibited and reproduced by numerical simulation.

  4. V404 Cyg - an Interacting Black-Hole Low-Mass X-ray Binary

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Mauerhan, Jon; Graham, Melissa

    2015-07-01

    This DDT proposal is prompted by the June 15, 2015 outburst of V404 Cyg, a black-hole (BH) low-mass X-ray binary (LMXB). This outburst stands out since it is the first black hole system with a measured parallax, lying at a distance of only 2.39+/-0.14 kpc. An extensive and loosely organized multi-wavelength campaign is already underway by the astronomical community. One of the missing pieces of the puzzle is the mid-infrared (IR). Combined with radio, optical, and X-ray data, the mid-IR will help to discriminate discriminate between an accretion disk, jet emission, or circumstellar dust scenarios. Spitzer offers a unique opportunity to observe at these wavelengths. Here we propose 4 very short (5-minutes at 3.6 and 4.5 micron) observations of IRAC hotometry to search for the presence of warm dust and, if present, constrain the heating mechanism.

  5. Models of very-low-mass stars, brown dwarfs and exoplanets

    PubMed Central

    Allard, F.; Homeier, D.; Freytag, B.

    2012-01-01

    Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets. PMID:22547243

  6. Search for Light Higgs and Low Mass Dark Matter at Belle

    NASA Astrophysics Data System (ADS)

    Seong, Ilsoo

    2017-01-01

    We report a search for a light CP-odd Higgs boson A0, which can be produced in ϒ transitions and decay to low mass Dark Matter (DM). We search for evidence of on-shell and off-shell production of the light Higgs in ϒ(1S) decays via tagged dipion transitions from ϒ(2S) to ϒ(1S). We present the first Belle search for final states with a single high energy photon and missing energy in the mass range MA0 <= 9.2 GeV and MDM <= 4.5 GeV with a data sample of 157.3 × 106 ϒ(2S) decays. We also discuss the implications of our results for direct dark matter searches.

  7. Low-mass, intrinsically-hard high temperature radiator. Final report, Phase I

    SciTech Connect

    1990-07-15

    This paper reports on the investigation of layered ceramic/metal composites in the design of low-mass hardened radiators for space heat rejection systems. The investigation is part of the Strategic Defence Initiative. This effort evaluated the use of layered composites as a material to form thin-walled, vacuum leaktight heat pipes. The heat pipes would be incorporated into a large heat pipe radiator for waste heat rejection from a space nuclear power source. Composite materials evaluations were performed on combinations of refractory metals and ceramic powders. Fabrication experiments were performed to demonstrate weldability. Two titanium/titanium diboride composite tubes were successfully fabricated into potassium heat pipes and operated at temperatures in excess of 700C. Testing and analysis for composite tubes are described in the report. The study has verified the feasibility of using layered composites for forming thin-walled, light weight heat pipe tubes for use in hardened space radiators.

  8. A NEW TWIST IN THE EVOLUTION OF LOW-MASS STARS

    SciTech Connect

    Denissenkov, Pavel A.

    2012-07-01

    We show that the evolutionary track of a low-mass red giant should make an extended zigzag on the Hertzsprung-Russel diagram just after the bump luminosity if fast internal rotation and enhanced extra mixing in the radiative zone bring the temperature gradient close to the adiabatic one. This can explain both the location and peculiar surface chemical composition of Li-rich K giants studied by Kumar et al. We also discuss a striking resemblance between the photometric and composition peculiarities of these stars and giant components of RS CVn binaries. We demonstrate that the observationally constrained values of the temperature gradient in the Li-rich K giants agree with the required rate of extra mixing only if the turbulence that is believed to be responsible for this extra mixing is highly anisotropic, with its associated transport coefficients in the horizontal direction strongly dominating over those in the vertical direction.

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

    NASA Astrophysics Data System (ADS)

    Greissl, Julia Jennifer

    2010-12-01

    As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (≤ 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second

  10. The formation of the first galaxies and the transition to low-mass star formation

    NASA Astrophysics Data System (ADS)

    Greif, T. H.; Schleicher, D. R. G.; Johnson, J. L.; Jappsen, A.-K.; Klessen, R. S.; Clark, P. C.; Glover, S. C. O.; Stacy, A.; Bromm, V.

    2008-12-01

    The formation of the first galaxies at redshifts z ~ 10-15 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding their assembly process with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. In this context we emphasize the importance and influence of selecting appropriate initial conditions for the star formation process. We revisit the notion of a critical metallicity resulting in the transition from primordial to present-day initial mass functions and highlight its dependence on additional cooling mechanisms and the exact initial conditions. We also review recent work on the ability of dust cooling to provide the transition to present-day low-mass star formation. In particular, we highlight the extreme conditions under which this transition mechanism occurs, with violent fragmentation in dense gas resulting in tightly packed clusters.

  11. Toward a Complete Census of the Low Mass IMF in the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Robberto, Massimo; Andersen, Morten; Barman, Travis; Bellini, Andrea; da Rio, Nicola; de Mink, Selma; Hillenbrand, Lynne A.; Lu, Jessica R.; Luhman, Kevin; Manara, Carlo Felice; Meyer, Michael; Platais, Imants; Pueyo, Laurent; Soderblom, David; Soummer, Remi; Stahler, Steve; Tan, Jonathan Charles

    2015-08-01

    A 52-orbit Hubble Treasury Program is currently under way to investigate two fundamental questions of star formation: a) the low- mass tail of the IMF, down to a few Jupiter masses; b) the dynamical evolution of clusters, as revealed by stellar proper motions. The program targets the Orion Nebula Cluster using WFC3 and ACS in coordinated parallel mode to perform a synoptic survey in the 1.345micron H2O feature and in the F775W Ic broad-band. In this poster we present early results from the IR survey, aimed at discovering and classify all brown dwarfs and planetary-mass objects in the field, extending the IMF down to lowest masses formed by gravitational collapse. Using the latest generation of high contrast image processing we are also searching for faint companions, reaching down to sub-arcsecond separations and 10-4 flux ratios.

  12. Proper Motions and Parallaxes of Very Low-Mass Stars using DCT Astrometry

    NASA Astrophysics Data System (ADS)

    Skinner, Julie N.; West, Andrew A.; Faherty, Jacqueline K.; Muirhead, Philip Steven

    2017-01-01

    Very low-mass stars (VLMs) are the smallest, least luminous stars in our galaxy, but nonetheless form one of the dominant (baryonic) populations. Precise distances and kinematics of VLMs can provide constraints on the smallest extremes of star formation, as well as important boundary constraints on the star formation process in general. However, Gaia will only be ~70% complete at the faint magnitudes of these objects. We present preliminary results from a program to measure parallaxes and proper motions for a nearby sample of 85 VLMs using the Large Monolithic Imager at the 4.3m Discovery Channel Telescope. We present proper motions for the entire sample and preliminary parallaxes for a few sources. These measurements will complement Gaia observations and allow us to construct high quality luminosity and mass functions, which will help to distinguish between VLM formation scenarios.

  13. VizieR Online Data Catalog: A grid of 1D low-mass star formation models (Vaytet+, 2017)

    NASA Astrophysics Data System (ADS)

    Vaytet, N.; Haugbolle, T.

    2016-11-01

    We ran 143 1D simulations of gravitationally collapsing Bonnor-Ebert spheres, varying the initial mass, radius and temperature of the parent cloud. The properties of the first and second Larson cores are reported. The simulation outputs for each run are provided (one separate file per snapshot), as well as the initial parameters and core properties in a summary tablec1.dat. All the data from the simulations (figures and raw data for every output) are publicly available at this address: http://starformation.hpc.ku.dk/grid-of-protostars. (2 data files).

  14. Oscillations of red dwarfs in evolved low-mass binaries with neutron stars

    NASA Technical Reports Server (NTRS)

    Sarna, Marek J.; Lee, Umin; Muslimov, Alexander G.

    1994-01-01

    We investigate a novel aspect of a problem related to the properties of low-mass binaries (LMBs) with millisecond pulsars: the pulsations of the red dwarf (donor) companion of the neutron star (NS). The illumination of the donor star by the pulsar's high-energy nonthermal radiation and relativistic wind may substantially affect its structure. We present a quantitative analysis of the oscillation spectrum of a red dwarf which has evolved in an LMB and has undergone the stage of evaporation. We calculate the p- and g-modes for red dwarfs with masses in the interval (0.2-0.6) stellar mass. For comparison, similar calculations are presented for zero age main-sequence (ZAMS) stars of the same masses. For less massive donor stars (approximately 0.2 stellar mass) the oscillation spectrum becomes quantitatively different from that of their ZAMS counterparts. The differnce is due to the fact that a ZAMS star of 0.2 stellar mass is fully convective, while the donor star in an LMB is expected to be far from thermal equilibrium and not fully convective. As a result, in contrast to a low-mass ZAMS star, a red dwarf of the same mass in an LMB allows the existence of g-modes. We also consider tidally forced g-modes, and perform a linear analysis of these oscillations for different degrees of nonsynchronism between the orbital and spin rotation of the red dwarf component. We demonstrate the existence of a series of reasonances for the low-order g-modes which may occur in LMBs at a late stage of their evolution. We discuss the possibility that these oscillations may trigger Roche lobe overflow and sudden mass loss by the donor star. Further implications of this effect for gamma- and X-ray burst phenomena are outlined.

  15. Angular momentum transport efficiency in post-main sequence low-mass stars

    NASA Astrophysics Data System (ADS)

    Spada, F.; Gellert, M.; Arlt, R.; Deheuvels, S.

    2016-05-01

    Context. Using asteroseismic techniques, it has recently become possible to probe the internal rotation profile of low-mass (≈1.1-1.5 M⊙) subgiant and red giant stars. Under the assumption of local angular momentum conservation, the core contraction and envelope expansion occurring at the end of the main sequence would result in a much larger internal differential rotation than observed. This suggests that angular momentum redistribution must be taking place in the interior of these stars. Aims: We investigate the physical nature of the angular momentum redistribution mechanisms operating in stellar interiors by constraining the efficiency of post-main sequence rotational coupling. Methods: We model the rotational evolution of a 1.25M⊙ star using the Yale Rotational stellar Evolution Code. Our models take into account the magnetic wind braking occurring at the surface of the star and the angular momentum transport in the interior, with an efficiency dependent on the degree of internal differential rotation. Results: We find that models including a dependence of the angular momentum transport efficiency on the radial rotational shear reproduce very well the observations. The best fit of the data is obtained with an angular momentum transport coefficient scaling with the ratio of the rotation rate of the radiative interior over that of the convective envelope of the star as a power law of exponent ≈3. This scaling is consistent with the predictions of recent numerical simulations of the Azimuthal Magneto-Rotational Instability. Conclusions: We show that an angular momentum transport process whose efficiency varies during the stellar evolution through a dependence on the level of internal differential rotation is required to explain the observed post-main sequence rotational evolution of low-mass stars.

  16. Tracing low-mass galaxy clusters using radio relics: the discovery of Abell 3527-bis

    NASA Astrophysics Data System (ADS)

    de Gasperin, F.; Intema, H. T.; Ridl, J.; Salvato, M.; van Weeren, R.; Bonafede, A.; Greiner, J.; Cassano, R.; Brüggen, M.

    2017-01-01

    Context. Galaxy clusters undergo mergers that can generate extended radio sources called radio relics. Radio relics are the consequence of merger-induced shocks that propagate in the intra cluster medium (ICM). Aims: In this paper we analyse the radio, optical and X-ray data from a candidate galaxy cluster that has been selected from the radio emission coming from a candidate radio relic detected in NRAO VLA Sky Survey (NVSS). Our aim is to clarify the nature of this source and prove that under certain conditions radio emission from radio relics can be used to trace relatively low-mass galaxy clusters. Methods: We observed the candidate galaxy cluster with the Giant Meterwave Radio Telescope (GMRT) at three different frequencies. These datasets have been analysed together with archival data from ROSAT in the X-ray and with archival data from the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) telescope in four different optical bands. Results: We confirm the presence of a 1 Mpc long radio relic located in the outskirts of a previously unknown galaxy cluster. We confirm the presence of the galaxy cluster through dedicated optical observations and using archival X-ray data. Due to its proximity and similar redshift to a known Abell cluster, we named it Abell 3527-bis. The galaxy cluster is amongst the least massive clusters known to host a radio relic. Conclusions: We showed that radio relics can be effectively used to trace a subset of relatively low-mass galaxy clusters that might have gone undetected in X-ray or Sunyaev-Zel'dovich (SZ) surveys. This technique might be used in future deep, low-frequency surveys such as those carried on by the Low Frequency Array (LOFAR), the Upgraded GMRT (uGMRT) and, ultimately, the Square Kilometre Array (SKA).

  17. THE MASS DISTRIBUTION OF COMPANIONS TO LOW-MASS WHITE DWARFS

    SciTech Connect

    Andrews, Jeff J.; Price-Whelan, Adrian M.; Agüeros, Marcel A.

    2014-12-20

    Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. In this work, we construct a hierarchical probabilistic model to infer properties of unseen companion stars given observations of the orbital period and projected radial velocity of the primary star. We apply this model to three mock samples of low-mass white dwarfs (LMWDs; M ≲ 0.45 M {sub ☉}) and a sample of post-common-envelope binaries. We use a mixture of two Gaussians to model the WD and neutron star (NS) companion mass distributions. Our model successfully recovers the initial parameters of these test data sets. We then apply our model to 55 WDs in the extremely low-mass (ELM) WD Survey. Our maximum a posteriori model for the WD companion population has a mean mass μ{sub WD} = 0.74 M {sub ☉}, with a standard deviation σ{sub WD} = 0.24 M {sub ☉}. Our model constrains the NS companion fraction f {sub NS} to be <16% at 68% confidence. We make samples from the posterior distribution publicly available so that future observational efforts may compute the NS probability for newly discovered LMWDs.

  18. The black hole-host galaxy relation for very low mass quasars

    NASA Astrophysics Data System (ADS)

    Sanghvi, J.; Kotilainen, J. K.; Falomo, R.; Decarli, R.; Karhunen, K.; Uslenghi, M.

    2014-12-01

    Recently, the relation between the masses of the black hole (MBH) and the host galaxy (Mhost) in quasars has been probed down to the parameter space of MBH ˜ 108 M⊙ and Mhost ˜ 1011 M⊙ at z < 0.5. In this study, we have investigated the MBH-Mhost log-linear relation for a sample of 37 quasars with low black hole masses (107 M⊙ < MBH < 108.3 M⊙) at 0.5 < z < 1.0. The black hole masses were derived using virial mass estimates from Sloan Digital Sky Survey (SDSS) optical spectra. For 25 quasars, we detected the presence of the host galaxy from deep near-infrared H-band imaging, whereas upper limits for the host galaxy luminosity (mass) were estimated for the 12 unresolved quasars. We combined our previous studies with the results from this work to create a sample of 89 quasars at z < 1.0 having a large range of black hole masses (107 M⊙ < MBH < 1010 M⊙) and host galaxy masses (1010 M⊙ < Mhost < 1013 M⊙). Most of the quasars at the low-mass end lie below the extrapolation of the local relation. This apparent break in the linearity of the entire sample is due to increasing fraction of disc-dominated host galaxies in the low-mass quasars. After correcting for the disc component, and considering only the bulge component, the bilinear regression for the entire quasar sample holds over 3.5 dex in both the black hole mass and the bulge mass, and is in very good agreement with the local relation. We advocate secular evolution of discs of galaxies being responsible for the relatively strong disc domination.

  19. The High-Energy Radiation Environment of Planets around Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya; Miles, Brittany; Barman, Travis; Peacock, Sarah

    2015-12-01

    Low-mass stars are the dominant planet hosts averaging about one planet per star. Many of these planets orbit in the canonical habitable zone (HZ) of the star where, if other conditions allowed, liquid water may exist on the surface.A planet’s habitability, including atmospheric retention, is strongly dependent on the star’s ultraviolet (UV) emission, which chemically modifies, ionizes, and even erodes the atmosphere over time including the photodissociation of important diagnostic molecules, e.g. H2O, CH4, and CO2. The UV spectral slope of a low-mass star can enhance atmospheric lifetimes, and increase the detectability of biologically generated gases. But, a different slope may lead to the formation of abiotic oxygen and ozone producing a false-positive biosignature for oxygenic photosynthesis. Realistic constraints on the incident UV flux over a planet’s lifetime are necessary to explore the cumulative effects on the evolution, composition, and fate of a HZ planetary atmosphere.NASA’s Galaxy Evolution Explorer (GALEX) provides a unique data set with which to study the broadband UV emission from many hundreds of M dwarfs. The GALEX satellite has imaged nearly 3/4 of the sky simultaneously in two UV bands: near-UV (NUV; 175-275 nm) and far-UV (FUV; 135-175 nm). With these data these, we are able to calculate the mean UV emission and its level of variability at these wavelengths over critical planet formation and evolution time scales to better understand the probable conditions in HZ planetary atmospheres.In the near future, dedicated CubeSats (miniaturized satellites for space research) to monitor M dwarf hosts of transiting exoplanets will provide the best opportunity to measure their UV variability, constrain the probabilities of detecting habitable (and inhabited) planets, and provide the correct context within which to interpret IR transmission and emission spectroscopy of transiting exoplanets.

  20. Angular momentum redistribution by mixed modes in evolved low-mass stars. I. Theoretical formalism

    NASA Astrophysics Data System (ADS)

    Belkacem, K.; Marques, J. P.; Goupil, M. J.; Sonoi, T.; Ouazzani, R. M.; Dupret, M. A.; Mathis, S.; Mosser, B.; Grosjean, M.

    2015-07-01

    Seismic observations by the space-borne mission Kepler have shown that the core of red giant stars slows down while evolving, requiring an efficient physical mechanism to extract angular momentum from the inner layers. Current stellar evolution codes fail to reproduce the observed rotation rates by several orders of magnitude and instead predict a drastic spin-up of red giant cores. New efficient mechanisms of angular momentum transport are thus required. In this framework, our aim is to investigate the possibility that mixed modes extract angular momentum from the inner radiative regions of evolved low-mass stars. To this end, we consider the transformed Eulerian mean (TEM) formalism, which allows us to consider the combined effect of both the wave momentum flux in the mean angular momentum equation and the wave heat flux in the mean entropy equation as well as their interplay with the meridional circulation. In radiative layers of evolved low-mass stars, the quasi-adiabatic approximation, the limit of slow rotation, and the asymptotic regime can be applied for mixed modes and enable us to establish a prescription for the wave fluxes in the mean equations. The formalism is finally applied to a 1.3 M⊙ benchmark model, representative of observed CoRoT and Kepler oscillating evolved stars. We show that the influence of the wave heat flux on the mean angular momentum is not negligible and that the overall effect of mixed modes is to extract angular momentum from the innermost region of the star. A quantitative and accurate estimate requires realistic values of mode amplitudes. This is provided in a companion paper. Appendix A is available in electronic form at http://www.aanda.org

  1. The star formation history of low-mass disk galaxies: A case study of NGC 300

    NASA Astrophysics Data System (ADS)

    Kang, Xiaoyu; Zhang, Fenghui; Chang, Ruixiang; Wang, Lang; Cheng, Liantao

    2016-01-01

    Context. Since NGC 300 is a bulgeless, isolated low-mass galaxy and it has not experienced radial migration during its evolution history, it can be treated as an ideal laboratory to test the simple galactic chemical evolution model. Aims: Our main aim is to investigate the main properties of the star formation history (SFH) of NGC 300 and compare its SFH with that of M 33 to explore the common properties and differences between these two nearby low-mass systems. Methods: We construct a simple chemical evolution model for NGC 300, assuming its disk forms gradually from continuous accretion of primordial gas and including the gas-outflow process. The model allows us to build a bridge between the SFH and observed data of NGC 300, in particular, the present-day radial profiles and global observed properties (e.g., cold gas mass, star formation rate, and metallicity). By means of comparing the model predictions with the corresponding observations, we adopt the classical χ2 methodology to find out the best combination of free parameters a, b, and bout. Results: Our results show that by assuming an inside-out formation scenario and an appropriate outflow rate, our model reproduces well most of the present-day observational values. The model not only reproduces well the radial profiles, but also the global observational data for the NGC 300 disk. Our results suggest that NGC 300 may experience a rapid growth of its disk. Through comparing the best-fitting, model-predicted SFH of NGC 300 with that of M 33, we find that the mean stellar age of NGC 300 is older than that of M 33 and there is a recent lack of primordial gas infall onto the disk of NGC 300. Our results also imply that the local environment may play a key role in the secular evolution of galaxy disks.

  2. Precise Black Hole Masses from Megamaser Disks: Black Hole-Bulge Relations at Low Mass

    NASA Astrophysics Data System (ADS)

    Greene, Jenny E.; Peng, Chien Y.; Kim, Minjin; Kuo, Cheng-Yu; Braatz, James A.; Impellizzeri, C. M. V.; Condon, James J.; Lo, K. Y.; Henkel, Christian; Reid, Mark J.

    2010-09-01

    The black hole (BH)-bulge correlations have greatly influenced the last decade of efforts to understand galaxy evolution. Current knowledge of these correlations is limited predominantly to high BH masses (M BHgsim108 M sun) that can be measured using direct stellar, gas, and maser kinematics. These objects, however, do not represent the demographics of more typical L < L* galaxies. This study transcends prior limitations to probe BHs that are an order of magnitude lower in mass, using BH mass measurements derived from the dynamics of H2O megamasers in circumnuclear disks. The masers trace the Keplerian rotation of circumnuclear molecular disks starting at radii of a few tenths of a pc from the central BH. Modeling of the rotation curves, presented by Kuo et al., yields BH masses with exquisite precision. We present stellar velocity dispersion measurements for a sample of nine megamaser disk galaxies based on long-slit observations using the B&C spectrograph on the Dupont telescope and the Dual Imaging Spectrograph on the 3.5 m telescope at Apache Point. We also perform bulge-to-disk decomposition of a subset of five of these galaxies with Sloan Digital Sky Survey imaging. The maser galaxies as a group fall below the M BH-σ* relation defined by elliptical galaxies. We show, now with very precise BH mass measurements, that the low-scatter power-law relation between M BH and σ* seen in elliptical galaxies is not universal. The elliptical galaxy M BH-σ* relation cannot be used to derive the BH mass function at low mass or the zero point for active BH masses. The processes (perhaps BH self-regulation or minor merging) that operate at higher mass have not effectively established an M BH-σ* relation in this low-mass regime.

  3. Investigating Low-Mass Binary Stars And Brown Dwarfs with Near-Infrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Mace, Gregory Nathan

    The mass of a star at formation determines its subsequent evolution and demise. Low-mass stars are the most common products of star formation and their long main-sequence lifetimes cause them to accumulate over time. Star formation also produces many substellar-mass objects known as brown dwarfs, which emerge from their natal molecular clouds and continually cool as they age, pervading the Milky Way. Low-mass stars and brown dwarfs exhibit a wide range of physical characteristics and their abundance make them ideal subjects for testing formation and evolution models. I have examined a pair of pre-main sequence spectroscopic binaries and used radial velocity variations to determine orbital solutions and mass ratios. Additionally, I have employed synthetic spectra to estimate their effective temperatures and place them on theoretical Hertzsprung-Russell diagrams. From this analysis I discuss the formation and evolution of young binary systems and place bounds on absolute masses and radii. I have also studied the late-type T dwarfs revealed by the Wide-field Infrared Survey Explorer (WISE). This includes the exemplar T8 subdwarf Wolf 1130C, which has the lowest inferred metallicity in the literature and spectroscopic traits consistent with old age. Comparison to synthetic spectra implies that the dispersion in near-infrared colors of late-type T dwarfs is a result of age and/or thin sulfide clouds. With the updated census of the L, T, and Y dwarfs we can now study specific brown dwarf subpopulations. Finally, I present a number of future studies that would develop our understanding of the physical qualities of T dwarf color outliers and disentangle the tracers of age and atmospheric properties.

  4. PRECISE BLACK HOLE MASSES FROM MEGAMASER DISKS: BLACK HOLE-BULGE RELATIONS AT LOW MASS

    SciTech Connect

    Greene, Jenny E.; Peng, Chien Y.; Kim, Minjin; Kuo, Cheng-Yu; Braatz, James A.; Impellizzeri, C. M. Violette; Condon, James J.; Lo, K. Y.; Henkel, Christian; Reid, Mark J.

    2010-09-20

    The black hole (BH)-bulge correlations have greatly influenced the last decade of efforts to understand galaxy evolution. Current knowledge of these correlations is limited predominantly to high BH masses (M{sub BH{approx}}>10{sup 8} M{sub sun}) that can be measured using direct stellar, gas, and maser kinematics. These objects, however, do not represent the demographics of more typical L < L* galaxies. This study transcends prior limitations to probe BHs that are an order of magnitude lower in mass, using BH mass measurements derived from the dynamics of H{sub 2}O megamasers in circumnuclear disks. The masers trace the Keplerian rotation of circumnuclear molecular disks starting at radii of a few tenths of a pc from the central BH. Modeling of the rotation curves, presented by Kuo et al., yields BH masses with exquisite precision. We present stellar velocity dispersion measurements for a sample of nine megamaser disk galaxies based on long-slit observations using the B and C spectrograph on the Dupont telescope and the Dual Imaging Spectrograph on the 3.5 m telescope at Apache Point. We also perform bulge-to-disk decomposition of a subset of five of these galaxies with Sloan Digital Sky Survey imaging. The maser galaxies as a group fall below the M{sub BH}-{sigma}{sub *} relation defined by elliptical galaxies. We show, now with very precise BH mass measurements, that the low-scatter power-law relation between M{sub BH} and {sigma}{sub *} seen in elliptical galaxies is not universal. The elliptical galaxy M{sub BH}-{sigma}{sub *} relation cannot be used to derive the BH mass function at low mass or the zero point for active BH masses. The processes (perhaps BH self-regulation or minor merging) that operate at higher mass have not effectively established an M{sub BH}-{sigma}{sub *} relation in this low-mass regime.

  5. DETECTING PLANETS AROUND VERY LOW MASS STARS WITH THE RADIAL VELOCITY METHOD

    SciTech Connect

    Reiners, A.; Bean, J. L.; Dreizler, S.; Seifahrt, A.; Huber, K. F.; Czesla, S.

    2010-02-10

    The detection of planets around very low-mass stars with the radial velocity (RV) method is hampered by the fact that these stars are very faint at optical wavelengths where the most high-precision spectrometers operate. We investigate the precision that can be achieved in RV measurements of low mass stars in the near-infrared (NIR) Y-, J-, and H-bands, and we compare it to the precision achievable in the optical assuming comparable telescope and instrument efficiencies. For early-M stars, RV measurements in the NIR offer no or only marginal advantage in comparison with optical measurements. Although they emit more flux in the NIR, the richness of spectral features in the optical outweighs the flux difference. We find that NIR measurement can be as precise as optical measurements in stars of spectral type {approx}M4, and from there the NIR gains in precision toward cooler objects. We studied potential calibration strategies in the NIR finding that a stable spectrograph with a ThAr calibration can offer enough wavelength stability for m s{sup -1} precision. Furthermore, we simulate the wavelength-dependent influence of activity (cool spots) on RV measurements from optical to NIR wavelengths. Our spot simulations reveal that the RV jitter does not decrease as dramatically toward longer wavelengths as often thought. The jitter strongly depends on the details of the spots, i.e., on spot temperature and the spectral appearance of the spot. At low temperature contrast ({approx}200 K), the jitter shows a decrease toward the NIR up to a factor of 10, but it decreases substantially less for larger temperature contrasts. Forthcoming NIR spectrographs will allow the search for planets with a particular advantage in mid- and late-M stars. Activity will remain an issue, but simultaneous observations at optical and NIR wavelengths can provide strong constraints on spot properties in active stars.

  6. Low-mass molecular dynamics simulation: A simple and generic technique to enhance configurational sampling

    SciTech Connect

    Pang, Yuan-Ping

    2014-09-26

    Highlights: • Reducing atomic masses by 10-fold vastly improves sampling in MD simulations. • CLN025 folded in 4 of 10 × 0.5-μs MD simulations when masses were reduced by 10-fold. • CLN025 folded as early as 96.2 ns in 1 of the 4 simulations that captured folding. • CLN025 did not fold in 10 × 0.5-μs MD simulations when standard masses were used. • Low-mass MD simulation is a simple and generic sampling enhancement technique. - Abstract: CLN025 is one of the smallest fast-folding proteins. Until now it has not been reported that CLN025 can autonomously fold to its native conformation in a classical, all-atom, and isothermal–isobaric molecular dynamics (MD) simulation. This article reports the autonomous and repeated folding of CLN025 from a fully extended backbone conformation to its native conformation in explicit solvent in multiple 500-ns MD simulations at 277 K and 1 atm with the first folding event occurring as early as 66.1 ns. These simulations were accomplished by using AMBER forcefield derivatives with atomic masses reduced by 10-fold on Apple Mac Pros. By contrast, no folding event was observed when the simulations were repeated using the original AMBER forcefields of FF12SB and FF14SB. The results demonstrate that low-mass MD simulation is a simple and generic technique to enhance configurational sampling. This technique may propel autonomous folding of a wide range of miniature proteins in classical, all-atom, and isothermal–isobaric MD simulations performed on commodity computers—an important step forward in quantitative biology.

  7. The Metallicity Evolution of Low Mass Galaxies: New Contraints at Intermediate Redshift

    NASA Technical Reports Server (NTRS)

    Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

    2013-01-01

    We present abundance measurements from 26 emission-line-selected galaxies at z approx. 0.6-0.7. By reaching stellar masses as low as 10(exp 8) M stellar mass, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 10(exp 9)M stellar mass. For the portion of our sample above M is greater than 10(exp 9)M (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M* relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation.We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

  8. Low Mass Printable Devices for Energy Capture, Storage, and Use for Space Exploration Missions

    NASA Technical Reports Server (NTRS)

    Frazier, Donald O.; Singer, Christopher E.; Ray, William J.; Fuller, Kirk A.

    2010-01-01

    The energy-efficient, environmentally friendly technology that will be presented is the result of a Space Act Agreement between -Technologies Worldwide, Inc., and the National Aeronautics and Space Administration s (NASA s) Marshall Space Flight Center (MSFC). This work combines semiconductor and printing technologies to advance lightweight electronic and photonic devices having excellent potential for commercial and exploration applications, and is an example of industry and government cooperation that leads to novel inventions. Device development involves three energy generation and consumption projects: 1) a low mass efficient (low power, low heat emission) micro light-emitting diode (LED) area lighting device; 2) a low-mass omni-directional efficient photovoltaic (PV) device with significantly improved energy capture; and 3) a new approach to building supercapacitors. These three technologies - energy capture, storage, and usage (e.g., lighting) - represent a systematic approach for building efficient local micro-grids that are commercially feasible; furthermore, these same technologies will be useful for lightweight power generation that enables inner planetary missions using smaller launch vehicles and facilitates surface operations. The PV device model is a two-sphere, light-trapped sheet approximately 2-mm thick. The model suggests a significant improvement over current thin film systems. All three components may be printed in line by printing sequential layers on a standard screen or flexographic direct impact press using the threedimensional printing technique (3DFM) patented by NthDegree. MSFC is testing the robustness of prototype devices in the harsh space and lunar surface environments, and available results will be reported. Unlike many traditional light sources, this device does not contain toxic compounds, and the LED component has passed stringent off-gassing tests required for potential manifesting on spacecraft such as the International Space

  9. Low-mass, intrinsically-hard high-temperature radiator. Final report, Phase I

    SciTech Connect

    1990-06-15

    Thermacore, Inc. of Lancaster, Pennsylvania has completed a Phase I SBIR program to investigate the use of layered ceramic/metal composites in the design of low-mass hardened radiators for space heat rejection systems. The program is being monitored by the Los Alamos National Laboratory (LANL) for the Strategic Defense Initiative Organization (SDIO). This effort evaluated the use of layered composites as a material to form thin-walled, vacuum leaktight heat pipes. The heat pipes would be incorporated into a large heat pipe radiator for waste heat rejection from a space nuclear power source. This approach forms an attractive alternative to metal or silicon-carbon fiber reinforced metal heat pipes by offering a combination of low mass and improved fabricability. Titanium has been shown to have a yield strength too low at 875{degrees}K to be a useful radiator material. A silicon carbide fiber reinforced titanium material appears to have sufficient strength at 875{degrees}K. but cannot be welded due to the continuous fibers, and the preferred heat pipe working fluid (potassium) has been demonstrated to be incompatible with silicon carbide at 875{degrees}K. Moreover, titanium does not appear to be acceptable for radiators subjected to anticipated laser threats. As part of this effort, Thermacore performed composite material evaluations on combinations of refractory metals and ceramic powders. Layered composite tube samples with wall thicknesses as thin as 0.012 inches were developed. Fabrication experiments were performed that demonstrated the weldability of layered composites. Two titanium/titanium diboride composite tubes were successfully fabricated into potassium heat pipes and operated at temperatures in excess of 700{degrees}C. A hybrid composite tube was also fabricated into a potassium heat pipe. The tube was composed of alternating layers of niobium-1% zirconium foil and layers of a mixture of titanium powder and titanium diboride powder.

  10. A Multi-Fiber Spectroscopic Search for Low-mass Young Stars in Orion OB1

    NASA Astrophysics Data System (ADS)

    Loerincs, Jacqueline; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

    2017-01-01

    We present here results of a low resolution spectroscopic followup of candidate low-mass pre-main sequence stars in the Orion OB1 association. Our targets were selected from the CIDA Variability Survey of Orion (CVSO), and we used the Michigan/Magellan Fiber Spectrograph (M2FS) on the Magellan Clay 6.5m telescope to obtain spectra of 500 candidate T Tauri stars distributed in seven 0.5 deg diameter fields, adding to a total area of ~5.5 deg2. We identify young stars by looking at the distinctive Hα 6563 Å emission and Lithium Li I 6707 Å absorption features characteristic of young low mass pre-main sequence stars. Furthermore, by measuring the strength of their Hα emission lines, confirmed T Tauri stars can be classified as either Classical T Tauris (CTTS) or Weak-line T Tauris (WTTS), which give indication of whether the star is actively accreting material from a gas and dust disk surrounding the star, which may be the precursor of a planetary system. We confirm a total of 90 T Tauri stars, of which 50% are newly identified young members of Orion; out of the 49 new detections,15 are accreting CTTS, and of these all but one are found in the OB1b sub-region. This result is in line with our previous findings that this region is much younger than the more extended Orion OB1a sub-association. The M2FS results add to our growing census of young stars in Orion, that is allowing us to characterize in a systematic and consistent way the distribution of stellar ages across the entire complex, in order to building a complete picture of star formation in this, one of nearest most active sites of star birth.

  11. A New γ-Ray Loud, Eclipsing Low-mass X-Ray Binary

    NASA Astrophysics Data System (ADS)

    Strader, Jay; Li, Kwan-Lok; Chomiuk, Laura; Heinke, Craig O.; Udalski, Andrzej; Peacock, Mark; Shishkovsky, Laura; Tremou, Evangelia

    2016-11-01

    We report the discovery of an eclipsing low-mass X-ray binary at the center of the 3FGL error ellipse of the unassociated Fermi/Large Area Telescope γ-ray source 3FGL J0427.9-6704. Photometry from OGLE and the SMARTS 1.3 m telescope and spectroscopy from the SOAR telescope have allowed us to classify the system as an eclipsing low-mass X-ray binary (P = 8.8 hr) with a main-sequence donor and a neutron-star accretor. Broad double-peaked H and He emission lines suggest the ongoing presence of an accretion disk. Remarkably, the system shows separate sets of absorption lines associated with the accretion disk and the secondary, and we use their radial velocities to find evidence for a massive (˜1.8-1.9 M ⊙) neutron-star primary. In addition to a total X-ray eclipse with a duration of ˜2200 s observed with NuSTAR, the X-ray light curve also shows properties similar to those observed among known transitional millisecond pulsars: short-term variability, a hard power-law spectrum ({{Γ }}˜ 1.7), and a comparable 0.5-10 keV luminosity (˜ 2.4× {10}33 erg s-1). We find tentative evidence for a partial (˜ 60 % ) γ-ray eclipse at the same phase as the X-ray eclipse, suggesting the γ-ray emission may not be confined to the immediate region of the compact object. The favorable inclination of this binary is promising for future efforts to determine the origin of γ-rays among accreting neutron stars.

  12. An Astrometric Companion to the Nearby Metal-Poor, Low-Mass Star LHS 1589

    NASA Astrophysics Data System (ADS)

    Lépine, Sébastien; Rich, R. Michael; Shara, Michael M.; Cruz, Kelle L.; Skemer, Andrew

    2007-10-01

    We report the discovery of a companion to the high proper motion star LHS 1589, a nearby high-velocity, low-mass subdwarf. The companion (LHS 1589B) is located 0.224''+/-0.004'' to the southwest of the primary (LHS 1589A), and is 0.5 mag fainter than the primary in the Ks band. The pair was resolved with the IRCAL infrared camera at Lick Observatory, operating with the Laser Guide Star Adaptive Optics system. A low-resolution spectrum of the unresolved pair obtained at the MDM observatory shows the source to be consistent with a cool subdwarf of spectral subtype sdK7.5. A photometric distance estimate places the metal-poor system at a distance d=81+/-18 pc from the Sun. We also measure a radial velocity Vrad=67+/-8 km s-1, which, together with the proper motion and estimated distance, suggests that the pair is roaming the inner Galactic halo on a highly eccentric orbit. With a projected orbital separation s=18.1+/-4.8 AU, and a crude estimate of the system's total mass, we estimate the orbital period of the system to be in the range 75 yr low-mass stars. Based on observations performed with the Laser Guide Star Adaptive Optics system at the Lick Observatory, operated by the University of California system. Based on observations conducted at the MDM observatory, operated jointly by the University of Michigan, Dartmouth College, the Ohio State University, Columbia University, and the University of Ohio.

  13. Discovery of a low-mass companion to the F7V star HD 984

    NASA Astrophysics Data System (ADS)

    Meshkat, T.; Bonnefoy, M.; Mamajek, E. E.; Quanz, S. P.; Chauvin, G.; Kenworthy, M. A.; Rameau, J.; Meyer, M. R.; Lagrange, A.-M.; Lannier, J.; Delorme, P.

    2015-11-01

    We report the discovery of a low-mass companion to the nearby (d = 47 pc) F7V star HD 984. The companion is detected 0.19 arcsec away from its host star in the L' band with the Apodized Phase Plate on NaCo/Very Large Telescope and was recovered by L'-band non-coronagraphic imaging data taken a few days later. We confirm the companion is comoving with the star with SINFONI integral field spectrograph H + K data. We present the first published data obtained with SINFONI in pupil-tracking mode. HD 984 has been argued to be a kinematic member of the 30 Myr-old Columba group, and its HR diagram position is not altogether inconsistent with being a zero-age main sequence star of this age. By consolidating different age indicators, including isochronal age, coronal X-ray emission, and stellar rotation, we independently estimate a main-sequence age of 115 ± 85 Myr (95 per cent CL) which does not rely on this kinematic association. The mass of directly imaged companions are usually inferred from theoretical evolutionary tracks, which are highly dependent on the age of the star. Based on the age extrema, we demonstrate that with our photometric data alone, the companion's mass is highly uncertain: between 33 and 96 MJup (0.03-0.09 M⊙) using the COND evolutionary models. We compare the companion's SINFONI spectrum with field dwarf spectra to break this degeneracy. Based on the slope and shape of the spectrum in the H band, we conclude that the companion is an M6.0 ± 0.5 dwarf. The age of the system is not further constrained by the companion, as M dwarfs are poorly fit on low-mass evolutionary tracks. This discovery emphasizes the importance of obtaining a spectrum to spectral type companions around F-stars.

  14. Formation of Black Hole Low-mass X-Ray Binaries in Hierarchical Triple Systems

    NASA Astrophysics Data System (ADS)

    Naoz, Smadar; Fragos, Tassos; Geller, Aaron; Stephan, Alexander P.; Rasio, Frederic A.

    2016-05-01

    The formation of black hole (BH) low-mass X-ray binaries (LMXB) poses a theoretical challenge, as low-mass companions are not expected to survive the common-envelope scenario with the BH progenitor. Here we propose a formation mechanism that skips the common-envelope scenario and relies on triple-body dynamics. We study the evolution of hierarchical triples following the secular dynamical evolution up to the octupole-level of approximation, including general relativity, tidal effects, and post-main-sequence evolution such as mass loss, changes to stellar radii, and supernovae. During the dynamical evolution of the triple system the “eccentric Kozai-Lidov” mechanism can cause large eccentricity excitations in the LMXB progenitor, resulting in three main BH-LMXB formation channels. Here we define BH-LMXB candidates as systems where the inner BH-companion star crosses its Roche limit. In the “eccentric” channel (˜81% of the LMXBs in our simulations) the donor star crosses its Roche limit during an extreme eccentricity excitation while still on a wide orbit. Second, we find a “giant” LMXB channel (˜11%), where a system undergoes only moderate eccentricity excitations but the donor star fills its Roche-lobe after evolving toward the giant branch. Third, we identify a “classical” channel (˜8%), where tidal forces and magnetic braking shrink and circularize the orbit to short periods, triggering mass-transfer. Finally, for the giant channel we predict an eccentric (˜0.3-0.6) preferably inclined (˜40°, ˜140°) tertiary, typically on a wide enough orbit (˜104 au) to potentially become unbound later in the triple evolution. While this initial study considers only one representative system and neglects BH natal kicks, we expect our scenario to apply across a broad region of parameter space for triple-star systems.

  15. Discovery of wide low and very low-mass binary systems using Virtual Observatory tools

    NASA Astrophysics Data System (ADS)

    Gálvez-Ortiz, M. C.; Solano, E.; Lodieu, N.; Aberasturi, M.

    2017-04-01

    The frequency of multiple systems and their properties are key constraints of stellar formation and evolution. Formation mechanisms of very low-mass (VLM) objects are still under considerable debate, and an accurate assessment of their multiplicity and orbital properties is essential for constraining current theoretical models. Taking advantage of the virtual observatory capabilities, we looked for comoving low and VLM binary (or multiple) systems using the Large Area Survey of the UKIDSS LAS DR10, SDSS DR9 and the 2MASS Catalogues. Other catalogues (WISE, GLIMPSE, SuperCosmos, etc.) were used to derive the physical parameters of the systems. We report the identification of 36 low and VLM (∼M0-L0 spectral types) candidates to binary/multiple system (separations between 200 and 92 000 au), whose physical association is confirmed through common proper motion, distance and low probability of chance alignment. This new system list notably increases the previous sampling in their mass-separation parameter space (∼100). We have also found 50 low-mass objects that we can classify as ∼L0-T2 according to their photometric information. Only one of these objects presents a common proper motion high-mass companion. Although we could not constrain the age of the majority of the candidates, probably most of them are still bound except four that may be under disruption processes. We suggest that our sample could be divided in two populations: one tightly bound wide VLM systems that are expected to last more than 10 Gyr, and other formed by weak bound wide VLM systems that will dissipate within a few Gyr.

  16. Detection of Formamide, the Simplest but Crucial Amide, in a Solar-type Protostar

    NASA Astrophysics Data System (ADS)

    Kahane, C.; Ceccarelli, C.; Faure, A.; Caux, E.

    2013-02-01

    Formamide (NH2CHO), the simplest possible amide, has recently been suggested to be a central species in the synthesis of metabolic and genetic molecules, the chemical basis of life. In this Letter, we report the first detection of formamide in a protostar, IRAS 16293-2422, which may be similar to the Sun and solar system progenitor. The data combine spectra from the millimeter and submillimeter TIMASSS survey with recent, more sensitive observations at the IRAM 30 m telescope. With an abundance relative to H2 of ~10-10, formamide appears as abundant in this solar-type protostar as in the two high-mass star-forming regions, Orion-KL and SgrB2, where this species has previously been detected. Given the largely different UV-illuminated environments of the three sources, the relevance of UV photolysis of interstellar ices in the synthesis of formamide is therefore questionable. Assuming that this species is formed in the gas phase via the neutral-neutral reaction between the radical NH2 and H2CO, we predict an abundance in good agreement with the value derived from our observations. The comparison of the relative abundance [NH2CHO]/[H2O] in IRAS 16293-2422 and in the coma of the comet Hale-Bopp supports the similarity between interstellar and cometary chemistry. Our results thus suggest that the abundance of some cometary organic volatiles could reflect gas phase rather than grain-surface interstellar chemistry.

  17. THE DYNAMICS OF THE ENVELOPE SURROUNDING THE PROTOSTAR HH 211 mm

    SciTech Connect

    Tanner, Joel D.; Arce, Hector G. E-mail: hector.arce@yale.edu

    2011-01-01

    We present a study of the structure and dynamics of the dense gas surrounding the HH 211 mm source, using Very Large Array (VLA) observations of the ammonia (1,1) and (2,2) inversion transitions. We find that the envelope around this Class 0 source has an elongated geometry, extending about 10{sup 4} AU in the direction perpendicular to the well-known HH 211 jet, and exhibits a velocity distribution consistent with rotation along the major axis. Our VLA observations indicate that the envelope is mostly in virial equilibrium. However, comparing our data with results from previous studies, it appears that the gas within approximately 0.005 pc of the central protostar is undergoing dynamical collapse. The size of this collapsing radius may constrain the amount of mass that can eventually infall into the forming star. We also find that the envelope is mostly internally heated, most probably by radiation from the central protostar. In addition, we detect evidence of outflow-envelope interaction in the ammonia data. These include a velocity gradient in the dense gas along the outflow axis and significant line broadening that is spatially correlated with the jet and could be the result of outflow-induced turbulence in the envelope.

  18. THE EXTRAORDINARY FAR-INFRARED VARIATION OF A PROTOSTAR: HERSCHEL/PACS OBSERVATIONS OF LRLL54361

    SciTech Connect

    Balog, Zoltan; Detre, Örs H.; Bouwmann, Jeroen; Nielbock, Markus; Klaas, Ulrich; Krause, Oliver; Henning, Thomas; Muzerolle, James; Flaherty, Kevin; Furlan, Elise; Gutermuth, Rob; Juhasz, Attila; Bally, John; Marton, Gabor

    2014-07-10

    We report Herschel/Photodetector Array Camera and Spectrometer (PACS) photometric observations at 70 μm and 160 μm of LRLL54361—a suspected binary protostar that exhibits periodic (P = 25.34 days) flux variations at shorter wavelengths (3.6 μm and 4.5 μm) thought to be due to pulsed accretion caused by binary motion. The PACS observations show unprecedented flux variation at these far-infrared wavelengths that are well correlated with the variations at shorter wavelengths. At 70 μm the object increases its flux by a factor of six while at 160 μm the change is about a factor of two, consistent with the wavelength dependence seen in the far-infrared spectra. The source is marginally resolved at 70 μm with varying FWHM. Deconvolved images of the sources show elongations exactly matching the outflow cavities traced by the scattered light observations. The spatial variations are anti-correlated with the flux variation, indicating that a light echo is responsible for the changes in FWHM. The observed far-infrared flux variability indicates that the disk and envelope of this source is periodically heated by the accretion pulses of the central source, and suggests that such long wavelength variability in general may provide a reasonable proxy for accretion variations in protostars.

  19. Young Stellar Populations in MYStIX Star-forming Regions: Candidate Protostars

    NASA Astrophysics Data System (ADS)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Povich, Matthew S.

    2016-12-01

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  20. An ALMA Search for Substructure, Fragmentation, and Hidden Protostars in Starless Cores in Chamaeleon I

    NASA Astrophysics Data System (ADS)

    Dunham, Michael M.; Offner, Stella S. R.; Pineda, Jaime E.; Bourke, Tyler L.; Tobin, John J.; Arce, Héctor G.; Chen, Xuepeng; Di Francesco, James; Johnstone, Doug; Lee, Katherine I.; Myers, Philip C.; Price, Daniel; Sadavoy, Sarah I.; Schnee, Scott

    2016-06-01

    We present an Atacama Large Millimeter/submillimeter Array (ALMA) 106 GHz (Band 3) continuum survey of the complete population of dense cores in the Chamaeleon I molecular cloud. We detect a total of 24 continuum sources in 19 different target fields. All previously known Class 0 and Class I protostars in Chamaeleon I are detected, whereas all of the 56 starless cores in our sample are undetected. We show that the Spitzer+Herschel census of protostars in Chamaeleon I is complete, with the rate at which protostellar cores have been misclassified as starless cores calculated as <1/56, or <2%. We use synthetic observations to show that starless cores collapsing following the turbulent fragmentation scenario are detectable by our ALMA observations when their central densities exceed ˜108 cm-3, with the exact density dependent on the viewing geometry. Bonnor-Ebert spheres, on the other hand, remain undetected to central densities at least as high as 1010 cm-3. Our starless core non-detections are used to infer that either the star-formation rate is declining in Chamaeleon I and most of the starless cores are not collapsing, matching the findings of previous studies, or that the evolution of starless cores are more accurately described by models that develop less substructure than predicted by the turbulent fragmentation scenario, such as Bonnor-Ebert spheres. We outline future work necessary to distinguish between these two possibilities.

  1. Discovery of calcite in the solar type protostar NGC 1333-IRAS 4

    NASA Astrophysics Data System (ADS)

    Ceccarelli, C.; Caux, E.; Tielens, A. G. G. M.; Kemper, F.; Waters, L. B. F. M.; Phillips, T.

    2002-11-01

    We present observations, obtained with ISO-LWS, of the continuum between 50-200 mu m of the solar type protostar IRAS 4, in the NGC 1333 complex. The continuum presents an excess, around 95 mu m, that we demonstrate must be a dust feature. We compared the 95 mu m excess with the calcite feature at 92 mu m and find that it fits the observations reasonably well. There may be a further contribution from hydrous silicates at ~ 100 mu m, but this seems a less robust result. The detected calcite mass is ~ 8 x 10-5 Msun and represents about 1% of the warm ( ~ 23 K) dust mass surrounding IRAS 4. This is only the second observation indicating the presence of carbonates outside the solar system, and the first revealing calcite in a young protostar. It is remarkable and intriguing that in all the objects where calcite has been detected so far, namely meteorites, planetary nebulae and IRAS 4, it represents from 0.3 to 1% of the dust mass. This new detection of calcite strengthens the claim by Kemper et al. (2002a) that calcite formation does not necessarely requires liquid water. We suggest that calcite forms at the surface of the grains, where water ice layers may locally have an enhanced mobility caused by heating due to hard X-rays emitted by the central object.

  2. SIEMENS ADVANCED QUANTRA FTICR MASS SPECTROMETER FOR ULTRA HIGH RESOLUTION AT LOW MASS

    SciTech Connect

    Spencer, W; Laura Tovo, L

    2008-07-08

    The Siemens Advanced Quantra Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometer was evaluated as an alternative instrument to large double focusing mass spectrometers for gas analysis. High resolution mass spectrometers capable of resolving the common mass isomers of the hydrogen isotopes are used to provide data for accurate loading of reservoirs and to monitor separation of tritium, deuterium, and helium. Conventional double focusing magnetic sector instruments have a resolution that is limited to about 5000. The Siemens FTICR instrument achieves resolution beyond 400,000 and could possibly resolve the tritium ion from the helium-3 ion, which differ by the weight of an electron, 0.00549 amu. Working with Y-12 and LANL, SRNL requested Siemens to modify their commercial Quantra system for low mass analysis. To achieve the required performance, Siemens had to increase the available waveform operating frequency from 5 MHz to 40 MHz and completely redesign the control electronics and software. However, they were able to use the previous ion trap, magnet, passive pump, and piezo-electric pulsed inlet valve design. NNSA invested $1M in this project and acquired four systems, two for Y-12 and one each for SRNL and LANL. Siemens claimed a $10M investment in the Quantra systems. The new Siemens Advanced Quantra demonstrated phenomenal resolution in the low mass range. Resolution greater than 400,000 was achieved for mass 2. The new spectrometer had a useful working mass range to 500 Daltons. However, experiments found that a continuous single scan from low mass to high was not possible. Two useful working ranges were established covering masses 1 to 6 and masses 12 to 500 for our studies. A compromise performance condition enabled masses 1 to 45 to be surveyed. The instrument was found to have a dynamic range of about three orders of magnitude and quantitative analysis is expected to be limited to around 5 percent without using complex fitting algorithms

  3. FIRST SCIENCE OBSERVATIONS WITH SOFIA/FORCAST: PROPERTIES OF INTERMEDIATE-LUMINOSITY PROTOSTARS AND CIRCUMSTELLAR DISKS IN OMC-2

    SciTech Connect

    Adams, Joseph D.; Herter, Terry L.; Gull, George E.; Henderson, Charles P.; Schoenwald, Justin; Stacey, Gordon; Osorio, Mayra; Macias, Enrique; Thomas Megeath, S.; Fischer, William J.; Ali, Babar; D'Alessio, Paola; De Buizer, James M.; Shuping, Ralph Y.; Keller, Luke D.; Morris, Mark R.; Remming, Ian S.; Stanke, Thomas; Stutz, Amelia; and others

    2012-04-20

    We examine eight young stellar objects in the OMC-2 star-forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, Two Micron All Sky Survey, Atacama Pathfinder Experiment, and other results in the literature. We show the spectral energy distributions (SED) of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modeled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 Multiplication-Sign 0.25 pc region; these sources have luminosities ranging from 300 L{sub Sun} to 20 L{sub Sun }. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of {approx}50 L{sub Sun} and mass infall rate of {approx}10{sup -4} M{sub Sun} yr{sup -1}.

  4. SUBARCSECOND ANALYSIS OF THE INFALLING–ROTATING ENVELOPE AROUND THE CLASS I PROTOSTAR IRAS 04365+2535

    SciTech Connect

    Sakai, Nami; Oya, Yoko; López-Sepulcre, Ana; Watanabe, Yoshimasa; Yamamoto, Satoshi; Sakai, Takeshi; Hirota, Tomoya; Aikawa, Yuri; Ceccarelli, Cecilia; Lefloch, Bertrand; Kahane, Claudine; Caux, Emmanuel; Vastel, Charlotte

    2016-04-01

    Subarcsecond images of the rotational line emission of CS and SO have been obtained toward the Class I protostar IRAS 04365+2535 in TMC-1A with ALMA. A compact component around the protostar is clearly detected in the CS and SO emission. The velocity structure of the compact component of CS reveals infalling–rotating motion conserving the angular momentum. It is well explained by a ballistic model of an infalling–rotating envelope with the radius of the centrifugal barrier (one-half of the centrifugal radius) of 50 au, although the distribution of the infalling gas is asymmetric around the protostar. The distribution of SO is mostly concentrated around the radius of the centrifugal barrier of the simple model. Thus, a drastic change in chemical composition of the gas infalling onto the protostar is found to occur at a 50 au scale probably due to accretion shocks, demonstrating that the infalling material is significantly processed before being delivered into the disk.

  5. MEASUREMENT OF HDCO/H{sub 2}CO RATIOS IN THE ENVELOPES OF EXTREMELY COLD PROTOSTARS IN ORION

    SciTech Connect

    Kang, Miju; Choi, Minho; Stutz, Amelia M.; Tatematsu, Ken’ichi

    2015-11-20

    We present observations of HDCO and H{sub 2}CO emission toward a sample of 15 Class 0 protostars in the Orion A and B clouds. Of these, 11 protostars are Herschel-identified PACS Bright Red Sources (PBRSs) and 4 are previously identified protostars. Our observations revealed the chemical properties of the PBRS envelope for the first time. The column densities of HDCO and H{sub 2}CO are derived from single-dish observations at an angular resolution of ∼20″ (∼8400 AU). The degree of deuteration in H{sub 2}CO ([HDCO]/[H{sub 2}CO]) was estimated to range from 0.03 to 0.31. The deuterium fractionation of most PBRSs (70%) is similar to that of the non-PBRS sources. Three PBRSs (30%) exhibit high deuterium fractionation, larger than 0.15. The large variation of the deuterium fractionation of H{sub 2}CO in the whole PBRS sample may reflect the diversity in the initial conditions of star-forming cores. There is no clear correlation between the [HDCO]/[H{sub 2}CO] ratio and the evolutionary sequence of protostars.

  6. VizieR Online Data Catalog: H2O + CH3OH maser survey of Orion protostar

    NASA Astrophysics Data System (ADS)

    Kang, M.; Lee, J.-E.; Choi, M.; Choi, Y.; Kim, K.-T.; di Francesco, J.; Park, Y.-S.

    2015-04-01

    Out of the protostars listed in the Herschel Orion Protostar Survey (HOPS) catalogue (Fischer et al. 2010A&A...518L.122F; Stutz et al. 2013, J/ApJ/767/36), we selected protostars showing line wings in the CO(J=2->1) line spectra obtained with the Seoul Radio Astronomy Observatory 6m telescope. In the Orion molecular cloud complex 99 protostars were observed using the KVN 21m radio antennas in the single-dish telescope mode during the 2010 Mar-2010 Jun and 2011-2012 observing seasons. The observations were carried out with the KVN Yonsei telescope at Seoul, the KVN Ulsan telescope at Ulsan, and the KVN Tamna telescope at Seogwipo, Korea. The target lines were the H2O(616->523) (22.23508GHz) line and the CH3OH (70->61 A+), (80->71A+), and (6-1->50E) lines at 44.06943, 95.169516, and 132.890800GHz, respectively. (6 data files).

  7. The Herschel Orion Protostar Survey: Correcting for Inclination in BLT Diagrams and Reassessing the Class 0 Lifetime

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Megeath, S.; Stutz, A. M.; Tobin, J. J.; Ali, B.; Stanke, T.; Osorio, M.; Furlan, E.; HOPS Team

    2013-01-01

    We describe recent results from the Herschel Orion Protostar Survey (HOPS), a multiwavelength study of Spitzer-identified protostars in the Orion Molecular Cloud complex. Over 300 protostars in the Orion A and B molecular clouds, the largest star-forming region in the nearest 500 pc, have been observed with 70 μm and 160 μm Herschel/PACS imaging and spectroscopy and with near-IR, mid-IR, and submillimeter imaging and spectroscopy. Using a custom grid of radiative transfer models, we have fit the resulting spectral energy distributions of the sources to estimate their fundamental properties, including infall rate, luminosity, and outflow cavity angle. We also use the model fits to correct the bolometric luminosities and temperatures (BLT properties) of the sources for the effects of foreground extinction and inclination. After the inclination correction, we find that many of the putative young Class 0 sources seem to be highly inclined, more evolved Class I sources. Furthermore, we have discovered a class of protostars previously unidentified by Spitzer that may be young or highly inclined Class 0 sources. We re-evaluate the Class 0 lifetime in light of these new results.

  8. The L723 Low-Mass Star Forming Protostellar System: Resolving a Double Core

    NASA Astrophysics Data System (ADS)

    Girart, J. M.; Rao, R.; Estalella, R.

    2009-03-01

    We present 1.35 mm Submillimeter Array (SMA) observations around the low-mass Class 0 source IRAS 19156+1906, at the center of the LDN 723 (L723) dark cloud. We detected emission from dust as well as emission from H2CO 30,3-20,2, DCN 3-2, and CN 2-1 lines, which arise from two cores, SMA 1 and SMA 2, separated by 2farcs9 (880 AU in projected distance). SMA 2 is associated with the previously detected source VLA 2. Weak SiO 5-4 emission is detected, possibly tracing a region of interaction between the dense envelope and the outflow. We modeled the dust and H2CO emission from the two cores. The results from the modeling show that the cores have similar physical properties (density and temperature distribution) but that SMA 2 has a larger p-H2CO abundance (by a factor of 3-10) than SMA 1. The p-H2CO abundances' findings are compatible with the value of the outer part of the circumstellar envelopes associated with Class 0 sources. SMA 2 is harboring an active multiple low-mass protostellar system and powering at least one molecular outflow. In contrast, there are no known signs of outflow activity toward SMA 1. This suggests that SMA 2 is more evolved than SMA 1. The kinematics of the two sources show marginal evidence of infall and rotation motions. The mass detected by the SMA observation, which trace scales of lsim1000 AU, is only a small fraction of the mass contained in the large-scale molecular envelope, which suggests that L723 is still in a very early phase of star formation. Despite the apparent quiescent nature of the L723, fragmentation is occurring at the center of the cloud at different scales. Thus, at sime1000 AU, the cloud has fragmented in two cores: SMA 1 and SMA 2. At the same time, at least one of these cores, SMA 2, has undergone additional fragmentation at scales of sime150 AU, forming a multiple stellar system.

  9. Nova Scorpii and Coalescing Low-Mass Black Hole Binaries as LIGO Sources

    NASA Astrophysics Data System (ADS)

    Sipior, Michael S.; Sigurdsson, Steinn

    2002-06-01

    Double neutron star (NS-NS) binaries, analogous to the well-known Hulse-Taylor pulsar PSR 1913+16 (documented by Hulse & Taylor in 1974), are guaranteed-to-exist sources of high-frequency gravitational radiation detectable by LIGO. There is considerable uncertainty in the estimated rate of coalescence of such systems (see the work of Phinney in 1991, Narayan and coworkers in 1991, and Kalogera and coworkers in 2001), with conservative estimates of ~1 per 106 yr per galaxy, and optimistic theoretical estimates 1 or more mag larger. Formation rates of low-mass black hole (BH)-neutron star binaries may be higher than those of NS-NS binaries and may dominate the detectable LIGO signal rate. Rate estimates for such binaries are plagued by severe model uncertainties. Recent estimates by Portegies Zwart & Yungelson in 1998 and De Donder & Vanbeveren in 1998 suggest that BH-BH binaries do not coalesce at significant rates despite being formed at high rates. We estimate the enhanced coalescence rate for BH-BH binaries due to weak asymmetric kicks during the formation of low-mass black holes like Nova Sco (see the work of Brandt, Podsiadlowski, & Sigurdsson in 1995) and find they may contribute significantly to the LIGO signal rate, possibly dominating the phase I detectable signals if the range of black hole masses for which there is significant kick is broad enough. For a standard Salpeter initial mass function, assuming mild natal kicks, we project that the R6 merger rate (the rate of mergers per 106 yr in a Milky Way-like galaxy) of BH-BH systems is ~0.5, smaller than that of NS-NS systems. However, the higher chirp mass of these systems produces a signal nearly 4 times greater, on average, with a commensurate increase in search volume, hence, our claim that BH-BH mergers (and, to a lesser extent, BH-NS coalescence) should comprise a significant fraction of the signal seen by LIGO. The BH-BH coalescence channel considered here also predicts that a substantial fraction of

  10. ASAS J083241+2332.4: A NEW EXTREME LOW MASS RATIO OVERCONTACT BINARY SYSTEM

    SciTech Connect

    Sriram, K.; Malu, S.; Vivekananda Rao, P.; Choi, C. S.

    2016-03-15

    We present the R- and V-band CCD photometry and Hα line studies of an overcontact binary ASAS J083241+2332.4. The light curves exhibit totality along with a trace of the O’Connell effect. The photometric solution indicates that this system falls into the category of extreme low-mass ratio overcontact binaries with a mass ratio, q ∼ 0.06. Although a trace of the O’ Connell effect is observed, constancy of the Hα line along various phases suggest that a relatively higher magnetic activity is needed for it to show a prominent fill-in effect. The study of O–C variations reveals that the period of the binary shows a secular increase at the rate of dP/dt ∼ 0.0765 s years{sup −1}, which is superimposed by a low, but significant, sinusoidal modulation with a period of ∼8.25 years. Assuming that the sinusoidal variation is due to the presence of a third body, orbital elements have been derived. There exist three other similar systems, SX Crv, V857 Her, and E53, which have extremely low mass ratios and we conclude that ASAS J083241+2332.4 resembles SX Crv in many respects. Theoretical studies indicate that at a critical mass ratio range, q{sub critical} = 0.07–0.09, overcontact binaries should merge and form a fast rotating star, but it has been suggested that q{sub critical} can continue to fall up to 0.05 depending on the primary's mass and structure. Moreover, the obtained fill-out factors (50%–70%) indicate that mass loss is considerable and hydrodynamical simulations advocate that mass loss from L{sub 2} is mandatory for a successful merging process. Comprehensively, the results indicate that ASAS J083241+2332.4 is at a stage of merger. The pivotal role played by the subtle nature of the derived mass ratio in forming a rapidly rotating star has been discussed.

  11. Direct imaging search for planets around low-mass stars and spectroscopic characterization of young exoplanets

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan Peter

    Low--mass stars between 0.1--0.6 M⊙ are the most abundant members our galaxy and may be the most common sites of planet formation, but little is known about the outer architecture of their planetary systems. We have carried out a high-contrast adaptive imaging search for gas giant planets between 1--13 MJup around 122 newly identified young M dwarfs in the solar neighborhood ( ≲ 35 pc). Half of our targets are younger than 145 Myr, and 90% are younger than 580 Myr. After removing 39 resolved stellar binaries, our homogeneous sample of 83 single young M dwarfs makes it the largest imaging search for planets around low--mass stars to date. Our H- and K- band coronagraphic observations with Subaru/HiCIAO and Keck/NIRC2 achieve typical contrasts of 9--13 mag and 12--14 mag at 100, respectively, which corresponds to limiting masses of ˜1--10 M Jup at 10--30 AU for most of our sample. We discovered four brown dwarfs with masses between 25--60 MJup at projected separations of 4--190 AU. Over 100 candidate planets were discovered, nearly all of which were found to be background stars from follow-up second epoch imaging. Our null detection of planets nevertheless provides strong statistical constraints on the occurrence rate of giant planets around M dwarfs. Assuming circular orbits and a logarithmically-flat power law distribution in planet mass and semi--major axis of the form d 2N=(dloga dlogm) infinity m0 a0, we measure an upper limit (at the 95% confidence level) of 8.8% and 12.6% for 1--13 MJup companions between 10--100 AU for hot start and cold start evolutionary models, respectively. For massive gas giant planets in the 5--13 M Jup range like those orbiting HR 8799, GJ 504, and beta Pictoris, we find that fewer than 5.3% (7.8%) of M dwarfs harbor these planets between 10--100 AU for a hot start (cold start) formation scenario. Our best constraints are for brown dwarf companions; the frequency of 13--75 MJup companions between (de--projected) physical

  12. The Metallicity Evolution of Low-mass Galaxies: New Constraints at Intermediate Redshift

    NASA Astrophysics Data System (ADS)

    Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

    2013-06-01

    We present abundance measurements from 26 emission-line-selected galaxies at z ~ 0.6-0.7. By reaching stellar masses as low as 108 M ⊙, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 109 M ⊙. For the portion of our sample above M > 109 M ⊙ (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M * relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation. We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption. 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

  13. Low mass binary neutron star mergers: Gravitational waves and neutrino emission

    NASA Astrophysics Data System (ADS)

    Foucart, Francois; Haas, Roland; Duez, Matthew D.; O'Connor, Evan; Ott, Christian D.; Roberts, Luke; Kidder, Lawrence E.; Lippuner, Jonas; Pfeiffer, Harald P.; Scheel, Mark A.

    2016-02-01

    Neutron star mergers are among the most promising sources of gravitational waves for advanced ground-based detectors. These mergers are also expected to power bright electromagnetic signals, in the form of short gamma-ray bursts, infrared/optical transients powered by r-process nucleosynthesis in neutron-rich material ejected by the merger, and radio emission from the interaction of that ejecta with the interstellar medium. Simulations of these mergers with fully general relativistic codes are critical to understand the merger and postmerger gravitational wave signals and their neutrinos and electromagnetic counterparts. In this paper, we employ the Spectral Einstein Code to simulate the merger of low mass neutron star binaries (two 1.2 M⊙ neutron stars) for a set of three nuclear-theory-based, finite temperature equations of state. We show that the frequency peaks of the postmerger gravitational wave signal are in good agreement with predictions obtained from recent simulations using a simpler treatment of gravity. We find, however, that only the fundamental mode of the remnant is excited for long periods of time: emission at the secondary peaks is damped on a millisecond time scale in the simulated binaries. For such low mass systems, the remnant is a massive neutron star which, depending on the equation of state, is either permanently stable or long lived (i.e. rapid uniform rotation is sufficient to prevent its collapse). We observe strong excitations of l =2 , m =2 modes, both in the massive neutron star and in the form of hot, shocked tidal arms in the surrounding accretion torus. We estimate the neutrino emission of the remnant using a neutrino leakage scheme and, in one case, compare these results with a gray two-moment neutrino transport scheme. We confirm the complex geometry of the neutrino emission, also observed in previous simulations with neutrino leakage, and show explicitly the presence of important differences in the neutrino luminosity, disk

  14. Low Mass Blood Peptides Discriminative of Inflammatory Bowel Disease (IBD) Severity: A Quantitative Proteomic Perspective*

    PubMed Central

    Yau, Yunki; Duo, Xizi; Zeng, Ming; Campbell, Beth; Shin, Sean; Luber, Raphael; Redmond, Diane; Leong, Rupert W. L.

    2016-01-01

    Breakdown of the protective gut barrier releases effector molecules and degradation products into the blood stream making serum and plasma ideal as a diagnostic medium. The enriched low mass proteome is unexplored as a source of differentiators for diagnosing and monitoring inflammatory bowel disease (IBD) activity, that is less invasive than colonoscopy. Differences in the enriched low mass plasma proteome (<25 kDa) were assessed by label-free quantitative mass-spectrometry. A panel of marker candidates were progressed to validation phase and “Tier-2” FDA-level validated quantitative assay. Proteins important in maintaining gut barrier function and homeostasis at the epithelial interface have been quantitated by multiple reaction monitoring in plasma and serum including both inflammatory; rheumatoid arthritis controls, and non-inflammatory healthy controls; ulcerative colitis (UC), and Crohn's disease (CD) patients. Detection by immunoblot confirmed presence at the protein level in plasma. Correlation analysis and receiver operator characteristics were used to report the sensitivity and specificity. Peptides differentiating controls from IBD originate from secreted phosphoprotein 24 (SPP24, p = 0.000086, 0.009); whereas those in remission and healthy can be differentiated in UC by SPP24 (p = 0.00023, 0.001), α-1-microglobulin (AMBP, p = 0.006) and CD by SPP24 (p = 0.019, 0.05). UC and CD can be differentiated by Guanylin (GUC2A, p = 0.001), and Secretogranin-1 (CHGB p = 0.035). Active and quiescent disease can also be differentiated in UC and CD by CHGB (p ≤ 0.023) SPP24 (p ≤ 0.023) and AMBP (UC p = 0.046). Five peptides discriminating IBD activity and severity had very little-to-no correlation to erythrocyte sedimentation rate, C-reactive protein, white cell or platelet counts. Three of these peptides were found to be binding partners to SPP24 protein alongside other known matrix proteins. These proteins have the potential to improve diagnosis and

  15. Low Mass Blood Peptides Discriminative of Inflammatory Bowel Disease (IBD) Severity: A Quantitative Proteomic Perspective.

    PubMed

    Wasinger, Valerie C; Yau, Yunki; Duo, Xizi; Zeng, Ming; Campbell, Beth; Shin, Sean; Luber, Raphael; Redmond, Diane; Leong, Rupert W L

    2016-01-01

    Breakdown of the protective gut barrier releases effector molecules and degradation products into the blood stream making serum and plasma ideal as a diagnostic medium. The enriched low mass proteome is unexplored as a source of differentiators for diagnosing and monitoring inflammatory bowel disease (IBD) activity, that is less invasive than colonoscopy. Differences in the enriched low mass plasma proteome (<25 kDa) were assessed by label-free quantitative mass-spectrometry. A panel of marker candidates were progressed to validation phase and "Tier-2" FDA-level validated quantitative assay. Proteins important in maintaining gut barrier function and homeostasis at the epithelial interface have been quantitated by multiple reaction monitoring in plasma and serum including both inflammatory; rheumatoid arthritis controls, and non-inflammatory healthy controls; ulcerative colitis (UC), and Crohn's disease (CD) patients. Detection by immunoblot confirmed presence at the protein level in plasma. Correlation analysis and receiver operator characteristics were used to report the sensitivity and specificity. Peptides differentiating controls from IBD originate from secreted phosphoprotein 24 (SPP24, p = 0.000086, 0.009); whereas those in remission and healthy can be differentiated in UC by SPP24 (p = 0.00023, 0.001), α-1-microglobulin (AMBP, p = 0.006) and CD by SPP24 (p = 0.019, 0.05). UC and CD can be differentiated by Guanylin (GUC2A, p = 0.001), and Secretogranin-1 (CHGB p = 0.035). Active and quiescent disease can also be differentiated in UC and CD by CHGB (p ≤ 0.023) SPP24 (p ≤ 0.023) and AMBP (UC p = 0.046). Five peptides discriminating IBD activity and severity had very little-to-no correlation to erythrocyte sedimentation rate, C-reactive protein, white cell or platelet counts. Three of these peptides were found to be binding partners to SPP24 protein alongside other known matrix proteins. These proteins have the potential to improve diagnosis and evaluate

  16. A HERSCHEL SURVEY OF COLD DUST IN DISKS AROUND BROWN DWARFS AND LOW-MASS STARS

    SciTech Connect

    Harvey, Paul M.; Evans, Neal J. II; Henning, Thomas; Liu Yao; Wolf, Sebastian; Menard, Francois; Pinte, Christophe; Pascucci, Ilaria E-mail: nje@astro.as.utexas.edu E-mail: wolf@astrophysik.uni-kiel.de E-mail: yliu@pmo.ac.cn E-mail: christophe.pinte@obs.ujf-grenoble.fr E-mail: pascucci@lpl.arizona.edu

    2012-08-10

    We report the complete photometric results from our Herschel study which is the first comprehensive program to search for far-infrared emission from cold dust around young brown dwarfs (BDs). We surveyed 50 fields containing 51 known or suspected BDs and very low mass stars that have evidence of circumstellar disks based on Spitzer photometry and/or spectroscopy. The objects with known spectral types range from M3 to M9.5. Four of the candidates were subsequently identified as extragalactic objects. Of the remaining 47 we have successfully detected 36 at 70 {mu}m and 14 at 160 {mu}m with signal-to-noise ratio (S/N) greater than 3, as well as several additional possible detections with low S/N. The objects exhibit a range of [24]-[70] {mu}m colors suggesting a range in mass and/or structure of the outer disk. We present modeling of the spectral energy distributions of the sample and discuss trends visible in the data. Using two Monte Carlo radiative transfer codes we investigate disk masses and geometry. We find a very wide range in modeled total disk masses from less than 10{sup -6} M{sub Sun} up to 10{sup -3} M{sub Sun} with a median disk mass of the order of 3 Multiplication-Sign 10{sup -5} M{sub Sun }, suggesting that the median ratio of disk mass to central object mass may be lower than for T Tauri stars. The disk scale heights and flaring angles, however, cover a range consistent with those seen around T Tauri stars. The host clouds in which the young BDs and low-mass stars are located span a range in estimated age from {approx}1-3 Myr to {approx}10 Myr and represent a variety of star-forming environments. No obvious dependence on cloud location or age is seen in the disk properties, though the statistical significance of this conclusion is not strong.

  17. Characterizing Low-Mass Planets in Kepler's Multi-Planet Systems with Transit Timing

    NASA Astrophysics Data System (ADS)

    Jontof-Hutter, Daniel; Lissauer, Jack; Rowe, Jason; Fabrycky, Daniel

    2014-11-01

    The Kepler mission has revealed an abundance of planets in a regime of mass and size that is absent from the Solar System. This includes systems of high multiplicity within 1 AU, where low-mass volatile-rich planets have been observed in compact orbital configurations. Smaller, rocky planets have also been observed in such systems. The existing sample of characterized planets on the mass-radius diagram shows no abrupt transition from rocky planets to those that must be volatile-rich, but characteristic trends are beginning to emerge. More precise characterizations of planets by mass, radius, and incident flux will aid in revealing fundamental properties of a common class of exoplanets. There is a small sample of exoplanets with known masses and radii, mostly hot jupiters whose radii are known from transit depths, and whose masses are determined from radial velocity spectroscopy (RV). In the absence of mass determinations via RV observations, transit timing variations (TTVs) offer a chance to probe perturbations between planets that pass close to one another or are near resonance, and hence dynamical fits to observed transit times can be used to measure planetary masses and orbital parameters. Such modelling with Kepler data probes planetary masses over orbital periods ranging from ~5-100 days, complementing the sample of RV detections. Furthermore, in select cases, dynamical fits to observed TTVs can tightly constrain the orbital eccentricity vectors, which can, alongside the transit light curve, tightly constrain the density and radius of the host star, and hence reduce the uncertainty on planetary radius. TTV studies have revealed a class of low-mass low-density objects with a substantial mass fraction in the form of a voluminous H-rich atmosphere. To these we add precise mass measurements of the outer planets of Kepler-33, a compact system with five known transiting planets, three of which show detectable transit timing variations. These results will be placed

  18. Ambipolar diffusion in low-mass star formation. I. General comparison with the ideal magnetohydrodynamic case

    NASA Astrophysics Data System (ADS)

    Masson, J.; Chabrier, G.; Hennebelle, P.; Vaytet, N.; Commerçon, B.

    2016-03-01

    results for a given magnetisation, showing that the physical dissipation processes truly dominate numerical diffusion. We demonstrate severe limits of the ideal MHD formalism; it yields unphysical behaviours in the long-term evolution of the system. This includes counter-rotation inside the outflow or magnetic tower, interchange instabilities, and flux redistribution triggered by numerical diffusion. These effects are not observed in non-ideal MHD. Disks with Keplerian velocity profiles are found to form around the protostar in all our non-ideal MHD simulations, with a final mass and size that strongly depend on the initial magnetisation. This ranges from a few 10-2M⊙ and ~20-30 au for the most magnetised case (μ = 2) to ~2 × 10-1M⊙ and ~40-80 au for a lower magnetisation (μ = 5). In all cases, these disks remain significantly smaller than disks found in pure hydrodynamical simulations. Ambipolar diffusion thus bears a crucial impact on the regulation of magnetic flux and angular momentum transport during the collapse of a prestellar core and the formation of the resulting protostellar core-disk system, enabling the formation and growth of rotationally supported structures.

  19. Characterizing the Youngest Herschel-detected Protostars. II. Molecular Outflows from the Millimeter and the Far-infrared

    NASA Astrophysics Data System (ADS)

    Tobin, John J.; Stutz, Amelia M.; Manoj, P.; Megeath, S. Thomas; Karska, Agata; Nagy, Zsofia; Wyrowski, Friedrich; Fischer, William J.; Watson, Dan M.; Stanke, Thomas

    2016-11-01

    We present Combined Array for Research in Millimeter-wave Astronomy (CARMA) CO (J=1\\to 0) observations and Herschel PACS spectroscopy, characterizing the outflow properties toward extremely young and deeply embedded protostars in the Orion molecular clouds. The sample comprises a subset of the Orion protostars known as the PACS Bright Red Sources (PBRS; Stutz et al.). We observed 14 PBRS with CARMA and 8 of these 14 with Herschel, acquiring full spectral scans from 55 to 200 μm. Outflows are detected in CO (J=1\\to 0) from 8 of 14 PBRS, with two additional tentative detections; outflows are also detected from the outbursting protostar HOPS 223 (V2775 Ori) and the Class I protostar HOPS 68. The outflows have a range of morphologies; some are spatially compact, <10,000 au in extent, while others extend beyond the primary beam. The outflow velocities and morphologies are consistent with being dominated by intermediate inclination angles (80° ≥ i ≥ 20°). This confirms the interpretation of the very red 24-70 μm colors of the PBRS as a signpost of high envelope densities, with only one (possibly two) cases of the red colors resulting from edge-on inclinations. We detect high-J (J up > 13) CO lines and/or H2O lines from 5 of 8 PBRS and only for those with detected CO outflows. The far-infrared CO rotation temperatures of the detected PBRS are marginally colder (˜230 K) than those observed for most protostars (˜300 K), and only one of these five PBRS has detected [O i] 63 μm emission. The high envelope densities could be obscuring some [O i] emission and cause a ˜20 K reduction to the CO rotation temperatures. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  20. Constraints on low-mass WIMPs from the EDELWEISS-III dark matter search

    NASA Astrophysics Data System (ADS)

    Armengaud, E.; Arnaud, Q.; Augier, C.; Benoît, A.; Benoît, A.; Bergé, L.; Bergmann, T.; Billard, J.; Blümer, J.; de Boissière, T.; Bres, G.; Broniatowski, A.; Brudanin, V.; Camus, P.; Cazes, A.; Chapellier, M.; Charlieux, F.; Dumoulin, L.; Eitel, K.; Filosofov, D.; Foerster, N.; Fourches, N.; Garde, G.; Gascon, J.; Gerbier, G.; Giuliani, A.; Grollier, M.; Gros, M.; Hehn, L.; Hervé, S.; Heuermann, G.; Humbert, V.; De Jésus, M.; Jin, Y.; Jokisch, S.; Juillard, A.; Kéfélian, C.; Kleifges, M.; Kozlov, V.; Kraus, H.; Kudryavtsev, V. A.; Le-Sueur, H.; Lin, J.; Mancuso, M.; Marnieros, S.; Menshikov, A.; Navick, X.-F.; Nones, C.; Olivieri, E.; Pari, P.; Paul, B.; Piro, M.-C.; Poda, D. V.; Queguiner, E.; Robinson, M.; Rodenas, H.; Rozov, S.; Sanglard, V.; Schmidt, B.; Scorza, S.; Siebenborn, B.; Tcherniakhovski, D.; Vagneron, L.; Weber, M.; Yakushev, E.; Zhang, X.

    2016-05-01

    We present the results of a search for elastic scattering from galactic dark matter in the form of Weakly Interacting Massive Particles (WIMPs) in the 4-30 GeV/c2 mass range. We make use of a 582 kg-day fiducial exposure from an array of 800 g Germanium bolometers equipped with a set of interleaved electrodes with full surface coverage. We searched specifically for ~ 2.5-20 keV nuclear recoils inside the detector fiducial volume. As an illustration the number of observed events in the search for 5 (resp. 20) GeV/c2 WIMPs are 9 (resp. 4), compared to an expected background of 6.1 (resp. 1.4). A 90% CL limit of 4.3 × 10-40 cm2 (resp. 9.4 × 10-44 cm2) is set on the spin-independent WIMP-nucleon scattering cross-section for 5 (resp. 20) GeV/c2 WIMPs. This result represents a 41-fold improvement with respect to the previous EDELWEISS-II low-mass WIMP search for 7 GeV/c2 WIMPs. The derived constraint is in tension with hints of WIMP signals from some recent experiments, thus confirming results obtained with different detection techniques.

  1. LOW-MASS AGNs AND THEIR RELATION TO THE FUNDAMENTAL PLANE OF BLACK HOLE ACCRETION

    SciTech Connect

    Gültekin, Kayhan; King, Ashley L.; Miller, Jon M.; Cackett, Edward M.; Pinkney, Jason

    2014-06-20

    We put active galactic nuclei (AGNs) with low-mass black holes on the fundamental plane of black hole accretion—the plane that relates X-ray emission, radio emission, and mass of an accreting black hole—to test whether or not the relation is universal for both stellar-mass and supermassive black holes. We use new Chandra X-ray and Very Large Array radio observations of a sample of black holes with masses less than 10{sup 6.3} M {sub ☉}, which have the best leverage for determining whether supermassive black holes and stellar-mass black holes belong on the same plane. Our results suggest that the two different classes of black holes both belong on the same relation. These results allow us to conclude that the fundamental plane is suitable for use in estimating supermassive black hole masses smaller than ∼10{sup 7} M {sub ☉}, in testing for intermediate-mass black holes, and in estimating masses at high accretion rates.

  2. On the existence of low-mass dark matter and its direct detection.

    PubMed

    Bateman, James; McHardy, Ian; Merle, Alexander; Morris, Tim R; Ulbricht, Hendrik

    2015-01-27

    Dark Matter (DM) is an elusive form of matter which has been postulated to explain astronomical observations through its gravitational effects on stars and galaxies, gravitational lensing of light around these, and through its imprint on the Cosmic Microwave Background (CMB). This indirect evidence implies that DM accounts for as much as 84.5% of all matter in our Universe, yet it has so far evaded all attempts at direct detection, leaving such confirmation and the consequent discovery of its nature as one of the biggest challenges in modern physics. Here we present a novel form of low-mass DM χ that would have been missed by all experiments so far. While its large interaction strength might at first seem unlikely, neither constraints from particle physics nor cosmological/astronomical observations are sufficient to rule out this type of DM, and it motivates our proposal for direct detection by optomechanics technology which should soon be within reach, namely, through the precise position measurement of a levitated mesoscopic particle which will be perturbed by elastic collisions with χ particles. We show that a recently proposed nanoparticle matter-wave interferometer, originally conceived for tests of the quantum superposition principle, is sensitive to these collisions, too.

  3. ORBITAL SOLUTIONS FOR TWO YOUNG, LOW-MASS SPECTROSCOPIC BINARIES IN OPHIUCHUS

    SciTech Connect

    Rosero, V.; Prato, L.; Wasserman, L. H.; Rodgers, B. E-mail: lprato@lowell.edu E-mail: brodgers@gemini.edu

    2011-01-15

    We report the orbital parameters for ROXR1 14 and RX J1622.7-2325Nw, two young, low-mass, and double-lined spectroscopic binaries recently discovered in the Ophiuchus star-forming region. Accurate orbital solutions were determined from over a dozen high-resolution spectra taken with the Keck II and Gemini South telescopes. These objects are T Tauri stars with mass ratios close to unity and periods of {approx}5 and {approx}3 days, respectively. In particular, RX J1622.7-2325Nw shows a non-circularized orbit with an eccentricity of 0.30, higher than any other short-period pre-main-sequence (PMS) spectroscopic binary known to date. We speculate that the orbit of RX J1622.7-2325Nw has not yet circularized because of the perturbing action of a {approx}1'' companion, itself a close visual pair. A comparison of known young spectroscopic binaries (SBs) and main-sequence (MS) SBs in the eccentricity-period plane shows an indistinguishable distribution of the two populations, implying that orbital circularization occurs in the first 1 Myr of a star's lifetime. With the results presented in this paper we increase by {approx}4% the small sample of PMS spectroscopic binary stars with known orbital elements.

  4. Testing Low-Mass Stellar Models: Three New Detached Eclipsing Binaries below 0.75Msun

    NASA Astrophysics Data System (ADS)

    López-Morales, M.; Shaw, J. S.

    2007-06-01

    Full tests of stellar models below 1Msun have been hindered until now by the scarce number of precise measurements of the stars' most fundamental parameters: their masses and radii. With current observational techniques, the required precision to distinguish between different models (errors < 2-3 %) can only be achieved using detached eclipsing binaries where 1) both stars are similar in mass, i.e. q = M1/M2 ˜ 1.0, and 2) each star is a main sequence object below 1Msun. Until 2003 only three such binaries had been found and analyzed in detail. Two new systems were published in 2005 (Creevey et al.; López-Morales & Ribas), almost doubling the previous number of data points. Here we present preliminary results for 3 new low-mass detached eclipsing binaries. These are the first studied systems from our sample of 41 new binaries (Shaw & López-Morales, this proceedings). We also provide an updated comparison between the Mass-Radius and the Mass-Teff relations predicted by the models and the observational data from detached eclipsing binaries.

  5. The Kinematics of the Nebular Shells Around Low Mass Progenitors of PNe with Low Metallicity

    NASA Astrophysics Data System (ADS)

    Pereyra, Margarita; López, José Alberto; Richer, Michael G.

    2016-03-01

    We analyze the internal kinematics of 26 planetary nebulae (PNe) with low metallicity that appear to derive from progenitor stars of the lowest masses, including the halo PN population. Based upon spatially resolved, long-slit, echelle spectroscopy drawn from the San Pedro Mártir Kinematic Catalog of PNe, we characterize the kinematics of these PNe measuring their global expansion velocities based upon the largest sample used to date for this purpose. We find kinematics that follow the trends observed and predicted in other studies, but also find that most of the PNe studied here tend to have expansion velocities less than 20 km s-1 in all of the emission lines considered. The low expansion velocities that we observe in this sample of low metallicity PNe with low mass progenitors are most likely a consequence of a weak central star (CS) wind driving the kinematics of the nebular shell. This study complements previous results that link the expansion velocities of the PN shells with the characteristics of the CS. The observations reported herein were acquired at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM), B. C., Mexico.

  6. Thermohaline mixing: a physical mechanism governing the photospheric composition of low-mass giants

    NASA Astrophysics Data System (ADS)

    Charbonnel, C.; Zahn, J.-P.

    2007-05-01

    Aims:Numerous spectroscopic observations provide compelling evidence for a non-canonical mixing process that modifies the surface abundances of Li, C and N of low-mass red giants when they reach the bump in the luminosity function. Eggleton and collaborators have proposed that a molecular weight inversion created by the ^3He(^3He, 2p)^4He reaction may be at the origin of this mixing, and relate it to the Rayleigh-Taylor instability. We argue that one is actually dealing with a double diffusive instability referred to as thermohaline convection and we discuss its influence on the red giant branch. Methods: We compute stellar models of various initial metallicities that include thermohaline mixing, which is treated as a diffusive process based on the prescription given originally by Ulrich for the turbulent diffusivity produced by the thermohaline instability in stellar radiation zones. Results: Thermohaline mixing simultaneously accounts for the observed behaviour of the carbon isotopic ratio and of the abundances of Li, C and N in the upper part of the red giant branch. It significantly reduces the ^3He production with respect to canonical evolution models as required by measurements of ^3He/H in galactic HII regions. Conclusions: Thermohaline mixing is a fundamental physical process that must be included in stellar evolution modeling.

  7. General Relativistic Simulations of Low-Mass Magnetized Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Giacomazzo, Bruno

    2017-01-01

    We will present general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) systems that produce long-lived neutron stars (NSs) after merger. While the standard scenario for short gamma-ray bursts (SGRBs) requires the formation after merger of a spinning black hole surrounded by an accretion disk, other theoretical models, such as the time-reversal scenario, predict the formation of a long-lived magnetar. The formation of a long-lived magnetar could in particular explain the X-ray plateaus that have been observed in some SGRBs. Moreover, observations of NSs with masses of 2 solar masses indicate that the equation of state of NS matter should support masses larger than that. Therefore a significant fraction of BNS mergers will produce long-lived NSs. This has important consequences both on the emission of gravitational wave signals and on their electromagnetic counterparts. We will discuss GRMHD simulations of ``low-mass'' magnetized BNS systems with different equations of state and mass ratios. We will describe the properties of their post-merger remnants and of their gravitational and electromagnetic emission.

  8. Micromachined low-mass RF front-end for beam steering radar

    NASA Astrophysics Data System (ADS)

    Vahidpour, M.; Moallem, M.; East, J.; Sarabandi, K.

    2012-06-01

    Sensors for autonomous small robotic platforms must be low mass, compact size and low power due to the limited space. For such applications, as the dimensions of the structures shrink, standard machining methods are not suitable because of low fabrication tolerances and high cost in assembly. Commonly, the structures show a high degree of fabrication complexity due to error in alignment, air gaps between conductive parts, poor metal contact, inaccuracy in patterning because of non-contact lithography, complex assemblies of various parts, and high number of steps needed for construction. However, micromachining offers high fabrication precision, provides easy fabrication and integration with active devices and hence is suitable for manufacturing high MMW and submillimeter-wave frequency structures. A radar design compatible with micromachining process is developed to fabricate a Y-band high resolution radar structure with a slot-fed patch array antenna. A multi-step silicon DRIE process is developed for the fabrication of the waveguide structure while the slots are suspended on a thin oxide/nitride/oxide membrane to form the top cover of the waveguide trenches and the patch elements are suspended on a thin Parylene membrane. Gold thermocompression bonding and Parylene bonding are used to assemble different parts of the antenna. These processes result in a compact (4.5 cm × 3.5 cm × 1.5 mm) and light-weight (5 g) radar.

  9. Formation of low-mass condensations in molecular cloud cores via thermal instability

    NASA Astrophysics Data System (ADS)

    Nejad-Asghar, Mohsen

    2011-06-01

    Low-mass condensations (LMCs) have been observed within molecular cloud cores. In this study, we investigate the effect of the application of isobaric thermal instability (TI) in forming these LMCs. For this purpose, we first investigate the occurrence of TI in molecular clouds. Then, to study the significance of linear isobaric TI, we use a contracting axisymmetric cylindrical core with an axial magnetic field. Consideration of cooling and heating mechanisms in molecular clouds shows that including the heating due to ambipolar diffusion can lead to the occurrence of TI on a time-scale smaller than the dynamical time-scale. Application of linear perturbation analysis shows that isobaric TI can take place in the outer regions of molecular cloud cores. Furthermore, the results show that perturbations with wavelengths greater than few astronomical units are protected from the destabilization property of thermal conduction, so that they can grow to form LMCs. Thus, the results show that the mechanism of TI can be used to explain the formation of LMCs as the progenitors of collapsing protostellar entities, brown dwarfs or protoplanets.

  10. GJ 3236: A NEW BRIGHT, VERY LOW MASS ECLIPSING BINARY SYSTEM DISCOVERED BY THE MEARTH OBSERVATORY

    SciTech Connect

    Irwin, Jonathan; Charbonneau, David; Berta, Zachory K.; Quinn, Samuel N.; Latham, David W.; Torres, Guillermo; Blake, Cullen H.; Burke, Christopher J.; Esquerdo, Gilbert A.; Fueresz, Gabor; Mink, Douglas J.; Nutzman, Philip; Szentgyorgyi, Andrew H.; Calkins, Michael L.; Falco, Emilio E.; Bloom, Joshua S.; Starr, Dan L.

    2009-08-20

    We report the detection of eclipses in GJ 3236, a bright (I = 11.6), very low mass binary system with an orbital period of 0.77 days. Analysis of light and radial velocity curves of the system yielded component masses of 0.38 {+-} 0.02 M{sub sun} and 0.28 {+-} 0.02 M{sub sun}. The central values for the stellar radii are larger than the theoretical models predict for these masses, in agreement with the results for existing eclipsing binaries, although the present 5% observational uncertainties limit the significance of the larger radii to approximately 1{sigma}. Degeneracies in the light curve models resulting from the unknown configuration of surface spots on the components of GJ 3236 currently dominate the uncertainties in the radii, and could be reduced by obtaining precise, multiband photometry covering the full orbital period. The system appears to be tidally synchronized and shows signs of high activity levels as expected for such a short orbital period, evidenced by strong H{alpha} emission lines in the spectra of both components. These observations probe an important region of mass-radius parameter space around the predicted transition to fully convective stellar interiors, where there are a limited number of precise measurements available in the literature.

  11. Near infrared photometric and optical spectroscopic study of 22 low mass star clusters embedded in nebulae

    NASA Astrophysics Data System (ADS)

    Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

    2008-02-01

    Aims:Among the star clusters in the Galaxy, those embedded in nebulae represent the youngest group, which has only recently been explored. The analysis of a sample of 22 candidate embedded stellar systems in reflection nebulae and/or HII environments is presented. Methods: We employed optical spectroscopic observations of stars in the directions of the clusters carried out at CASLEO (Argentina) together with near infrared photometry from the 2MASS catalogue. Our analysis is based on source surface density, colour-colour diagrams and on theoretical pre-main sequence isochrones. We take into account the field star contamination by carrying out a statistical subtraction. Results: The studied objects have the characteristics of low mass systems. We derive their fundamental parameters. Most of the cluster ages are younger than 2 Myr. The studied embedded stellar systems in reflection nebulae and/or HII region complexes do not have stars of spectral types earlier than B. The total stellar masses locked in the clusters are in the range 20-220 M⊙. They are found to be gravitationally unstable and are expected to dissolve in a timescale of a few Myr. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

  12. Photometric and spectroscopic study of low mass embedded star clusters in reflection nebulae

    NASA Astrophysics Data System (ADS)

    Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

    2005-02-01

    An analysis of the candidate embedded stellar systems in the reflection nebulae vdBH-RN 26, vdBH-RN} 38, vdBH-RN} 53a, GGD 20, ESO 95-RN 18 and NGC 6595 is presented. Optical spectroscopic data from CASLEO (Argentina) in conjunction with near infrared photometry from the 2MASS Point Source Catalogue were employed. The analysis is based on source surface density, colour-colour and colour-magnitude diagrams together with theoretical pre-main sequence isochrones. We take into account the field population affecting the analysis by carrying out a statistical subtraction. The fundamental parameters for the stellar systems were derived. The resulting ages are in the range 1-4 Myr and the objects are dominated by pre-main sequence stars. The observed masses locked in the clusters are less than 25 M⊙. The studied systems have no stars of spectral types earlier than B, indicating that star clusters do not necessarily evolve through an HII region phase. The relatively small locked mass combined with the fact that they are not numerous in catalogues suggests that these low mass clusters are not important donors of stars to the field populations. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

  13. Effects of non-standard neutrino emission on the evolution of low-mass stars

    NASA Astrophysics Data System (ADS)

    Arceo-Díaz, S.; Schröder, K.-P.; Jack, D.; Zuber, K.

    2014-10-01

    Using the {Pools et al. (1995)} version of the STARS code with updated numerical tables for neutrino plasmon decay ({Kantor et al. 2007}), along with the reinterpretation of the Reimers mass-loss prescription by {Schröder et al. (2005)}, we analyze the consequences of enhanced neutrino emission on the internal structure and late evolution of the degenerated cores in low-mass stars, the non-standard increase in tip-RGB luminosity and the impact on the calibration of the Reimers mass-loss mechanism and the changes driven in post-RGB phases. With synthetic spectra generated with the PHOENIX code {Baron & Hauschildt et al. (1997)}, we also study the dependence of the non-standard increase in brightness on the selected NIR photometric band. By comparing our stellar evolutionary models with the synthetic spectra and the photometric data base of ω-Cen by {Sollima et al. (2004)}, we find the limit value μ_{ν}≤ 2.2× 10^{-12}μ_{B}.

  14. Shapiro Delay in the Low Mass Binary Millisecond Pulsar J1713+0747

    NASA Astrophysics Data System (ADS)

    Camilo, F.; Foster, R. S.; Wolszczan, A.

    1993-12-01

    The binary millisecond pulsar J1713+0747 (P=4.57 ms;P_b=67.8 d) was discovered in a systematic continuing survey for millisecond pulsars with the Arecibo radio telescope (Foster, Wolszczan & Camilo 1993, ApJ, 410, L91). We have carried out multi-frequency observations of this object at approximately bi-weekly intervals. With an rms residual in the predicted vs. observed times-of-arrival (TOAs) of <0.5 mu sec, and a large characteristic age, tau_c ~ 10(10) yr, this object is one of the most precise celestial clocks among all known pulsars. We detect a signature in the TOA residuals which is most naturally interpreted in terms of a general relativistic ``Shapiro Delay'', caused as the pulsar signals traverse the gravitational potential well of its ~ 0.2 M_sun companion, with the orbital angular momentum of the system lying nearly parallel to the plane of the sky. With this information we can determine the mass of the (presumed) white dwarf companion star, and the inclination angle of the orbit. Knowing the pulsar mass function (0.0079 M_sun), we can in turn determine the mass of the pulsar itself. This measurement is important, among other reasons, for comparisons against the evolutionary scenarios that predict substantial mass accretion by the pulsar as it is spun up to millisecond periods by mass transfer from its companion in a low mass x-ray binary phase.

  15. Orientation birefringence of cross-linked rubber containing low-mass compound

    NASA Astrophysics Data System (ADS)

    Kiyama, Ayumi; Nobukawa, Shogo; Yamauchi, Masayuki

    2015-05-01

    Molecular orientation of low-mass compounds (LMCs) in a cross-linked rubber is studied in order to obtain the basic information on the dynamics of LMC molecules in a polymer beyond the glass transition temperature. A small amount of LMCs such as 4-cyano-4'-pentylbiphenyl (5CB), tricresylphosphate (TCP), and styrene-based tackifier (TF) is added into polybutadiene rubber (BR). After cross-linking reaction, the sheet samples are used to evaluate the orientation birefringence during stretching and stress relaxation. The rectangular films, cut out from the cross-linked sheets, are set in a uniaxial stretching machine equipped with an optical system to measure both birefringence and tensile stress simultaneously. It is confirmed that orientation birefringence is proportional to the stress for not only pure cross-linked BR, but also cross-linked BR containing an LMC in a wide range of strain. Even after stretching, the birefringence does not change as far as the sample is kept at a constant strain. The results suggest that the LMC molecules are forced to orient with polymer chains by the strong intermolecular orientation correlation. Because of the LMC orientation, the stress-optical coefficient CR is enhanced by the addition of 5CB and TCP, but depressed by TF. Therefore, the LMC doping can be used to control the birefringence of a retardation film.

  16. On the Existence of Low-Mass Dark Matter and its Direct Detection

    PubMed Central

    Bateman, James; McHardy, Ian; Merle, Alexander; Morris, Tim R.; Ulbricht, Hendrik

    2015-01-01

    Dark Matter (DM) is an elusive form of matter which has been postulated to explain astronomical observations through its gravitational effects on stars and galaxies, gravitational lensing of light around these, and through its imprint on the Cosmic Microwave Background (CMB). This indirect evidence implies that DM accounts for as much as 84.5% of all matter in our Universe, yet it has so far evaded all attempts at direct detection, leaving such confirmation and the consequent discovery of its nature as one of the biggest challenges in modern physics. Here we present a novel form of low-mass DM χ that would have been missed by all experiments so far. While its large interaction strength might at first seem unlikely, neither constraints from particle physics nor cosmological/astronomical observations are sufficient to rule out this type of DM, and it motivates our proposal for direct detection by optomechanics technology which should soon be within reach, namely, through the precise position measurement of a levitated mesoscopic particle which will be perturbed by elastic collisions with χ particles. We show that a recently proposed nanoparticle matter-wave interferometer, originally conceived for tests of the quantum superposition principle, is sensitive to these collisions, too. PMID:25622565

  17. Angular Momentum Evolution of Young Very Low Mass Stars and Brown Dwarfs: The Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Rodríguez-Ledesma, M. V.; Mundt, R.; Eislöffel, J.; Herbst, W.

    2008-12-01

    The rotational periods of young late-type stars and brown dwarfs (BDs) can be derived from photometric light curves, due to the rotational brightness modulation by surface features (i.e. magnetic cool spots). These kind of studies give important constrains on certain aspects of the so-called angular momentum problem of star formation. We report the first results of an extensive rotational period study of young stellar objects (YSOs) down into the BD mass regime in the Orion Nebula Cluster (ONC, d=450pc, age ˜ 1Myr). Our results are based on an deep photometric monitoring campaign, using the Wide Field Imager (WFI) camera on the ESO/MPG 2.2 meter telescope in La Silla, Chile. We found that 487 objects show detectable periodic light modulations, 377 of which are new detections. In addition 124 are potential BDs. This is by far the most extensive and complete rotational periods data set in the very low mass (VLM) star and BD regime. The spatial distribution of the variable objects, their rotational periods as well as the amplitude of the brightness modulation have been analyzed clearly indicating different stellar properties inside and outside the half-mass cluster radius of the ONC (R_{cluster} = 6.7'). In addition, we studied the dependence of the periodic brightness modulation on the magnitude (mass) of the objects and performed a comparison of the found period distribution with those of higher-mass objects in the ONC ( te{H2002}).

  18. Statistics of Low-Mass Companions to Stars: Implications for Their Origin

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.; Black, D. C.

    2001-01-01

    One of the more significant results from observational astronomy over the past few years has been the detection, primarily via radial velocity studies, of low-mass companions (LMCs) to solar-like stars. The commonly held interpretation of these is that the majority are "extrasolar planets" whereas the rest are brown dwarfs, the distinction made on the basis of apparent discontinuity in the distribution of M sin i for LMCs as revealed by a histogram. We report here results from statistical analysis of M sin i, as well as of the orbital elements data for available LMCs, to rest the assertion that the LMCs population is heterogeneous. The outcome is mixed. Solely on the basis of the distribution of M sin i a heterogeneous model is preferable. Overall, we find that a definitive statement asserting that LMCs population is heterogeneous is, at present, unjustified. In addition we compare statistics of LMCs with a comparable sample of stellar binaries. We find a remarkable statistical similarity between these two populations. This similarity coupled with marked populational dissimilarity between LMCs and acknowledged planets motivates us to suggest a common origin hypothesis for LMCs and stellar binaries as an alternative to the prevailing interpretation. We discuss merits of such a hypothesis and indicate a possible scenario for the formation of LMCs.

  19. Self-consistent evolution of accreting low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Baraffe, I.; Elbakyan, V. G.; Vorobyov, E. I.; Chabrier, G.

    2017-01-01

    We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst accretion and its impact on the central stellar temperature, the growth of the stellar radiative core and the accretion of fresh Li from the accretion disk. Only consistent models could reveal such a subtle combination of effects. This new result could explain the recent, puzzling observations of Li-excess of fast rotators in the young cluster NGC 2264. Present self-consistent accreting models are available in electronic form.

  20. Constraints on low-mass WIMP interactions on 19F from PICASSO

    NASA Astrophysics Data System (ADS)

    Archambault, S.; Behnke, E.; Bhattacharjee, P.; Bhattacharya, S.; Dai, X.; Das, M.; Davour, A.; Debris, F.; Dhungana, N.; Farine, J.; Gagnebin, S.; Giroux, G.; Grace, E.; Jackson, C. M.; Kamaha, A.; Krauss, C.; Kumaratunga, S.; Lafrenière, M.; Laurin, M.; Lawson, I.; Lessard, L.; Levine, I.; Levy, C.; MacDonald, R. P.; Marlisov, D.; Martin, J.-P.; Mitra, P.; Noble, A. J.; Piro, M.-C.; Podviyanuk, R.; Pospisil, S.; Saha, S.; Scallon, O.; Seth, S.; Starinski, N.; Stekl, I.; Wichoski, U.; Xie, T.; Zacek, V.

    2012-05-01

    Recent results from the PICASSO dark matter search experiment at SNOLAB are reported. These results were obtained using a subset of 10 detectors with a total target mass of 0.72 kg of 19F and an exposure of 114 kgd. The low backgrounds in PICASSO allow recoil energy thresholds as low as 1.7 keV to be obtained which results in an increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below 10 GeV/c2. No dark matter signal was found. Best exclusion limits in the spin dependent sector were obtained for WIMP masses of 20 GeV/c2 with a cross section on protons of σpSD=0.032 pb (90% C.L.). In the spin independent sector close to the low mass region of 7 GeV/c2 favoured by CoGeNT and DAMA/LIBRA, cross sections larger than σpSI=1.41×10-4 pb (90% C.L.) are excluded.

  1. Low-mass gas envelopes around accreting cores embedded in radiative 3D discs

    NASA Astrophysics Data System (ADS)

    Lega, Elena; Lambrechts, Michiel

    2016-10-01

    Planets with a core mass larger than few Earth masses and a gaseous envelope not exceeding about 10% of the total mass budget are common. Such planets are present in the Solar System (Uranus, Neptune) and are frequently observed around other stars.Our knowledge about the evolution of gas envelopes is mainly based on 1D models. However, such models cannot investigate the complex interaction between the forming envelope and the surrounding gas disc.In this work we perform 3D hydrodynamics simulations accounting for energy transfer and radiative cooling using the FARGOCA code (Lega et al., MNRAS 440, 2014). In addition to the usually considered heatingsources, namely viscous and compressional heating, we have modeled the energy deposited by the accretion of solids.We show that the thermal evolution of the envelope of a 5 Earth mass core is mainly dominated by compressional heating for accretion rates lower than 5 Earth masses per 105 years.Additionally, we demonstrate efficient gas circulation through the envelope. Under certain conditions, the competition between gas circulation and cooling of the envelope can efficiently delay the onset of runaway accretion. This could help in explaining the population of planets with low-mass gas envelope.

  2. Low-mass dark matter search using ionization signals in XENON100

    NASA Astrophysics Data System (ADS)

    Aprile, E.; Aalbers, J.; Agostini, F.; Alfonsi, M.; Amaro, F. D.; Anthony, M.; Arneodo, F.; Barrow, P.; Baudis, L.; Bauermeister, B.; Benabderrahmane, M. L.; Berger, T.; Breur, P. A.; Brown, A.; Brown, E.; Bruenner, S.; Bruno, G.; Budnik, R.; Buss, A.; Bütikofer, L.; Cardoso, J. M. R.; Cervantes, M.; Cichon, D.; Coderre, D.; Colijn, A. P.; Conrad, J.; Cussonneau, J. P.; Decowski, M. P.; de Perio, P.; di Gangi, P.; di Giovanni, A.; Duchovni, E.; Ferella, A. D.; Fieguth, A.; Franco, D.; Fulgione, W.; Galloway, M.; Garbini, M.; Geis, C.; Goetzke, L. W.; Greene, Z.; Grignon, C.; Gross, E.; Hasterok, C.; Hogenbirk, E.; Itay, R.; Kaminsky, B.; Kessler, G.; Kish, A.; Landsman, H.; Lang, R. F.; Levinson, L.; Le Calloch, M.; Levy, C.; Linde, F.; Lindemann, S.; Lindner, M.; Lopes, J. A. M.; Lyashenko, A.; Manfredini, A.; Marrodán Undagoitia, T.; Masbou, J.; Massoli, F. V.; Masson, D.; Mayani, D.; Melgarejo Fernandez, A. J.; Meng, Y.; Messina, M.; Micheneau, K.; Miguez, B.; Molinario, A.; Murra, M.; Naganoma, J.; Oberlack, U.; Orrigo, S. E. A.; Pakarha, P.; Pelssers, B.; Persiani, R.; Piastra, F.; Pienaar, J.; Plante, G.; Priel, N.; Rauch, L.; Reichard, S.; Reuter, C.; Rizzo, A.; Rosendahl, S.; Rupp, N.; Dos Santos, J. M. F.; Sartorelli, G.; Scheibelhut, M.; Schindler, S.; Schreiner, J.; Schumann, M.; Scotto Lavina, L.; Selvi, M.; Shagin, P.; Simgen, H.; Stein, A.; Thers, D.; Tiseni, A.; Trinchero, G.; Tunnell, C. D.; von Sivers, M.; Wall, R.; Wang, H.; Weber, M.; Wei, Y.; Weinheimer, C.; Wulf, J.; Zhang, Y.; Xenon Collaboration

    2016-11-01

    We perform a low-mass dark matter search using an exposure of 30 kg ×yr with the XENON100 detector. By dropping the requirement of a scintillation signal and using only the ionization signal to determine the interaction energy, we lowered the energy threshold for detection to 0.7 keV for nuclear recoils. No dark matter detection can be claimed because a complete background model cannot be constructed without a primary scintillation signal. Instead, we compute an upper limit on the WIMP-nucleon scattering cross section under the assumption that every event passing our selection criteria could be a signal event. Using an energy interval from 0.7 keV to 9.1 keV, we derive a limit on the spin-independent WIMP-nucleon cross section that excludes WIMPs with a mass of 6 GeV /c2 above 1.4 ×10-41 cm2 at 90% confidence level.

  3. THE KINEMATICS OF THE NEBULAR SHELLS AROUND LOW MASS PROGENITORS OF PNe WITH LOW METALLICITY

    SciTech Connect

    Pereyra, Margarita; López, José Alberto; Richer, Michael G. E-mail: jal@astrosen.unam.mx

    2016-03-15

    We analyze the internal kinematics of 26 planetary nebulae (PNe) with low metallicity that appear to derive from progenitor stars of the lowest masses, including the halo PN population. Based upon spatially resolved, long-slit, echelle spectroscopy drawn from the San Pedro Mártir Kinematic Catalog of PNe, we characterize the kinematics of these PNe measuring their global expansion velocities based upon the largest sample used to date for this purpose. We find kinematics that follow the trends observed and predicted in other studies, but also find that most of the PNe studied here tend to have expansion velocities less than 20 km s{sup −1} in all of the emission lines considered. The low expansion velocities that we observe in this sample of low metallicity PNe with low mass progenitors are most likely a consequence of a weak central star (CS) wind driving the kinematics of the nebular shell. This study complements previous results that link the expansion velocities of the PN shells with the characteristics of the CS.

  4. DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. XIII. DZ PISCIUM WITH INTRINSIC LIGHT VARIABILITY

    SciTech Connect

    Yang, Y.-G.; Dai, H.-F.; Qian, S.-B.; Soonthornthum, B. E-mail: qsb@ynao.ac.cn

    2013-08-01

    New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson-Devinney (W-D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7({+-} 1.0)%, identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., LC{sub 2} in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are P{sub mod} = 11.89({+-} 0.19) yr and A = 0.0064({+-} 0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light-time effect due to the third body. The long-term period increases at a rate of dP/dt=+7.43({+-}0.17) Multiplication-Sign 10{sup -7} days yr{sup -1}, which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J{sub spin}/J{sub orb} > 1/3.

  5. A Low-mass Black Hole in the Nearby Seyfert Galaxy UGC 06728

    NASA Astrophysics Data System (ADS)

    Bentz, Misty C.; Batiste, Merida; Seals, James; Garcia, Karen; Kuzio de Naray, Rachel; Peters, Wesley; Anderson, Matthew D.; Jones, Jeremy; Lester, Kathryn; Machuca, Camilo; Parks, J. Robert; Pope, Crystal L.; Revalski, Mitchell; Roberts, Caroline A.; Saylor, Dicy; Sevrinsky, R. Andrew; Turner, Clay

    2016-11-01

    We present the results of a recent reverberation mapping campaign for UGC 06728, a nearby low-luminosity Seyfert 1 in a late-type galaxy. Nightly monitoring in the spring of 2015 allowed us to determine an Hβ time delay of τ =1.4+/- 0.8 days. Combined with the width of the variable Hβ line profile, we determine a black hole mass of {M}{BH}=(7.1+/- 4.0)× {10}5 {M}⊙ . We also constrain the bulge stellar velocity dispersion from higher-resolution long-slit spectroscopy along the galaxy minor axis and find {σ }\\star =51.6+/- 4.9 km s-1. The measurements presented here are in good agreement with both the {R}{BLR}{--}L relationship and the {M}{BH}{--}{σ }\\star relationship for active galactic nuclei. Combined with a previously published spin measurement, our mass determination for UGC 06728 makes it the lowest-mass black hole that has been fully characterized, and thus an important object to help anchor the low-mass end of black hole evolutionary models.

  6. Low-mass X-ray binaries and globular clusters streamers and arcs in NGC 4278

    SciTech Connect

    D'Abrusco, R.; Fabbiano, G.; Brassington, N. J.

    2014-03-01

    We report significant inhomogeneities in the projected two-dimensional spatial distributions of low-mass X-ray binaries (LMXBs) and globular clusters (GCs) of the intermediate mass elliptical galaxy NGC 4278. In the inner region of NGC 4278, a significant arc-like excess of LMXBs extending south of the center at ∼50'' in the western side of the galaxy can be associated with a similar overdensity of the spatial distribution of red GCs from Brassington et al. Using a recent catalog of GCs produced by Usher et al. and covering the whole field of the NGC 4278 galaxy, we have discovered two other significant density structures outside the D {sub 25} isophote to the W and E of the center of NGC 4278, associated with an overdensity and an underdensity, respectively. We discuss the nature of these structures in the context of the similar spatial inhomogeneities discovered in the LMXBs and GCs populations of NGC 4649 and NGC 4261, respectively. These features suggest streamers from disrupted and accreted dwarf companions.

  7. Investigating the Low-Mass Stellar Initial Mass Function in Draco

    NASA Astrophysics Data System (ADS)

    Sotoudeh, Seyed Soroush

    We present new analysis of the low-mass stellar initial mass function (˜0.4-0.8Mȯ) in the Local Group dwarf spheroidal galaxy, Draco. Using archival HST/ACS and WFC3 optical imaging, we construct deep color-magnitude (CMD) diagrams in 3 different felds at 3 different galactocentric radii and measure the IMF by modeling the resolved lower main sequence. We model the optical color-magnitude diagrams of each feld assuming two different IMF models (power-law, log-normal), five different stellar evolution libraries (Padova, BaSTI, Dartmouth, Victoria, PARSEC), and a binary star model. For a single-sloped power-law IMF model, we find that the IMF slope steepens by up to 0.7 dex for radii between 150 and 300pc, while the binary fraction remains approximately constant. The absolute values of the IMF slopes at any radius depend strongly on the adopted stellar models, suggesting that current knowledge of the lower-main sequence stars is uncertain. In fact, utilizing different stellar models has resulted in up to 0.67 dex difference in the IMF slope. All fields show more consistent log-normal parameters, which are also in reasonable agreement with values for a standard Chabrier IMF. However, there are large degeneracies between the characteristic mass and dispersion of the log-normal, that can only be reduced with data that extends to lower stellar masses.

  8. Evidence for Simultaneous Jets and Disk Winds in Luminous Low-mass X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Homan, Jeroen; Neilsen, Joseph; Allen, Jessamyn L.; Chakrabarty, Deepto; Fender, Rob; Fridriksson, Joel K.; Remillard, Ronald A.; Schulz, Norbert

    2016-10-01

    Recent work on jets and disk winds in low-mass X-ray binaries (LMXBs) suggests that they are to a large extent mutually exclusive, with jets observed in spectrally hard states and disk winds observed in spectrally soft states. In this paper we use existing literature on jets and disk winds in the luminous neutron star (NS) LMXB GX 13+1, in combination with archival Rossi X-ray Timing Explorer data, to show that this source is likely able to produce jets and disk winds simultaneously. We find that jets and disk winds occur in the same location on the source’s track in its X-ray color-color diagram. A further study of literature on other luminous LMXBs reveals that this behavior is more common, with indications for simultaneous jets and disk winds in the black hole LMXBs V404 Cyg and GRS 1915+105 and the NS LMXBs Sco X-1 and Cir X-1. For the three sources for which we have the necessary spectral information, we find that simultaneous jets/winds all occur in their spectrally hardest states. Our findings indicate that in LMXBs with luminosities above a few tens of percent of the Eddington luminosity, jets and disk winds are not mutually exclusive, and the presence of disk winds does not necessarily result in jet suppression.

  9. THE FORMATION OF SUPERMASSIVE BLACK HOLES FROM LOW-MASS POP III SEEDS

    SciTech Connect

    Whalen, Daniel J.; Fryer, Chris L.

    2012-09-01

    The existence of 10{sup 9} M{sub Sun} black holes (BHs) in massive galaxies by z {approx} 7 is one of the great unsolved mysteries in cosmological structure formation. One theory argues that they originate from the BHs of Pop III stars at z {approx} 20 and then accrete at the Eddington limit down to the epoch of reionization, which requires that they have constant access to rich supplies of fuel. Because early numerical simulations suggested that Pop III stars were {approx}>100 M{sub Sun }, the supermassive black hole (SMBH) seeds considered up to now were 100-300 M{sub Sun }. However, there is a growing numerical and observational consensus that some Pop III stars were tens of solar masses, not hundreds, and that 20-40 M{sub Sun} BHs may have been much more plentiful at high redshift. However, we find that natal kicks imparted to 20-40 M{sub Sun} Pop III BHs during formation eject them from their halos and hence their fuel supply, precluding them from Eddington-limit growth. Consequently, SMBHs are far less likely to form from low-mass Pop III stars than from very massive ones.

  10. Fast and accurate mock catalogue generation for low-mass galaxies

    NASA Astrophysics Data System (ADS)

    Koda, Jun; Blake, Chris; Beutler, Florian; Kazin, Eyal; Marin, Felipe

    2016-06-01

    We present an accurate and fast framework for generating mock catalogues including low-mass haloes, based on an implementation of the COmoving Lagrangian Acceleration (COLA) technique. Multiple realisations of mock catalogues are crucial for analyses of large-scale structure, but conventional N-body simulations are too computationally expensive for the production of thousands of realizations. We show that COLA simulations can produce accurate mock catalogues with a moderate computation resource for low- to intermediate-mass galaxies in 1012 M⊙ haloes, both in real and redshift space. COLA simulations have accurate peculiar velocities, without systematic errors in the velocity power spectra for k ≤ 0.15 h Mpc-1, and with only 3-per cent error for k ≤ 0.2 h Mpc-1. We use COLA with 10 time steps and a Halo Occupation Distribution to produce 600 mock galaxy catalogues of the WiggleZ Dark Energy Survey. Our parallelized code for efficient generation of accurate halo catalogues is publicly available at github.com/junkoda/cola_halo.

  11. A Novel Device for Measuring Respirable Dustiness Using Low Mass Powder Samples

    PubMed Central

    O’Shaughnessy, Patrick T.; Kang, Mitchell; Ellickson, Daniel

    2013-01-01

    Respirable dustiness represents the tendency of a powder to generate respirable airborne dust during handling and therefore indicates the propensity for a powder to become an inhalation hazard. The dustiness of fourteen powders, including ten different nanopowders, was evaluated with the use of a novel low mass dustiness tester (LMDT) designed to minimize the use of the test powder. The aerosol created from 15-mg powder samples falling down a tube were measured with an aerodynamic particle sizer (APS). Particle counts integrated throughout the pulse of aerosol created by the falling powder were used to calculate a respirable dustiness mass fraction (D, mg/kg). An amorphous silicon dioxide nanopowder produced a respirable D of 121.4 mg/kg which was significantly higher than all other powders (p<0.001). Many nanopowders produced D values of that were not significantly different from large-particle powders such as Arizona Road Dust and Bentonite clay. In general, fibrous nanopowders and powders with primary particles > 100 nm are not as dusty as those containing granular, nano-sized primary particles. The method used here, incorporating an APS, represents a deviation from a standard method but resulted in dustiness values comparable to other standard methods. PMID:22335240

  12. Chemical and Physical Characterization of Collapsing Low-mass Prestellar Dense Cores

    NASA Astrophysics Data System (ADS)

    Hincelin, U.; Commerçon, B.; Wakelam, V.; Hersant, F.; Guilloteau, S.; Herbst, E.

    2016-05-01

    The first hydrostatic core, also called the first Larson core, is one of the first steps in low-mass star formation as predicted by theory. With recent and future high-performance telescopes, the details of these first phases are becoming accessible, and observations may confirm theory and even present new challenges for theoreticians. In this context, from a theoretical point of view, we study the chemical and physical evolution of the collapse of prestellar cores until the formation of the first Larson core, in order to better characterize this early phase in the star formation process. We couple a state-of-the-art hydrodynamical model with full gas-grain chemistry, using different assumptions for the magnetic field strength and orientation. We extract the different components of each collapsing core (i.e., the central core, the outflow, the disk, the pseudodisk, and the envelope) to highlight their specific physical and chemical characteristics. Each component often presents a specific physical history, as well as a specific chemical evolution. From some species, the components can clearly be differentiated. The different core models can also be chemically differentiated. Our simulation suggests that some chemical species act as tracers of the different components of a collapsing prestellar dense core, and as tracers of the magnetic field characteristics of the core. From this result, we pinpoint promising key chemical species to be observed.

  13. Calibrating the Mass-Radius-Temperature Relation in the Low-Mass Regime

    NASA Astrophysics Data System (ADS)

    Gomez Maqueo Chew, Yilen; Hebb, Leslie; Faedi, Francesca; Keating, Katie M.; Stassun, Keivan; Pollacco, Don; Rodler, Florian; Collier Cameron, Andrew

    2013-08-01

    We request a total of 9 nights with FLAMINGOS at the KPNO 2.1m to obtain the J and Ks-band light curves of low-mass M dwarfs in eclipsing binaries with F/G/K primaries. This is part of a larger effort to constrain the mass-radius-temperature relation as a function of activity and metallicity at the bottom of the main sequence with unprecedented large number statistics. With these observations, we will determine the temperature of the M dwarfs by comparing the secondary eclipse depth with the primary temperature as measured from spectral synthesis. The measurement of the secondary eclipse is only possible in the near- infrared, where the M dwarfs are brighter. To achieve precise measurements, the observations require a temporal coverage of the secondary minimum, and part of the out-of-eclipse phases. The comprehensive modeling of the binaries, including radial velocity and multi-band light curves, will allow us to fully determine their fundamental properties, including masses, radii and temperatures.

  14. Orbital period change of the low-mass X-ray binary EXO 0748-676

    NASA Technical Reports Server (NTRS)

    Asai, Kazumi; Dotani, Tadayasu; Nagase, Fumiaki; Corbet, Robin H. D.; Shaham, Jacob

    1992-01-01

    The transient low-mass X-ray binary, EXO 0748-676, discovered with EXOSAT, is known to exhibit eclipses of a 492-s duration with a 3.82-hr period, intensity dips at pre-eclipse phases and type-I X-ray bursts. We observed this source with Ginga in 1989 March, 1990 December, 1991 January, and 1991 August and determined nine eclipse center times. Combining these eclipse center times with the previous result of the EXOSAT observations, we find that the orbital period of this source is not decaying monotonically, contrary to the previously reported suggestion. Instead, it shows a more complex behavior. A quadratic fit to the eclipse data yields a positive rate of change in orbital period with an approximate rate of 0.9 x 10 exp 7/yr, although the EXOSAT observations made in 1985 do not fit this trend. A sinusoidal function gives a better fit to the observed orbital period changes with a period of about 12 yr and an amplitude of about 44 lt-s, although the period is much longer than the observation interval of about 6.5 yr. Possible mechanisms for the orbital period change are discussed.

  15. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    NASA Astrophysics Data System (ADS)

    Silva, Hector O.; Sotani, Hajime; Berti, Emanuele

    2016-07-01

    The lowest neutron star masses currently measured are in the range 1.0-1.1 M⊙, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass M/M⊙ = 1.174 ± 0.004 (Martinez et al. 2015) in a double neutron star system suggests that low-mass</