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Sample records for low-mass protostellar systems

  1. 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.

  2. 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

  3. Chemistry in low-mass protostellar and protoplanetary regions.

    PubMed

    van Dishoeck, Ewine F

    2006-08-15

    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

  4. Rotation and Outflow Motions in the Very Low-Mass Class 0 Protostellar System HH 211 at Subarcsecond Resolution

    NASA Astrophysics Data System (ADS)

    Lee, Chin-Fei; Hirano, Naomi; Palau, Aina; Ho, Paul T. P.; Bourke, Tyler L.; Zhang, Qizhou; Shang, Hsien

    2009-07-01

    HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J = 8 - 7), and HCO+ (J = 4 - 3) emission at up to ~0farcs2 resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of ~ 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of ~50 ± 15 M Jup (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (~200 AU) low-speed (~2 km s-1) outflow is seen in HCO+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to ~100 AU from SMM1. It is seen with a "C-shaped" bending. It has a transverse width of lsim 40 AU and a velocity of ~ 170 ± 60 km s-1. A possible velocity gradient is seen consistently across its innermost pair of knots, ~0.5 km s-1 at ~10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of lsim 5 AU km s-1 and thus must be launched from the very inner edge of the disk near the corotation radius.

  5. 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.

  6. Occurrence of instability through the protostellar accretion disks by landing of low-mass condensations

    NASA Astrophysics Data System (ADS)

    Elyasi, Mahjubeh; Nejad-Asghar, Mohsen

    2016-06-01

    Low-mass condensations (LMCs) are observed inside the envelope of the collapsing molecular cloud cores. In this research, we investigate the effects of landing LMCs for occurrence of instability through the protostellar accretion disks. We consider some regions of the disk where duration of infalling and landing of the LMCs are shorter than the orbital period. In this way, we can consider the landing LMCs as density bumps and grooves in the azimuthal direction of an initial thin axisymmetric steady state self-gravitating protostellar accretion disk (nearly Keplerian). Using the linear effects of the bump quantities, we obtain a characteristic equation for growth/decay rate of bumps; we numerically solve it to find occurrence of instability. We also evaluate the minimum-growth-time-scale (MGTS) and the enhanced mass accretion rate. The results show that infalling and landing of the LMCs in the inner regions of the protostellar accretion disks can cause faster unstable modes and less enhanced accretion rates relative to the outer regions. Also, more fragmentation of landed LMCs in the azimuthal direction have less chance for instability, and then can produce more values of enhanced mass accretion rate.

  7. From nearby low-mass protostars to high redshift starbursts: protostellar outflows tracing the IMF

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; Bergin, Edwin

    2015-08-01

    Embedded low-mass protostars are notoriously difficult to observe even in the nearest Galactic high-mass clusters where they outnumber the high-mass protostars by orders of magnitude. Thus, without a good tracer of the low-mass population, we do not have a good handle on the shape of the initial (core) mass function, leaving little hope for extrapolating to extragalactic regions where we will never have neither the sensitivity nor the resolution to directly observe this population. A good tracer of the low-mass population is needed.One such physical tracer is outflows. Outflow emission is directly proportional to envelope mass, and outflows are predominantly active during the deeply embedded phases of star formation. What is required for this method to work is species and transitions tracing outflows uniquely such that any signal is not diluted by the surrounding cloud, such as certain methanol transitions, water, high-J CO (J > 10).I will present a statistical model of a forming high-mass cluster. The model includes what we currently know about Galactic high-mass clusters and incorporates outflow emission from low-mass protostars. The latter component is obtained from observations of tens of nearby embedded low-mass protostellar outflows in the above-mentioned tracers. The model is benchmarked against ALMA and Herschel-HIFI observations of Galactic clusters proving the concept, and preliminary extrapolations to the extragalactic regime are presented. With this new probe, and traditional probes of the distant star formation which predominantly trace high mass stars, we will be able to explore the IMF in starburst galaxies from low to high redshift.

  8. The Turbulent Fragmentation Origin of Low-Mass Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Offner, Stella; Kratter, K. M.; Matzner, C. D.; Krumholz, M. R.; Klein, R. I.

    2011-01-01

    Using self-gravitating, radiation-hydrodynamic simulations, we compare turbulent fragmentation and disk fragmentation as avenues for forming low-mass binary systems. We employ two dimensionless parameters to characterize the infall rate onto protostellar systems, describe disks' susceptability to fragmentation, and place limits on protostellar system multiplicity. While protostellar disks are predominatly stable in the presence of radiative feedback, purely hydrodynamic systems exhibit fundamentally different parameters and are strongly susceptible to disk fragmentation. Consequently, we find that turbulent fragmentation, occuring on thousand AU scales, is the more common mode of fragmentation and is likely responsible for producing most low-mass binary systems. Although fragmentation in young embedded protostellar disks cannot be directly imaged, turbulent fragmentation on these scales is potentially observable.

  9. Molecular inventories and chemical evolution of low-mass protostellar envelopes

    NASA Astrophysics Data System (ADS)

    Jørgensen, J. K.; Schöier, F. L.; van Dishoeck, E. F.

    2004-03-01

    This paper presents the first substantial study of the chemistry of the envelopes around a sample of 18 low-mass pre- and protostellar objects for which physical properties have previously been derived from radiative transfer modeling of their dust continuum emission. Single-dish line observations of 24 transitions of 9 molecular species (not counting isotopes) including HCO+, N2H+, CS, SO, SO2, HCN, HNC, HC3N and CN are reported. The line intensities are used to constrain the molecular abundances by comparison to Monte Carlo radiative transfer modeling of the line strengths. In general the nitrogen-bearing species together with HCO+ and CO cannot be fitted by a constant fractional abundance when the lowest excitation transitions are included, but require radial dependences of their chemistry since the intensity of the lowest excitation lines are systematically underestimated in such models. A scenario is suggested in which these species are depleted in a specific region of the envelope where the density is high enough that the freeze-out timescale is shorter than the dynamical timescale and the temperature low enough that the molecule is not evaporated from the icy grain mantles. This can be simulated by a ``drop'' abundance profile with standard (undepleted) abundances in the inner- and outermost regions and a drop in abundance in between where the molecule freezes out. An empirical chemical network is constructed on the basis of correlations between the abundances of various species. For example, it is seen that the HCO+ and CO abundances are linearly correlated, both increasing with decreasing envelope mass. This is shown to be the case if the main formation route of HCO+ is through reactions between CO and H3+, and if the CO abundance still is low enough that reactions between H3+ and N2 are the main mechanism responsible for the removal of H3+. Species such as CS, SO and HCN show no trend with envelope mass. In particular no trend is seen between

  10. The Formation of Low-mass Binary Star Systems Via Turbulent Fragmentation

    NASA Astrophysics Data System (ADS)

    Offner, Stella S. R.; Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; Klein, Richard I.

    2010-12-01

    We characterize the infall rate onto protostellar systems forming in self-gravitating radiation-hydrodynamics simulations. Using two dimensionless parameters to determine the disks' susceptibility to gravitational fragmentation, we infer limits on protostellar system multiplicity and the mechanism of binary formation. We show that these parameters give robust predictions even in the case of marginally resolved protostellar disks. We find that protostellar systems with radiation feedback predominately form binaries via turbulent fragmentation, not disk instability, and predict that turbulent fragmentation is the dominant channel for binary formation for low-mass stars. We clearly demonstrate that systems forming in simulations including radiative feedback have fundamentally different parameters than those in purely hydrodynamics simulations.

  11. Pre-protostellar and low-mass star forming clouds in Cepheus

    NASA Astrophysics Data System (ADS)

    Nikolić, Silvana

    2004-12-01

    The structure of this monograph is as follows: a general overview of the interstellar medium is given in Chapter 2. Chapter 3 deals with basic molecular structure, line radiation, and molecular clouds in general; in Chapter 4 principles of star-formation are given, with an emphasis on low-mass stars; chemistry is discussed in Chapter 5, in Chapters 6-10 results of the research papers are presented.

  12. Near-infrared multiwavelength imaging polarimetry of the low-mass proto-stellar object HL Tauri

    NASA Astrophysics Data System (ADS)

    Murakawa, K.; Oya, S.; Pyo, T.-S.; Ishii, M.

    2008-12-01

    We present the {JHK}-band high-resolution polarimetric images of the low-mass proto-stellar object HL Tau using the adaptive optics-equipped CIAO instrument on the Subaru telescope. Our polarization images show a butterfly-shaped polarization disk with an ˜0.9 arcsec × 3.0 arcsec extension. In the nebula, where polarization vectors are centro-symmetrically aligned, the polarization is as high as PJ ˜30%, P_H˜42%, and PK ˜55%. On the other hand, low polarizations of P<3% in the J, H, and K bands and a low color excess ratio of EJ-H/EH-K=1.1 compared to the standard cloud value of 1.75 are detected towards the central star. We estimated the upper limit of the grain sizes a_max to be 0.4 μm in the nebula and ⪆0.7 μm in the line of sight towards the central star. Our high-resolution polarimetric data, which spatially resolves the polarization disk, provides us with important information about grain growth in the region close to the central star.

  13. Orbital Motions in Binary Protostellar Systems

    NASA Astrophysics Data System (ADS)

    Rodríguez, L. F.

    2004-08-01

    Using high-resolution ( ˜ 0to z @. hss ''1), multi-epoch Very Large Array observations, we have detected orbital motions in several low-luminosity protobinary systems in the Taurus and ρ Ophiuchus molecular complexes. The masses obtained from Kepler's third law are of the order of 0.5 to 2 M⊙, as expected for such low-mass protostars. The relatively large bolometric luminosities of these young systems corroborates the notion that protostars obtain most of their luminosity from accretion and not from nuclear reactions. In addition, in one of the sources studied (a multiple system in Taurus), a low-mass young star has shown a drastic change in its orbit after a close approach with another component of the system, presumed to be a double star. The large proper motion achieved by this low mass protostar (20 km s-1), suggests an ejection from the system.

  14. Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destruction

    NASA Astrophysics Data System (ADS)

    Suutarinen, A. N.; Kristensen, L. E.; Mottram, J. C.; Fraser, H. J.; van Dishoeck, E. F.

    2014-05-01

    Water in outflows from protostars originates either as a result of gas-phase synthesis from atomic oxygen at T ≳ 200 K, or from sputtered ice mantles containing water ice. We aim to quantify the contribution of the two mechanisms that lead to water in outflows, by comparing observations of gas-phase water to methanol (a grain surface product) towards three low-mass protostars in NGC 1333. In doing so, we also quantify the amount of methanol destroyed in outflows. To do this, we make use of James Clerk Maxwell Telescope and Herschel-Heterodyne Instrument for the Far-Infrared data of H2O, CH3OH and CO emission lines and compare them to RADEX non-local thermodynamic equilibrium excitation simulations. We find up to one order of magnitude decrease in the column density ratio of CH3OH over H2O as the velocity increases in the line wings up to ˜15 km s-1. An independent decrease in X(CH3OH) with respect to CO of up to one order of magnitude is also found in these objects. We conclude that gas-phase formation of H2O must be active at high velocities (above 10 km s-1 relative to the source velocity) to re-form the water destroyed during sputtering. In addition, the transition from sputtered water at low velocities to form water at high velocities must be gradual. We place an upper limit of two orders of magnitude on the destruction of methanol by sputtering effects.

  15. 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.

  16. Observational dynamics of low-mass stellar systems

    NASA Astrophysics Data System (ADS)

    Frank, M. J.

    The last fifteen years have seen the discovery of new types of low-mass stellar systems that bridge the gap between the once well-separated regimes of galaxies and of star clusters. Whether such objects are considered galaxies depends also on the definition of the term ``galaxy'', and several possible criteria are based on their internal dynamics (e.g. the common concept that galaxies contain dark matter). Moreover, studying the internal dynamics of low-mass stellar systems may also help understand their origin and evolutionary history. The focus of this paper is on two classes of stellar systems at the interface between star clusters and dwarf galaxies: ultra-compact dwarf galaxies (UCDs) and diffuse Galactic globular clusters (GCs). A review of our current knowledge on the properties of UCDs is provided and dynamical considerations applying to diffuse GCs are introduced. In the following, recent observational results on the internal dynamics of individual UCDs and diffuse Galactic globular clusters are presented. Partly based on observations obtained at the European Southern Observatory, Chile (Observing Programmes 078.B-0496(B) and 081.B-0282). Doctoral Thesis Award Lecture 2013

  17. 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.

  18. The low mass ratio contact binary system V728 Herculis

    NASA Astrophysics Data System (ADS)

    Erkan, N.; Ulaş, B.

    2016-07-01

    We present the orbital period study and the photometric analysis of the contact binary system V728 Her. Our orbital period analysis shows that the period of the system increases (dP / dt = 1.92 ×10-7 dyr-1) and the mass transfer rate from the less massive component to more massive one is 2.51 ×10-8 M⊙y-1 . In addition, an advanced sinusoidal variation in period can be attributed to the light-time effect by a tertiary component or the Applegate mechanism triggered by the secondary component. The simultaneous multicolor BVR light and radial velocity curves solution indicates that the physical parameters of the system are M1 = 1.8M⊙ , M2 = 0.28M⊙ , R1 = 1.87R⊙ , R2 = 0.82R⊙ , L1 = 5.9L⊙ , and L2 = 1.2L⊙ . We discuss the evolutionary status and conclude that V728 Her is a deep (f = 81%), low mass ratio (q = 0.16) contact binary system.

  19. Water in star-forming regions with Herschel (WISH). V. The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.; Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.; Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.

    2014-12-01

    Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims: We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods: We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results: Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H2 densities of order 105 - 108 cm-3 and H2O column densities of order 1016 - 1018 cm-2. H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU. Conclusions: Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose

  20. 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 sta bility necessary in low - mass vertex detector sy s tems . 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. Fin ally, comments are made on future directions to be considered in using present materials effectively and in developing new materials.

  1. 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

  2. Design and Manufacturing of Extremely Low Mass Flight Systems

    NASA Technical Reports Server (NTRS)

    Johnson, Michael R.

    2002-01-01

    Extremely small flight systems pose some unusual design and manufacturing challenges. The small size of the components that make up the system generally must be built with extremely tight tolerances to maintain the functionality of the assembled item. Additionally, the total mass of the system is extremely sensitive to what would be considered small perturbations in a larger flight system. The MUSES C mission, designed, built, and operated by Japan, has a small rover provided by NASA that falls into this small flight system category. This NASA-provided rover is used as a case study of an extremely small flight system design. The issues that were encountered with the rover portion of the MUSES C program are discussed and conclusions about the recommended mass margins at different stages of a small flight system project are presented.

  3. AGC 226067: A possible interacting low-mass system

    NASA Astrophysics Data System (ADS)

    Adams, E. A. K.; Cannon, J. M.; Rhode, K. L.; Janesh, W. F.; Janowiecki, S.; Leisman, L.; Giovanelli, R.; Haynes, M. P.; Oosterloo, T. A.; Salzer, J. J.; Zaidi, T.

    2015-08-01

    We present Arecibo, GBT, VLA, and WIYN/pODI observations of the ALFALFA source AGC 226067. Originally identified as an ultra-compact high velocity cloud and candidate Local Group galaxy, AGC 226067 is spatially and kinematically coincident with the Virgo cluster, and the identification by multiple groups of an optical counterpart with no resolved stars supports the interpretation that this systems lies at the Virgo distance (D = 17 Mpc). The combined observations reveal that the system consists of multiple components: a central H i source associated with the optical counterpart (AGC 226067), a smaller H i-only component (AGC 229490), a second optical component (AGC 229491), and extended low-surface brightness H i. Only ~1/4 of the single-dish H i emission is associated with AGC 226067; as a result, we find MHI/Lg ~ 6M⊙/L⊙ which is lower than previous work. At D = 17 Mpc, AGC 226067 has an H i mass of 1.5 × 107M⊙ and Lg = 2.4 × 106L⊙, AGC 229490 (the H i-only component) has MHI = 3.6 × 106M⊙, and AGC 229491 (the second optical component) has Lg = 3.6 × 105L⊙. The nature of this system of three sources is uncertain: AGC 226067 and AGC 229490 may be connected by an H i bridge, and AGC 229490 and AGC 229491 are separated by only 0.5'. The current data do not resolve the H i in AGC 229490 and its origin is unclear. We discuss possible scenarios for this system of objects: an interacting system of dwarf galaxies, accretion of material onto AGC 226067, or stripping of material from AGC 226067.

  4. Do siblings always form and evolve simultaneously? Testing the coevality of multiple protostellar systems through SEDs

    NASA Astrophysics Data System (ADS)

    Murillo, N. M.; van Dishoeck, E. F.; Tobin, J. J.; Fedele, D.

    2016-07-01

    Context. Multiplicity is common in field stars and among protostellar systems. Models suggest two paths of formation: turbulent fragmentation and protostellar disk fragmentation. Aims: We attempt to find whether or not the coevality frequency of multiple protostellar systems can help to better understand their formation mechanism. The coevality frequency is determined by constraining the relative evolutionary stages of the components in a multiple system. Methods: Spectral energy distributions (SEDs) for known multiple protostars in Perseus were constructed from literature data. Herschel PACS photometric maps were used to sample the peak of the SED for systems with separations ≥7″, a crucial aspect in determining the evolutionary stage of a protostellar system. Inclination effects and the surrounding envelope and outflows were considered to decouple source geometry from evolution. This together with the shape and derived properties from the SED was used to determine each system's coevality as accurately as possible. SED models were used to examine the frequency of non-coevality that is due to geometry. Results: We find a non-coevality frequency of 33 ± 10% from the comparison of SED shapes of resolved multiple systems. Other source parameters suggest a somewhat lower frequency of non-coevality. The frequency of apparent non-coevality that is due to random inclination angle pairings of model SEDs is 17 ± 0.5%. Observations of the outflow of resolved multiple systems do not suggest significant misalignments within multiple systems. Effects of unresolved multiples on the SED shape are also investigated. Conclusions: We find that one-third of the multiple protostellar systems sampled here are non-coeval, which is more than expected from random geometric orientations. The other two-thirds are found to be coeval. Higher order multiples show a tendency to be non-coeval. The frequency of non-coevality found here is most likely due to formation and enhanced by

  5. Southern Very Low Mass Stars and Brown Dwarfs in Wide Binary and Multiple Systems

    NASA Astrophysics Data System (ADS)

    Caballero, José Antonio

    2007-09-01

    The results of the Königstuhl survey in the Southern Hemisphere are presented. I have searched for common proper motion companions to 173 field very low mass stars and brown dwarfs with spectral types >M5.0 V and magnitudes J<~14.5 mag. I have measured for the first time the common proper motion of two new wide systems containing very low mass components, Königstuhl 2 AB and 3 A-BC. Together with Königstuhl 1 AB and 2M 0126-50 AB, they are among the widest systems in their respective classes (r=450-11,900 AU). I have determined the minimum frequency of field wide multiples (r>100 AU) with late-type components at 5.0%+/-1.8% and the frequency of field wide late-type binaries with mass ratios q>0.5 at 1.2%+/-0.9%. These values represent a key diagnostic of evolution history and low-mass star and brown dwarf formation scenarios. In addition, the proper motions of 62 field very low mass dwarfs are measured here for the first time.

  6. The ALMA view of the protostellar system HH212. The wind, the cavity, and the disk

    NASA Astrophysics Data System (ADS)

    Codella, C.; Cabrit, S.; Gueth, F.; Podio, L.; Leurini, S.; Bachiller, R.; Gusdorf, A.; Lefloch, B.; Nisini, B.; Tafalla, M.; Yvart, W.

    2014-08-01

    Context. Because it is viewed simply edge-on, the HH212 protostellar system is an ideal laboratory for studying the interplay of infall, outflow, and rotation in the earliest stages of low-mass star formation. Aims: We wish to exploit the unmatched combination of high angular resolution, high sensitivity, high-imaging fidelity, and spectral coverage provided by ALMA to shed light on the complex kinematics of the innermost central regions of HH212. Methods: We mapped the inner 10″ (4500 AU) of the HH212 system at ≃0.5″ resolution in several molecular tracers and in the 850 μm dust continuum using the ALMA interferometer in band 7 in the extended configuration of the Early Science Cycle 0 operations. Results: Within a single ALMA spectral set-up, we simultaneously identify all the crucial ingredients known to be involved in the star formation recipe: (i) the fast, collimated bipolar SiO jet driven by the protostar; (ii) the large-scale swept-up CO outflow; (iii) the flattened rotating and infalling envelope, with bipolar cavities carved by the outflow (in C17O(3-2)); and (iv) a rotating wide-angle flow that fills the cavities and surrounds the axial jet (in C34S(7-6)). In addition, the compact high-velocity C17O emission (±1.9-3.5 km s-1 from systemic) shows a velocity gradient along the equatorial plane consistent with a rotating disk of ≃0farcs2 = 90 AU around a ≃0.3 ± 0.1 M⊙ source. The rotating disk is possibly Keplerian. Conclusions: HH212 is the third Class 0 protostar with possible signatures of a Keplerian disk of radius ≥30 AU. The warped geometry in our CS data suggests that this large Keplerian disk might result from misaligned magnetic and rotation axes during the collapse phase. The wide-angle CS flow suggests that disk winds may be present in this source. Appendix A is available in electronic form at http://www.aanda.orgFinal reduced ALMA cubes (FITS) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp

  7. The Wasp-Waist Nebula: VLA Ammonia Observations of the Molecular Core Envelope In a Unique Class 0 Protostellar System

    NASA Technical Reports Server (NTRS)

    Wiseman, Jennifer

    2010-01-01

    The Wasp-Waist Nebula was discovered in the IRAC c2d survey of the Ophiuchus starforming clouds. It is powered by a well-isolated, low-luminosity, low-mass Class 0 object. Its weak outflow has been mapped in the CO (3-2) transition with the JCMT, in 2.12 micron H2 emission with WIRC (the Wide-Field Infrared Camera) on the Hale 5-meter, and, most recently, in six H2 mid-infrared lines with the IRS (InfraRed Spectrograph) on-board the Spitzer Space Telescope; possible jet twisting structure may be evidence of unique core dynamics. Here, we report results of recent VLA ammonia mapping observations of the dense gas envelope feeding the central core protostellar system. We describe the morphology, kinematics, and angular momentum characteristics of this unique system. The results are compared with the envelope structure deduced from IRAC 8-micron absorption of the PAH (polycyclic aromatic hydrocarbon) background emission from the cloud.

  8. Kinematics of the Envelope and Two Bipolar Jets in the Class 0 Protostellar System L1157

    NASA Astrophysics Data System (ADS)

    Kwon, Woojin; Fernández-López, Manuel; Stephens, Ian W.; Looney, Leslie W.

    2015-11-01

    A massive envelope and a strong bipolar outflow are the two main structures characterizing the youngest protostellar systems. In order to understand the physical properties of a bipolar outflow and the relationship with those of the envelope, we obtained a mosaic map covering the whole bipolar outflow of the youngest protostellar system L1157 with about 5″ angular resolution in CO J = 2-1 using the Combined Array for Research in Millimeter-wave Astronomy. By utilizing these observations of the whole bipolar outflow, we estimate its physical properties and show that they are consistent with multiple jets. We also constrain a preferred precession direction. In addition, we observed the central envelope structure with 2″ resolution in the λ =1.3 and 3 mm continua and various molecular lines: C17O, C18O, 13CO, CS, CN, N2H+, CH3OH, H2O, SO, and SO2. All of the CO isotopes and CS, CN, and N2H+ have been detected and imaged. We marginally detected the features that can be interpreted as a rotating inner envelope in C17O and C18O and as an infalling outer envelope in N2H+. We also estimated the envelope and central protostellar masses and found that the dust-opacity spectral index changes with radius.

  9. The Infrared Reflection Nebula Around the Protostellar System in S140

    NASA Technical Reports Server (NTRS)

    Harker, D.; Bregman, J.; Tielens, A. G. G. M.; Temi, P.; Rank, D.; Morrison, David (Technical Monitor)

    1994-01-01

    We have studied the protostellar system in S140 at 2.2, 3.1 and 3.45 microns using a 128x128 InSb array at the Lick Observatory 3m telescope. Besides the protostellar sources, the data reveal a bright infrared reflection nebula. We have developed a simple model of this region and derived the physical conditions. IRSI is surrounded by a dense dusty disk viewed almost edge-on. Photons leaking out through the poles illuminate almost directly north and south the inner edge of a surrounding shell of molecular gas, Analysis of the observed colors and intensities of the NIR light, using Mie scattering theory, reveal that the dust grains in the molecular cloud are somewhat larger than in the general diffuse interstellar medium. Moreover, the incident light has a "cool" color temperature, approximately equals 800K, and likely originates from a dust photosphere close to the protostar. Finally, we find little H2O ice associated with the dusty disk around IRSI. Most of the 3.1 micron ice extinction arises instead from cool intervening molecular cloud material. We have compared our infrared dust observations with millimeter and radio observations of molecular gas associated with this region. The large scale structure observable in the molecular gas is indicative of the interaction between the protostellar wind and the surrounding molecular cloud rather than the geometry of the protostellar disk. We conclude that S140 is a young blister formed by this outflow on the side of a molecular cloud and viewed edge-on.

  10. Keplerian Circumbinary Disk and Accretion Streams around the Protostellar Binary System L1551 NE

    NASA Astrophysics Data System (ADS)

    Takakuwa, S.; Saito, M.; Lim, J.; Saigo, K.; Hanawa, T.; Matsumoto, T.

    2013-10-01

    We show our recent observational results of L1551 NE, an archetypal binary protostellar system, in the 0.9-mm dust continuum emission and the C18O (J=3-2) emission with the SubMillimeter Array (SMA). The SMA results show firm evidence for a Keplerian circumbinary disk, circumstellar disks, and an inner clearing in the circumbinary disk, in L1551 NE. We demonstrate that future observations of L1551 NE with Atacama Large Millimeter and submillimeter Array (ALMA) have the potential to unveil the theoretically-predicted “accretion streams” that channel material from the circumbinary disk to the individual circumstellar disks.

  11. 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.

  12. The physical parameters of the low-mass multiple system LHS1070 from Spectral synthesis analysis

    NASA Astrophysics Data System (ADS)

    Rajpurohit, A. S.; Reylé, C.; Schultheis, M.; Leinert, C.; Allard, F.

    2011-12-01

    LHS1070 is a nearby multiple systems of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limit. The primary of the system consist of a mid-M dwarf and two components are late-M to L dwarf, at the star-brown dwarf transition. It makes it even more valuable to understand the formation of dust in cool stellar atmospheres.This work aims to determine the fundamental parameters of LHS1070 and to test recent model atmospheres.We compared the well calibrated data in the optical and infra-red with synthetic spectra computed from recent cool stars atmosphere models. We derived the physical parameters T_{eff}, radius and log g for three components of LHS1070. The models which include the formation and settle of dust are able to reproduce and describe the main features of the visible to IR spectra of the components.

  13. 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.

  14. DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. XI. V1191 CYGNI

    SciTech Connect

    Zhu, L. Y.; Qian, S. B.; He, J. J.; Liu, L.

    2011-10-15

    Complete CCD photometric light curves in BV(RI){sub c} bands obtained on one night in 2009 for the short-period close-binary system V1191 Cygni are presented. A new photometric analysis with the 2003 version of the Wilson-Van Hamme code shows that V1191 Cyg is a W-type overcontact binary system and suggests that it has a high degree of overcontact (f = 68.6%) with very low mass ratio, implying that it is at the late stage of overcontact evolution. The absolute parameters of V1191 Cyg are derived using spectroscopic and photometric solutions. Combining new determined times of light minimum with others published in the literature, the period change of the binary star is investigated. A periodic variation, with a period of 26.7 years and an amplitude of 0.023 days, was discovered to be superimposed on a long-term period increase (dP/dt = +4.5({+-} 0.1) x 10{sup -7} days yr{sup -1}). The cyclic period oscillation may be caused by the magnetic activity cycles of either of the components or the light-time effect due to the presence of a third body with a mass of m{sub 3} = 0.77 M{sub sun} and an orbital radius of a{sub 3} = 7.6 AU, when this body is coplanar to the orbit of the eclipsing pair. The secular orbital period increase can be interpreted as a mass transfer from the less massive component to the more massive one. With the period increases, V1191 Cyg will evolve from its present low mass ratio, high filled overcontact state to a rapidly rotating single star when its orbital angular momentum is less than three times the total spin angular momentum. V1191 Cyg is too blue for its orbital period and it is an unusual W-type overcontact system with such a low mass ratio and high fill-out overcontact configuration, which is worth monitoring continuously in the future.

  15. ASAS J083241+2332.4: A New Extreme Low Mass Ratio Overcontact Binary System

    NASA Astrophysics Data System (ADS)

    Sriram, K.; Malu, S.; Choi, C. S.; Vivekananda Rao, P.

    2016-03-01

    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-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, qcritical = 0.07-0.09, overcontact binaries should merge and form a fast rotating star, but it has been suggested that qcritical 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 L2 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.

  16. Discovery and Characterization of Wide Binary Systems with a Very Low Mass Component

    NASA Astrophysics Data System (ADS)

    Baron, Frédérique; Lafrenière, David; Artigau, Étienne; Doyon, René; Gagné, Jonathan; Davison, Cassy L.; Malo, Lison; Robert, Jasmin; Nadeau, Daniel; Reylé, Céline

    2015-03-01

    We report the discovery of 14 low-mass binary systems containing mid-M to mid-L dwarf companions with separations larger than 250 AU. We also report the independent discovery of nine other systems with similar characteristics that were recently discovered in other studies. We have identified these systems by searching for common proper motion sources in the vicinity of known high proper motion stars, based on a cross-correlation of wide area near-infrared surveys (2MASS, SDSS, and SIMP). An astrometric follow-up, for common proper motion confirmation, was made with SIMON and/or CPAPIR at the Observatoire du Mont Mégantic 1.6 m and CTIO 1.5 m telescopes for all the candidates identified. A spectroscopic follow-up was also made with GMOS or GNIRS at Gemini to determine the spectral types of 11 of our newly identified companions and 10 of our primaries. Statistical arguments are provided to show that all of the systems we report here are very likely to be physical binaries. One of the new systems reported features a brown dwarf companion: LSPM J1259+1001 (M5) has an L4.5 (2M1259+1001) companion at ˜340 AU. This brown dwarf was previously unknown. Seven other systems have a companion of spectral type L0-L1 at a separation in the 250-7500 AU range. Our sample includes 14 systems with a mass ratio below 0.3.

  17. Characterization of the Very-low-mass Secondary in the GJ 660.1AB System

    NASA Astrophysics Data System (ADS)

    Aganze, Christian; Burgasser, Adam J.; Faherty, Jacqueline K.; Choban, Caleb; Escala, Ivanna; Lopez, Mike A.; Jin, Yuhui; Tamiya, Tomoki; Tallis, Melisa; Rockward, Willie

    2016-02-01

    We present a spectroscopic analysis of the low-mass binary star system GJ 660.1AB, a pair of nearby M dwarfs for which we have obtained separated near-infrared spectra (0.9-2.5 μm) with the SpeX spectrograph. The spectrum of GJ 660.1B is distinctly peculiar, with a triangular-shaped 1.7 μm peak that initially suggests that it is a low-surface-gravity, young brown dwarf. However, we rule out this hypothesis and determine instead that this companion is a mild subdwarf (d/sdM7) based on the subsolar metallicity of the primary, [Fe/H] = -0.63 ± 0.06. Comparison of the near-infrared spectrum of GJ 660.1B to two sets of spectral models yields conflicting results, with a common effective temperature of Teff = 2550-2650 K, but alternately low surface gravity ({log}g = {4.4}-0.5+0.5) and very low metallicity ([M/H] = -{0.96}-0.24+0.19), or high surface gravity ({log}g = 5.0-5.5) and slightly subsolar metallicity ([M/H] = -{0.20}-0.19+0.13). We conjecture that insufficient condensate opacity and excessive collision-induced H2 absorption in the models bias them toward low surface gravities and a metallicity that is inconsistent with the primary and points toward improvements needed in the spectral modeling of metal-poor, very-low-mass dwarfs. The peculiar spectral characteristics of GJ 660.1B emphasize that care is needed when interpreting surface gravity features in the spectra of ultracool dwarfs.

  18. 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.

  19. Combining Astrometry and Light-time Effect: Low-mass Companions around Eclipsing Systems

    NASA Astrophysics Data System (ADS)

    Ribas, I.

    2005-07-01

    We discuss a method to determine orbital properties and masses of low-mass bodies orbiting eclipsing binaries based on combined analyses of light-travel time (LTT) and astrometry. The presence of a third body causes the relative distance of the eclipsing pair to the Earth to change as it orbits the barycenter of the triple system, thus causing periodic variations of the eclipse arrival times. Studies of the eclipsing systems V471 Tau and R CMa are presented to illustrate the method. The eclipse timings of V471 Tau indicate the presence of a third body with substellar minimum mass. In R CMa the companion is an M-type star or a white dwarf with a minimum mass of about 0.3 M⊙. The same reflex motion responsible for LTT effects also causes a displacement of the binary pair around the barycenter. The combination of the LTT analysis and accurate astrometry leads to the determination of the orbital inclination and thus to a full characterization of the orbital and physical properties of the tertiary component. With the upcoming microarcsecond-level astrometric missions, the technique that we discuss can be successfully applied to detect long-period planetary-size objects and brown dwarfs around eclipsing binaries.

  20. MAGNETIC FIELD STRUCTURE IN THE FLATTENED ENVELOPE AND JET IN THE YOUNG PROTOSTELLAR SYSTEM HH 211

    SciTech Connect

    Lee, Chin-Fei; Rao, Ramprasad; Hirano, Naomi; Ho, Paul T. P.; Hwang, Hsiang-Chih; Ching, Tao-Chung; Lai, Shih-Ping

    2014-12-10

    HH 211 is a young Class 0 protostellar system with a flattened envelope, a possible rotating disk, and a collimated jet. We have mapped it with the Submillimeter Array in the 341.6 GHz continuum and SiO J = 8-7 at ∼0.''6 resolution. The continuum traces the thermal dust emission in the flattened envelope and the possible disk. Linear polarization is detected in the continuum in the flattened envelope. The field lines implied from the polarization have different orientations, but they are not incompatible with current gravitational collapse models, which predict a different orientation depending on the region/distance. Also, we might have detected for the first time polarized SiO line emission in the jet due to the Goldreich-Kylafis effect. Observations at higher sensitivity are needed to determine the field morphology in the jet.

  1. DISENTANGLING THE ENTANGLED: OBSERVATIONS AND ANALYSIS OF THE TRIPLE NON-COEVAL PROTOSTELLAR SYSTEM VLA1623

    SciTech Connect

    Murillo, Nadia M.; Lai, Shih-Ping E-mail: slai@phys.nthu.edu.tw

    2013-02-10

    Commonplace at every evolutionary stage, multiple protostellar systems (MPSs) are thought to be formed through fragmentation, but it is unclear when and how. The youngest MPSs, which have not yet undergone much evolution, provide important constraints to this question. It is then of interest to disentangle early stage MPSs. In this Letter we present the results of our work on VLA1623 using our observations and archival data from the Submillimeter Array. Our continuum and line observations trace VLA1623's components, outflow, and envelope, revealing unexpected characteristics. We construct the spectral energy distribution (SED) for each component using the results of our work and data from literature, as well as derive physical parameters from continuum and perform a simple kinematical analysis of the circumstellar material. Our results show VLA1623 to be a triple non-coeval system composed of VLA1623A, B, and W, with each source driving its own outflow and unevenly distributed circumstellar material. From the SED, physical parameters, and IR emission we conclude that VLA1623A and W are Class 0 and Class I protostars, respectively, and together drive the bulk of the observed outflow. Furthermore, we find two surprising results, first the presence of a rotating disk-like structure about VLA1623A with indications of pure Keplerian rotation, which, if real, would make it one of the first evidence of Keplerian disk structures around Class 0 protostars. Second, we find VLA1623B to be a bona fide extremely young protostellar object between the starless core and Class 0 stages.

  2. Possible planet formation in the young, low-mass, multiple stellar system GG Tau A.

    PubMed

    Dutrey, Anne; Di Folco, Emmanuel; Guilloteau, Stéphane; Boehler, Yann; Bary, Jeff; Beck, Tracy; Beust, Hervé; Chapillon, Edwige; Gueth, Fredéric; Huré, Jean-Marc; Pierens, Arnaud; Piétu, Vincent; Simon, Michal; Tang, Ya-Wen

    2014-10-30

    The formation of planets around binary stars may be more difficult than around single stars. In a close binary star (with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks around each star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars. Given that the inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing material must be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one million years). Gas flowing through disk cavities has been detected in single star systems. A circumbinary disk was discovered around the young low-mass binary system GG Tau A (ref. 7), which has recently been shown to be a hierarchical triple system. It has one large inner disk around the single star, GG Tau Aa, and shows small amounts of shocked hydrogen gas residing within the central cavity, but other than a single weak detection, the distribution of cold gas in this cavity or in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragments emitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that the flow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planet formation to occur there. These results show the complexity of planet formation around multiple stars and confirm the general picture predicted by numerical simulations. PMID:25355359

  3. 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

  4. Eccentricity Evolution of Extrasolar Multiple Planetary Systems Due to the Depletion of Nascent Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Nagasawa, M.; Lin, D. N. C.; Ida, S.

    2003-04-01

    Most extrasolar planets are observed to have eccentricities much larger than those in the solar system. Some of these planets have sibling planets, with comparable masses, orbiting around the same host stars. In these multiple planetary systems, eccentricity is modulated by the planets' mutual secular interaction as a consequence of angular momentum exchange between them. For mature planets, the eigenfrequencies of this modulation are determined by their mass and semimajor axis ratios. However, prior to the disk depletion, self-gravity of the planets' nascent disks dominates the precession eigenfrequencies. We examine here the initial evolution of young planets' eccentricity due to the apsidal libration or circulation induced by both the secular interaction between them and the self-gravity of their nascent disks. We show that as the latter effect declines adiabatically with disk depletion, the modulation amplitude of the planets' relative phase of periapsis is approximately invariant despite the time-asymmetrical exchange of angular momentum between planets. However, as the young planets' orbits pass through a state of secular resonance, their mean eccentricities undergo systematic quantitative changes. For applications, we analyze the eccentricity evolution of planets around υ Andromedae and HD 168443 during the epoch of protostellar disk depletion. We find that the disk depletion can change the planets' eccentricity ratio. However, the relatively large amplitude of the planets' eccentricity cannot be excited if all the planets had small initial eccentricities.

  5. PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS

    SciTech Connect

    Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Tamura, Motohide

    2015-01-01

    We present results from a high-contrast adaptive optics imaging search for giant planets and brown dwarfs (≳1 M {sub Jup}) around 122 newly identified nearby (≲40 pc) young M dwarfs. Half of our targets are younger than 135 Myr and 90% are younger than the Hyades (620 Myr). After removing 44 close stellar binaries (implying a stellar companion fraction of >35.4% ± 4.3% within 100 AU), 27 of which are new or spatially resolved for the first time, our remaining sample of 78 single M dwarfs makes this the largest imaging search for planets around young low-mass stars (0.1-0.6 M {sub ☉}) to date. Our H- and K-band coronagraphic observations with Keck/NIRC2 and Subaru/HiCIAO achieve typical contrasts of 12-14 mag and 9-13 mag at 1'', respectively, which correspond to limiting planet masses of 0.5-10 M {sub Jup} at 5-33 AU for 85% of our sample. We discovered four young brown dwarf companions: 1RXS J235133.3+312720 B (32 ± 6 M {sub Jup}; L0{sub −1}{sup +2}; 120 ± 20 AU), GJ 3629 B (64{sub −23}{sup +30} M {sub Jup}; M7.5 ± 0.5; 6.5 ± 0.5 AU), 1RXS J034231.8+121622 B (35 ± 8 M {sub Jup}; L0 ± 1; 19.8 ± 0.9 AU), and 2MASS J15594729+4403595 B (43 ± 9 M {sub Jup}; M8.0 ± 0.5; 190 ± 20 AU). Over 150 candidate planets were identified; we obtained follow-up imaging for 56% of these but all are consistent with background stars. Our null detection of planets enables strong statistical constraints on the occurrence rate of long-period giant planets around single M dwarfs. We infer an upper limit (at the 95% confidence level) of 10.3% and 16.0% for 1-13 M {sub Jup} planets between 10-100 AU for hot-start and cold-start (Fortney) evolutionary models, respectively. Fewer than 6.0% (9.9%) of M dwarfs harbor massive gas giants in the 5-13 M {sub Jup} range like those orbiting HR 8799 and β Pictoris between 10-100 AU for a hot-start (cold-start) formation scenario. The frequency of brown dwarf (13-75 M {sub Jup}) companions to single

  6. Planets around Low-mass Stars (PALMS). IV. The Outer Architecture of M Dwarf Planetary Systems

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Tamura, Motohide

    2015-01-01

    We present results from a high-contrast adaptive optics imaging search for giant planets and brown dwarfs (gsim1 M Jup) around 122 newly identified nearby (lsim40 pc) young M dwarfs. Half of our targets are younger than 135 Myr and 90% are younger than the Hyades (620 Myr). After removing 44 close stellar binaries (implying a stellar companion fraction of >35.4% ± 4.3% within 100 AU), 27 of which are new or spatially resolved for the first time, our remaining sample of 78 single M dwarfs makes this the largest imaging search for planets around young low-mass stars (0.1-0.6 M ⊙) to date. Our H- and K-band coronagraphic observations with Keck/NIRC2 and Subaru/HiCIAO achieve typical contrasts of 12-14 mag and 9-13 mag at 1'', respectively, which correspond to limiting planet masses of 0.5-10 M Jup at 5-33 AU for 85% of our sample. We discovered four young brown dwarf companions: 1RXS J235133.3+312720 B (32 ± 6 M Jup; L0+2-1; 120 ± 20 AU), GJ 3629 B (64+30-23 M Jup; M7.5 ± 0.5; 6.5 ± 0.5 AU), 1RXS J034231.8+121622 B (35 ± 8 M Jup; L0 ± 1; 19.8 ± 0.9 AU), and 2MASS J15594729+4403595 B (43 ± 9 M Jup; M8.0 ± 0.5; 190 ± 20 AU). Over 150 candidate planets were identified; we obtained follow-up imaging for 56% of these but all are consistent with background stars. Our null detection of planets enables strong statistical constraints on the occurrence rate of long-period giant planets around single M dwarfs. We infer an upper limit (at the 95% confidence level) of 10.3% and 16.0% for 1-13 M Jup planets between 10-100 AU for hot-start and cold-start (Fortney) evolutionary models, respectively. Fewer than 6.0% (9.9%) of M dwarfs harbor massive gas giants in the 5-13 M Jup range like those orbiting HR 8799 and β Pictoris between 10-100 AU for a hot-start (cold-start) formation scenario. The frequency of brown dwarf (13-75 M Jup) companions to single M dwarfs between 10-100 AU is 2.8+2.4-1.5%. Altogether we find that giant planets, especially massive ones, are rare

  7. Rotationally driven Fragmentation in the Formation of the Binary Protostellar System L1551 IRS 5

    NASA Astrophysics Data System (ADS)

    Lim, Jeremy; Yeung, Paul K. H.; Hanawa, Tomoyuki; Takakuwa, Shigehisa; Matsumoto, Tomoaki; Saigo, Kazuya

    2016-08-01

    Both bulk rotation and local turbulence have been widely suggested to drive the fragmentation in collapsing cores that produces multiple star systems. Even when the two mechanisms predict different alignments for stellar spins and orbits, subsequent internal or external interactions can drive multiple systems toward or away from alignment, thus masking their formation processes. Here, we demonstrate that the geometrical and dynamical relationship between a binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel, not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 years indicate an orbital motion related to that of the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smaller than observed, the remaining solutions favor a circular or low-eccentricity orbit tilted by up to ∼25° from the circumstellar disks. Turbulence-driven fragmentation can generate local angular momentum to produce a coplanar binary system, but this would have no particular relationship to the system’s surrounding envelope. Instead, the observed properties conform with predictions for rotationally driven fragmentation. If the fragments were produced at different heights or on opposite sides of the mid-plane in the flattened central region of a rotating core, the resulting protostars would then exhibit circumstellar disks parallel with the surrounding envelope but tilted from the orbital plane, as is observed.

  8. 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.

  9. Deep, Low Mass Ratio Overcontact Binary Systems. XIII. DZ Piscium with Intrinsic Light Variability

    NASA Astrophysics Data System (ADS)

    Yang, Y.-G.; Qian, S.-B.; Zhang, L.-Y.; Dai, H.-F.; Soonthornthum, B.

    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., LC2 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 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)\\times 10^{-7}{\\,days\\, yr^{-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 spin/J orb > 1/3.

  10. 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}.

  11. Wide Low-Mass Tertiary Companions of Binary Star Systems as a Test of Star Formation Theories

    NASA Astrophysics Data System (ADS)

    Douglas, Stephanie; Allen, P.

    2012-01-01

    We will present the status of a common proper motion search for wide low-mass stellar and sub-stellar companions to known white dwarf-M dwarf binary systems. I-band observations were made using the 31" NURO telescope at Lowell Observatory. Candidate companions are selected using astrometry from our own data and 2MASS photometry. We have begun to spectroscopically confirm candidates that pass our selection criteria. The ultimate goal of the search is to test star formation theories which predict that close binary systems form by transferring angular momentum to a third companion. To this end, we will model the physical companion population and perform Bayesian statistical analysis to determine the best-fit population model to our data. Here we will present our spectroscopically confirmed companions as well as the preliminary results of our population models and statistical analysis.

  12. RESOLVING THE sin(I) DEGENERACY IN LOW-MASS MULTI-PLANET SYSTEMS

    SciTech Connect

    Batygin, Konstantin; Laughlin, Gregory

    2011-04-01

    Long-term orbital evolution of multi-planet systems under tidal dissipation often converges to a stationary state, known as the tidal fixed point. The fixed point is characterized by a lack of oscillations in the eccentricities and apsidal alignment among the orbits. Quantitatively, the nature of the fixed point is dictated by mutual interactions among the planets as well as non-Keplerian effects. We show that if a roughly coplanar system hosts a hot, sub-Saturn mass planet, and is tidally relaxed, separation of planet-planet interactions and non-Keplerian effects in the equations of motion leads to a direct determination of the true masses of the planets. Consequently, a 'snap-shot' observational determination of the orbital state resolves the sin(I) degeneracy and opens up a direct avenue toward identification of the true lowest-mass exoplanets detected. We present an approximate, as well as a general, mathematical framework for computation of the line-of-sight inclination of secular systems, and apply our models illustratively to the 61 Vir system. We conclude by discussing the observability of planetary systems to which our method is applicable and we set our analysis into a broader context by presenting a current summary of the various possibilities for determining the physical properties of planets from observations of their orbital states.

  13. The very low mass triple system - G208-44AB and G208-45

    NASA Technical Reports Server (NTRS)

    Mccarthy, D. W., Jr.; Henry, Todd J.; Fleming, Thomas A.; Saffer, Rex A.; Liebert, James

    1988-01-01

    The nearby (4.7 pc) system G208-44/45 is the closest known stellar triple beyond the Centaurus system. The close astrometric pair 44AB has been resolved using IR speckle interferometry in the JHK bands, yielding individual masses of 0.14 + or - 0.03 solar and 0.10 + or - 0.02 solar for A and B, respectively. The absolute K magnitudes are 8.9 and 10.0, respectively, while the distant component 45 has K = 9.1 and should therefore have a mass slightly below that of 44A. The JHK colors and spectral types are consistent with these values. These results indicate that 44B is the lowest luminosity component known in an astrometric binary and suggest that it could be substellar. Both 44AB and 45 show strong chromospheric H-alpha and Ca II emission. The system kinematics, large implied rotation rate of 44AB, and level of chromospheric activity in the side component suggest a relatively young system.

  14. Deep, Low Mass Ratio Overcontact Binary Systems. V. The Lowest Mass Ratio Binary V857 Herculis

    NASA Astrophysics Data System (ADS)

    Qian, S.-B.; Zhu, L.-Y.; Soonthornthum, B.; Yuan, J.-Z.; Yang, Y.-G.; He, J.-J.

    2005-09-01

    Charge-coupled device (CCD) photometric light curves in the B, V, and R bands of the complete eclipsing binary star V857 Her are presented. It is shown that the light curves of the W UMa-type binary are symmetric and of A type according to Binnendijk's classification. Our four epochs of light minimum along with others compiled from the literature were used to revise the period and study the period change. Weak evidence indicates that the orbital period of V857 Her may show a continuous increase at a rate of dP/dt=+2.90×10-7 days yr-1. The photometric parameters of the system were determined with the 2003 version of the Wilson-Devinney code. It is shown that V857 Her is a deep overcontact binary system with f=83.8%+/-5.1%. The derived mass ratio of q=0.06532+/-0.0002 suggests that it has the lowest mass ratio among overcontact binary systems. As the orbital period increases, the decrease of the mass ratio will cause it to evolve into a single rapidly rotating star when it meets the more familiar criterion that the orbital angular momentum be less than 3 times the total spin angular momentum. To understand the evolutionary state of the system, long-term photometric monitoring and spectroscopic observations will be required.

  15. FORMATION OF MULTIPLE-SATELLITE SYSTEMS FROM LOW-MASS CIRCUMPLANETARY PARTICLE DISKS

    SciTech Connect

    Hyodo, Ryuki; Ohtsuki, Keiji; Takeda, Takaaki E-mail: ohtsuki@tiger.kobe-u.ac.jp

    2015-01-20

    Circumplanetary particle disks would be created in the late stage of planetary formation either by impacts of planetary bodies or disruption of satellites or passing bodies, and satellites can be formed by accretion of disk particles spreading across the Roche limit. Previous N-body simulation of lunar accretion focused on the formation of single-satellite systems from disks with large disk-to-planet mass ratios, while recent models of the formation of multiple-satellite systems from disks with smaller mass ratios do not take account of gravitational interaction between formed satellites. In the present work, we investigate satellite accretion from particle disks with various masses, using N-body simulation. In the case of accretion from somewhat less massive disks than the case of lunar accretion, formed satellites are not massive enough to clear out the disk, but can become massive enough to gravitationally shepherd the disk outer edge and start outward migration due to gravitational interaction with the disk. When the radial location of the 2:1 mean motion resonance of the satellite reaches outside the Roche limit, the second satellite can be formed near the disk outer edge, and then the two satellites continue outward migration while being locked in the resonance. Co-orbital satellites are found to be occasionally formed on the orbit of the first satellite. Our simulations also show that stochastic nature involved in gravitational interaction and collision between aggregates in the tidal environment can lead to diversity in the final mass and orbital architecture, which would be expected in satellite systems of exoplanets.

  16. Finite element simulations of low-mass readout cables for the CBM Silicon Tracking System using RAPHAEL

    NASA Astrophysics Data System (ADS)

    Singla, M.; Chatterji, S.; Müller, W. F. J.; Kleipa, V.; Heuser, J. M.

    2014-01-01

    The first three-dimensional simulation study of thin multi-line readout cables using finite element simulation tool RAPHAEL is being reported. The application is the Silicon Tracking System (STS) of the fixed-target heavy-ion experiment Compressed Baryonic Matter (CBM), under design at the forthcoming accelerator center FAIR in Germany. RAPHAEL has been used to design low-mass analog readout cables with minimum possible Equivalent Noise Charge (ENC). Various trace geometries and trace materials have been explored in detail for this optimization study. These cables will bridge the distance between the microstrip detectors and the signal processing electronics placed at the periphery of the silicon tracking stations. SPICE modeling has been implemented in Sentaurus Device to study the transmission loss (dB loss) in cables and simulation has been validated with measurements. An optimized design having minimum possible ENC, material budget and transmission loss for the readout cables has been proposed.

  17. 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.

  18. Development of low mass optical readout for high data bandwidth systems.

    SciTech Connect

    Underwood, D.; DeLurgio, P.; Drake, G.; Fernando, W.; Lopez, D.; Salvachua-Ferrando, B.; Stanek, R.

    2010-10-01

    At Argonne National Laboratory the High Energy Physics and Center for Nanoscale Materials Divisions are working on a project to develop a new generation of detector readout using high speed data transfer optical devices that can be implemented in particle physics or for long distances. Free-space communications devices offer the potential for reductions in mass, power, and cost of data paths for on-board trigger and readout of tracking detectors. The project involves three areas of study: light modulation, the design and construction of MEMS optical devices, and the control systems for maintaining precise laser light positioning. We demonstrate an optical link in air over one meter and with low error rate at 1 Gb/s. We demonstrate steering of an optical beam over a meter with a precision of 5 micrometers utilizing a MEMS mirror and reflected light in the feedback loop. For early testing, light modulation tests with a fiber link using Li-Niobate modulators and a data generation and error checking chip are done at 1 Gb/s. Many companies and universities are developing modulators which will be incorporated into CMOS chips. We are doing radiation hardness studies for one of the materials involved. Laser light will need to be steered on to and kept centered on the detector in the presence of thermal or mechanical motion, etc. This steering will be controlled by MEMS mirrors. Polycrystalline and crystalline silicon based mirror designs are being studied. We review the current status of the project and outline plans for the future development of the system.

  19. A closely packed system of low-mass, low-density planets transiting Kepler-11.

    PubMed

    Lissauer, Jack J; Fabrycky, Daniel C; Ford, Eric B; Borucki, William J; Fressin, Francois; Marcy, Geoffrey W; Orosz, Jerome A; Rowe, Jason F; Torres, Guillermo; Welsh, William F; Batalha, Natalie M; Bryson, Stephen T; Buchhave, Lars A; Caldwell, Douglas A; Carter, Joshua A; Charbonneau, David; Christiansen, Jessie L; Cochran, William D; Desert, Jean-Michel; Dunham, Edward W; Fanelli, Michael N; Fortney, Jonathan J; Gautier, Thomas N; Geary, John C; Gilliland, Ronald L; Haas, Michael R; Hall, Jennifer R; Holman, Matthew J; Koch, David G; Latham, David W; Lopez, Eric; McCauliff, Sean; Miller, Neil; Morehead, Robert C; Quintana, Elisa V; Ragozzine, Darin; Sasselov, Dimitar; Short, Donald R; Steffen, Jason H

    2011-02-01

    When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47 days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation. PMID:21293371

  20. Angular Momentum Loss in the Envelope–Disk Transition Region of the HH 111 Protostellar System: Evidence for Magnetic Braking?

    NASA Astrophysics Data System (ADS)

    Lee, Chin-Fei; Hwang, Hsiang-Chih; Li, Zhi-Yun

    2016-08-01

    HH 111 is a Class I protostellar system at a distance of ˜400 pc, with the central source VLA 1 associated with a rotating disk deeply embedded in a flattened envelope. Here we present the observations of this system at ˜0.″6 (240 au) resolution in C18O (J = 2 — 1) and a 230 GHz continuum obtained with the Atacama Large Millimeter/Submillimeter Array, and in SO ({N}J = {5}6-{4}5) obtained with the Submillimeter Array. The observations show for the first time how a Keplerian rotating disk can be formed inside a flattened envelope. The flattened envelope is detected in C18O, extending out to ≳2400 au from the VLA 1 source. It has a differential rotation, with the outer part (≳2000 au) better described by a rotation that has constant specific angular momentum, and the innermost part (≲160 au) by a Keplerian rotation. The rotationally supported disk is therefore relatively compact in this system, which is consistent with the dust continuum observations. Most interestingly, if the flow is in steady state, there is a substantial drop in specific angular momentum in the envelope–disk transition region from 2000 to 160 au, by a factor of ˜3. Such a decrease is not expected outside a disk formed from simple hydrodynamic core collapse, but can happen naturally if the core is significantly magnetized, because magnetic fields can be trapped in the transition region outside the disk by the ram pressure of the protostellar accretion flow, which can lead to efficient magnetic braking. In addition, SO shock emission is detected around the outer radius of the disk and could trace an accretion shock around the disk.

  1. On the origin of the IMF: First detection of a low-mass star ejected from a triple stellar system

    NASA Astrophysics Data System (ADS)

    Loinard, L.; Rodriguez, L. F.; Rodriguez, M.

    2002-12-01

    Using high-resolution, multi-epoch VLA observations, we have detected orbital motions in several low-luminosity protobinary systems in the Taurus and rho-Ophiuchus molecular complexes. The masses obtained from Kepler's third law are of the order of 0.5 to 1 Msun, as would have been expected for such low-mass protostars. In addition, in one of the sources studied (a triple system in Taurus), one of the three component appears to have been recently ejected from the system. During the first 15 of the 20 years covered by the observations, this component has been on a closed elliptical orbit with a velocity of a few km/s, but in the last 5 years, it has started to spiral out at high speed (20 km/s). Such an ejection is not unexpected in a triple system, because such systems are thought to exhibit chaotic behaviours. However, this is the first time that it is detected directly. The implications for the IMF will be discussed

  2. The Discovery of a Second Luminous Low Mass X-Ray Binary System in the Globular Cluster M15

    NASA Technical Reports Server (NTRS)

    White, Nicholas E.; Angelini, Lorella

    2001-01-01

    Using the Chandra X-ray Observatory we have discovered a second bright X-ray source in the globular cluster M15 that is 2.7" to the west of AC211, the previously known low mass X-ray binary (LMXB) in this system. Prior to the 0.5" imaging capability of Chandra this second source could not have been resolved from AC211. The luminosity and spectrum of this new source, which we call M15-X2, are consistent with it also being a LMXB system. This is the first time that two LMXBs have been seen to be simultaneously active in a globular cluster. The new source, M15-X2, is coincident with a 18th U magnitude very blue star. The discovery of a second LMXB in M15 clears up a long standing puzzle where the X-ray and optical properties of AC211 appear consistent with the central source being hidden behind an accretion disk corona, and yet also showed a luminous X-ray burst suggesting the neutron star is directly visible. This discovery suggests instead that the X-ray burst did not come from AC211, but rather from the newly discovered X-ray source. We discuss the implications of this discovery for X-ray observations of globular clusters in nearby galaxies.

  3. Adaptive Optics imaging of VHS 1256-1257: A Low Mass Companion to a Brown Dwarf Binary System

    NASA Astrophysics Data System (ADS)

    Stone, Jordan M.; Skemer, Andrew J.; Kratter, Kaitlin M.; Dupuy, Trent J.; Close, Laird M.; Eisner, Josh A.; Fortney, Jonathan J.; Hinz, Philip M.; Males, Jared R.; Morley, Caroline V.; Morzinski, Katie M.; Ward-Duong, Kimberly

    2016-02-01

    Recently, Gauza et al. reported the discovery of a companion to the late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companion’s absolute photometry suggests its mass and atmosphere are similar to the HR 8799 planets. However, as a wide companion to a late-type star, it is more accessible to spectroscopic characterization. We discovered that the primary of this system is an equal-magnitude binary. For an age ˜300 Myr the A and B components each have a mass of {64.6}-2.0+0.8 {M}{Jup}, and the b component has a mass of {11.2}-1.8+9.7, making VHS 1256-1257 only the third brown dwarf triple system. There exists some tension between the spectrophotometric distance of 17.2 ± 2.6 pc and the parallax distance of 12.7 ± 1.0 pc. At 12.7 pc VHS 1256-1257 A and B would be the faintest known M7.5 objects, and are even faint outliers among M8 types. If the larger spectrophotmetric distance is more accurate than the parallax, then the mass of each component increases. In particular, the mass of the b component increases well above the deuterium burning limit to ˜ 35 {M}{Jup} and the mass of each binary component increases to {73}-17+20 {M}{Jup}. At 17.1 pc, the UVW kinematics of the system are consistent with membership in the AB Dor moving group. The architecture of the system resembles a hierarchical stellar multiple suggesting it formed via an extension of the star formation process to low masses. Continued astrometric monitoring will resolve this distance uncertainty and will provide dynamical masses for a new benchmark system.

  4. Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions

    NASA Astrophysics Data System (ADS)

    Vogt, N.; Schmidt, T. O. B.; Neuhäuser, R.; Bedalov, A.; Roell, T.; Seifahrt, A.; Mugrauer, M.

    2012-10-01

    masses twice as high as this value or more. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components, while extremely low-mass secondary components are hard to find for both high and low mass primaries owing to the much higher dynamic range and the faintness of the secondaries. Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 076.C-0292(A), 078.C-0535(A), 080.C-0424(A), 082.C-0489(A), 084.C-0364(B), 086.C-0638(A) & 086.C-0600(B), the Hubble Space Telescope under program ID GO-8716 and data obtained from the ESO/ST-ECF Science Archive Facility from the Paranal Observatory under program IDs 075.C-0042(A), 076.C-0579(A), 278.C-5070(A) and from the Hubble Space Telescope under programme IDs SNAP-7387, GO-11164. Appendix A is available in electronic form at http://www.aanda.org

  5. Gravitoturbulence in magnetized protostellar discs

    NASA Astrophysics Data System (ADS)

    Riols, A.; Latter, H.

    2016-08-01

    Gravitational instability (GI) features in several aspects of protostellar disc evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer regions of protostellar discs may also be coupled to magnetic fields, which could then modify the development of GI. To understand the basic elements of their interaction, we perform local 2D ideal and resistive magnetohydrodynamics simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravitoturbulent state, characterized by considerable magnetic energy and stress and a surprisingly large Toomre parameter Q ≳ 10. This result has potential implications for disc structure, vertical thickness, ionization, etc. Our simulations also reveal the existence of long-lived and dense `magnetic islands' or plasmoids. Lastly, we find that the presence of a magnetic field has little impact on the fragmentation criterion of the disc. Though our focus is on protostellar discs, some of our results may be relevant for the outer radii of AGN.

  6. DEEP, LOW-MASS RATIO OVERCONTACT BINARY SYSTEMS. XII. CK BOOTIS WITH POSSIBLE CYCLIC MAGNETIC ACTIVITY AND ADDITIONAL COMPANION

    SciTech Connect

    Yang, Y.-G.; Qian, S.-B.; Soonthornthum, B. E-mail: qsb@ynao.ac.cn

    2012-05-15

    We present precision CCD photometry, a period study, and a two-color simultaneous Wilson code solution of the short-period contact binary CK Bootis. The asymmetric light curves were modeled by a dark spot on the primary component. The result identifies that CK Boo is an A-type W UMa binary with a high fillout of f = 71.7({+-} 4.4)%. From the O - C curve, it is found that the orbital period changes in a complicated mode, i.e., a long-term increase with two sinusoidal variations. One cyclic oscillation with a period of 10.67({+-} 0.20) yr may result from magnetic activity cycles, which are identified by the variability of Max. I - Max. II. Another sinusoidal variation (i.e., A = 0.0131 days({+-} 0.0009 days) and P{sub 3} = 24.16({+-} 0.64) yr) may be attributed to the light-time effect due to a third body. This kind of additional companion can extract angular momentum from the central binary system. The orbital period secularly increases at a rate of dP/dt = +9.79 ({+-}0.80) Multiplication-Sign 10{sup -8} days yr{sup -1}, which may be interpreted by conservative mass transfer from the secondary to the primary. This kind of deep, low-mass ratio overcontact binaries may evolve into a rapid-rotating single star, only if the contact configuration do not break down at J{sub spin} > (1/3)J{sub orb}.

  7. Deep, Low Mass Ratio Overcontact Binary Systems. VI. AH Cancri in the Old Open Cluster M67

    NASA Astrophysics Data System (ADS)

    Qian, S.-B.; Liu, L.; Soonthornthum, B.; Zhu, L.-Y.; He, J.-J.

    2006-06-01

    CCD photometric light curves in the B and V bands obtained in 2001 and in the V band obtained in 2002 of AH Cnc in the old open cluster M67 are presented. It is shown that AH Cnc is a total-eclipsing binary and its light curves correspond to a typical A type according to Binnendijk's classification. The variations of the light curve around the primary minimum and second maximum were found. Our nine epochs of light minimum monitored from 2001 to 2005, including others collected from the literature, were used to create the first study of the period changes of the binary system. A cyclic oscillation with a period of 36.5 yr and an amplitude of 0.0237 days was discovered to be superposed on a continuous period increase (dP/dt=3.99×10-7 days yr-1). Weak evidence indicates that there exists another small-amplitude period oscillation (A4=0.0035 days, P4=7.75 yr). The symmetric light curves in the B and V bands obtained in 2001 were analyzed with the 2003 version of the Wilson-Devinney code. It is confirmed that AH Cnc is a deep overcontact binary system with a high degree of overcontact f=58.5%+/-4.5% and a low mass ratio of q=0.1682+/-0.0012. The existence of the third light and the cyclic period oscillation both may suggest that AH Cnc is a triple system containing an unseen third body. The tertiary component may have played an important role in the origin of the overcontact binary star by removing angular momentum from the central system, which would cause it to have a short initial orbital period and thus evolve into an overcontact configuration by angular momentum loss. The long-term period increase can be interpreted as a mass transfer from the less massive component to the more massive one. As the orbital period increases, the decrease of the mass ratio will cause it finally to evolve into a single rapid-rotating star when the system meets the more familiar criterion that the orbital angular momentum be less than 3 times the total spin angular momentum. Therefore

  8. Diversity of planetary systems in low-mass disks. Terrestrial-type planet formation and water delivery

    NASA Astrophysics Data System (ADS)

    Ronco, M. P.; de Elía, G. C.

    2014-07-01

    Context. Several studies, observational and theoretical, suggest that planetary systems with only rocky planets are the most common in the Universe. Aims: We study the diversity of planetary systems that might form around Sun-like stars in low-mass disks without gas-giant planets. We focus especially on the formation process of terrestrial planets in the habitable zone (HZ) and analyze their water contents with the goal to determine systems of astrobiological interest. In addition, we study the formation of planets on wide orbits because they can be detected with the microlensing technique. Methods: N-body simulations of high resolution were developed for a wide range of surface density profiles. A bimodal distribution of planetesimals and planetary embryos with different physical and orbital configurations was used to simulate the planetary accretion process. The surface density profile combines a power law for the inside of the disk of the form r-γ, with an exponential decay to the outside. We performed simulations adopting a disk of 0.03 M⊙ and values of γ = 0.5, 1 and 1.5. Results: All our simulations form planets in the HZ with different masses and final water contents depending on the three different profiles. For γ = 0.5, our simulations produce three planets in the HZ with masses ranging from 0.03 M⊕ to 0.1 M⊕ and water contents between 0.2 and 16 Earth oceans (1 Earth ocean =2.8 × 10-4 M⊕). For γ = 1, three planets form in the HZ with masses between 0.18 M⊕ and 0.52 M⊕ and water contents from 34 to 167 Earth oceans. Finally, for γ = 1.5, we find four planets in the HZ with masses ranging from 0.66 M⊕ to 2.21 M⊕ and water contents between 192 and 2326 Earth oceans. This profile shows distinctive results because it is the only one of those studied here that leads to the formation of water worlds. Conclusions: Since planetary systems with γ = 1 and 1.5 present planets in the HZ with suitable masses to retain a long-lived atmosphere and

  9. Protostellar Interferometric Line Survey (PILS): Constraining the formation of complex organic molecules with ALMA

    NASA Astrophysics Data System (ADS)

    Jorgensen, Jes K.; Coutens, Audrey; Bourke, Tyler L.; Favre, Cecile; Garrod, Robin; Lykke, Julie; Mueller, Holger; Oberg, Karin I.; Schmalzl, Markus; van der Wiel, Matthijs; van Dishoeck, Ewine; Wampfler, Susanne F.

    2015-08-01

    Understanding how, when and where complex organic and potentially prebiotic molecules are formed is a fundamental goal of astrochemistry and an integral part of origins of life studies. Already now ALMA is showing its capabilities for studies of the chemistry of solar-type stars with its high sensitivity for faint lines, high spectral resolution which limits line confusion, and high angular resolution making it possible to study the structure of young protostars on solar-system scales. We here present the first results from a large unbiased survey “Protostellar Interferometric Line Survey (PILS)” targeting one of the astrochemical template sources, the low-mass protostellar binary IRAS 16293-2422. The survey is more than an order of magnitude more sensitive than previous surveys of the source and provide imaging down to 25 AU scales (radius) around each of the two components of the binary. An example of one of the early highlights from the survey is unambiguous detections of the (related) prebiotic species glycolaldehyde, ethylene glycol (two lowest energy conformers), methyl formate and acetic acid. The glycolaldehyde-ethylene glycol abundance ratio is high in comparison to comets and other protostars - but agrees with previous measurements, e.g., in the Galactic Centre clouds possibly reflecting different environments and/or evolutionary histories. Complete mapping of this and other chemical networks in comparison with detailed chemical models and laboratory experiments will reveal the origin of complex organic molecules in a young protostellar system and investigate the link between these protostellar stages and the early Solar System.

  10. Angular momentum exchange by gravitational torques and infall in the circumbinary disk of the protostellar system L1551 NE

    SciTech Connect

    Takakuwa, Shigehisa; Ho, Paul T. P.; Saito, Masao; Saigo, Kazuya; Matsumoto, Tomoaki; Lim, Jeremy; Hanawa, Tomoyuki

    2014-11-20

    We report an ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C{sup 18}O (3-2), and {sup 13}CO (3-2) lines at a ∼1.6 times higher resolution and a ∼6 times higher sensitivity than those of our previous SubMillimeter Array (SMA) observations, which revealed a r ∼ 300 AU scale circumbinary disk in Keplerian rotation. The 0.9 mm continuum shows two opposing U-shaped brightenings in the circumbinary disk and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

  11. Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE

    NASA Astrophysics Data System (ADS)

    Takakuwa, Shigehisa; Saito, Masao; Saigo, Kazuya; Matsumoto, Tomoaki; Lim, Jeremy; Hanawa, Tomoyuki; Ho, Paul T. P.

    2014-11-01

    We report an ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SubMillimeter Array (SMA) observations, which revealed a r ~ 300 AU scale circumbinary disk in Keplerian rotation. The 0.9 mm continuum shows two opposing U-shaped brightenings in the circumbinary disk and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

  12. Deuterated water in low-mass protostars

    NASA Astrophysics Data System (ADS)

    Coutens, Audrey; Vastel, Charlotte; Chess Collaboration; Wish Collaboration; Hexos Collaboration

    2013-07-01

    In addition to its dominant role in the cooling of warm gas and in the oxygen chemistry, water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. Observations of deuterated water are an important complement for studies of H2O to understand how water forms and how it has evolved from cold prestellar cores to protoplanetary disks and consequently oceans for the Earth's specific, but probably not isolated, case. Several deuterated water transitions were observed with the Herschel/HIFI (Heterodyne Instrument for Far Infrared) instrument towards three low-mass protostars: IRAS 16293-2422, NGC1333 IRAS4A and NGC1333 IRAS4B. In the first source, both HDO and D2O lines are detected, thanks to the unbiased spectral survey carried out by the CHESS key program (Vastel et al. 2010, Coutens et al. 2013a). In the framework of a collaboration between the CHESS, WISH and HEXOS programs, two HDO key lines were observed towards the two other protostars. In addition, complementary observations were carried out with several ground-based single-dish telescopes (IRAM-30m, JCMT, APEX). We used the non-LTE RATRAN spherical model (Hogerheijde & van der Tak 2000) to determine the HDO abundance distribution throughout the protostellar envelope. An abundance jump at 100 K is required to reproduce the line profiles. Indeed, water molecules trapped in the icy grain mantles thermally desorb in the hot corinos, the inner warm regions of the protostellar envelopes. We also obtain that it is necessary to add a water-rich external absorbing layer to reproduce the absorbing components of the HDO and D2O fundamental transitions in all sources (Coutens et al. 2012, 2013a,b). The results derived for the different sources will be then presented and discussed.

  13. New Extinction and Mass Estimates of the Low-mass Companion 1RXS 1609 B with the Magellan AO System: Evidence of an Inclined Dust Disk

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Barman, Travis S.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa P.; Rodigas, Timothy J.; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa

    2015-07-01

    We used the Magellan adaptive optics system to image the 11 Myr substellar companion 1RXS 1609 B at the bluest wavelengths to date (z‧ and Ys). Comparison with synthetic spectra yields a higher temperature than previous studies of {T}{eff}=2000+/- 100 {{K}} and significant dust extinction of {A}V={4.5}-0.7+0.5 mag. Mass estimates based on the DUSTY tracks gives 0.012-0.015 {M}⊙ , making the companion likely a low-mass brown dwarf surrounded by a dusty disk. Our study suggests that 1RXS 1609 B is one of the ˜25% of Upper Scorpius low-mass members harboring disks, and it may have formed like a star and not a planet out at ˜320 AU. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

  14. Planet Forming Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Lubow, Stephen

    1998-01-01

    The project achieved many of its objectives. The main area of investigation was the interaction of young binary stars with surrounding protostellar disks. A secondary objective was the interaction of young planets with their central stars and surrounding disks. The grant funds were used to support visits by coinvestigators and visitors: Pawel Artymowicz, James Pringle, and Gordon Ogilvie. Funds were also used to support travel to meetings by Lubow and to provide partial salary support.

  15. RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION

    SciTech Connect

    Tomida, Kengo; Tomisaka, Kohji; Matsumoto, Tomoaki; Hori, Yasunori; Saigo, Kazuya; Okuzumi, Satoshi; Machida, Masahiro N. E-mail: tomisaka@th.nao.ac.jp E-mail: saigo.kazuya@nao.ac.jp E-mail: okuzumi@nagoya-u.jp

    2013-01-20

    We report the first three-dimensional radiation magnetohydrodynamic (RMHD) simulations of protostellar collapse with and without Ohmic dissipation. We take into account many physical processes required to study star formation processes, including a realistic equation of state. We follow the evolution from molecular cloud cores until protostellar cores are formed with sufficiently high resolutions without introducing a sink particle. The physical processes involved in the simulations and adopted numerical methods are described in detail. We can calculate only about one year after the formation of the protostellar cores with our direct three-dimensional RMHD simulations because of the extremely short timescale in the deep interior of the formed protostellar cores, but successfully describe the early phase of star formation processes. The thermal evolution and the structure of the first and second (protostellar) cores are consistent with previous one-dimensional simulations using full radiation transfer, but differ considerably from preceding multi-dimensional studies with the barotropic approximation. The protostellar cores evolve virtually spherically symmetric in the ideal MHD models because of efficient angular momentum transport by magnetic fields, but Ohmic dissipation enables the formation of the circumstellar disks in the vicinity of the protostellar cores as in previous MHD studies with the barotropic approximation. The formed disks are still small (less than 0.35 AU) because we simulate only the earliest evolution. We also confirm that two different types of outflows are naturally launched by magnetic fields from the first cores and protostellar cores in the resistive MHD models.

  16. The Evolution of Matter in the Embedded Stages of Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Jorgensen, Jes; Lommen, D.; Bourke, T. L.; van Dishoeck, E. F.; Wilner, D.; PROSAC Team

    2008-03-01

    One of the most important questions about low-mass star formation is how circumstellar disks form and evolve through the embedded protostellar stages. We present the results of high angular resolution (1-2"; 200-400 AU) observations from a large program, PROSAC, studying embedded low-mass protostars (Class 0 and I objects) with the Submillimeter Array. In total 17 sources have been observed in a variety of lines of common molecular species together with continuum at (sub)millimeter wavelengths. The continuum observations reveal the presence of compact emission on the smallest scales in all sources which can best be attributed to thermal emission from dust in the circumstellar disks. The inferred masses of the central disks are comparable for both Class 0 and I objects suggesting that disks are formed and rapidly grow in size early in the evolution of the protostars. Line observations of the more evolved Class I systems reveal rotational signatures which in turn constrain the central stellar masses. Together with single-dish continuum data, these observations for the first time allow us to trace evolution of the mass of the stars, disks and envelopes through these pivotal stages.

  17. Encounters with Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.

    1992-12-01

    A numerical study of encounters between stars with circumstellar disks has bee completed. Cross sections and rates for disk tilt, disk disruption, and binary formation are estimated using a large data base of encounter simulations. The consequences of these results for star-forming regions and our solar system are discussed. A numerical code is developed which is capable of evolving a mixture of stars and gas in three dimensions. The algorithm is based on the method of smoothed-particle hydrodynamics combined with the heirarchical tree method of computing gravitational forces. The code is tested by simulating the collision between two sheets of gas and the radial pulsations of a polytropic gas sphere. A protostellar-disk model is developed based on simple assumptions. Test encounters are performed to determine the sensitivity of measured quantities on algorithm parameters, such as the gravitational tolerance and viscosity. It is shown that the solar system could have had an encounter shortly after its formation of sufficient strength to generate the observed obliquity yet retain enough mass and radial extent to form the planetary system. For the Orion B clusters as a whole, it is estimated that during a one-million-year period of time a few percent of the stars will experience an enoucnter that results in a disk tilt of 7 degrees or greater. For the central regions of NGC 2024 and the Trapezium cluster values of 24% and 39% are obtained, respectively. Encounters between equal-mass stars with periastra of 0.5, 1.0, 1.5, and 2.0 disk radii will retain on average about 15%, 40%, 55%, and 75% of the disk mass, respectively. For encounters that do not penetrate the disk a minimum of 15% of the mass is retained. Even in dense environments the characteristic lifetime of a disk due to disruptive encounters can be many millions of years. On average, an encounter that penetrates the disk will dissipate an amount of orbital energy equal to approximately 50% of the initial

  18. The solar neighborhood. XXXIII. Parallax results from the CTIOPI 0.9 m program: trigonometric parallaxes of Nearby low-mass active and young systems

    SciTech Connect

    Riedel, Adric R.; Cruz, Kelle L.; Finch, Charlie T.; Henry, Todd J.; Jao, Wei-Chun; White, Russel J.; Gies, Douglas R.; Dieterich, Sergio B.; Winters, Jennifer G.; Davison, Cassy L.; Subasavage, John P.; Malo, Lison; Rodriguez, David R.; Nelan, Edmund P.; Blunt, Sarah C.; Rice, Emily L.; Ianna, Philip A.

    2014-04-01

    We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing Research Consortium On Nearby Stars photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log (L{sub X} /L {sub bol}) > –3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9 m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5 m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHK{sub S} photometry from the Two Micron All Sky Survey point source catalog, X-ray data from the ROSAT All-Sky Survey, and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of β Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous ≈30 Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25 pc of the Sun.

  19. VizieR Online Data Catalog: 6.7GHz methanol masers survey of low-mass YSO (Minier+, 2003)

    NASA Astrophysics Data System (ADS)

    Minier, V.; Ellingsen, S. P.; Norris, R. P.; Booth, R. S.

    2003-07-01

    We report the results of a search for 6.7-GHz methanol masers toward low-mass young stellar objects (YSOs) and (pre)protostellar condensations with the Australia Telescope Compact Array (ATCA). Our sample consisted of 13 class 0 protostars and 44 class I YSOs as well as 66 (pre)protostellar condensations. A single detection was obtained toward NGC 2024: FIR4 in the Orion B region. This is the first detection of a 6.7-GHz methanol maser in Orion. The nature of FIR4 has been a subject of debate with some evidence suggesting that it is a very cold high-mass (pre)protostellar condensation and others arguing that it is a low-mass YSO. The discovery of a methanol maser associated with this source is inconsistent with both of these hypotheses and we suggest that FIR4 probably harbours an intermediate- or high-mass YSO. (1 data file).

  20. IDENTIFICATION OF A WIDE, LOW-MASS MULTIPLE SYSTEM CONTAINING THE BROWN DWARF 2MASS J0850359+105716

    SciTech Connect

    Faherty, Jacqueline K.; Burgasser, Adam J.; Bochanski, John J.; Looper, Dagny L.; West, Andrew A.; Van der Bliek, Nicole S.

    2011-03-15

    We report our discovery of NLTT 20346 as an M5+M6 companion system to the tight binary (or triple) L dwarf 2MASS J0850359+105716. This nearby ({approx}31 pc), widely separated ({approx}7700 AU) quadruple system was identified through a cross-match of proper motion catalogs. Follow-up imaging and spectroscopy of NLTT 20346 revealed it to be a magnetically active M5+M6 binary with components separated by {approx}2'' (50-80 AU). Optical spectroscopy of the components shows only moderate H{alpha} emission corresponding to a statistical age of {approx}5-7 Gyr for both M dwarfs. However, NLTT 20346 is associated with the XMM-Newton source J085018.9+105644, and based on X-ray activity the age of NLTT 20346 is between 250 and 450 Myr. Strong Li absorption in the optical spectrum of 2MASS J0850+1057 indicates an upper age limit of 0.8-1.5 Gyr, favoring the younger age for the primary. Using evolutionary models in combination with an adopted system age of 0.25-1.5 Gyr indicates a total mass for 2MASS J0850+1057 of 0.07 {+-} 0.02 M{sub sun}, if it is a binary. NLTT 20346/2MASS J0850+1057 joins a growing list of hierarchical systems containing brown dwarf binaries and is among the lowest binding energy associations found in the field. Formation simulations via gravitational fragmentation of massive extended disks have successfully produced a specific analog to this system.

  1. Coordinated X-Ray, Ultraviolet, Optical, and Radio Observations of the PSR J1023+0038 System in a Low-mass X-Ray Binary State

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko; Archibald, Anne M.; Bassa, Cees; Deller, Adam T.; Halpern, Jules P.; Heald, George; Hessels, Jason W. T.; Janssen, Gemma H.; Lyne, Andrew G.; Moldón, Javier; Paragi, Zsolt; Patruno, Alessandro; Perera, Benetge B. P.; Stappers, Ben W.; Tendulkar, Shriharsh P.; D'Angelo, Caroline R.; Wijnands, Rudy

    2015-06-01

    The PSR J1023+0038 binary system hosts a neutron star and a low-mass, main-sequence-like star. It switches on year timescales between states as an eclipsing radio millisecond pulsar and a low-mass X-ray binary (LMXB). We present a multi-wavelength observational campaign of PSR J1023+0038 in its most recent LMXB state. Two long XMM-Newton observations reveal that the system spends ˜70% of the time in a ≈3 × 1033 erg s-1 X-ray luminosity mode, which, as shown in Archibald et al., exhibits coherent X-ray pulsations. This emission is interspersed with frequent lower flux mode intervals with ≈ 5× {10}32 erg s-1 and sporadic flares reaching up to ≈1034 erg s-1, with neither mode showing significant X-ray pulsations. The switches between the three flux modes occur on timescales of order 10 s. In the UV and optical, we observe occasional intense flares coincident with those observed in X-rays. Our radio timing observations reveal no pulsations at the pulsar period during any of the three X-ray modes, presumably due to complete quenching of the radio emission mechanism by the accretion flow. Radio imaging detects highly variable, flat-spectrum continuum radiation from PSR J1023+0038, consistent with an origin in a weak jet-like outflow. Our concurrent X-ray and radio continuum data sets do not exhibit any correlated behavior. The observational evidence we present bears qualitative resemblance to the behavior predicted by some existing “propeller” and “trapped” disk accretion models although none can account for key aspects of the rich phenomenology of this system.

  2. Observations of Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Ménard, F.

    2004-12-01

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This chapter focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g., ˜140pc for Taurus), a planetary system like ours (with diameter ≃ 50AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35". Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1" resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.

  3. The HARPS search for southern extra-solar planets. XXVIII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems

    NASA Astrophysics Data System (ADS)

    Lovis, C.; Ségransan, D.; Mayor, M.; Udry, S.; Benz, W.; Bertaux, J.-L.; Bouchy, F.; Correia, A. C. M.; Laskar, J.; Lo Curto, G.; Mordasini, C.; Pepe, F.; Queloz, D.; Santos, N. C.

    2011-04-01

    Context. Low-mass extrasolar planets are presently being discovered at an increased pace by radial velocity and transit surveys, which opens a new window on planetary systems. Aims: We are conducting a high-precision radial velocity survey with the HARPS spectrograph, which aims at characterizing the population of ice giants and super-Earths around nearby solar-type stars. This will lead to a better understanding of their formation and evolution, and will yield a global picture of planetary systems from gas giants down to telluric planets. Methods: Progress has been possible in this field thanks in particular to the sub-m s-1 radial velocity precision achieved by HARPS. We present here new high-quality measurements from this instrument. Results: We report the discovery of a planetary system comprising at least five Neptune-like planets with minimum masses ranging from 12 to 25 M⊕, orbiting the solar-type star HD 10180 at separations between 0.06 and 1.4 AU. A sixth radial velocity signal is present at a longer period, probably caused by a 65-M⊕ object. Moreover, another body with a minimum mass as low as 1.4 M⊕ may be present at 0.02 AU from the star. This is the most populated exoplanetary system known to date. The planets are in a dense but still well separated configuration, with significant secular interactions. Some of the orbital period ratios are fairly close to integer or half-integer values, but the system does not exhibit any mean-motion resonances. General relativity effects and tidal dissipation play an important role to stabilize the innermost planet and the system as a whole. Numerical integrations show long-term dynamical stability provided true masses are within a factor ~3 from minimum masses. We further note that several low-mass planetary systems exhibit a rather "packed" orbital architecture with little or no space left for additional planets. In several cases, semi-major axes are fairly regularly spaced on a logarithmic scale, giving rise

  4. Chemical Evolution of Protostellar Matter

    NASA Technical Reports Server (NTRS)

    Langer, William D.; vanDishoeck, Ewine F.; Bergin, Edwin A.; Blake, Geoffrey A.; Tielens, Alexander G. G. M.; Velusamy, Thangasamy; Whittet, Douglas C. B.

    2000-01-01

    We review the chemical processes that are important in the evolution from a molecular cloud core to a protostellar disk. These cover both gas phase and gas grain interactions. The current observational and theoretical state of this field are discussed.

  5. 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.

  6. High Resolution Imaging of Very Low Mass Spectral Binaries: Three Resolved Systems and Detection of Orbital Motion in an L/T Transition Binary

    NASA Astrophysics Data System (ADS)

    Bardalez Gagliuffi, Daniella C.; Gelino, Christopher R.; Burgasser, Adam J.

    2015-11-01

    We present high resolution Laser Guide Star Adaptive Optics imaging of 43 late-M, L and T dwarf systems with Keck/NIRC2. These include 17 spectral binary candidates, systems whose spectra suggest the presence of a T dwarf secondary. We resolve three systems: 2MASS J1341-3052, SDSS J1511+0607 and SDSS J2052-1609 the first two are resolved for the first time. All three have projected separations <8 AU and estimated periods of 14-80 years. We also report a preliminary orbit determination for SDSS J2052-1609 based on six epochs of resolved astrometry between 2005 and 2010. Among the 14 unresolved spectral binaries, 5 systems were confirmed binaries but remained unresolved, implying a minimum binary fraction of {47}-11+12% for this sample. Our inability to resolve most of the spectral binaries, including the confirmed binaries, supports the hypothesis that a large fraction of very low mass systems have relatively small separations and are missed with direct imaging. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

  7. Protostellar Collapse with a Shock

    NASA Technical Reports Server (NTRS)

    Tsai, John C.; Hsu, Juliana J. L.

    1995-01-01

    We reexamine both numerically and analytically the collapse of the singular isothermal sphere in the context of low-mass star formation. We consider the case where the onset of collapse is initiated by some arbitrary process which is accompanied by a central output of either heat or kinetic energy. We find two classes of numerical solutions describing this manner of collapse. The first approaches in time the expansion wave solution of Shu, while the second class is characterized by an ever-decreasing central accretion rate and the presence of an outwardly propagating weak shock. The collapse solution which represents the dividing case between these two classes is determined analytically by a similarity analysis. This solution shares with the expansion wave solution the properties that the gas remains stationary with an r(sup -2) density profile at large radius and that, at small radius, the gas free-falls onto a nascent core at a constant rate which depends only on the isothermal sound speed. This accretion rate is a factor of approx. 0.1 that predicted by the expansion wave solution. This reduction is due in part to the presence of a weak shock which propagates outward at 1.26 times the sound speed. Gas in the postshock region first moves out subsonically but is then decelerated and begins to collapse. The existence of two classes of numerical collapse solutions is explained in terms of the instability to radial perturbations of the analytic solution. Collapse occurring in the manner described by some of our solutions would eventually unbind a finite-sized core. However, this does not constitute a violation of the instability properties of the singular isothermal sphere which is unstable both to collapse and to expansion. To emphasize this, we consider a purely expanding solution for isothermal spheres. This solution is found to be self-similar and results in a uniform density core in the central regions of the gas. Our solutions may be relevant to the 'luminosity

  8. Protostellar Collapse with a Shock

    NASA Technical Reports Server (NTRS)

    Tsai, John C.; Hsu, Juliana J.

    1995-01-01

    We reexamine both numerically and analytically the collapse of the singular isothermal sphere in the context of low-mass star formation. We consider the case where the onset of collapse is initiated by some arbitrary process which is accompanied by a central output of either heat or kinetic energy. We find two classes of numerical solutions describing this manner of collapse. The first approaches in time the expansion wave solution of Shu, while the second class is characterized by an ever-decreasing central accretion rate and the presence of an outwardly propagating weak shock. The collapse solution which represents the dividing case between these two classes is determined analytically by a similarity analysis. This solution shares with the expansion wave solution the properties that the gas remains stationary with an r(exp -2) density profile at large radius and that, at small radius, the gas free-falls onto a nascent core at a constant rate which depends only on the isothermal sound speed. This accretion rate is a factor of approx. 0.1 that predicted by the expansion wave solution. This reduction is due in part to the presence of a weak shock which propagates outward at 1.26 times the sound speed. Gas in the postshock region first moves out subsonically but is then decelerated and begins to collapse. The existence of two classes of numerical collapse solutions is explained in terms of the instability to radial perturbations of the analytic solution. Collapse occurring in the manner described by some of our solutions would eventually unbind a finite-sized core. However, this does not constitute a violation of the instability properties of the singular isothermal sphere which is unstable both to collapse and to expansion. To emphasize this, we consider a purely expanding solution for isothermal spheres. This solution is found to be self-similar and results in a uniform density core in the central regions of the gas. Our solutions may be relevant to the 'luminosity

  9. Taking into account the effects of component proximity on the spectral-line profiles of stars in low-mass X-ray binary systems

    NASA Astrophysics Data System (ADS)

    Petrov, V. S.; Antokhina, E. A.; Cherepashchuk, A. M.

    2015-05-01

    An exact calculation of CaI λ6439 Å absorption profiles in the spectra of optical stars in low-mass X-ray binary systems is carried out. The calculations are used to revise a formula relating the rotational broadening of lines and the component-mass ratio. In the case of modest (substantial) X-ray heating, failure to take into account the tidal-rotational deformation of the figure of the star leads to overestimation (underestimation) of the mass of the relativistic object. The radial-velocity curves of optical stars are modeled for binary systems with various parameters and X-ray heating powers k x ; corresponding tables of K corrections are presented. Refined values for the component-mass ratio q = 23 ± 1, black-hole mass M x = 8.4 ± 0.5, and optical-star mass M v = 0.36 ± 0.07 for the GS 2023+338 (V404 Cyg) system are presented.

  10. Modeling of Radiative Transfer in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    VonAllmen, Paul; Turner, Neal

    2007-01-01

    This program implements a spectral line, radiative transfer tool for interpreting Spitzer Space Telescope observations by matching them with models of protostellar disks for improved understanding of planet and star formation. The Spitzer Space Telescope detects gas phase molecules in the infrared spectra of protostellar disks, with spectral lines carrying information on the chemical composition of the material from which planets form. Input to the software includes chemical models developed at JPL. The products are synthetic images and spectra for comparison with Spitzer measurements. Radiative transfer in a protostellar disk is primarily affected by absorption and emission processes in the dust and in molecular gases such as H2, CO, and HCO. The magnitude of the optical absorption and emission is determined by the population of the electronic, vibrational, and rotational energy levels. The population of the molecular level is in turn determined by the intensity of the radiation field. Therefore, the intensity of the radiation field and the population of the molecular levels are inter-dependent quantities. To meet the computational challenges of solving for the coupled radiation field and electronic level populations in disks having wide ranges of optical depths and spatial scales, the tool runs in parallel on the JPL Dell Cluster supercomputer with C++ and Fortran compiler with a Message Passing Interface. Because this software has been developed on a distributed computing platform, the modeling of systems previously beyond the reach of available computational resources is possible.

  11. 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.

  12. New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Barman, Travis S.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa; Rodigas, Timothy J.; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa

    2015-03-01

    We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and YS . With our new photometry and T eff ~ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has AV = 3.4 ± 1.1 mag, and a mass of 14-24 MJ according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Hα emission and a mass accretion rate ~6 × 10-10 M ⊙ yr-1, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', YS ) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

  13. GMRT detections of low-mass young stars at 323 and 608 MHz

    NASA Astrophysics Data System (ADS)

    Ainsworth, Rachael E.; Scaife, Anna M. M.; Green, David A.; Coughlan, Colm P.; Ray, Tom P.

    2016-06-01

    We present the results of a pathfinder project conducted with the Giant Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low radio frequencies. The goal of these investigations is to locate the break in the free-free spectrum where the optical depth equals unity in order to constrain physical parameters of these systems, such as the mass of the ionized gas surrounding these young stars. We detect all three target sources, L1551 IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz (wavelengths 90 and 50 cm, respectively). These are the first detections of low-mass young stellar objects at such low frequencies. We combine these new GMRT data with archival information to construct the spectral energy distributions for each system and find a continuation of the optically thin free-free spectra extrapolated from higher radio frequencies to 323 MHz for each target. We use these results to place limits on the masses of the ionized gas and average electron densities associated with these young systems on scales of ˜1000 au. Future observations with higher angular resolution at lower frequencies are required to constrain these physical parameters further.

  14. 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.

  15. 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.

  16. 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.

  17. Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue. III. Two new low-mass systems with rapidly evolving spots

    NASA Astrophysics Data System (ADS)

    Hełminiak, K. G.; Konacki, M.; Złoczewski, K.; Ratajczak, M.; Reichart, D. E.; Ivarsen, K. M.; Haislip, J. B.; Crain, J. A.; Foster, A. C.; Nysewander, M. C.; Lacluyze, A. P.

    2011-03-01

    Aims: We present the results of our spectroscopic and photometric analysis of two newly discovered low-mass detached eclipsing binaries found in the All-Sky Automated Survey (ASAS) catalogue: ASAS J093814-0104.4 and ASAS J212954-5620.1. Methods: Using the Grating Instrument for Radiation Analysis with a Fibre-Fed Echelle (GIRAFFE) on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory (SAAO) and the University College London Echelle Spectrograph (UCLES) on the 3.9-m Anglo-Australian Telescope, we obtained high-resolution spectra of both objects and derived their radial velocities (RVs) at various orbital phases. The RVs of both objects were measured with the two-dimensional cross-correlation technique (TODCOR) using synthetic template spectra as references. We also obtained V and I band photometry using the 1.0-m Elizabeth telescope at SAAO and the 0.4-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) located at the Cerro Tololo Inter-American Observatory (CTIO). The orbital and physical parameters of the systems were derived with PHOEBE and JKTEBOP codes. We compared our results with several sets of widely-used isochrones. Results: Our multi-epoch photometric observations demonstrate that both objects show significant out-of-eclipse modulations, which vary in time. We believe that this effect is caused by stellar spots, which evolve on time scales of tens of days. For this reason, we constructed our models on the basis of photometric observations spanning short time scales (less than a month). Our modeling indicates that (1) ASAS J093814-0104.04 is a main sequence active system with nearly-twin components with masses of M1 = 0.771 ± 0.033 M⊙, M2 = 0.768 ± 0.021 M⊙ and radii of R1 = 0.772 ± 0.012 R⊙ and R2 = 0.769 ± 0.013 R⊙. (2) ASAS J212954-5620.1 is a main sequence active binary with component masses of M1 = 0.833 ± 0.017 M⊙, M2 = 0.703 ± 0.013 M⊙ and radii of R1 = 0.845 ± 0.012 R⊙ and R2

  18. Ejection of gaseous clumps from gravitationally unstable protostellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.

    2016-05-01

    Aims: We investigate the dynamics of gaseous clumps formed via gravitational fragmentation in young protostellar disks, focusing on the fragments that are ejected from the disk via many-body gravitational interaction. Methods: Numerical hydrodynamics simulations were employed to study the evolution of young protostellar disks that were formed from the collapse of rotating pre-stellar cores. Results: The protostellar disks that formed in our models undergo gravitational fragmentation driven by continuing mass-loading from parental collapsing cores. Several fragments can be ejected from the disk during the early evolution, but the low-mass fragments (<15 MJup) disperse, which creates spectacular bow-type structures while passing through the disk and collapsing core. The least massive fragment that survived the ejection (21 MJup) straddles the planetary-mass limit, while the most massive ejected fragments (145 MJup) can break up into several pieces, leading to the ejection of wide separation binary clumps in the brown-dwarf mass range. About half of the ejected fragments are gravitationally bound, the majority are supported by rotation against gravity, and all fragments have the specific angular momentum that is much higher than that expected for brown dwarfs. We found that the internal structure of the ejected fragments is distinct from what would be expected for gravitationally contracting clumps formed via molecular cloud fragmentation, which can help in differentiating their origin. Conclusions: The ejection of fragments is an important process, which is inherent to massive protostellar disks, and which produces freely floating pre-brown dwarf cores, regulates the disk and stellar masses and, potentially, enriches the intracluster medium with processed dust and complex organics.

  19. Thirty New Low-mass Spectroscopic Binaries

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya L.; Hebb, Leslie; Liu, Michael C.; Reid, I. Neill; Collier Cameron, Andrew

    2010-06-01

    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 rot to determine the true orbital parameters. For those with no P 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. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope and by the WASP Consortium. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. The CFHT is operated by the National Research Council of Canada

  20. ALMA results of the pseudodisk, rotating disk, and jet in the continuum and HCO{sup +} in the protostellar system HH 212

    SciTech Connect

    Lee, Chin-Fei; Hirano, Naomi; Shang, Hsien; Ho, Paul T. P.; Krasnopolsky, Ruben; Zhang, Qizhou

    2014-05-10

    HH 212 is a nearby (400 pc) Class 0 protostellar system showing several components that can be compared with theoretical models of core collapse. We have mapped it in the 350 GHz continuum and HCO{sup +} J = 4-3 emission with ALMA at up to ∼0.''4 resolution. A flattened envelope and a compact disk are seen in the continuum around the central source, as seen before. The HCO{sup +} kinematics shows that the flattened envelope is infalling with small rotation (i.e., spiraling) into the central source, and thus can be identified as a pseudodisk in the models of magnetized core collapse. Also, the HCO{sup +} kinematics shows that the disk is rotating and can be rotationally supported. In addition, to account for the missing HCO{sup +} emission at low-redshifted velocity, an extended infalling envelope is required, with its material flowing roughly parallel to the jet axis toward the pseudodisk. This is expected if it is magnetized with an hourglass B-field morphology. We have modeled the continuum and HCO{sup +} emission of the flattened envelope and disk simultaneously. We find that a jump in density is required across the interface between the pseudodisk and the disk. A jet is seen in HCO{sup +} extending out to ∼500 AU away from the central source, with the peaks upstream of those seen before in SiO. The broad velocity range and high HCO{sup +} abundance indicate that the HCO{sup +} emission traces internal shocks in the jet.

  1. Modeling the System Parameters of 2M 1533+3759: A New Longer Period Low-Mass Eclipsing sdB+dM Binary

    NASA Astrophysics Data System (ADS)

    For, B.-Q.; Green, E. M.; Fontaine, G.; Drechsel, H.; Shaw, J. S.; Dittmann, J. A.; Fay, A. G.; Francoeur, M.; Laird, J.; Moriyama, E.; Morris, M.; Rodríguez-López, C.; Sierchio, J. M.; Story, S. M.; Strom, A.; Wang, C.; Adams, S. M.; Bolin, D. E.; Eskew, M.; Chayer, P.

    2010-01-01

    We present new photometric and spectroscopic observations for 2M 1533+3759 (= NSVS 07826147), the seventh eclipsing subdwarf B star + M dwarf (sdB+dM) binary ever found. It has an orbital period of 0.16177042 days, or ~3.88 hr, significantly longer than the 2.3-3.0 hr periods of the other known eclipsing sdB+dM systems. Spectroscopic analysis of the hot primary yields T eff = 29230 ± 125 K, log g = 5.58 ± 0.03, and log N(He)/N(H) = -2.37 ± 0.05. The sdB velocity amplitude is K 1 = 71.1 ± 1.0 km s-1. The only detectable light contribution from the secondary is due to the surprisingly strong reflection effect, whose peak-to-peak BVRI amplitudes are 0.10, 0.13, 0.15, and 0.19 mag, respectively. Light-curve modeling produced several solutions corresponding to different values of the system mass ratio, q (M 2/M 1), but only one is consistent with a core helium burning star, q = 0.301. The orbital inclination is 86fdg6. The sdB primary mass is M 1 = 0.376 ± 0.055 M sun and its radius is R 1 = 0.166 ± 0.007 R sun. 2M 1533+3759 joins PG 0911+456 (and possibly also HS 2333+3927) in having an unusually low mass for an sdB star. SdB stars with masses significantly lower than the canonical value of 0.48 M sun, down to as low as 0.30 M sun, were theoretically predicted by Han et al., but observational evidence has only recently begun to confirm the existence of such stars. The existence of core helium burning stars with masses lower than 0.40-0.43 M sun implies that at least some sdB progenitors have initial main-sequence masses of 1.8-2.0 M sun or more, i.e., they are at least main-sequence A stars. The orbital separation in 2M 1533+3759 is a = 0.98 ± 0.04R sun. The secondary has M 2 = 0.113 ± 0.017 M sun, R 2 = 0.152 ± 0.005R sun, and T_eff_{2} = 3100 ± 600 K, consistent with a main-sequence M5 star. If 2M 1533+3759 becomes a cataclysmic variable (CV), its orbital period will be 1.6 hr, below the CV period gap.

  2. THE BINARY FRACTION OF LOW-MASS WHITE DWARFS

    SciTech Connect

    Brown, Justin M.; Kilic, Mukremin; Brown, Warren R.; Kenyon, Scott J.

    2011-04-01

    We describe spectroscopic observations of 21 low-mass ({<=}0.45 M{sub sun}) white dwarfs (WDs) from the Palomar-Green survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction of single, low-mass WDs is {<=}30%. We discuss the potential formation channels for these single stars including binary mergers of lower-mass objects. However, binary mergers are not likely to explain the observed number of single low-mass WDs. Thus, additional formation channels, such as enhanced mass loss due to winds or interactions with substellar companions, are likely.

  3. Imaging chemical differentiation around the low-mass protostar L483-mm

    NASA Astrophysics Data System (ADS)

    Jørgensen, J. K.

    2004-09-01

    This paper presents a millimeter wavelength aperture-synthesis study of the spatial variations of the chemistry in the envelope around the deeply embedded low-mass protostar L483-mm on ˜1000 AU (5 arcsec) scales. Lines of 8 molecular species including CN, C18O, CS, C34S, HCN, H13CN, HCO+ and N2H+ have been observed using the Owens Valley Radio Observatory Millimeter Array. Continuum emission at 2.7-3.4 mm is well-fit by an envelope model based on previously reported submillimeter continuum images down to the sensitivity of the interferometer without introducing a disk/compact source, in contrast to what is seen for other protostellar objects. A velocity gradient in dense material close to the central protostar is traced by HCN, CS and N2H+, and is perpendicular to the large-scale CO outflow, with a pattern consistent with rotation around a ˜1 M⊙ central object. Velocity gradients in the propagation direction of the outflow suggest a clear interaction between the outflowing material and ``quiescent'' core. Significant differences are observed between the emission morphologies of various molecular species. The C18O interferometer observations are fit with a ``drop'' abundance profile where CO is frozen-out in a region of the envelope with temperatures lower than 40 K and densities higher than 1.5 × 105 cm-3, which is also required to reproduce previously reported single-dish observations. The N2H+ emission strongly resembles that of NH3 and is found to be absent toward the central continuum source. This is a direct consequence of the high CO abundances in the inner region as illustrated by a chemical model for the L483 envelope. The observed CN emission forms a spatial borderline between the outflowing and quiescent material probed by, respectively, HCO+ and N2H+, and also shows intermediate velocities compared to these two species. A scenario is suggested in which CN is enhanced in the walls of an outflow cavity due to the impact of UV irradiation either from

  4. SP-100 low mass shield design

    NASA Astrophysics Data System (ADS)

    Carlson, D. E.

    1985-09-01

    The shielding considerations for an unmanned space reactor system are somewhat different from those for a terrestrial reactor. An unmanned operation in space implies that only a shadow shield, rather than a 4(PI) one, is required to protect payload hardware that typically can tolerate 10(4) to 10(6) times more radiation than can a human crew. On the other hand, the system mass, of which the radiation shield can be a significant fraction, is a severe constraint for space reactors and not normally a problem with terrestrial ones. The object of this paper is to briefly summarize advancements made on various aspects of low mass shield design for space reactors, including materials and their arrangements, geometric factors and their potential impact on system design optimization, and proposed new configuration concepts for further mass reduction.

  5. On the tidal interaction between protostellar disks and companions

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Papaloizou, J. C. B.

    1993-01-01

    Formation of protoplanets and binary stars in a protostellar disk modifies the structure of the disk. Through tidal interactions, energy and angular momentum are transferred between the disk and protostellar or protoplanetary companion. We summarize recent progress in theoretical investigations of the disk-companion tidal interaction. We show that low-mass protoplanets excite density waves at their Lindblad resonances and that these waves are likely to be dissipated locally. When a protoplanet acquires sufficient mass, its tidal torque induces the formation of a gap in the vicinity of its orbit. Gap formation leads to the termination of protoplanetary growth by accretion. For proto-Jupiter to attain its present mass, we require that (1) the primordial solar nebula is heated by viscous dissipation; (2) the viscous evolution time scale of the nebula is comparable to the age of typical T Tauri stars with circumstellar disks; and (3) the mass distribution in the nebula is comparable to that estimated from a minimum-mass nebula model.

  6. MISALIGNMENT OF MAGNETIC FIELDS AND OUTFLOWS IN PROTOSTELLAR CORES

    SciTech Connect

    Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Meredith Hughes, A.; Bolatto, Alberto D.; Jameson, Katherine; Mundy, Lee; Pound, Marc W.; Carpenter, John M.; Lamb, James W.; Pillai, Thushara; Crutcher, Richard M.; Hakobian, Nicholas S.; Kwon, Woojin; Looney, Leslie W.; Fiege, Jason D.; Franzmann, Erica; Houde, Martin; Matthews, Brenda C.; and others

    2013-05-10

    We present results of {lambda}1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with {approx}2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of {approx}1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.

  7. DIAGNOSTIC LINE EMISSION FROM EXTREME ULTRAVIOLET AND X-RAY-ILLUMINATED DISKS AND SHOCKS AROUND LOW-MASS STARS

    SciTech Connect

    Hollenbach, David; Gorti, U.

    2009-10-01

    Extreme ultraviolet (EUV; 13.6 eV low-mass stars to thousands of degrees and ionize species with ionization potentials greater than 13.6 eV. Shocks generated by protostellar winds can also heat and ionize the same species close to the star/disk system. These processes produce diagnostic lines (e.g., [Ne II] 12.8 {mu}m and [O I] 6300 A) that we model as functions of key parameters such as EUV luminosity and spectral shape, X-ray luminosity and spectral shape, and wind mass loss rate and shock speed. Comparing our models with observations, we conclude that either internal shocks in the winds or X-rays incident on the disk surfaces often produce the observed [Ne II] line, although there are cases where EUV may dominate. Shocks created by the oblique interaction of winds with disks are unlikely [Ne II] sources because these shocks are too weak to ionize Ne. Even if [Ne II] is mainly produced by X-rays or internal wind shocks, the neon observations typically place upper limits of {approx}<10{sup 42} s{sup -1} on the EUV photon luminosity of these young low-mass stars. The observed [O I] 6300 A line has both a low velocity component (LVC) and a high velocity component. The latter likely arises in internal wind shocks. For the former we find that X-rays likely produce more [O I] luminosity than either the EUV layer, the transition layer between the EUV and X-ray layer, or the shear layer where the protostellar wind shocks and entrains disk material in a radial flow across the surface of the disk. Our soft X-ray models produce [O I] LVCs with luminosities up to 10{sup -4} L{sub sun}, but may not be able to explain the most luminous LVCs.

  8. Star Formation in Low Mass Magnetized Cores: The Formation of Disks and Outflows

    NASA Astrophysics Data System (ADS)

    Duffin, Dennis F.

    2012-10-01

    Protostellar discs are generally thought to drive molecular outflows and jets observed in star forming regions, but there has been some debate as to how they form. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. Recently it has been argued that the magnetic brake is so strong that early protostellar disks cannot form. We have performed 3D ideal magnetohydrodynamic (MHD) simulations of collapsing Bonnor-Ebert spheres, employing sink particles within an AMR grid and using a cooling function to model radiative cooling of the gas. This allows us to follow the formation and early evolution of the accretion disc (2-8)×10^4 years further into the Class 0 phase of its evolution. We form a rotationally dominated disc with a radius of 100 AU embedded inside a transient, unstable, flattened, rotating structure extending out to 2000 AU. The inner disc becomes unstable to a warping instability due to the magnetic structure of the outflow, warping 30 deg with respect to the rotation-axis by the end of the simulation. The disc is unstable to a Parker instability and sheds magnetic loops, degrading the orientation of the mean threading field. This reduces and locally reverses the magnetic braking torque of the large scale field back upon the disc. The reduction of magnetic braking allows a nearly Keplerian disc to form and may be the key way in which low mass stellar systems produce rotationally dominated discs. We discuss the relevance of our disc misalignment concerning the formation of mis-aligned hot Jupiters. Protostellar outflows are implicated in clearing mass from collapsing cores, and limiting the final mass of newly formed stars. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. The simulations generate outflows which are precessing, kinked, contain internal

  9. Pseudocepheids. III - The low-mass stars

    NASA Astrophysics Data System (ADS)

    Eggen, O. J.

    1986-04-01

    Light and color curves in four-color, H-beta, and (RI) photometric systems are presented for 20 low-mass pseudocepheids. Members of the Wolf 630 group and the cluster M67 are used to establish the positions of both variable and nonvariable giants with near solar abundance in the luminosity-temperature plane for old disk population stars, while members of Omega Cen and of Kapteyn's Star Group are used for the low metal abundance halo giants. The low-mass pseudocepheids discussed are divided into two main categories, based on the amplitude of light variation. The smaller amplitude stars, characterized by R CrB and RY Sgr in the old disk population, show the R CrB syndrome of occasional deep light minima, as does UW Cen. The small amplitude variables in the halo population, BL Tel and LN Hya, do not show the R CrB syndrome and their periods are longer than those of old disk stars. Large amplitude variables, with periods ranging from 10 to 150 days, are all halo objects with stability of period and form of light curve an obvious function of the period. Cen and BL Tel are members of Kapteyn's Star Group, and the spectroscopic orbital elements of the latter indicate a mass near 0.5 solar mass for the pseudocepheid and 1 solar mass for the late-type giant companion. Far-infrared observations are important in exploring the correlations between the presence and character of circumstellar dust shells and other post-AGB star parameters.

  10. 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

  11. (abstract) The Circumstellar Environment of the Extremely Young Protostellar Source L1448IRS3

    NASA Technical Reports Server (NTRS)

    Tereby, S.; Padgett, Deborah L.

    1994-01-01

    The class 0 sources form an interesting new category of protostellar objects. Many have strong millimeter continuum emission and exhibit jetlike outflows. There are suggestions that these objects are systematically younger than typical embedded (class I) sources. We are investigating the properties of class 0 sources to determine whether they are indeed very young or perhaps represent extreme physical conditions, such as rapid rotation. We present millimeter interferometric data for the class 0 object known as L1448 IRS3. This young low-mass star has extremely strong millimeter continuum emission. The interferometer data show the emission is resolved on a scale of a few arcseconds (1000 AU) This suggests the bulk of the dust continuum emission originates in an 'infall' envelope rather than a protostar disk. In addition, the C180 line data display a strong velocity gradiant which indicates the dense core is rapidly rotating. We compare our data with the predictions of protostellar collapse models.

  12. Fundamental Properties of Low-Mass Stars and Brown Dwarfs

    SciTech Connect

    Liu, Michael C.; Dupuy, Trent J.; Stassun, Keivan G.; Allard, France; Blake, Cullen H.; Bonnefoy, M.; Cody, Ann Marie; Kraus, Adam; Day-Jones, A. C.; Lopez-Morales, Mercedes

    2009-02-16

    Precise measurements of the fundamental properties of low-mass stars and brown dwarfs are key to understanding the physics underlying their formation and evolution. While there has been great progress over the last decade in studying the bulk spectrophotometric properties of low-mass objects, direct determination of their masses, radii, and temperatures have been very sparse. Thus, theoretical predictions of low-mass evolution and ultracool atmospheres remain to be rigorously tested. The situation is alarming given that such models are widely used, from the determination of the low-mass end of the initial mass function to the characterization of exoplanets.An increasing number of mass, radius, and age determinations are placing critical constraints on the physics of low-mass objects. A wide variety of approaches are being pursued, including eclipsing binary studies, astrometric-spectroscopic orbital solutions, interferometry, and characterization of benchmark systems. In parallel, many more systems suitable for concerted study are now being found, thanks to new capabilities spanning both the very widest (all-sky surveys) and very narrowest (diffraction-limited adaptive optics) areas of the sky. This Cool Stars 15 splinter session highlighted the current successes and limitations of this rapidly growing area of precision astrophysics.

  13. Particle simulation of supersonic convection in the protostellar nebula

    NASA Astrophysics Data System (ADS)

    Riegger, J. M.

    1995-02-01

    For the simulation of compressible convection and a possible description of inner processes in meteorites a new algorithm for particle-in-cell methods in particle simulation is developed, which allows a direct description of the inner pressure by use of individual particle temperatures and therefore a description of gas dynamics without the approximations of perturbation theory. The simulation of nonadiabatic processes in superadiabatic stratified atmospheres leads to the self-organization of convection cells and to supersonic convection and instationary shock front systems for high Rayleigh numbers Ra > 5 × 10 5 as they are received by other numerical methods. The transport of material through shock fronts yields much faster temperature and pressure changes than ordinary convective transport in the subsonic range. Tracing the values of state along the pathlines shows that fast entropy increases occur either within shock fronts or due to local dissipation in turbulences. Transport through shock front systems results in multiple rapid temperature changes per cycle. Investigations on the local convective structure of the protostellar nebula with a simple radiative transfer and standard opacities and accretion rates indicate supersonic convection and multiple shock front systems in the outer layers of the solar nebula due to radiative cooling. Supersonic convection provides a very effective mechanism of dissipation for the protostellar nebula and makes a contribution to the discussion on the turbulent structure of the protostellar nebula and to the formation of chrondrules.

  14. The Formation and Fragmentation of Primordial Protostellar Discs

    NASA Astrophysics Data System (ADS)

    Clark, Paul C.; Glover, Simon C. O.; Smith, Rowan J.; Greif, Thomas H.; Klessen, Ralf S.; Bromm, Volker

    2010-11-01

    We study the formation and evolution of the protostellar discs that form around the first stars in the Universe. Using sink particles, we replace the gravitationally bound gas at densities higher than 1015 cm-3 and radii greater than 3 AU from the central protostellar core, with an accreting point mass that is able to gravitationally interact with the surrounding gas. We find the disc is gravitationally (or `Toomre') unstable, and is dominated by a strong m = 2 spiral mode. Although the angular momentum transport is dominated by a combination of gravitational torques and Reynolds stresses, which are extremely efficient mechanisms, the disc is unable to process the infalling material and grows increasingly gravitationally unstable. During the build-up of the disc, the temperature in the gas is regulated by a combination of H2 line cooling, collision-induced emission and H2 dissociation, which together help to offset heating from the gravitational collapse and feedback from the protostar. Once the disc starts to fragment, H2 dissociation keeps the gas almost isothermal as the collapse of the fragment progresses. The fragmentation occurs when the protostar/disc system is only 230 yr old and at a distance of ~20 AU from its sibling, by which point the central protostar has a mass of ~1 Msolar. Given the angular momentum of the new protostellar system, it is likely that the protostars will grow to become a massive binary system.

  15. Infall-driven protostellar accretion and the solution to the luminosity problem

    SciTech Connect

    Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke

    2014-12-10

    We investigate the role of mass infall in the formation and evolution of protostars. To avoid ad hoc initial and boundary conditions, we consider the infall resulting self-consistently from modeling the formation of stellar clusters in turbulent molecular clouds. We show that infall rates in turbulent clouds are comparable to accretion rates inferred from protostellar luminosities or measured in pre-main-sequence stars. They should not be neglected in modeling the luminosity of protostars and the evolution of disks, even after the embedded protostellar phase. We find large variations of infall rates from protostar to protostar, and large fluctuations during the evolution of individual protostars. In most cases, the infall rate is initially of order 10{sup –5} M {sub ☉} yr{sup –1}, and may either decay rapidly in the formation of low-mass stars, or remain relatively large when more massive stars are formed. The simulation reproduces well the observed characteristic values and scatter of protostellar luminosities and matches the observed protostellar luminosity function. The luminosity problem is therefore solved once realistic protostellar infall histories are accounted for, with no need for extreme accretion episodes. These results are based on a simulation of randomly driven magnetohydrodynamic turbulence on a scale of 4 pc, including self-gravity, adaptive-mesh refinement to a resolution of 50 AU, and accreting sink particles. The simulation yields a low star formation rate, consistent with the observations, and a mass distribution of sink particles consistent with the observed stellar initial mass function during the whole duration of the simulation, forming nearly 1300 sink particles over 3.2 Myr.

  16. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    SciTech Connect

    Taquet, Vianney; Charnley, Steven B.; Sipilä, Olli

    2014-08-10

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H{sub 2} and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  17. Cyclic period changes and the light-time effect in eclipsing binaries: A low-mass companion around the system VV Ursae Majoris

    NASA Astrophysics Data System (ADS)

    Tanrıver, Mehmet

    2015-04-01

    In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O-C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M⊙, and the semi-major axis of its orbit is 10.75 AU.

  18. THE FREQUENCY OF LOW-MASS EXOPLANETS

    SciTech Connect

    O'Toole, S. J.; Jones, H. R. A.; Tinney, C. G.; Bailey, J.; Wittenmyer, R. A.; Butler, R. P.; Marcy, G. W.; Carter, B.

    2009-08-20

    We report first results from the Anglo-Australian Telescope Rocky Planet Search-an intensive, high-precision Doppler planet search targeting low-mass exoplanets in contiguous 48 night observing blocks. On this run, we targeted 24 bright, nearby and intrinsically stable Sun-like stars selected from the Anglo-Australian Planet Search's main sample. These observations have already detected one low-mass planet reported elsewhere (HD 16417b), and here we reconfirm the detection of HD 4308b. Further, we have Monte Carlo simulated data from this run on a star-by-star basis to produce robust detection constraints. These simulations demonstrate clear differences in the exoplanet detectability functions from star to star due to differences in sampling, data quality and intrinsic stellar stability. They reinforce the importance of star-by-star simulation when interpreting the data from Doppler planet searches. These simulations indicate that for some of our target stars we are sensitive to close-orbiting planets as small as a few Earth masses. The two low-mass planets present in our 24-star sample indicate that the exoplanet minimum mass function at low masses is likely to be a flat {alpha} {approx} -1 (for dN/dM {proportional_to} M {sup {alpha}}) and that between 15% {+-} 10% (at {alpha} = -0.3) and 48% {+-} 34% (at {alpha} = -1.3) of stars host planets with orbital periods of less than 16 days and minimum masses greater than 3 M {sub +}.

  19. Broad N2H+ Emission toward the Protostellar Shock L1157-B1

    NASA Astrophysics Data System (ADS)

    Codella, C.; Viti, S.; Ceccarelli, C.; Lefloch, B.; Benedettini, M.; Busquet, G.; Caselli, P.; Fontani, F.; Gómez-Ruiz, A.; Podio, L.; Vasta, M.

    2013-10-01

    We present the first detection of N2H+ toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ~0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originated from the dense (>=105 cm-3) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N2H+ column density of a few 1012 cm-2 corresponding to an abundance of (2-8) × 10-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 104 yr, i.e., for more than the shock kinematical age (sime2000 yr). Modeling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 104 cm-3, and then further compressed and accelerated by the shock.

  20. Molecular emission in chemically active protostellar outflows

    NASA Astrophysics Data System (ADS)

    Lefloch, B.

    2011-12-01

    Protostellar outflows play an important role in the dynamical and chemical evolution of cloud through shocks. The Herschel Space Observatory (HSO) brings new insight both on the molecular content and the physical conditions in protostellar shocks through high spectral and angular resolution studies of the emission of major gas cooling agents and hydrides. The Herschel/CHESS key-program is carrying out an in depth study of the prototypical shock region L1157-B1. Analysis of the line profiles detected allows to constrain the formation/destruction route of various molecular species, in relation with the predictions of MHD shock models. The Herschel/WISH key-program investigates the properties and origin of water emission in a broad sample of protostellar outflows and envelopes. Implications of the first results for future studies on mass-loss phenomena are discussed.

  1. Resolving the Discrepancy of Low-Mass Stars with IGRINS

    NASA Astrophysics Data System (ADS)

    Riddle, Andrew; Kraus, Adam L.

    2015-01-01

    Observed properties of low-mass stars (M < 0.8 solar msses) have been found to be in disagreement with stellar models, the observed radii being inflated and the observed temperatures being too low. To study this discrepancy, we are observing a sample of low-mass eclipsing binaries using the 2.7-m Harlan J. Smith telescope at McDonald Observatory as well as the LCOGT network to increase the number of well-characterized systems. We are also using IGRINS, a new high resolution (R=40,000) IR (H+K) spectrograph on the 2.7-m HJST, to measure the fundamental stellar parameters (Teff, R, M, abundances, activity) of a sample of eclipsing binaries consisting of two low-mass components. Finally, to calibrate these eclipsing binaries, we are observing a temperature calibration sample of single M dwarfs with precise temperature measurements from interferometry and a metallicity calibration sample of M dwarfs in wide binaries with solar-type stars. Relationships between these parameters will help us better understand the discrepancy between models and observed properties of low-mass stars.

  2. From Prestellar to Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Aikawa, Yuri; Wakelam, Valentine; Hersant, Franck; Garrod, Robin; Herbst, Eric

    2012-07-01

    We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from dense cloud cores to protostellar cores. We solve a gas-grain reaction network, which is extended to include multi-deuterated species, using a 1-D radiative hydrodynamic model with infalling fluid parcels to derive molecular distribution in assorted evolutionary stages. We find that the abundances of large organic species in the central region increase with time. The duration of the warm-up phase, in which large organic species are efficiently formed, is longer in infalling fluid parcels at later stages. Formation of unsaturated carbon chains in the CH4 sublimation zone (warm carbon chain chemistry) is more effective in later stage. The carbon ion, which reacts with CH4 to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are both heavily deuterated, mainly because their mother molecules have high D/H ratios, which are set in the cold phase. The observed CH2DOH/CH3OH ratio towards protostars is reproduced if we assume that the grain-surface exchange and abstraction reactions of CH3OH + D occurs efficiently. In our 1-D collapse model, the fluid parcels directly fall into the protostar, and the warm-up phase in the fluid parcels is rather short. But, in reality, a circumstellar disk is formed, and fluid parcels will stay there for a longer timescale than a free-fall time. We investigate the molecular evolution in such a disk by assuming that a fluid parcel stays at a constant temperature (i.e. a fixed disk radius) after the infall. The species CH3OCH3 and HCOOCH3 become more abundant in the disk than in the envelope. Both have high D/H abundance ratios as well.

  3. HEATING AND COOLING PROTOSTELLAR DISKS

    SciTech Connect

    Hirose, S.; Turner, N. J. E-mail: neal.turner@jpl.nasa.gov

    2011-05-10

    We examine heating and cooling in protostellar disks using three-dimensional radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well coupled to magnetic fields, and sustains a turbulent accretion flow driven by magnetorotational instability, while the interior is resistive and magnetically dead. The turbulent layers are heated by absorbing the light from the central star and by dissipating the magnetic fields. They are optically thin to their own radiation and cool inefficiently. The optically thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations in the fields move the starlight-absorbing surface up and down. The height ranges between 13% and 24% of the radius over timescales of several orbits, with implications for infrared variability. The fields are buoyant, so the accretion heating occurs higher in the atmosphere than the stresses. The heating is localized around current sheets, caused by magnetorotational instability at lower elevations and by Parker instability at higher elevations. Gas in the sheets is heated above the stellar irradiation temperature, even though accretion is much less than irradiation power when volume averaged. The hot optically thin current sheets might be detectable through their line emission.

  4. Protostellar Disk Formation Traced by Chemistry

    NASA Astrophysics Data System (ADS)

    Sakai, N.

    2015-12-01

    Recent ALMA observations are revealing formation processes of a disk structure around a young protostars at an unprecedented spatial resolution. A few recent highlights in this area are reviewed with particular emphasis on chemistry. Our discovery of centrifugal barrier of an infalling rotating envelope gas and associated drastic chemical change are presented as an example. Chemical compositions can be used to explore not only the chemical evolution from protostellar cores to protoplanetary disks but also the physical formation process of rotationally supported disks in protostellar sources.

  5. Modeling the Submillimeter Dust Continuum Emission from Nearby Low Mass Star Forming Cores

    NASA Astrophysics Data System (ADS)

    Shirley, Y. L.; Young, C. H.; Evans, N. J., II; Rawlings, J. M. C.

    2001-12-01

    Current theories of a low mass star formation predict the evolution of the density distribution, n({r}, t), temperature distribution, T({r}, t), and the velocity field ,{v}({r}, t), of the envelope of protostellar cores with time. Optically thin dust emission at submillimeter wavelengths provides a powerful diagnostic to constrain the envelope density and temperature structure. In this study, thirty-nine low mass cores were mapped with SCUBA at 850 and 450 μ m on the JCMT during sixteen nights between January 1998 and February 2000. The sources were selected from the earliest phases (pre-T Tauri) in the proposed evolutionary scheme for low mass protostars (6 Pre-protostellar Cores (PPCs), 15 Class 0, 18 Class I) with luminosities indicative of low mass star formation (Lbol < 50 Lsun) and with distances less than 450 pc. High signal-to-noise maps allowed azimuthally averaged radial profiling out to 60 arcseconds from the continuum centroid. The similarities and differences in the submillimeter continuum emission properties of the envelopes of PPCs, Class 0, and Class I sources on 103 to 104 AU scales are summarized. We have modeled the normalized radial intensity distributions and spectral energy distributions (SED) for sixteen sources from the SCUBA survey (3 PPCs, 7 Class 0, and 6 Class I) using a one dimensional radiative transfer code (Egan, Leung, & Spagna 1988) with internal heating from a central protostar (Class 0 and I objects) and external heating from the interstellar radiation field (all objects) to calculate the dust temperature distribution. Power law, Bonnor-Ebert, Shu inside-out collapse, and Plummer density distributions were tested to match the observed normalized radial profiles and observed SED simultaneously. Realistic beam profiles and chopping were used to simulate the observations. We find Bonnor-Ebert spheres with central densities of 105 to 106 cm-3 reproduce the PPC radial profiles while power law models (n(r) ~ r-p, p = 1.1 - 2

  6. Modelling water in the envelopes of low-mass protostars

    NASA Astrophysics Data System (ADS)

    van Kempen, Tim A.; Jørgensen, Jes K.; Hogerheijde, Michiel R.; van Dishoeck, Ewine F.

    Using sophisticated spherically symmetric radiative transfer models for gas and dust, we simulate the emission of H2O and its isotopes for the circumstellar envelopes around class 0 protostars, as preparatory science for the ESA cornerstone mission Herschel and its spectrometer, HIFI. L483mm is taken as an example. We probe a wide range of models in which dust, freeze-out and a large variety of abundance structures and optical depths are taken into account. A sample of water lines is selected that are observable by Herschel. Expected fluxes for these lines are derived from the models, convolved with the Herschel beam size. 1. Introduction Water has been detected by the LWS instruments aboard ISO in low-mass protostars (e.g. Ceccarelli et al. 1999, Giannini et al. 2001). The origin of the water lines is still subject of discussion, however. It has been theorized to originate in both the outflow and the quiescent infalling envelope. Ceccarelli et al. (1999) place the water in the small (200 AU), dense (> 107cm-3) and warm (> 100 K) region of the protostellar envelope. The ESA Herschel mission and in particular the HIFI instrument are particularly well suited to observe rotational far-infrared and submillimeter water lines in these environments and test the various models. 2. Approach We started with the physical structure deduced by Jørgensen (2004) for L483mm (Lbol = 9Lsol, Menv10K = 4.4Msol, D=200 pc), giving the density and temperature profiles for a typical protostellar envelope. These profiles are the result of a dust radiative transfer calculation with DUSTY (Ivezic & Elitzur, 1997). The line radiative transfer is subsequently calculated through RATRAN, developed by Hogerheijde & van der Tak (2000). The dust to gas ratio has been set at 1:100, the dust opacities are approximated by the OH5 (Ossenkopf & Henning 1994) at a density of 106cm-3. To simulate the abundance of the water molecule, we have used trial abundances with the assumption that water freezes out

  7. COUNTING LOW-MASS STARS IN INTEGRATED LIGHT

    SciTech Connect

    Conroy, Charlie; Van Dokkum, Pieter

    2012-03-01

    Low-mass stars (M {approx}< 0.4 M{sub Sun }) are thought to comprise the bulk of the stellar mass of galaxies but they constitute only of order 1 percent of the bolometric luminosity of an old stellar population. Directly estimating the number of low-mass stars from integrated flux measurements of old stellar systems is therefore possible but very challenging, given the numerous variables that can affect the light at the percent level. Here we present a new population synthesis model created specifically for the purpose of measuring the low-mass initial mass function (IMF) down to {approx}0.1 M{sub Sun} for metal-rich stellar populations with ages in the range 3-13.5 Gyr. Our fiducial model is based on the synthesis of three separate isochrones, and a combination of optical and near-IR empirical stellar libraries in order to produce integrated light spectra over the wavelength interval 0.35 {mu}m < {lambda} < 2.4 {mu}m at a resolving power of R Almost-Equal-To 2000. New synthetic stellar atmospheres and spectra have been computed in order to model the spectral variations due to changes in individual elemental abundances including C, N, Na, Mg, Si, Ca, Ti, Fe, and generic {alpha} elements. We demonstrate the power of combining blue spectral features with surface gravity-sensitive near-IR features in order to simultaneously constrain the low-mass IMF, stellar population age, metallicity, and abundance pattern from integrated light measurements. Finally, we show that the shape of the low-mass IMF can also be directly constrained by employing a suite of surface gravity-sensitive spectral features, each of which is most sensitive to a particular mass interval.

  8. Discovery of low mass objects in Taurus

    NASA Technical Reports Server (NTRS)

    Forrest, W. J.; Ninkov, Z.; Garnett, J. D.; Skrutskie, M. F.; Shure, M.

    1989-01-01

    In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member.

  9. Molecule survival in magnetized protostellar disk winds. II. Predicted H2O line profiles versus Herschel/HIFI observations

    NASA Astrophysics Data System (ADS)

    Yvart, W.; Cabrit, S.; Pineau des Forêts, G.; Ferreira, J.

    2016-01-01

    Context. The origin of molecular protostellar jets and their role in extracting angular momentum from the accreting system are important open questions in star formation research. In the first paper of this series we showed that a dusty magneto-hydrodynamic (MHD) disk wind appeared promising to explain the pattern of H2 temperature and collimation in the youngest jets. Aims: We wish to see whether the high-quality H2O emission profiles of low-mass protostars, observed for the first time by the HIFI spectrograph on board the Herschel satellite, remain consistent with the MHD disk wind hypothesis, and which constraints they would set on the underlying disk properties. Methods: We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH key program towards a sample of 29 low-mass Class 0 and Class 1 protostars. Results: A dusty MHD disk wind launched from 0.2-0.6 AU AU to 3-25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component observed in low-mass protostars, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1-3 times the disk accretion rate in the wind ejection region. It is also compatible with the typical disk size and bolometric luminosity in the observed targets. However, the narrower line profiles in Class 1 sources suggest that MHD disk winds in these sources, if present, would have to be slower and/or less water rich than in Class 0 sources. Conclusions: MHD disk winds appear as a valid (though not unique) option to consider for the origin of the broad H2O component in low-mass protostars. ALMA appears ideally suited to

  10. 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.

  11. Habitable Zones Around Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Kopparapu, Ravi Kumar; Kasting, J. F.; Ramirez, R.

    2011-09-01

    Classically, the circumstellar habitable zone (HZ) is defined as the region inside which a terrestrial mass planet, with adequate supplies of carbon, water, and internal heat, can sustain liquid water on its surface (Kasting et al. 1993). A conservative estimate for the width of the HZ in our Solar system is 0.93-1.48 AU, assuming that the inner edge is limited by water loss and the outer edge is determined by the maximum greenhouse limit for a dense CO2 atmosphere. These numbers are revisions of ones published by Kasting et al. (1993), based on new climate modeling results. Kasting et al. obtained HZ boundaries for stars with effective temperatures between 3700 K and 7200 K--limits that do not include main-sequence M-dwarfs. In this study we use an updated 1-D radiative-convective, cloud-free climate model to estimate the width of the HZ around these low mass stars. Significant improvements in our climate model include: (1) updated collision-induced absorption coefficients for CO2 (critical for dense CO2 atmospheres at the outer edge) and (2) a revised Rayleigh scattering coefficient for H2O (important for water loss at the inner edge). Assuming Earth-like planets with CO2/H2O/N2 atmospheres, the width of the HZ is 0.24-0.44 AU around an early M star (Teff = 3600 K) and 0.05-0.09 AU for a late M star (Teff = 2800 K). As our model does not include the radiative effects of clouds, the actual HZ boundaries may extend further in both directions than our conservative estimates. Nonetheless, current ground-based surveys (e.g., the MEARTH project) and future space-based characterization missions (e.g., JWST/TPF) may be able to use these HZ boundaries to help guide their efforts to find habitable planets around main-sequence stars. (We acknowledge funding from NASA Astrobiology Institute's Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C.)

  12. Numerical simulations of protostellar jets

    NASA Astrophysics Data System (ADS)

    Suttner, Gerhard; Smith, Michael D.; Yorke, Harold W.; Zinnecker, Hans

    Molecular jets announce the successful birth of a protostar. We develop here a model for the jets and their environments, adapting a multi-dimensional hydrocode to follow the molecular-atomic transitions of hydrogen. We examine powerful outflows into dense gas. The cocoon which forms around a jet is a very low density cavity of atomic gas. These atoms originate from strong shocks which dissociate the molecules. The rest of the molecules are either within the jet or swept up into very thin layers. Pulsed jets produce wider cavities and molecular layers which can grow onto resolvable jet knots. Three-dimensional simulations produce shocked molecular knots, distorted and multiple bow shocks and arclike structures. Spectroscopic and excitation properties of the hydrogen molecules are calculated. In the infrared, strong emission is seen from shocks within the jet (when pulsed) as well as from discrete regions along the cavity walls. Excitation, as measured by line ratios, is not generally constant. Broad double-peaked, shifted emission lines are predicted. The jet model for protostellar outflows is confronted with the constraints imposed by CO spectroscopic observations. From the three dimensional simulations we calculate line profiles and construct position-velocity diagrams for the (low-J) CO transitions. We find (1) the profiles imply power law variation of integrated brightness with velocity over a wide range of velocities, (2) the velocity field resembles a `Hubble Law' and (3) a hollow-shell structure at low velocities becomes an elongated lobe at high velocities. Deviations from the simple power law dependence of integrated brightness versus velocity occur at high velocities in our simulations. The curve first dips to a shallow minimum and then rises rapidly and peaks sharply. Reanalysis of the NGC 2264G and Cepheus E data confirm these predictions. We identify these two features with a jet-ambient shear layer and the jet itself. A deeper analysis reveals that

  13. Using FU Orionis outbursts to constrain self-regulated protostellar disk models

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Lin, D. N. C.

    1994-01-01

    One-dimensional, convective, vertical structure models and one dimensional time-dependent, radial diffusion models are combined to create a self-consistent picture in which FU Orionis outbursts occur in young stellar objects (YSOs) as the result of a large-scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. Although active accretion disks have long been postulated to be ubiqitous among low-mass YSOs, few constraints have until now been imposed on physical conditions in these disks. By fitting the results of time-dependent disk models to observed timescales of FU Orionis events, we estimate the magnitude of the effective viscous stress in the inner disk (r approximately less than 1 AU) to be, in accordance with an ad hoc 'alpha' prescription, the product of the local sound speed, pressure scale height, and an efficiency factor alpha of 10(exp -4) where hydrogen is neutral and 10(exp 3) where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of dm(sub crit)/dt = 5 x 10(exp 7) solar mass/yr independent of the magnitude of alpha for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of dm(sub in)/dt = 1-10) x 10(exp -6) solar mass/yr produce observed FU Orionis timescales consistent with estimates of spherical molecular cloud core collapse rates. Modeled ionization fronts are typically initiated near the inner edge of the disk and propogate out to a distance of several tens of stellar radii. Beyond this region, the disk transports mass steadily inward at the supplied constant infall rate. Mass flowing through the innermost disk annulus is equal to dm

  14. Shockingly low water abundances in Herschel/PACS observations of low-mass protostars in Perseus

    NASA Astrophysics Data System (ADS)

    Karska, A.; Kristensen, L. E.; van Dishoeck, E. F.; Drozdovskaya, M. N.; Mottram, J. C.; Herczeg, G. J.; Bruderer, S.; Cabrit, S.; Evans, N. J.; Fedele, D.; Gusdorf, A.; Jørgensen, J. K.; Kaufman, M. J.; Melnick, G. J.; Neufeld, D. A.; Nisini, B.; Santangelo, G.; Tafalla, M.; Wampfler, S. F.

    2014-12-01

    Context. Protostars interact with their surroundings through jets and winds impinging on the envelope and creating shocks, but the nature of these shocks is still poorly understood. Aims: Our aim is to survey far-infrared molecular line emission from a uniform and significant sample of deeply-embedded low-mass young stellar objects (YSOs) in order to characterize shocks and the possible role of ultraviolet radiation in the immediate protostellar environment. Methods: Herschel/PACS spectral maps of 22 objects in the Perseus molecular cloud were obtained as part of the William Herschel Line Legacy (WILL) survey. Line emission from H2O, CO, and OH is tested against shock models from the literature. Results: Observed line ratios are remarkably similar and do not show variations with physical parameters of the sources (luminosity, envelope mass). Most ratios are also comparable to those found at off-source outflow positions. Observations show good agreement with the shock models when line ratios of the same species are compared. Ratios of various H2O lines provide a particularly good diagnostic of pre-shock gas densities, nH ~ 105 cm-3, in agreement with typical densities obtained from observations of the post-shock gas when a compression factor on the order of 10 is applied (for non-dissociative shocks). The corresponding shock velocities, obtained from comparison with CO line ratios, are above 20 km s-1. However, the observations consistently show H2O-to-CO and H2O-to-OH line ratios that are one to two orders of magnitude lower than predicted by the existing shock models. Conclusions: The overestimated model H2O fluxes are most likely caused by an overabundance of H2O in the models since the excitation is well-reproduced. Illumination of the shocked material by ultraviolet photons produced either in the star-disk system or, more locally, in the shock, would decrease the H2O abundances and reconcile the models with observations. Detections of hot H2O and strong OH

  15. Study of Decay Mechanisms in B-→Λc+p¯π- Decays and Observation of Low-Mass Structure in the Λc+p¯ System

    NASA Astrophysics Data System (ADS)

    Gabyshev, N.; Abe, K.; Abe, K.; Adachi, I.; Aihara, H.; Asano, Y.; Aulchenko, V.; Aushev, T.; Bakich, A. M.; Bitenc, U.; Bizjak, I.; Blyth, S.; Bondar, A.; Bozek, A.; Bračko, M.; Brodzicka, J.; Browder, T. E.; Chang, P.; Chao, Y.; Chen, A.; Chen, W. T.; Cheon, B. G.; Chistov, R.; Choi, S.-K.; Choi, Y.; Chuvikov, A.; Cole, S.; Dalseno, J.; Danilov, M.; Dash, M.; Drutskoy, A.; Eidelman, S.; Enari, Y.; Fratina, S.; Gershon, T.; Gokhroo, G.; Golob, B.; Gorišek, A.; Hara, T.; Hayashii, H.; Hazumi, M.; Hokuue, T.; Hoshi, Y.; Hou, S.; Hou, W.-S.; Hsiung, Y. B.; Iijima, T.; Imoto, A.; Inami, K.; Ishikawa, A.; Itoh, R.; Iwasaki, M.; Iwasaki, Y.; Kang, J. H.; Kang, J. S.; Kataoka, S. U.; Katayama, N.; Kawai, H.; Kawasaki, T.; Khan, H. R.; Kichimi, H.; Kim, H. J.; Kim, H. O.; Kim, S. K.; Kim, S. M.; Kinoshita, K.; Korpar, S.; Krokovny, P.; Kumar, S.; Kuo, C. C.; Kuzmin, A.; Kwon, Y.-J.; Lange, J. S.; Leder, G.; Lesiak, T.; Lin, S.-W.; Mandl, F.; Matsumoto, T.; Mikami, Y.; Mitaroff, W.; Miyake, H.; Miyata, H.; Mizuk, R.; Nagamine, T.; Nagasaka, Y.; Nakano, E.; Nakao, M.; Nakazawa, H.; Natkaniec, Z.; Nishida, S.; Nitoh, O.; Ogawa, S.; Ohshima, T.; Okabe, T.; Okuno, S.; Olsen, S. L.; Onuki, Y.; Ozaki, H.; Palka, H.; Park, C. W.; Park, H.; Parslow, N.; Peak, L. S.; Pestotnik, R.; Piilonen, L. E.; Rozanska, M.; Sagawa, H.; Sakai, Y.; Sato, N.; Schietinger, T.; Schneider, O.; Schwartz, A. J.; Senyo, K.; Seuster, R.; Sevior, M. E.; Shibuya, H.; Sidorov, V.; Singh, J. B.; Somov, A.; Stamen, R.; Stanič, S.; Starič, M.; Sumiyoshi, T.; Suzuki, S. Y.; Tajima, O.; Takasaki, F.; Tamai, K.; Tamura, N.; Tanaka, M.; Teramoto, Y.; Tian, X. C.; Tsuboyama, T.; Tsukamoto, T.; Uehara, S.; Uglov, T.; Ueno, K.; Uno, S.; Urquijo, P.; Varner, G.; Varvell, K. E.; Villa, S.; Wang, C. H.; Wang, M.-Z.; Xie, Q. L.; Yabsley, B. D.; Yamaguchi, A.; Yamamoto, H.; Yamashita, Y.; Yamauchi, M.; Yang, Heyoung; Zhang, C. C.; Zhang, J.; Zhang, L. M.; Zhang, Z. P.; Zhilich, V.; Žontar, D.

    2006-12-01

    Using a sample of 152×106 BB¯ pairs accumulated with the Belle detector at the KEKB e+e- collider, we study the decay mechanism of three-body charmed decay B-→Λc+p¯π-. The intermediate two-body decay B-→Σc(2455)0p¯ is observed for the first time with a branching fraction of (3.7±0.7±0.4±1.0)×10-5 and a statistical significance of 8.4σ. We also observe a low-mass enhancement in the (Λc+p¯) system, which can be parametrized as a Breit-Wigner function with a mass of (3.35-0.02+0.01±0.02)GeV/c2 and a width of (0.07-0.03+0.04±0.04)GeV/c2. We measure its branching fraction to be (3.9-0.7+0.8±0.4±1.0)×10-5 with a statistical significance of 6.2σ. The errors are statistical, systematic, and that of the Λc+→pK-π+ decay branching fraction.

  16. Subarcsecond resolution observations of warm water toward three deeply embedded low-mass protostars

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    Context. Water is present during all stages of star formation: as ice in the cold outer parts of protostellar envelopes and dense inner regions of circumstellar disks, and as gas in the envelopes close to the protostars, in the upper layers of circumstellar disks and in regions of powerful outflows and shocks. Because of its key importance in the understanding of its origin in our own solar system, following the evolution of water all the way to the planet-forming disk is a fundamental task in research in star formation and astrochemistry. Aims: In this paper we probe the mechanism regulating the warm gas-phase water abundance in the innermost hundred AU of deeply embedded (Class 0) low-mass protostars, and investigate its chemical relationship to other molecular species during these stages. Methods: Millimeter wavelength thermal emission from the para-H218O 31,3 - 22,0 (Eu = 203.7 K) line was imaged at high angular resolution (0.75 arcsec; 190 AU) with the IRAM Plateau de Bure Interferometer toward the deeply embedded low-mass protostars NGC 1333-IRAS2A and NGC 1333-IRAS4A. Results: Compact H218O emission is detected toward IRAS2A and one of the components in the IRAS4A binary; in addition CH3OCH3, C2H5CN, and SO2 are detected. Extended water emission is seen toward IRAS2A, possibly associated with the outflow. Conclusions: The results complement a previous detection of the same transition toward NGC 1333-IRAS4B. The detections in all systems suggests that the presence of water on ≲ 100 AU scales is a common phenomenon in embedded protostars and that the non-detections of hot water with Spitzer toward the two systems studied in this paper are likely due to geometry and high extinction at mid-infrared wavelengths. We present a scenario in which the origin of the emission from warm water is in a flattened disk-like structure dominated by inward motions rather than rotation. The gas-phase water abundance varies between the sources, but is generally much lower than

  17. Low-mass companions to Bright Giants

    NASA Astrophysics Data System (ADS)

    Niedzielski, A.; Wolszczan, A.; Nowak, G.; Adamów, M.; Deka, B.; Górecka, M.; Kowalik, K.

    2014-04-01

    systems evolution - the main goal of PTPS. The sample was optimized for HET and HRS. It contains relatively bright stars with V in the range of 9-12 mag, randomly distributed over the northern hemisphere. After 2-3 epochs or precise RV HET observations all stars with amplitudes exceeding the HET/HRS PSF FWHM - 5 km s-1 (SB1) or below 5?ERV - ˜ 20-50 m s (single) were rejected from further monitoring. Stars with significant cross-correlation profile variations were identified as SB2 and also excluded. All remaining 300 stars are systematically monitored in search for low-mass companions. Over a dozen stars with planetary-mass companions have already been discovered (Niedzielski et al. 2007, 2009a, b; Gettel et al. 2012a, b; Nowak et al. 2013). Here I will present our new results concerning the most luminous giants with log(L/LSun)> 2, presumably post Horizontal Branch stars.

  18. Infrared spectra of protostellar collapse

    NASA Technical Reports Server (NTRS)

    Hollenbach, David J.; Ceccarelli, Cecilia; Neufeld, David A.; Tielens, Alexander G. G. M.

    1995-01-01

    Theoretical models of the formation of low mass stars by cloud collapse predict that OI(63 micrometers) and IR rotational lines of CO and H2O dominate the cooling in the freefalling region 10-1000 AU from the protostar. The freefalling gas supersonically hits the protoplanetary disk orbiting the protostar, forming an accretion shock with strong IR emission in rotational lines of H2O and OH, and OI(63 microns). The accretion shock spectra and line profiles depend on the mass flux through the shock and the typical distance r-bar at which the freefalling gas strikes the disk. The line widths are of order the Keplerian speed, or approx. 10(r-bar/10AU)(exp -0.5) km/s, for the accretion shock lines, and less for the lines from the infalling gas. Measurements of the IR line fluxes and profiles from the freefalling gas and the accretion shock diagnoses how a protostar and disk are formed and requires high sensitivity and high spectral and spatial resolving power. SOFIA will be the optimum observatory for many of these lines, although ISO will contribute and the KAO may make a few pioneering detections.

  19. Spectroscopic Observations of Nearby Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Vican, Laura; Zuckerman, B. M.; Rodriguez, D.

    2014-01-01

    Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity. By cross-correlating the GALEX Catalog with the WISE and 2MASS Point Source Catalogs, we have identified more than 2,000 stars whose UV excesses suggest ages in the 10-100 Myr range. We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2,000 stars spectroscopically. We measured the equivalent width of lithium at 6708 A absorption and H-alpha emission lines. Out of a total of 122 stars observed with the Kast grating spectrometer, we find that roughly 10% have strong lithium absorption features. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars. In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile. This submission presents work for the GALNYSS project and should be linked to abstracts submitted by David Rodriguez, Laura Vican, and Joel Kastner.

  20. Discovery of Low Mass Binary with Super Jupiter Companion

    NASA Astrophysics Data System (ADS)

    Anthes Rich, Evan; Wisniewski, John P.; Hashimoto, Jun; Brandt, Timothy; Kuzuhara, Masayuki; Tamura, Motohide

    2015-12-01

    Transit and radial velocity surveys have been prolific in detecting ~2000 confirmed planets to date. While few directly imaged planets have detected, such systems provide a unique scientific opportunity to probe exoplanets at larger angular separation, younger ages, and study their atmospheres. We present new L- and M-band AO observations, obtained with IRCS on Subaru, of a super Jupiter companion orbiting a cool dwarf. We show that the central object is likely a binary, thereby making this system the first likely directly imaged planetary mass companion surrounding a low mass binary system.

  1. Protostellar formation in rotating interstellar clouds. VII - Opacity and fragmentation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1988-01-01

    This paper investigates the effect of variations in the Rosseland mean opacity of dust grains on numerical models of three-dimensional protostellar collapse and fragmentation. In particular, it is found that increasing the dust grain opacity by factors of three to four has little effect upon the gross characteristics of protostellar fragmentation. Consequently, theoretical quantities such as the estimated minimum protostellar mass for Population I star formation are insensitive to the precise value of the opacity.

  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. CCD Photometry of Low Mass Ratio Contact Binary FP Boo - IV

    NASA Astrophysics Data System (ADS)

    Oh, Kyu-Dong; Lee, Woo-Baik

    2009-03-01

    We present new B, V, and R CCD photometric light curves for the low mass ratio contact binay FP Boo. A new photometric solution and absolute physical dimensions of the system were derived by applying the Wilson-Devinney program to our observed light curves and to previously published Rucinski et al.'s radial velocity curves. From the H-R diagram of 24 low mass ratio contact binary system including FP Boo, the evolutionary stage of FP Boo was found to coincide with those of the general low mass ratio contact binary systems. The light curves obtained in this season show a small asymmetry in their shapes.

  4. 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.

  5. 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.

  6. A numerical model for the formation and long-term evolution of protostars and protostellar disks

    NASA Astrophysics Data System (ADS)

    Fateeva, A. M.; Zhilkin, A. G.; Pavlyuchenkov, Ya. N.; Vorobyov, E. I.

    2016-02-01

    We present a physical and numerical model for studying the formation and evolution of protostellar objects with solar and sub-solar masses. The model covers several evolutionary phases of these objects starting from the gravitational collapse of an initially unstable pre-stellar cloud, proceeding through the formation and collapse of the first hydrostatic core, and ending with the complete dissipation of the initial cloud and formation of a protostar and protostellar disk. The model is described by a system of MHD equations that includes Ohmic dissipation and ambipolar diffusion, and also a scheme for calculating the thermal and ionization structure of the cloud. We employ the multicomponent approach for computing the thermal structure of collapsing protostellar cloud, in which the dust and gas temperatures are treated separately, allowing us to accurately describe the initial stages of the cloud's gravitational contraction and collapse. We present the first results showing the structure of an initially quasi-equilibrium protostellar cloud during the first stages of gravitational collapse and subsequent evolution.

  7. Signatures of Chemical Evolution in Protostellar Nebulae

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A., III; Johnson, Natasha

    2011-01-01

    A decade ago observers began to take serious notice of the presence of crystalline silicate grains in the dust flowing away from some comets. While crystallinity had been seen in such objects previously, starting with the recognitions by Campins and Ryan (1990) that the 10 micron feature of Comet Halley resembled that of the mineral forsterite, most such observations were either ignored or dismissed as no path to explain such crystalline grains was available in the literature. When it was first suggested that an outward flow must be present to carry annealed silicate grains from the innermost regions of the Solar Nebula out to the regions where comets could form (Nuth, 1999; 2001) this suggestion was also dismissed because no such transport mechanism was known at the time. Since then not only have new models of nebular dynamics demonstrated the reality of long distance outward transport (Ciesla, 2007; 2008; 2009) but examination of older models (Boss, 2004) showed that such transport had been present but had gone unrecognized for many years. The most unassailable evidence for outward nebular transport came with the return of the Stardust samples from Comet Wild2, a Kuiper-belt comet that contained micron-scale grains of high temperature minerals resembling the Calcium-Aluminum Inclusions found in primitive meteorites (Zolensky et aI., 2006) that formed at T > 1400K. Now that outward transport in protostellar nebulae has been firmly established, a re-examination of its consequences for nebular gas is in order that takes into account both the factors that regulate both the outward flow as well as those that likely control the chemical composition of the gas. Laboratory studies of surface catalyzed reactions suggest that a trend toward more highly reduced carbon and nitrogen compounds in the gas phase should be correlated with a general increase in the crystallinity of the dust (Nuth et aI., 2000), but is such a trend actually observable? Unlike the Fischer-Tropsch or

  8. Evolutionary models of rotating low mass stars

    NASA Astrophysics Data System (ADS)

    Mendes, Luiz Themystokliz Sanctos

    1999-11-01

    We have investigated the combined effects of rotation and internal angular momentum redistribution on the structure and evolution of low mass stars, from the pre-main sequence to the main sequence phase. As a tool for that study, the ATON stellar evolutionary code (Mazzitelli 1989; Ventura et al. 1998) has been modified in order to include those effects. Rotation was implemented according to the equipotential technique developed by Kippenhahn & Thomas (1970) and later improved by Endal & Sofia (1976). Angular momentum redistribution in radiative regions was modeled through an advection-diffusion partial differential equation based on the framework originally introduced by Chaboyer & Zahn (1992), which is based on the sole assumption of stronger turbulent transport in the horizontal direction than in the vertical one. The diffusion coefficient of this equation is obtained from characteristic lengths and velocities of typical rotation-induced hydrodynamical instabilities. This improved code was used to compute a series of rotating low mass stellar models (with masses ranging from 1.2Modot down to 0.6 Modot). Regarding the structural (hydrostatic) effects of rotation, the general features of these models show that rotating stars behave as if they were non-rotating stars of slightly lower masses, in accordance with previous results by other researchers. A study of this mass-lowering effect for the considered range of masses shows that rotation decreases lithium depletion while the star is fully convective but increases it as soon as the star develops a radiative core. The net effect is a enhanced lithium depletion, in disagreement with observational data which suggest that faster rotators in young open clusters experience less lithium depletion. Angular momentum redistribution in the considered models is very effective in smoothing their internal angular velocity profile as soon as the star reaches the zero age main sequence, but fails to reproduce the flat solar

  9. 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

  10. The rotation of very low mass objects

    NASA Astrophysics Data System (ADS)

    Scholz, Alexander

    2004-10-01

    This dissertation contains an investigation of the rotation of very low mass objects, i.e. Brown Dwarfs and stars with masses <0.4 MS. Today, it is well-established that there are large populations of such VLM objects in open clusters and in the field, but our knowledge about their physical properties and evolution is still very limited. Contrary to their solar-mass siblings, VLM objects are fully convective throughout their evolution. Thus, they are not able to form a large-scale magnetic field like for example the sun. The magnetic field, in turn, is crucial for the regulation of rotation: Magnetic interaction between star and circumstellar disk ("disk-locking") and angular momentum losses through stellar winds have dominant influence on the rotational evolution. Thus, we can expect major differences in the rotational behaviour of VLM objects and solar-mass stars. The best method to investigate stellar rotation is to measure rotation periods. If a star exhibits surface features which are asymmetrically distributed, its brightness may be modulated with the rotation period. Thus, this dissertation is based on the analysis of photometric time series. Open clusters are an ideal environment for such a project, since they enable one to follow many objects at the same time. Additionally, they allow one to investigate the age and mass dependence of rotation, because distance and age of the clusters are known in good approximation. For this thesis, five open clusters were observed, which span an age range from 3 to 750 Myr. In three of them (SigmaOri, EpsilonOri, IC4665), VLM objects were identified by means of colour magnitude diagrams. The candidate lists for these three regions comprise at least 100 objects, for which photometry in at least three wavelength bands is available. About a fifth to a third of these candidates could be contaminating field stars in the fore- or background of the clusters. For the remaining two clusters (Pleiades and Praesepe), objects from

  11. A Protostellar Jet Emanating from a Hypercompact H ii Region

    NASA Astrophysics Data System (ADS)

    Guzmán, Andrés E.; Garay, Guido; Rodríguez, Luis F.; Contreras, Yanett; Dougados, Catherine; Cabrit, Sylvie

    2016-08-01

    We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 obtained using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock-ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact H ii region. By comparing with images taken 6 years earlier at 5 and 9 GHz using the same telescope, we assess the proper motions (PMs) of the radio sources. The outer west and east lobes exhibit PMs of 64 ± 12 and 48 ± 13 mas yr‑1, indicating velocities projected in the plane of the sky and receding from G345.4938+01.4677 of 520 and 390 {\\text{km s}}-1, respectively. The internal radio lobes also display PM signals consistently receding from the HMYSO with magnitudes of 17 ± 11 and 35 ± 10 mas yr‑1 for the inner west and east lobes, respectively. The morphology of the outer west lobe is that of a detached bow shock. At 17 and 19 GHz, the outer east lobe displays an arcuate morphology also suggesting a bow shock. These results show that disk accretion and jet acceleration—possibly occurring in a very similar way compared with low-mass protostars—is taking place in G345.4938+01.4677 despite the presence of ionizing radiation and the associated hypercompact H ii region.

  12. Testing the correlation between low mass planets and debris disks

    NASA Astrophysics Data System (ADS)

    Kalas, Paul

    2014-10-01

    The number of dusty debris disks has increased across all spectral types through recent infrared surveys. This has provided greater overlap with stars known to host extrasolar planets via RV surveys. New studies have therefore investigated how the different properties of host stars, exoplanets, and debris disks may be correlated, with the objective of giving empirical support to competing theories of planet formation and evolution. One such emerging correlation is that stars with only low mass planets are more likely to host prominent debris disks than stars that have at least one giant planet. If true, then M dwarfs should have abundant debris disks given that they more frequently have low mass planetary systems. However, the information needed to critically test these ideas is lacking. For most systems, the presence of an outer planet with >30 Earth masses has not been observationally tested, nor are there many M dwarf debris disks available for detailed scrutiny. Here we propose to use STIS coronagraphy to image for the first time the debris disks around three nearby stars in optical scattered light. Searching for sharp dust belt structures indirectly tests for the existence of outer planets that are otherwise undetectable by RV or adaptive optics planet searches. Moreover, two of our target stars are the most recently discovered M dwarf debris disks, both closer to the Sun than AU Mic. The scattered light observations of these two targets would present a major advance in characterizing how M dwarf debris disks co-evolve with planets under different stellar environments.

  13. 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.

  14. GGD 37: AN EXTREME PROTOSTELLAR OUTFLOW

    SciTech Connect

    Green, J. D.; Watson, D. M.; Forrest, W. J.; Kim, K. H.; Bergin, E.; Maret, S.; Melnick, G.; Tolls, V.; Sonnentrucker, P.; Sargent, B. A.; Raines, S. N.

    2011-01-01

    We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne V]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne V] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s{sup -1}. The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.

  15. A Catalog of Low-mass Star-forming Cores Observed with SHARC-II at 350 μm

    NASA Astrophysics Data System (ADS)

    Suresh, Akshaya; Dunham, Michael M.; Arce, Héctor G.; Evans, Neal J., II; Bourke, Tyler L.; Merello, Manuel; Wu, Jingwen

    2016-08-01

    We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350 μm. Our observations have an effective angular resolution of 10″, approximately 2.5 times higher than observations at the same wavelength obtained with the Herschel Space Observatory, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ∼3″, approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350 μm observations.

  16. 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.

  17. Water D/H Ratio In Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Persson, Magnus V.; Jørgensen, Jes K.; van Dishoeck, Ewine F.; Harsono, Daniel

    2013-07-01

    Water is an important molecule for our life on Earth, but its way from formation on the surfaces of dust grains to planets and the accompanying chemical processing are not well understood. Through evaporation in the warm inner regions of protostars, water brings complex organics and other species previously locked up in the ice into the gas phase. The water deuterium fractionation (HDO/H2O abundance ratio) has traditionally been used to infer the amount of water that was brought to the Earth by comets. Deducing this ratio in the warm gas of deeply-embedded low-mass protostars allows to extend the discussion of the origin of Earth's water to earlier evolutionary stages. This poster present high-angular resolution, ground based interferometric observations of both HDO and H2(18)O water isotopologues toward several Class~0 low-mass protostars. The emission is compact, and stems from the inner few 100 AU in all sources. The derived amount of deuterium fractionation in water, obtained assuming LTE and optically thin emission, is the same within the uncertainties in all sources and shows only small enhancements compared with Earth's oceans and solar system's comets.

  18. 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.

  19. Protostellar Outflow Evolution in Turbulent Environments

    SciTech Connect

    Cunningham, A; Frank, A; Carroll, J; Blackman, E; Quillen, A

    2008-04-11

    The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers-type turbulence and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.

  20. Protostellar Outflow Evolution in Turbulent Environments

    NASA Astrophysics Data System (ADS)

    Cunningham, Andrew J.; Frank, Adam; Carroll, Jonathan; Blackman, Eric G.; Quillen, Alice C.

    2009-02-01

    The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.

  1. The Spectral Signature of Accretion in Low-Mass Protostars: Observations and Non-LTE Modelling

    NASA Astrophysics Data System (ADS)

    Wiesemeyer, Helmut

    1997-06-01

    This work demonstrates the feasibility of a study bringing together theoretical concepts of the earliest phase of low-mass star formation and its observational evidence. Thus, two aspects have been considered: Observational evidence: In order to detect protostellar collapse by virtue of kinematical features in spectral line profiles, both optically thick and optically thin tracers are needed. According to Leung & Brown (1977, ApJ 214, L73), a protostellar envelope undergoing collapse exhibits a red-shifted self-absorption in a molecular line transition if the excitation gradient is negative. Optically thin emission (e.g. from the corresponding isotopomere's line) corroborates the conclusions by ruling out the case of independent components filling the observing beam. The nearby (d~200 pc) globular filament L 1082 (no. 9 from a catalog assembled by Schneider & Elmegreen, 1979, ApJS 41, 87) provides at least three candidates showing unambigeous footprints of protostellar collapse. By means of millimeter-interferometry (with the iram and bima interferometers Asz well as single dish spectroscopy and continuum imaging (using the iram 30 m telescope), these candidates were identified and characterized. As moderately optically thick high-density tracers, the CS (2,1), (3,2) and (5,4) transitions have been observed. The optically thin (2,1) lines of C34S and C18O were measured to confirm the evidence for collapse. Preliminary results from observations with isophot and isocam were used to better constrain the luminosity of one of the collapse candidates, which subsequently has been classified as an extreme Class 0 protostar. Theoretical concepts: For reasons evidenced by the observed column density distributions and by systematic shifts of the molecular line emission across the sources, spherically-symmetric collapse has to be ruled out. Instead, scenarios such as core formation in sheet-like clouds (as proposed by Hartmann et al., 1994, ApJ 430, L49) and magnetic accretion

  2. CCS and NH3 Emission Associated with Low-Mass Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    de Gregorio-Monsalvo, Itziar; Gómez, José F.; Suárez, Olga; Kuiper, Thomas B. H.; Rodríguez, Luis F.; Jiménez-Bailón, Elena

    2006-05-01

    In this work we present a sensitive and systematic single-dish survey of CCS emission (complemented with ammonia observations) at 1 cm, toward a sample of low- and intermediate-mass young star-forming regions known to harbor water maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain. Out of the 40 star-forming regions surveyed in the CCS (21-10) line, only six low-mass sources show CCS emission: one transitional object between the prestellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars (L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T Tauri star (NGC 2071 North). Since CCS is considered an ``early-time'' (<~105 yr) molecule, we explain these results by either proposing a revision of the classification of the age of NGC 2071 North and L1251A, or suggesting the possibility that the particular physical conditions and processes of each source affect the destruction/production of the CCS. No statistically significant relationship was found between the presence of CCS and parameters of the molecular outflows and their driving sources. Nevertheless, we found a significant relationship between the detectability of CCS and the ammonia peak intensity (higher in regions with CCS), but not with its integrated intensity. This tendency may suggest that the narrower ammonia line widths in the less turbulent medium associated with younger cores may compensate for the differences in ammonia peak intensity, rendering differences in integrated intensity negligible. From the CCS detection rate we derive a lifetime of this molecule of ~=(0.7-3)×104 yr in low-mass star-forming regions.

  3. Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Dong, Ruobing; Vorobyov, Eduard; Pavlyuchenkov, Yaroslav; Chiang, Eugene; Liu, Hauyu Baobab

    2016-06-01

    Protostellar (class 0/I) disks, which have masses comparable to those of their nascent host stars and are fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and millimeter-wave interferometry, we explore the observational signatures of GI in disks using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and millimeter dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of astronomical units, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane; therefore, arms scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. In contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes; such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At millimeter wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one hour integration times at ∼0.″1 resolution. Collapsed fragments having masses ≳1 M J can be detected by ALMA within ∼10 minutes.

  4. First Detection of Methanol in a Class O Protostellar Disk

    NASA Technical Reports Server (NTRS)

    Velusamy, T.; Langer, William D.; Goldsmith, Paul F.

    2000-01-01

    We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class O protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2", we detect spatially unresolved methanol in the 2(sub k) - 1(sub k) transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (approx. 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH3OH) is approx. 2 x l0(exp -8) in the flat disk model, and 3 x l0(exp -7) for the flared disk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter-wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a temperature probe. The research of TV and WL was conducted at the Jet Propulsion Laboratory, California Institute of Technology with support from the National Aeronautics and Space Administration.

  5. An IRAS Hires study of low mass star formation in the Taurus molecular ring

    NASA Technical Reports Server (NTRS)

    Terebey, Susan; Surace, Jason A.

    1994-01-01

    The Taurus molecular cloud supposedly has no star clusters but only isolated star formation. However, the Infrared Astronomical Satellite (IRAS) shows us that a small star cluster is currently forming in Taurus. Most of the sources are deeply embedded and are probably low-mass protostars. We use High Resolution (HiRes) images of the IRAS data from the Infrared Processing and Analysis Center (IPAC) to look for additional infrared members of the cluster. We also investigate the question of whether the infrared emission matches predictions for protostellar sources by examining whether the dust emission is resolved on scales of one arcminute (approx. 10(exp 17) cm). With the exception of a luminous visible star, HD 29647, we find that the sources L1527, TMC1A, TMC1, TMC1C, tMR1, and IC2087 are unresolved in the HiRes images at 60 microns. Further analysis of IC2087 shows that it is unresolved at all four IRAS wavelengths.

  6. Mass-luminosity relation of low mass stars.

    NASA Astrophysics Data System (ADS)

    Malkov, O. Yu.; Piskunov, A. E.; Shpil'Kina, D. A.

    1997-04-01

    The data on dynamic masses and multicolor photometry of 56 M-type components of binary/multiple systems was collected. Critical evaluation of late type stars bolometric correction scales have been performed. Our refined and reduced data is compared with published empirical and theoretical mass-luminosity relations. Our data does not exclude the existence of a step-like feature at M_V_=12mag. The best agreement between observations and theoretical models is found for recent calculations of D'Antona & Mazzitelli (1994ApJS...90..467D) with Alexander opacities. We conclude that present-day knowledge of the mass-luminosity relation at faintest magnitudes is not sufficient for making definite conclusions on the initial mass function of low mass stars.

  7. Dead Zone Accretion Flows in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Turner, Neal; Sano, T.

    2008-01-01

    Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is too high for magnetic forces to drive turbulence. We show that much of the dead zone nevertheless is active and flows toward the star while smooth, large-scale magnetic fields transfer the orbital angular momentum radially outward. Stellar X-ray and radionuclide ionization sustain a weak coupling of the dead zone gas to the magnetic fields, despite the rapid recombination of free charges on dust grains. Net radial magnetic fields are generated in the magnetorotational turbulence in the electrically conducting top and bottom surface layers of the disk, and reach the midplane by ohmic diffusion. A toroidal component to the fields is produced near the midplane by the orbital shear. The process is similar to the magnetization of the solar tachocline. The result is a laminar, magnetically driven accretion flow in the region where the planets form.

  8. Spitzer IRAC Detection of Protostellar Outflows

    NASA Astrophysics Data System (ADS)

    Ybarra, Jason E.; Lada, E. A.; Balog, Z.

    2009-01-01

    We will discuss a method for detecting shocked H2 emission in IRAC band images and distinguishing H2 knots from stellar sources. Using this method we will present Spitzer IRAC imaging of a recently discovered parsec scale protostellar outflow. This outflow was detected in all four IRAC bands. The proposed source of the outflow is an embedded Class 0 object detected in the MIPS images. This work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by an award issued by JPL/Caltech and also a NASA LTSA Grant NNG05GD66G

  9. Probing Pre-Protostellar Cores with Formaldehyde

    NASA Astrophysics Data System (ADS)

    Young, K. E.; Lee, J.-E.; Evans, N. J., II; Goldsmith, P. F.; Doty, S. D.

    2004-05-01

    We present maps of the 6 cm and 1.3 mm transitions of H2CO toward three cold, dense pre-protostellar cores: L1498, L1512, and L1544. The 6 cm transition is uniquely suited to probe high density gas at low temperature. Our models indicate that H2CO is depleted in the interiors of PPCs. Depletion significantly affects how H2CO probes the earliest stages of star formation. Multi-stage, self-consistent models, including gas--dust energetics, of both H2CO transitions are presented, and the implications of the results discussed. This work was supported by the National Aeronautics and Space Administration, the National Science Foundation, and the Research Corporation.

  10. Detection of Methanol in a Class 0 Protostellar Disk

    NASA Technical Reports Server (NTRS)

    Langer, W.; Velusamy, T.; Goldsmith, P.

    1999-01-01

    We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, class 0 protostellar object.

  11. 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.

  12. 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

  13. 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.

  14. Small low mass advanced PBR's for propulsion

    NASA Astrophysics Data System (ADS)

    Powell, J. R.; Todosow, M.; Ludewig, H.

    1993-10-01

    The advanced Particle Bed Reactor (PBR) to be described in this paper is characterized by relatively low power, and low cost, while still maintaining competition values for thrust/weight, specific impulse and operating times. In order to retain competitive values for the thrust/weight ratio while reducing the reactor size, it is necessary to change the basic reactor layout, by incorporating new concepts. The new reactor design concept is termed SIRIUS (Small Lightweight Reactor Integral Propulsion System). The following modifications are proposed for the reactor design to be discussed in this paper: Pre-heater (U-235 included in Moderator); Hy-C (Hydride/De-hydride for Reactor Control); Afterburner (U-235 impregnated into Hot Frit); and Hy-S (Hydride Spike Inside Hot Frit). Each of the modifications will be briefly discussed below, with benefits, technical issues, design approach, and risk levels addressed. The paper discusses conceptual assumptions, feasibility analysis, mass estimates, and information needs.

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

    DOE PAGESBeta

    Barreto, J.; Cease, H.; Diehl, H. T.; Estrada, J.; Flaugher, B.; Harrison, N.; Jones, J.; Kilminster, B.; Molina, J.; Smith, J.; et al

    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.

  16. 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.

  17. The Structure and Environmental Impacts of Protostellar Outflows in DR 21 and Orion

    NASA Astrophysics Data System (ADS)

    Wiseman, J. J.; Ho, P. T. P.; Brown, R.

    1997-12-01

    Regions of high-mass star formation are considerably more complicated than their low-mass counterparts. Recent HST NICMOS images of Orion-KL (Thompson et al. 1997) as well as sensitive ground-based infrared images of H_2 shock emission in the Orion outflow region (Chrysostomou et al. 1997, McCaughrean & Mac Low 1997, Schild et al. 1997) reveal intricate clumpy shock structures extending in nearly all radial directions from the source. The one radial direction in which the shock emission is particularly diminished is to the northeast, and it is precisely here that a molecular gas filament is present and highly heated, as though blocking the path of outflowing material from Orion-KL. We present our latest NH_3 (1,1), (2,2), and (3,3) VLA MEM mosaics of the Orion-KL region. We present evidence from temperature and chemical excitation gradients that the molecular gas cores along the filament extending to the northeast of Orion-KL are strongly heated by impacts from protostellar ejecta. These effects are seen in the core ``CS1'' 30'' northeast of IRc2 and also in cores at least twice as distant (1.5 pc). The DR 21 outflow region is also quite complex, with multiple molecular outflows extending from a multiple-component HII region. We present sensitive VLA maps of hydrogen recombination line emission, and we report the detection of bipolar ionized gas within the molecular outflow lobes. This detection gives observational evidence for the initial ionized inner structure of high mass protostellar outflows. Chrysostomou, A. et al. 1997, MNRAS, 289, 605 McCaughrean, M., & Mac Low, M.-M. 1997, AJ, 113, 391 Schild, H., Miller, S., & Tennyson, J. 1997, A&A, 319, 1037 Thompson, R., Rieke, M., Schneider, G., Stolovy, S., Erickson, E., & Axon, D. 1997, STSCI Early Release Observation PRC97-13

  18. IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

    NASA Technical Reports Server (NTRS)

    Remijan, Anthony J.; Hollis, J. M.

    2005-01-01

    We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH3CH2CN)) methyl formate (CH3OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emission has a spatial scale of approx. 20" and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of approx. 6" and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2" that map approx. 2" northeast of the A and B symmetry axis. The redshifted SiO is approx. 2" northwest of blueshifted SiO along a position angle of approx. 135deg which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive approx. 1.4 Solar Mass, interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous CO-13 emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and CO-13 data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array CO-12C data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.

  19. AN ADAPTIVE OPTICS SURVEY FOR CLOSE PROTOSTELLAR BINARIES

    SciTech Connect

    Connelley, Michael S.; Reipurth, Bo; Tokunaga, Alan T.

    2009-11-15

    In order to test the hypothesis that Class I protostellar binary stars are a product of ejections during the dynamical decay of nonhierarchical multiple systems, we combined the results of new adaptive optics (AO) observations of Class I protostars with our previously published AO data to investigate whether Class I protostars with a widely separated companion (r > 200 AU) are more likely to also have a close companion (r < 200 AU). In total, we observed 47 embedded young stellar objects (YSOs) with either the Subaru natural guide star AO system or the Keck laser guide star AO system. We found that targets with a widely separated companion within 5000 AU are not more likely to have a close companion. However, targets with another YSO within a projected separation of 25,000 AU are much more likely to have a close companion. Most importantly, every target with a close companion has another YSO within a projected separation of 25,000 AU. We came to the same conclusions after considering a restricted sample of targets within 500 pc and close companions wider than 50 AU to minimize incompleteness effects. The Orion star-forming region was found to have an excess of both close binaries and YSOs within 25,000 AU compared to other star-forming regions. We interpret these observations as strong evidence that many close Class I binary stars form via ejections and that many of the ejected stars become unbound during the Class I phase.

  20. DEUTERIUM FRACTIONATION AS AN EVOLUTIONARY PROBE IN MASSIVE PROTOSTELLAR/CLUSTER CORES

    SciTech Connect

    Chen, Huei-Ru; Wang, Mei-Yan; Liu, Sheng-Yuan; Su, Yu-Nung

    2011-12-20

    Clouds of high infrared extinction are promising sites of massive star/cluster formation. A large number of cloud cores discovered in recent years allow for the investigation of a possible evolutionary sequence among cores in early phases. We have conducted a survey of deuterium fractionation toward 15 dense cores in various evolutionary stages, from high-mass starless cores to ultracompact H II regions, in the massive star-forming clouds of high extinction, G34.43+0.24, IRAS 18151-1208, and IRAS 18223-1243, with the Submillimeter Telescope. Spectra of N{sub 2}H{sup +} (3-2), N{sub 2}D{sup +} (3-2), and C{sup 18}O (2-1) were observed to derive the deuterium fractionation of N{sub 2}H{sup +}, D{sub frac} {identical_to} N(N{sub 2}D{sup +})/N(N{sub 2}H{sup +}), as well as the CO depletion factor for every selected core. Our results show a decreasing trend in D{sub frac} with both gas temperature and line width. Since colder and quiescent gas is likely to be associated with less evolved cores, larger D{sub frac} appears to correlate with early phases of core evolution. Such decreasing trend resembles the behavior of D{sub frac} in the low-mass protostellar cores and is consistent with several earlier studies in high-mass protostellar cores. We also find a moderate increasing trend of D{sub frac} with the CO depletion factor, suggesting that sublimation of ice mantles alters the competition in the chemical reactions and reduces D{sub frac}. Our findings suggest a general chemical behavior of deuterated species in both low- and high-mass protostellar candidates at early stages. In addition, upper limits to the ionization degree are estimated to be within 2 Multiplication-Sign 10{sup -7} and 5 Multiplication-Sign 10{sup -6}. The four quiescent cores have marginal field-neutral coupling and perhaps favor turbulent cooling flows.

  1. WISE Detection of Low-Mass X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Wang, Zhongxiang

    2014-08-01

    I will report on the results from our search for the Wide-field Infrared Survey Explorer detection of the Galactic low-mass X-ray binaries. Among 187 catalogued binaries, we find 13 counterparts and two candidate counterparts. For the 13 counterparts, two (4 0614+091 and G 339-4) have already been confirmed by previous studies to have a jet and one (GR 1915+105) to have a candidate circumbinary disk, from which the detected infrared emission arose. Having collected the broad-band optical and near-infrared data in literature and constructed flux density spectra for the other 10 binaries, we identify that three (A0620-00, XTE J1118+480, and GX 1+4) are candidate circumbinary disk systems, four (Cen X-4, 4U 1700+24, 3A 1954+319, and Cyg X-2) had thermal emission from their companion stars, and three (Sco X-1, Her X-1, and Swift J1753.5-0127) are peculiar systems with the origin of their infrared emission rather uncertain. Discussion of the results and WISE counterparts' brightness distribution will be provided, which suggests that more than half of the LMXBs would have a jet, a circumbinary disk, or the both.

  2. VARIABLE ACCRETION OUTBURSTS IN PROTOSTELLAR EVOLUTION

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles E-mail: lhartm@umich.edu E-mail: gammie@illinois.edu

    2013-02-20

    We extend the one-dimensional, two-zone models of long-term protostellar disk evolution with infall of Zhu et al. to consider the potential effects of a finite viscosity in regions where the ionization is too low for the magnetorotational instability (MRI) to operate (the {sup d}ead zone{sup )}. We find that the presence of a small but finite dead zone viscosity, as suggested by simulations of stratified disks with MRI-active outer layers, can trigger inside-out bursts of accretion, starting at or near the inner edge of the disk, instead of the previously found outside-in bursts with zero dead zone viscosity, which originate at a few AU in radius. These inside-out bursts of accretion bear a qualitative resemblance to the outburst behavior of one FU Ori object, V1515 Cyg, in contrast to the outside-in burst models, which more closely resemble the accretion events in FU Ori and V1057 Cyg. Our results suggest that the type and frequency of outbursts are potentially a probe of transport efficiency in the dead zone. Simulations must treat the inner disk regions, R {approx}< 0.5 AU, to show the detailed time evolution of accretion outbursts in general and to observe the inside-out bursts in particular.

  3. Variable Accretion Outbursts in Protostellar Evolution

    NASA Astrophysics Data System (ADS)

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles

    2013-02-01

    We extend the one-dimensional, two-zone models of long-term protostellar disk evolution with infall of Zhu et al. to consider the potential effects of a finite viscosity in regions where the ionization is too low for the magnetorotational instability (MRI) to operate (the "dead zone"). We find that the presence of a small but finite dead zone viscosity, as suggested by simulations of stratified disks with MRI-active outer layers, can trigger inside-out bursts of accretion, starting at or near the inner edge of the disk, instead of the previously found outside-in bursts with zero dead zone viscosity, which originate at a few AU in radius. These inside-out bursts of accretion bear a qualitative resemblance to the outburst behavior of one FU Ori object, V1515 Cyg, in contrast to the outside-in burst models, which more closely resemble the accretion events in FU Ori and V1057 Cyg. Our results suggest that the type and frequency of outbursts are potentially a probe of transport efficiency in the dead zone. Simulations must treat the inner disk regions, R <~ 0.5 AU, to show the detailed time evolution of accretion outbursts in general and to observe the inside-out bursts in particular.

  4. Cluster Formation in Protostellar Outflow-driven Turbulence

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun; Nakamura, Fumitaka

    2006-04-01

    Most, perhaps all, stars go through a phase of vigorous outflow during formation. We examine, through three-dimensional MHD simulation, the effects of protostellar outflows on cluster formation. We find that the initial turbulence in the cluster-forming region is quickly replaced by motions generated by outflows. The protostellar outflow-driven turbulence (``protostellar turbulence'' for short) can keep the region close to a virial equilibrium long after the initial turbulence has decayed away. We argue that there exist two types of turbulence in star-forming clouds: a primordial (or ``interstellar'') turbulence and a protostellar turbulence, with the former transformed into the latter mostly in embedded clusters such as NGC 1333. Since the majority of stars are thought to form in clusters, an implication is that the stellar initial mass function is determined to a large extent by the stars themselves, through outflows that individually limit the mass accretion onto forming stars and collectively shape the environments (density structure and velocity field) in which most cluster members form. We speculate that massive cluster-forming clumps supported by protostellar turbulence gradually evolve toward a highly centrally condensed ``pivotal'' state, culminating in rapid formation of massive stars in the densest part through accretion.

  5. 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

  6. The thermal structure of low-mass cloud cores

    NASA Astrophysics Data System (ADS)

    Launhardt, Ralf; Stutz, Amelia; Schmiedecke, Anika; Henning, Thomas; Krause, Oliver; Balog, Zoltan; Beuther, Henrik; Kainulainen, Jouni; Linz, Hendrik; Lippok, Nils; Nielbock, Markus; Ragan, Sarah; Schmalzl, Markus; Shirley, Yancy; Steinacker, Juergen

    2013-07-01

    The evolution of the temperature and density structure of star-forming cloud cores is one of the key aspects in protostellar collapse models. Yet this structure, in particular the temperature, is not well-constrained observationally. In the framework of the EPoS Herschel key project, we observed the NIR extinction and FIR through mm dust emission from selected isolated nearby starless and protostellar cloud cores. Based on these data, we reconstruct the full dust temperature and density structure of the cores. We find that the thermal structure of all globules is completely dominated by external heating through the ISRF and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (7-11 K) with column densities of up to 10^23 cm^-2 and central volume densities of a few 10^5 cm^-3 (starless cores). The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules.

  7. BROAD N{sub 2}H{sup +} EMISSION TOWARD THE PROTOSTELLAR SHOCK L1157-B1

    SciTech Connect

    Codella, C.; Fontani, F.; Gómez-Ruiz, A.; Vasta, M.; Viti, S.; Ceccarelli, C.; Lefloch, B.; Podio, L.; Caselli, P.

    2013-10-10

    We present the first detection of N{sub 2}H{sup +} toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ∼0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N{sub 2}H{sup +}(1-0) line originated from the dense (≥10{sup 5} cm{sup –3}) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N{sub 2}H{sup +} column density of a few 10{sup 12} cm{sup –2} corresponding to an abundance of (2-8) × 10{sup –9}. The N{sub 2}H{sup +} abundance can be matched by a model of quiescent gas evolved for more than 10{sup 4} yr, i.e., for more than the shock kinematical age (≅2000 yr). Modeling of C-shocks confirms that the abundance of N{sub 2}H{sup +} is not increased by the passage of the shock. In summary, N{sub 2}H{sup +} is a fossil record of the pre-shock gas, formed when the density of the gas was around 10{sup 4} cm{sup –3}, and then further compressed and accelerated by the shock.

  8. Discovery of a Low-mass Companion Around HR 3549

    NASA Astrophysics Data System (ADS)

    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 MJ, 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.

  9. Assembly techniques for ultra-low mass drift chambers

    NASA Astrophysics Data System (ADS)

    Assiro, R.; Cascella, M.; Grancagnolo, F.; L'Erario, A.; Miccoli, A.; Rella, S.; Spedicato, M.; Tassielli, G.

    2014-03-01

    We presents a novel technique for the fast assembly of next generation ultra low mass drift chambers offering space point resolution of the order of 100 μm and high tolerance to pile-up. The chamber design has been developed keeping in mind the requirements for the search of rare processes: high resolutions (order of 100-200 KeV/c) for particles momenta in a range (50-100 MeV/c) totally dominated by the multiple scattering contribution (e.g., muon and kaon decay experiment such as MEG at PSI and Mu2e and ORKA at Fermilab). We describe a novel wiring strategy enabling the semiautomatic wiring of a complete layer with a high degree of control over wire tension and position. We also present feed-through-less wire anchoring system. These techniques have been already implemented at INFN-Lecce in the construction of a prototype drift chamber to be soon tested with cosmic rays and particle beams.

  10. Eccentricity versus Mass for Low-Mass Secondaries and Planets

    NASA Astrophysics Data System (ADS)

    Mazeh, Tsevi; Mayor, Michel; Latham, David W.

    1997-03-01

    Spectroscopic orbits have been reported for six unseen companions orbiting solar-type stars with minimum possible masses in the range 0.5-10 Jupiter masses. The four least massive companions, around 51 Peg, 47 UMa, 55 Cnc, and τ Boo, have nearly circular orbits, while the two most massive companions, around HD 114762 and 70 Vir, have eccentricities of 0.35 and 0.40. We compare the orbital eccentricities of these six planet candidates with the eccentricities of the planets in the solar system, of the three planets found around the pulsar PSR B1957+12, and of the low-mass secondaries in a subsample of the spectroscopic binaries from the Carney-Latham proper-motion survey. The distribution of eccentricities for the combined samples displays a striking pattern: the companions with masses smaller than about 5 Jupiter masses have circular orbits, while the more massive companions have eccentric orbits. We outline four possible scenarios that might have produced this pattern of eccentricity versus mass.

  11. Depletion of chlorine into HCl ice in a protostellar core. The CHESS spectral survey of OMC-2 FIR 4

    NASA Astrophysics Data System (ADS)

    Kama, M.; Caux, E.; López-Sepulcre, A.; Wakelam, V.; Dominik, C.; Ceccarelli, C.; Lanza, M.; Lique, F.; Ochsendorf, B. B.; Lis, D. C.; Caballero, R. N.; Tielens, A. G. G. M.

    2015-02-01

    Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances <10-5 has not yet been well studied. Aims: Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. Methods: We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H2 hyperfine collisional excitation rate coefficients. Results: A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9 × 10-11, a factor of only 10-3 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Conclusions: Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of ≲10-10 in most of the protostellar core. We find the [35Cl]/[37Cl] ratio in OMC-2 FIR 4 to be 3.2 ± 0.1, consistent with the solar system value. Appendices are available in electronic form at http://www.aanda.org

  12. 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.

  13. X-rays from protostellar jets: emission from continuous flows

    NASA Astrophysics Data System (ADS)

    Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.

    2007-02-01

    Context: Recently X-ray emission from protostellar jets has been detected with both XMM-Newton and Chandra satellites, but the physical mechanism which can give rise to this emission is still unclear. Aims: We performed an extensive exploration of the parameter space for the main parameters influencing the jet/ambient medium interaction. Aims include: 1) to constrain the jet/ambient medium interaction regimes leading to the X-ray emission observed in Herbig-Haro objects in terms of the emission by a shock forming at the interaction front between a continuous supersonic jet and the surrounding medium; 2) to derive detailed predictions to be compared with optical and X-ray observations of protostellar jets; 3) to get insight into the protostellar jet's physical conditions. Methods: We performed a set of two-dimensional hydrodynamic numerical simulations, in cylindrical coordinates, modeling supersonic jets ramming into a uniform ambient medium. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. Results: Our model explains the observed X-ray emission from protostellar jets in a natural way. In particular, we find that a protostellar jet that is less dense than the ambient medium well reproduces the observations of the nearest Herbig-Haro object, HH 154, and allows us to make detailed predictions of a possible X-ray source proper motion (v_sh ≈500 km s-1) detectable with Chandra. Furthermore, our results suggest that the simulated protostellar jets which best reproduce the X-rays observations cannot drive molecular outflows.

  14. Magnetic Fields in Early Protostellar Disk Formation

    NASA Astrophysics Data System (ADS)

    González-Casanova, Diego F.; Lazarian, Alexander; Santos-Lima, Reinaldo

    2016-03-01

    We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian & Vishniac model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called “magnetic braking catastrophe.” In particular, we provide a detailed study of the dynamics of a 0.5 M⊙ protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, “reconnection diffusion,” removes the magnetic flux from the disk; the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.

  15. Low-Mass Stirling Convertor Assembly Progress Update

    NASA Astrophysics Data System (ADS)

    Qiu, Songgang; Augenblick, John E.; Redinger, Darin L.

    2006-01-01

    Infinia is developing the next generation of space-ready Stirling Convertor Assemblies. Infinia has previously proposed a Low-Mass Stirling Convertor Assembly (SCA) design employing a flux-concentrating, moving-iron linear alternator. This paper describes further development of that proposed machine, including additional improvements and advancements. One significant change is a new, lighter-weight moving-magnet alternator design. Infinia has shown progress in the low mass design's development and testing: namely in the area of flexure spring rates, welding techniques on the flange, and a change to the alternator configuration. Progress has been made with the flat-top heater head design and its capabilities, as well. The changes described in this paper will significantly reduce the mass and increase the power density of the low-mass design.

  16. A Search for Protostellar Collapse in Late Class I Sources

    NASA Astrophysics Data System (ADS)

    Gregersen, E. M.; Mardones, D.; Evans, N. J., II; Myers, P. C.; Shirley, Y. L.; Wilson, C. D.

    2000-10-01

    Asymmetric spectra of optically thick spectral lines are associated with protostellar collapse in young stellar objects. Such asymmetries have been believed to be confined solely to the Class 0 stage, but collapse signatures have now been observed in Class I sources with Tbol < 200 K. We present partial results of a survey that extends earlier results in Class 0 and I sources of HCO+, a molecule that shows strong line asymmetry in simulations of collapsing clouds, to Class I sources with Tbol < 650 K to find when protostellar collapse ends and how infall motions change with time.

  17. The one dimensional collapse models of turbulent protostellar clouds

    NASA Astrophysics Data System (ADS)

    Zamozdra, S. N.

    The spherically-symmetric numerical modelling of the gravitational collapse of protostellar clouds is carried out, taking ambipolar diffusion and the pressure of Alfvenic turbulence into account. It is shown that the dependency of protostar formation time on ekg (the initial turbulent-to-gravitational energies ratio) is non-monotonic because it is determined by the complex interaction of large scale magnetosonic waves with the waves of turbulence amplification. Protostellar mass is almost independent on ekg while accretion rate variations with ekg can be of order of 10%.

  18. SLOAN LOW-MASS WIDE PAIRS OF KINEMATICALLY EQUIVALENT STARS (SLoWPoKES): A CATALOG OF VERY WIDE, LOW-MASS PAIRS

    SciTech Connect

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

    2010-06-15

    We present the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES), a catalog of 1342 very-wide (projected separation {approx}>500 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

  19. Infrared and Radio Observations of a Small Group of Protostellar Objects in the Molecular Core, L1251-C

    NASA Astrophysics Data System (ADS)

    Kim, Jungha; Lee, Jeong-Eun; Choi, Minho; Bourke, Tyler L.; Evans, Neal J., II; Di Francesco, James; Cieza, Lucas A.; Dunham, Michael M.; Kang, Miju

    2015-05-01

    We present a multi-wavelength observational study of a low-mass star-forming region, L1251-C, with observational results at wavelengths from the near-infrared to the millimeter. Spitzer Space Telescope observations confirmed that IRAS 22343+7501 is a small group of protostellar objects. The extended emission in the east-west direction with its intensity peak at the center of L1251A has been detected at 350 and 850 μm with the Caltech Submillimeter Observatory and James Clerk Maxwell telescopes, tracing dense envelope material around L1251A. The single-dish data from the Korean VLBI Network and TRAO telescopes show inconsistencies between the intensity peaks of several molecular emission lines and that of the continuum emission, suggesting complex distributions of molecular abundances around L1251A. The Submillimeter Array interferometer data, however, show intensity peaks of CO 2-1 and 13CO 2-1 located at the position of IRS 1, which is both the brightest source in the Infrared Array Camera image and the weakest source in the 1.3 mm dust-continuum map. IRS 1 is the strongest candidate for the driving source of the newly detected compact CO 2-1 outflow. Over the entire region (14‧ × 14‧) of L125l-C, 3 Class I and 16 Class II sources have been detected, including three young stellar objects (YSOs) in L1251A. A comparison between the average projected distance among the 19 YSOs in L1251-C and that among the 3 YSOs in L1251A suggests that L1251-C is an example of low-mass cluster formation where protostellar objects form in a small group.

  20. Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores

    NASA Astrophysics Data System (ADS)

    Furuya, K.; van Dishoeck, E. F.; Aikawa, Y.

    2016-02-01

    Recent interferometer observations have found that the D2O/HDO abundance ratio is higher than that of HDO/H2O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D2O/HDO ice ratio should be lower than the HDO/H2O ice ratio, if HDO and D2O ices are formed simultaneously with H2O ice. In this work, we propose that the observed feature, D2O/HDO > HDO/H2O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation as follows: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient; and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced as a result of the drop of the ortho-para ratio of H2, the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations, which traces the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H2O and D2O/HDO ratios. We also find that the majority of HDO and D2O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H2O ice is formed. This work demonstrates the power of the combination of the HDO/H2O and D2O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation, and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D2O/HDO > HDO/H2O, is common in low-mass protostellar sources.

  1. 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.

  2. LOW-MASS STAR FORMATION TRIGGERED BY EARLY SUPERNOVA EXPLOSIONS

    SciTech Connect

    Chiaki, Gen; Yoshida, Naoki; Kitayama, Tetsu

    2013-01-01

    We study the formation of low-mass and extremely metal-poor stars in the early universe. Our study is motivated by the recent discovery of a low-mass (M {sub *} {<=} 0.8 M {sub Sun }) and extremely metal-poor (Z {<=} 4.5 Multiplication-Sign 10{sup -5} Z {sub Sun }) star in the Galactic halo by Caffau et al. We propose a model that early supernova (SN) explosions trigger the formation of low-mass stars via shell fragmentation. We first perform one-dimensional hydrodynamic simulations of the evolution of an early SN remnant. We show that the shocked shell undergoes efficient radiative cooling and then becomes gravitationally unstable to fragment and collapse in about a million years. We then follow the thermal evolution of the collapsing fragments using a one-zone code. Our one-zone calculation treats chemistry and radiative cooling self-consistently in low-metallicity gas. The collapsing gas cloud evolves roughly isothermally, until it cools rapidly by dust continuum emission at the density 10{sup 13}-10{sup 14} cm{sup -3}. The cloud core then becomes unstable and fragments again. We argue that early SNe can trigger the formation of low-mass stars in the extremely metal-poor environment as Caffau et al. discovered recently.

  3. Enhancement of low-mass dileptons in heavy ion collisions

    SciTech Connect

    Li, G.Q.; Ko, C.M.; Brown, G.E. |

    1995-11-27

    Using a relativistic transport model for the expansion stage of S+Au collisions at 200 GeV/nucleon, we show that the recently observed enhancement of low-mass dileptons by the CERES Collaboration can be explained by the decrease of vector meson masses in hot and dense hadronic matter. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

  4. Lost in Secular Evolution: The Case of a Low-mass Classical Bulge

    NASA Astrophysics Data System (ADS)

    Saha, Kanak

    2015-06-01

    The existence of a classical bulge in disk galaxies holds an important clue to the assembly history of galaxies. Finding observational evidence of very low mass classical bulges, particularly in barred galaxies, including our Milky Way, is a challenging task as the bar-driven secular evolution might bring significant dynamical change to these bulges alongside the stellar disk. Using high-resolution N-body simulation, we show that if a cool stellar disk is assembled around a non-rotating low-mass classical bulge, the disk rapidly grows a strong bar within a few rotation timescales. Later, the bar-driven secular process transforms the initial classical bulge into a flattened rotating stellar system whose central part also has grown a barlike component rotating in sync with the disk bar. During this time, a boxy/peanut (hereafter B/P) bulge is formed via the buckling instability of the disk bar, and the vertical extent of this B/P bulge being slightly higher than that of the classical bulge, it encompasses the whole classical bulge. The resulting composite bulge appears to be both photometrically and kinematically identical to a B/P bulge without any obvious signature of the classical component. Our analysis suggests that many barred galaxies in the local universe might be hiding such low-mass classical bulges. We suggest that stellar population and chemodynamical analysis might be required in establishing evidence for such low-mass classical bulges.

  5. Low-mass Active Galactic Nuclei with Rapid X-Ray Variability

    NASA Astrophysics Data System (ADS)

    Ho, Luis C.; Kim, Minjin

    2016-04-01

    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 MBH = 1.2 × 106 M⊙ and median Lbol/LEdd = 0.44. The sample follows the MBH–σ* 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.

  6. A CHEMICAL VIEW OF PROTOSTELLAR-DISK FORMATION IN L1527

    SciTech Connect

    Sakai, Nami; Oya, Yoko; Watanabe, Yoshimasa; Yamamoto, Satoshi; Sakai, Takeshi; Hirota, Tomoya; Ceccarelli, Cecilia; Kahane, Claudine; Lopez-Sepulcre, Ana; Lefloch, Bertrand; Vastel, Charlotte; Bottinelli, Sandrine; Caux, Emmanuel; Coutens, Audrey; Aikawa, Yuri; Takakuwa, Shigehisa; Yen, Hsi-Wei; Ohashi, Nagayoshi

    2014-08-20

    Subarcsecond images of the rotational line emissions of CCH, CS, H{sub 2}CO, and CH{sub 3}OH have been obtained toward the low-mass protostar IRAS 04368+2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H{sub 2}CO and CH{sub 3}OH are centrally peaked. By analyzing the position-velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H{sub 2}CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH{sub 3}OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.

  7. Protostellar Multiplicity in Perseus Characterized by the VLA Nascent Disk and Multiplicity (VANDAM) Survey

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The formation of multiple star systems is thought to begin early in the star formation process. However, there have not been sufficient numbers of young protostars observed with high enough resolution to determine when and where most multiple systems form. To significantly improve our knowledge of protostellar multiplicity, we have carried out the VLA Nascent Disk and Multiplicity (VANDAM) survey, a 264 hour Jansky VLA program at wavelengths of 8 mm, 1 cm, 4 cm, and 6 cm toward all known Perseus protostars (N ~ 80) down to 15 AU (0.065") resolution. The unbiased nature of the survey has enabled us to conduct the most complete characterization of protostellar multiplicity to date, finding evidence for a bi-modal distribution of multiple protostar system separations. The bi-modal distribution may be evidence for multiple processes contributing to the formation of multiple systems. The inner peak at ~75 AU could be produced from disk fragmentation, while the outer peak at ~3000 AU could be produced by turbulent and/or rotational fragmentation Moreover, three systems are found to reside within larger, disk-like structures suggesting that they may be the product of disk fragmentation via gravitational instability. The results of this survey demonstrate the power and utility of unbiased surveys toward young stars.

  8. MICROLENSING DISCOVERY OF A POPULATION OF VERY TIGHT, VERY LOW MASS BINARY BROWN DWARFS

    SciTech Connect

    Choi, J.-Y.; Han, C.; Udalski, A.; Sumi, T.; Gaudi, B. S.; Gould, A.; Bennett, D. P.; Dominik, M.; Beaulieu, J.-P.; Tsapras, Y.; Bozza, V.; Abe, F.; Furusawa, K.; Itow, Y.; Bond, I. A.; Ling, C. H.; Botzler, C. S.; Freeman, M.; Chote, P.; Fukui, A.; Collaboration: MOA Collaboration; OGLE Collaboration; muFUN Collaboration; MiNDSTEp Consortium; PLANET Collaboration; RoboNet Collaboration; and others

    2013-05-10

    Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M{sub Sun} and 0.034 M{sub Sun }, and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of {approx}0.02 M{sub Sun }. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries.

  9. 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

  10. 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

  11. Low Mass Muscle Actuators (LoMMAs) Using Electroactive Polymers

    NASA Technical Reports Server (NTRS)

    Bar-Cohen, Y.; Xue, T.; Joffe, B.; Lih, S. S.; Willis, P.; Simpson, J.; Smith, J.; Clair, T.; Shahinpoor, M.

    1997-01-01

    NASA is using actuation devices for many space applications and there is an increasing need to cut their cost as well as reduce their size, mass, and power consumption. Existing transducing actuators, such as piezoceramics, are inducing limited displacement levels. Potentially, electroactive polymers (so called EAP) can be formed as inexpensive, low-mass, low-power, miniature muscle actuators that are superior to the widely used actuators.

  12. Low Mass Star Formation in the Norma Cloud

    NASA Astrophysics Data System (ADS)

    Reipurth, B.; Nielbock, M.

    2008-12-01

    A small filamentary cloud in Norma hosts a number of young low-mass stars in various stages of evolution, from visible Hα emission stars to embedded sources detected only in the sub-millimeter regime. The best known source is V346 Nor, an FU Orionis star that brightened in the early 1980s. The morphology of the cloud complex and an apparent age gradient along the cloud suggests that star formation in this region was triggered by an external event.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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, V_max^DM, 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, V_max^DM bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach V_max^DM. 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. Chemical tracers of episodic accretion in low-mass protostars

    NASA Astrophysics Data System (ADS)

    Visser, Ruud; Bergin, Edwin A.; Jørgensen, Jes K.

    2015-05-01

    Aims: Accretion rates in low-mass protostars can be highly variable in time. Each accretion burst is accompanied by a temporary increase in luminosity, heating up the circumstellar envelope and altering the chemical composition of the gas and dust. This paper aims to study such chemical effects and discusses the feasibility of using molecular spectroscopy as a tracer of episodic accretion rates and timescales. Methods: We simulate a strong accretion burst in a diverse sample of 25 spherical envelope models by increasing the luminosity to 100 times the observed value. Using a comprehensive gas-grain network, we follow the chemical evolution during the burst and for up to 105 yr after the system returns to quiescence. The resulting abundance profiles are fed into a line radiative transfer code to simulate rotational spectra of C18O, HCO+, H13CO+, and N2H+ at a series of time steps. We compare these spectra to observations taken from the literature and to previously unpublished data of HCO+ and N2H+ 6-5 from the Herschel Space Observatory. Results: The bursts are strong enough to evaporate CO throughout the envelope, which in turn enhances the abundance of HCO+ and reduces that of N2H+. After the burst, it takes 103-104 yr for CO to refreeze and for HCO+ and N2H+ to return to normal. The H2O snowline expands outwards by a factor of ~10 during the burst; afterwards, it contracts again on a timescale of 102-103 yr. The chemical effects of the burst remain visible in the rotational spectra for as long as 105 yr after the burst has ended, highlighting the importance of considering luminosity variations when analyzing molecular line observations in protostars. The spherical models are currently not accurate enough to derive robust timescales from single-dish observations. As follow-up work, we suggest that the models be calibrated against spatially resolved observations in order to identify the best tracers to be used for statistically significant source samples. Herschel

  15. 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.

  16. Period change investigation of the low mass ratio contact binary BO Ari

    NASA Astrophysics Data System (ADS)

    Kriwattanawong, W.; Tasuya, O.; Poojon, P.

    2016-04-01

    A photometric study and period change analysis for the A-type low mass ratio contact binary BO Ari is presented. The BVR light curves were fitted by using the Wilson-Devinney method. The photometric solution yields a low mass ratio of q = 0.1754(±0.0016) with a contact degree of f = 27.72%(±2.37%). We found a long-term orbital period decrease at a rate of dPdt = - 3.49 ×10-7 d yr-1. This result indicates that the system is undergoing mass transfer from the primary component to the secondary with a mass transfer rate of m˙1m1 = - 7.77 ×10-8 yr-1. With the period decrease, the inner and outer critical Roche surfaces will tighten and cause the degree of contact to increase. Therefore, BO Ari may evolve into a deeper contact system.

  17. 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).

  18. Angular Momentum Evolution in Young Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Pinzón, G.; de La Reza, R.

    2006-06-01

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

  19. 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.

  20. The timescale of low-mass proto-helium white dwarf evolution

    NASA Astrophysics Data System (ADS)

    Istrate, A. G.; Tauris, T. M.; Langer, N.; Antoniadis, J.

    2014-11-01

    Context. A large number of low-mass (≲0.20 M⊙) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show pulsations or to have a main-sequence star companion. There appear to be discrepancies between the current theoretical modelling of such low-mass He WDs and a number of key observed cases, indicating that their formation scenario yet remains to be fully understood. Aims: Here we investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). Our prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Our calculations are then compared to the most recent observational data. Methods: Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs with different initial values of donor star mass, neutron star mass, orbital period, and strength of magnetic braking. Subsequently, we followed the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. Results: We find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Δtproto = 0.5-2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The lowest WD mass for developing shell flashes is ~0.21 M⊙ for progenitor stars of mass M2 ≤ 1.5 M⊙ (and ~0.18 M⊙ for M2 = 1.6 M⊙). Conclusions: The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very low surface gravities and high effective temperatures. We find no evidence for Δtproto to depend on the occurrence of flashes and

  1. Observational Constraints on Low-Mass Stellar Evolution and Planet Formation

    NASA Astrophysics Data System (ADS)

    Birkby, Jayne Louise

    2011-07-01

    Low-mass stars (? < 1.0M⊙) account for more than 70% of the galactic stellar population yet models describing the evolution of their fundamental properties lack stringent observational constraints, especially at early ages. Furthermore, recent observations indicate a significant discrepancy between model predictions and the precise (2 - 3%) observed, dynamical masses and radii measured using low-mass eclipsing binary systems (EBs). Additionally, the theory of planet formation via core accretion predicts notably less hot-Jupiter formation around M-dwarfs (Mdot ? ≤ 0.6M⊙), but as yet, no large enough study exists to robustly test it. Further still, it is predicted that the dynamic environment of stellar clusters, in which most stars are believed to form, hampers planet formation, but again, current null detections of planets in stellar clusters are not statistically significant to test the theory. More observations are required to cement both the theory of low-mass stellar evolution and planet formation. This thesis aims to provide the necessary constraints by uncovering new low-mass EBs and transiting exoplanets in time-series photometry and follow-up spectroscopy from the Monitor project, a photometric monitoring campaign of low-mass stars in nine young open clusters, and in the WFCAM Transit Survey (WTS), a photometric monitoring campaign of ∼10,000 field M-dwarfs. Chapters 3 and 4 present my study of the young (130 Myr) cluster, M 50. I confirm three EB candidates as cluster members, including evidence that one of these is in a triple system with a wide-separation, low-mass tertiary component. The derived masses and radii for this system and one further double-lined, non-cluster member are presented, but these objects required dedicated, single-slit spectroscopic follow-up to yield the accuracy required to test pre-main sequence models. My non-detection of planets in this cluster is consistent with the results of all other cluster transit surveys. The

  2. Evolution of Intermediate and Low Mass Binary Systems

    SciTech Connect

    Eggleton, P P

    2005-10-25

    There are a number of binaries, fairly wide and with one or even two evolved giant components, that do not agree very well with conventional stellar evolution: the secondaries are substantially larger (oversized) than they should be because their masses are quite low compared with the primaries. I discuss the possibility that these binaries are former triples, in which a merger has occurred fairly recently in a short-period binary sub-component. Some mergers are expected, and may follow a phase of contact evolution. I suggest that in contact there is substantial transfer of luminosity between the components due to differential rotation, of the character observed by helioseismology in the Sun's surface convection zone.

  3. 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.

  4. On the formation redshift of 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 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).This is a pilot study for future surveys on dwarf galaxies at high redshift.

  5. 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).

  6. PROTOSTELLAR DISK FORMATION ENABLED BY WEAK, MISALIGNED MAGNETIC FIELDS

    SciTech Connect

    Krumholz, Mark R.; Crutcher, Richard M.; Hull, Charles L. H.

    2013-04-10

    The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally supported disks around most protostars, even when non-ideal magnetohydrodynamic (MHD) effects that allow the field and gas to decouple are taken into account. Using recent observations of magnetic field strengths and orientations in protostellar cores, we show that this conclusion is incorrect. The distribution of magnetic field strengths is very broad, and alignments between fields and angular momentum vectors within protostellar cores are essentially random. By combining the field strength and misalignment data with MHD simulations showing that disk formation is expected for both weak and misaligned fields, we show that these observations imply that we should expect disk fractions of {approx}10%-50% even when protostars are still deeply embedded in their parent cores, and even if the gas is governed by ideal MHD.

  7. SIMULATING PROTOSTELLAR JETS SIMULTANEOUSLY AT LAUNCHING AND OBSERVATIONAL SCALES

    SciTech Connect

    Ramsey, Jon P.; Clarke, David A.

    2011-02-10

    We present the first 2.5-dimensional magnetohydrodynamic (MHD) simulations of protostellar jets that include both the region in which the jet is launched magnetocentrifugally at scale lengths <0.1 AU and where the propagating jet is observed at scale lengths >10{sup 3} AU. These simulations, performed with the new adaptive mesh refinement MHD code AZEuS, reveal interesting relationships between conditions at the disk surface, such as the magnetic field strength, and direct observables such as proper motion, jet rotation, jet radius, and mass flux. By comparing these quantities with observed values, we present direct numerical evidence that the magnetocentrifugal launching mechanism is capable, by itself, of launching realistic protostellar jets.

  8. Protostellar formation in rotating interstellar clouds. VIII - Inner core formation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1989-01-01

    The results are presented of a variety of spherically symmetric one-dimensional (1D) calculations intended to determine the robustness of the dynamical hiccup phenomenon in protostellar cores. The 1D models show that the phenomenon is relatively insensitive to changes in the equations of state, numerical resolution, initial density and temperature, and the radiative transfer approximation. In 1D, the hiccup results in an explosive destruction of the entire inner protostellar core. Inner core formation is studied with a sequence of three-dimensional models which show that rapid inner core rotation stabilizes the hiccup instability. Instead, the inner core becomes quite flat and undergoes a cycle of binary fragmentation, binary decay into a single object surrounded by a bar, breakup of the bar into a binary, etc. When lesser amounts of rotation are involved, the inner core does hiccup somewhat, but mass is ejected in only a few directions, leading to several broad streams of ejecta.

  9. ENVIRONMENTAL EFFECTS ON THE METAL ENRICHMENT OF LOW-MASS GALAXIES IN NEARBY CLUSTERS

    SciTech Connect

    Petropoulou, V.; Vilchez, J.; Iglesias-Paramo, J.

    2012-04-20

    In this paper, we study the chemical history of low-mass star-forming (SF) galaxies in the local universe clusters Coma, A1367, A779, and A634. The aim of this work is to search for the imprint of the environment on the chemical evolution of these galaxies. Galaxy chemical evolution is linked to the star formation history, as well as to the gas interchange with the environment, and low-mass galaxies are well known to be vulnerable systems to environmental processes affecting both these parameters. For our study we have used spectra from the SDSS-III DR8. We have examined the spectroscopic properties of SF galaxies of stellar masses 10{sup 8}-10{sup 10} M{sub Sun }, located from the core to the cluster's outskirts. The gas-phase O/H and N/O chemical abundances have been derived using the latest empirical calibrations. We have examined the mass-metallicity relation of cluster galaxies, finding well-defined sequences. The slope of these sequences, for galaxies in low-mass clusters and galaxies at large cluster-centric distances, follows the predictions of recent hydrodynamic models. A flattening of this slope has been observed for galaxies located in the core of the two more massive clusters of the sample, principally in Coma, suggesting that the imprint of the cluster environment on the chemical evolution of SF galaxies should be sensitive to both the galaxy mass and the host cluster mass. The H I gas content of Coma and A1367 galaxies indicates that low-mass SF galaxies, located at the core of these clusters, have been severely affected by ram-pressure stripping (RPS). The observed mass-dependent enhancement of the metal content of low-mass galaxies in dense environments seems plausible, according to hydrodynamic simulations. This enhanced metal enrichment could be produced by the combination of effects such as wind reaccretion, due to pressure confinement by the intracluster medium (ICM), and the truncation of gas infall, as a result of the RPS. Thus, the

  10. 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.

  11. Revealing the dynamics of Class 0 protostellar discs with ALMA

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Sánchez-Monge, Á.; Walch, S.; Banerjee, R.

    2016-06-01

    We present synthetic ALMA observations of Keplerian, protostellar discs in the Class 0 stage studying the emission of molecular tracers like 13CO, C18O, HCO+, H13CO+, N2H+, and H2CO. We model the emission of discs around low- and intermediate-mass protostars. We show that under optimal observing conditions ALMA is able to detect the discs already in the earliest stage of protostellar evolution, although the emission is often concentrated to the innermost 50 au. Therefore, a resolution of a few 0.1 arcsec might be too low to detect Keplerian discs around Class 0 objects. We also demonstrate that under optimal conditions for edge-on discs Keplerian rotation signatures are recognisable, from which protostellar masses can be inferred. For this we here introduce a new approach, which allows us to determine protostellar masses with higher fidelity than before. Furthermore, we show that it is possible to reveal Keplerian rotation even for strongly inclined discs and that ALMA should be able to detect possible signs of fragmentation in face-on discs. In order to give some guidance for future ALMA observations, we investigate the influence of varying observing conditions and source distances. We show that it is possible to probe Keplerian rotation in inclined discs with an observing time of 2 h and a resolution of 0.1 arcsec, even in the case of moderate weather conditions. Furthermore, we demonstrate that under optimal conditions, Keplerian discs around intermediate-mass protostars should be detectable up to kpc distances.

  12. VizieR Online Data Catalog: Wind-driving protostellar accretion discs (Salmeron+, 2011)

    NASA Astrophysics Data System (ADS)

    Salmeron, R.; Konigl, A.; Wardle, M.

    2011-10-01

    We continue our study of weakly ionized protostellar accretion discs that are threaded by a large-scale magnetic field and power a centrifugally driven wind. It has been argued that there is already evidence in several protostellar systems that such a wind transports a significant fraction of the angular momentum from at least some part of the disc. We model this situation by considering a radially localized disc model in which the matter is everywhere well coupled to the field and the wind is the main repository of excess angular momentum. We consider stationary configurations in which magnetic diffusivity counters the shearing and advection of the magnetic field lines. In Wardle & Koenigl (1997, ASP Conf. Ser., 121, 561) we analysed the disc structure in the hydrostatic approximation (vertical motions neglected inside the disc) and presented exact disc/wind solutions for the ambipolar diffusivity regime. In Koenigl, Salmeron & Wardle (Paper I, 2010MNRAS.401..479K) we generalized the hydrostatic analysis to the Hall and Ohm diffusivity domains and used it to identify the disc parameter sub-regimes in which viable solutions with distinct physical properties can be expected to occur. In this paper we test the results of Paper I by deriving full numerical solutions (integrated through the sonic critical surface) of the disc equations in the Hall domain. (1 data file).

  13. The Main Sequence Luminosity Function of Low-Mass Globular Clusters

    NASA Astrophysics Data System (ADS)

    Smith, Graeme

    2009-07-01

    Theoretical work indicates that the dynamical evolution of globular clusters of low mass and low central concentration is strongly determined by mass-loss processes, such as stellar evaporation and tidal stripping, that can eventually lead to cluster dissolution. In fact, mass loss and cluster disruption is now considered to be a viable explanation for the form of the faint end of the Milky Way globular cluster luminosity function. A clear observational demonstration of the prevalence of cluster mass-loss would have ramifications not only for the dynamical evolution of individual globular clusters and their internal stellar mass distributions, but also for the relationships between halo field and cluster stars and the properties of globular cluster systems in galaxies. Our previous WFPC2 imaging of the low-mass diffuse halo cluster Palomar 5 revealed a main sequence deficient in stars compared to other low-concentration globular clusters of much higher mass, consistent with there having been a considerable loss of stars from this system. But is Pal 5 typical of low-mass, low-concentration halo clusters? We propose to place the mass-loss scenario on a firm observational footing {or otherwise} by using WFC3 imaging to measure the main-sequence stellar mass functions of two of the lowest-mass lowest-concentration globular clusters in the Milky Way, AM-4 and Palomar 13, in order to search for analogous evidence of stellar depletion.

  14. On the formation of galactic black hole low-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Jia, Kun; Li, Xiang-Dong

    2016-03-01

    Currently, there are 24 black hole (BH) X-ray binary systems that have been dynamically confirmed in the Galaxy. Most of them are low-mass X-ray binaries (LMXBs) comprised of a stellar-mass BH and a low-mass donor star. Although the formation of these systems has been extensively investigated, some crucial issues remain unresolved. The most noticeable one is that, the low-mass companion has difficulties in ejecting the tightly bound envelope of the massive primary during the spiral-in process. While initially intermediate-mass binaries are more likely to survive the common envelope (CE) evolution, the resultant BH LMXBs mismatch the observations. In this paper, we use both stellar evolution and binary population synthesis to study the evolutionary history of BH LMXBs. We test various assumptions and prescriptions for the supernova mechanisms that produce BHs, the binding energy parameter, the CE efficiency and the initial mass distributions of the companion stars. We obtain the birthrate and the distributions of the donor mass, effective temperature and orbital period for the BH LMXBs in each case. By comparing the calculated results with the observations, we put useful constraints on the aforementioned parameters. In particular, we show that it is possible to form BH LMXBs with the standard CE scenario if most BHs are born through failed supernovae.

  15. 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.

  16. 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.

  17. A Study of Radio Polarization in Protostellar Jets

    NASA Astrophysics Data System (ADS)

    Cécere, Mariana; Velázquez, Pablo F.; Araudo, Anabella T.; De Colle, Fabio; Esquivel, Alejandro; Carrasco-González, Carlos; Rodríguez, Luis F.

    2016-01-01

    Synchrotron radiation is commonly observed in connection with shocks of different velocities, ranging from relativistic shocks associated with active galactic nuclei, gamma-ray bursts, or microquasars, to weakly or non-relativistic flows such as those observed in supernova remnants. Recent observations of synchrotron emission in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow us to determine the jet and/or interstellar magnetic field structure, thus giving insights into the jet ejection and collimation mechanisms. In this paper, we compute for the first time polarized (synchrotron) and non-polarized (thermal X-ray) synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as a toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities of ˜1000 km s-1 and ˜10 times lighter than the environment can produce internal knots with significant synchrotron emission and thermal X-rays in the shocked region of the leading bow shock moving in a dense medium. While models with a purely toroidal magnetic field show a very large degree of polarization, models with a helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets.

  18. Spatial Distribution of Small Organics in Prestellar and Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Waalkes, William; Guzman, Viviana; Oberg, Karin I.

    2016-01-01

    In the interstellar medium, formaldehyde (H2CO) has efficient formation pathways in both the gas-phase and on the surfaces of dust grains. Methanol (CH3OH), on the other hand, is believed to form exclusively on grains as there are no efficient gas-phase reactions leading to CH3OH. We present observations taken with the IRAM 30m telescope of several H2CO and CH3OH lines in a prestellar and protostellar core. We investigated the formation pathways of H2CO and CH3OH by comparing their spatial distributions. We find that in the prestellar core, the two species are anti-correlated in the densest region, while their emission is correlated in the low-density region. In contrast, for the protostellar core we find a correlation in the distribution of both species. We conclude that in the protostellar source, H2CO and CH3OH form together on grains and have been thermally desorbed due to the central newly formed star. In the prestellar core, however, CH3OH forms on the ices and remains depleted in the coldest regions, while H2CO can form efficiently in the gas-phase. This work was supported in part by the NSF REU and DoD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution.

  19. PROTOSTELLAR OUTFLOWS AND RADIATIVE FEEDBACK FROM MASSIVE STARS

    SciTech Connect

    Kuiper, Rolf; Yorke, Harold W.; Turner, Neal J. E-mail: Harold.W.Yorke@jpl.nasa.gov

    2015-02-20

    We carry out radiation hydrodynamical simulations of the formation of massive stars in the super-Eddington regime including both their radiative feedback and protostellar outflows. The calculations start from a prestellar core of dusty gas and continue until the star stops growing. The accretion ends when the remnants of the core are ejected, mostly by the force of the direct stellar radiation in the polar direction and elsewhere by the reradiated thermal infrared radiation. How long the accretion persists depends on whether the protostellar outflows are present. We set the mass outflow rate to 1% of the stellar sink particle's accretion rate. The outflows open a bipolar cavity extending to the core's outer edge, through which the thermal radiation readily escapes. The radiative flux is funneled into the polar directions while the core's collapse proceeds near the equator. The outflow thus extends the ''flashlight effect'', or anisotropic radiation field, found in previous studies from the few hundred AU scale of the circumstellar disk up to the 0.1 parsec scale of the core. The core's flashlight effect allows core gas to accrete on the disk for longer, in the same way that the disk's flashlight effect allows disk gas to accrete on the star for longer. Thus although the protostellar outflows remove material near the core's poles, causing slower stellar growth over the first few free-fall times, they also enable accretion to go on longer in our calculations. The outflows ultimately lead to stars of somewhat higher mass.

  20. Where are the Low-mass Population III Stars?

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tomoaki; Sudo, Kae; Yokoi, Shingo; Hasegawa, Kenji; Tominaga, Nozomu; Susa, Hajime

    2016-07-01

    We study the number and the distribution of low-mass Population III (Pop III) stars in the Milky Way. In our numerical model, hierarchical formation of dark matter minihalos and Milky-Way-sized halos are followed by a high-resolution cosmological simulation. We model the Pop III formation in H2 cooling minihalos without metal under UV radiation of the Lyman–Werner bands. Assuming a Kroupa initial mass function (IMF) from 0.15 to 1.0 M ⊙ for low-mass Pop III stars, as a working hypothesis, we try to constrain the theoretical models in reverse by current and future observations. We find that the survivors tend to concentrate on the center of halo and subhalos. We also evaluate the observability of Pop III survivors in the Milky Way and dwarf galaxies, and constraints on the number of Pop III survivors per minihalo. The higher latitude fields require lower sample sizes because of the high number density of stars in the galactic disk, the required sample sizes are comparable in the high- and middle-latitude fields by photometrically selecting low-metallicity stars with optimized narrow-band filters, and the required number of dwarf galaxies to find one Pop III survivor is less than 10 at <100 kpc for the tip of red giant stars. Provided that available observations have not detected any survivors, the formation models of low-mass Pop III stars with more than 10 stars per minihalo are already excluded. Furthermore, we discuss the way to constrain the IMF of Pop III stars at a high mass range of ≳10 M ⊙.

  1. The different baryonic Tully–Fisher relations at low masses

    PubMed Central

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

    2016-01-01

    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, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$V_{\\rm max}^{\\rm DM}$\\end{document}, 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, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$V_{\\rm max}^{\\rm DM}$\\end{document} bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage

  2. The APOGEE Low-Mass Star Ancillary Project

    NASA Astrophysics Data System (ADS)

    Blake, Cullen; Mahadevan, Suvrath; Deshpande, Rohit; Bender, Chad F.; Terrien, Ryan; Crepp, Justin R.; Carlberg, Joleen K.; Nidever, David L.; Stassun, Keivan; Hawley, Suzanne L.; Hearty, Fred; Allende-Prieto, Carlos

    2015-01-01

    As a high-resolution, near-infrared, fiber-fed instrument, APOGEE presents a unique opportunity to obtain multi-epoch radial velocity measurements of a large number of low-mass stars. These observations will reveal unseen companions, improving our understanding of stellar multiplicity at the bottom of the Main Sequence, and may even identify candidate sub-stellar companions. These same data contains an unprecedented wealth of information about the kinematics, rotation, and metallicities of these stars. I will describe the status of our Ancillary Science program, and ongoing efforts to get the best possible radial velocity precision from the APOGEE data.

  3. Age discrimination among motions of low mass stars.

    NASA Astrophysics Data System (ADS)

    Upgren, A. R.

    Motions of low mass dwarf stars have become much better known than was the case when the concept of the basic solar motion was introduced. The group motions which they define show that older stars have mean motions directed inward towards the galactic center, as well as the well-known mean motion in the direction opposite to that of galactic rotation, when compared to younger stars. This radial motion difference is revealed among stars divided according to their emission intensities as well as kinematical age related parameters.

  4. Outer Atmospheres of Low Mass Stars — Flare Characteristics.

    NASA Astrophysics Data System (ADS)

    Lalitha, S.; Schmitt, J. H. M. M.

    2013-04-01

    We compare the coronal properties during flares on active low mass stars CN Leonis, AB Doradus A and Proxima Centauri observed with XMM-Newton. From the X-ray data we analyze the temporal evolution of temperature, emission measure and coronal abundance. The nature of these flares are with secondary events following the first flare peak in the light curve, raising the question regarding the involved magnetic structure. We infer from the plasma properties and the geometry of the flaring structure that the flare originates from a compact arcade rather than in a single loop.

  5. The Motion Verified Red Stars (MoVeRS) Catalog and Low-Mass Field Stars with Warm Dust

    NASA Astrophysics Data System (ADS)

    Theissen, Christopher; West, Andrew A.; Dhital, Saurav

    2016-01-01

    We present the Motion Verified Red Stars (MoVeRS) catalog of proper motion selected low-mass stars from SDSS, 2MASS, and WISE. These surveys provide a time baseline of ~12 years for sources found in all three surveys, and a precision better than 10 mas/year.The MoVeRS catalog is augmented with proper motions from SDSS+USNO-B and the full sample contains 8,735,004 photometric point-sources selected based on colors and their significant (2σ) proper motions. This catalog will be useful for finding new low-mass common proper motion systems, along with providing a large input catalog for numerous studies of low-mass stars. In addition, we use the MoVeRS catalog to present a preliminary sample of low-mass field stars exhibiting signatures of warm dust (mid-infrared excesses). Such systems are thought to originate from collisions of terrestrial planets, raising even more questions about the habitability of planetary systems around low-mass stars.

  6. 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.

  7. Low-mass Eclipsing Binaries in the Initial Kepler Data Release

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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 eff < 5500 K and orbital periods shorter than ~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 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. Doppler disc tomography applied to low-mass AGN spin

    NASA Astrophysics Data System (ADS)

    Middleton, Matthew J.; Ingram, Adam R.

    2015-01-01

    Doppler tomography can provide a powerful means of determining black hole spin when our view to the central regions are revealed and obscured by optically thick orbiting material, and can provide an independent estimate that does not suffer as many degeneracies as traditional methods. For low-mass active galactic nuclei (AGN), time-dependent obscuration is expected to leave a signature in the changing spectrum of the disc emission which extends into the soft X-ray bandpass. We create a spectral model incorporating Doppler tomography and apply it to the case of the low-mass (8 × 105 M⊙) AGN, RX J1301.9+2747 which shows unusual timing properties in the form of short-lived flares that we argue are best explained by the orbit of a window through an optically thick wind. Modelling the phase-resolved spectrum over the course of the highest data quality flare indicates a very low spin even when we relax our constraints. This is the lowest mass AGN for which a spin has been measured and the first via this technique. We note that, as the mass and spin are very low, this appears to favour supermassive black hole (SMBH) growth by chaotic rather than constant accretion.

  9. 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.

  10. 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.