The stellar upper mass limit in the solar neighborhood (original) (raw)
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Evidence for a fundamental stellar upper mass limit from clustered star formation
Monthly Notices of The Royal Astronomical Society, 2004
The observed masses of the most massive stars do not surpass about 150 Msolar. This may either be a fundamental upper mass limit which is defined by the physics of massive stars and/or their formation, or it may simply reflect the increasing sparsity of such very massive stars, so that the observation of even higher mass stars becomes unlikely in
Low-mass companions to solar-type stars
We present preliminary results from a coronagraphic survey of young nearby Sun-like stars using the Palomar and Keck adaptive optics systems. We have targeted 251 solar analogs (F5-K5) at 20-160 pc from the Sun, spanning the 3-3000 Myr age range. The youngest (<500 Myr) ≈100 of these have been imaged with deeper exposures to search for sub-stellar companions. The deep survey is sensitive to brown-dwarf companions at separations >0.5 ′′ from their host stars, with sensitivity extending to planetary-mass (5-15MJup) objects at wider (>3 ′′ ) separations. Based on the discovery of a number of new low-mass (<0.2M⊙) stellar companions, we infer that their frequency at >20 AU separations (probed via direct imaging) may be greater (≈12%) than that found from radial velocity surveys probing <4 AU separations (≈6%; . We also report the astrometric confirmation of the first sub-stellar companion from the survey -an L4 brown dwarf at a projected distance of 44 AU from the ≈500 Myrold star HD 49197. Based on this detection, we estimate that the frequency of sub-stellar companions to solar-type stars is at least 1%, and possibly of order a few per cent.
The Astrophysical Journal Supplement Series, 2009
We present results from an adaptive optics survey for substellar and stellar companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3 Myr to 3 Gyr age range with distances of 10-190 pc. Results from the survey include the discovery of two brown dwarf companions (HD 49197B and HD 203030B), 24 new stellar binaries, and a triple system. We infer that the frequency of 0.012-0.072 M ⊙ brown dwarfs in 28-1590 AU orbits around young solar analogs is 3.2 +3.1 −2.7 % (2σ limits). The result demonstrates that the deficiency of substellar companions at wide orbital separations from Sun-like stars is less pronounced than in the radial velocity "brown dwarf desert." We infer that the mass distribution of companions in 28-1590 AU orbits around solar-mass stars follows a continuous dN/dM 2 ∝ M −0.4 2 relation over the 0.01-1.0 M ⊙ secondary mass range. While this functional form is similar to the that for <0.1 M ⊙ isolated objects, over the entire 0.01-1.0 M ⊙ range the mass functions of companions and of isolated objects differ significantly. Based on this conclusion and on similar results from other direct imaging and radial velocity companion surveys in the literature, we argue that the companion mass function follows the same universal form over the entire range between 0-1590 AU in orbital semi-major axis and ≈0.01-20 M ⊙ in companion mass. In this context, the relative dearth of substellar versus stellar secondaries at all orbital separations arises naturally from the inferred form of the companion mass function.
Since the major review by Scalo (1986), significant progress has been achieved in constraining the mass function (MF) of low-mass stars. The break-throughs which today allow a much better understanding of the stellar luminosity function (LF) and the underlying MF are documented here and the resulting MF for Galactic field stars is confronted with microlensing data, the chemical enrichment history of the Galaxy, the Oort limit and well-studied open clusters.
Intermediate‐Mass Stars: Updated Models
The Astrophysical Journal, 1999
A new set of stellar models in the mass range 1.2 to 9 M ⊙ is presented. The adopted chemical compositions cover the typical galactic values, namely 0.0001 ≤ Z ≤ 0.02 and 0.23 ≤ Y ≤ 0.28. A comparison among the most recent compilations of similar stellar models is also discussed. The main conclusion is that the differencies among the various evolutionary results are still rather large.
Astronomy & Astrophysics, 2021
We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup , and radii between 0.81 and 1.66 RJup . These targets have masses near the uncertain lower limit of hydrogen core fusion (~73-96 MJup ), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 ± 0.1 Gyr) and TOI-681 (0.17 ± 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smalle...
SOUTHERN MASSIVE STARS AT HIGH ANGULAR RESOLUTION: OBSERVATIONAL CAMPAIGN AND COMPANION DETECTION
The Astrophysical Journal Supplement Series, 2014
Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories. Nevertheless, companions at separations between 1 and 100 milli-arcsec (mas) remain mostly unknown due to intrinsic observational limitations. At a typical distance of 2 kpc, this corresponds to projected physical separations of 2-200 AU. The Southern MAssive Stars at High angular resolution survey (smash+) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/SAM, respectively probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of ∆H < 4 and ∆H < 5. Taking advantage of NACO's field-of-view, we further uniformly searched for visual companions in an 8 -radius down to ∆H = 8. This paper describes the observations and data analysis, reports the discovery of almost 200 new companions in the separation range from 1 mas to 8 and presents the catalog of detections, including the first resolved measurements of over a dozen known long-period spectroscopic binaries.
HD?77407 and GJ?577: Two new young stellar binaries
Astronomy and Astrophysics, 2004
We present the first results from our search for close stellar and sub-stellar companions to young nearby stars on the northern sky. Our infrared imaging observations are obtained with the 3.5 m Calar Alto telescope and the AO system ALFA. With two epoch observations which were separated by about one year, we found two co-moving companion candidates, one close to HD 77407 and one close to GJ 577. For the companion candidate near GJ 577, we obtained an optical spectrum showing spectral type M 4.5; this candidate is a bound low-mass stellar companion confirmed by both proper motion and spectroscopy. We estimate the masses for HD 77407 B and GJ 577 B to be ∼0.3 to 0.5 M and ∼0.16 to 0.2 M , respectively. Compared to Siess et al. (2000) models, each of the two pairs appears co-eval with HD 77407 A, B being 10 to 40 Myrs and GJ 577 A, B being ≥100 Myrs old. We also took multi-epoch high-resolution spectra of HD 77407 to search for sub-stellar companions, but did not find any with 3 M Jup as upper mass (m sin i) limit (for up to 4 year orbits); however, we detected a long-term radial velocity trend in HD 77407 A, consistent with a ∼0.3 M companion at ∼50 AU separation, i.e. the one detected by the imaging. Hence, HD 77407 B is confirmed to be a bound companion to HD 77407 A. We also present limits for undetected, but detectable companions using a deep image of HD 77407 A and B, also observed with the Keck NIRC2 AO system; any brown dwarfs were detectable outside of 0.5 arcsec (17 AU at HD 77407), giant planets with masses from ∼6.5 to 12 M Jup were detectable at ≥1.5 arcsec.
Discovery of a Low-Mass Companion to the Solar-Type Star Tyc 2534-698-1
The Astrophysical Journal, 2009
Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M and an orbital period of ∼103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ∼ 6 millimags. The semimajor axis of the orbit places the companion in the "brown dwarf desert" and we discuss potential follow-up observations that could constrain the mass of the companion.
Galaxy And Mass Assembly (GAMA): stellar mass functions by Hubble type
We present an estimate of the galaxy stellar mass function and its division by morphological type in the local (0.025 < z < 0.06) Universe. Adopting robust morphological classifications as previously presented (Kelvin et al.) for a sample of 3727 galaxies taken from the Galaxy And Mass Assembly survey, we define a local volume and stellar mass limited sub-sample of 2711 galaxies to a lower stellar mass limit of {M}=10^{9.0} M_{{⊙}}. We confirm that the galaxy stellar mass function is well described by a double-Schechter function given by {M}^{*}=10^{10.64} M_{{⊙}}, α1 = -0.43, φ 1^{*}=4.18dex^{-1} Mpc^{-3}, α2 = -1.50 and φ 2^{*}=0.74dex^{-1} Mpc^{-3}. The constituent morphological-type stellar mass functions are well sampled above our lower stellar mass limit, excepting the faint little blue spheroid population of galaxies. We find approximately 71{}_{-4}^{+3} per cent of the stellar mass in the local Universe is found within spheroid-dominated galaxies; ellipticals and S0-Sas. The remaining 29{}_{-3}^{+4} per cent falls predominantly within late-type disc-dominated systems, Sab-Scds and Sd-Irrs. Adopting reasonable bulge-to-total ratios implies that approximately half the stellar mass today resides in spheroidal structures, and half in disc structures. Within this local sample, we find approximate stellar mass proportions for E : S0-Sa : Sab-Scd : Sd-Irr of 34 : 37 : 24 : 5.