scholarly journals Spectroscopy of Candidate Members of the Sco-Cen Complex*

2021 ◽  
Vol 163 (1) ◽  
pp. 26
Author(s):  
K. L. Luhman ◽  
T. L. Esplin
Keyword(s):  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Stellar Masses

Abstract We present spectroscopy of 285 previously identified candidate members of populations in the Sco-Cen complex, primarily Ophiuchus, Upper Sco, and Lupus. The spectra are used to measure spectral types and diagnostics of youth. We find that 269 candidates exhibit signatures of youth in our spectra or previous data, which is consistent with their membership in Sco-Cen. We have constructed compilations of candidate members of Ophiuchus, Upper Sco, and Lupus that have spectral classifications and evidence of youth, which contain a total of 2274 objects. In addition, we have used spectra from previous studies to classify three sources in Ophiuchus that have been proposed to be protostellar brown dwarfs: ISO Oph 70, 200, and 203. We measure spectral types of early M from those data, which are earlier than expected for young brown dwarfs based on evolutionary models (≳M6.5) and instead are indicative of stellar masses (∼0.6 M ⊙).

scholarly journals A Deep Large area Search for Low Luminosity Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 435-435
Author(s):  
Hugh R.A. Jones ◽  
Mike R.S. Hawkins
Keyword(s):  
Spectral Type ◽  
Low Temperatures ◽  
Current Model ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Spectral Indices ◽  
Late Type ◽  
Brown Dwarf ◽  
Large Area ◽  
M Dwarfs

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

scholarly journals Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

2018 ◽  
Vol 620 ◽  
pp. A196 ◽  
Author(s):  
Leila M. Calcaferro ◽  
Alejandro H. Córsico ◽  
Leandro G. Althaus ◽  
Alejandra D. Romero ◽  
S. O. Kepler
Keyword(s):  
Stellar Evolution ◽  
Effective Temperature ◽  
Evolutionary Models ◽  
Long Period ◽  
Low Mass ◽  
Complete Set ◽  
Effective Temperatures ◽  
Binary Evolution ◽  
Stellar Masses ◽  
Gravity Mode

Context. Some low-mass white-dwarf (WD) stars with H atmospheres currently being detected in our galaxy, show long-period g(gravity)-mode pulsations, and comprise the class of pulsating WDs called extremely low-mass variable (ELMV) stars. At present, it is generally believed that these stars have thick H envelopes. However, from stellar evolution considerations, the existence of low-mass WDs with thin H envelopes is also possible. Aims. We present a thorough asteroseismological analysis of ELMV stars on the basis of a complete set of fully evolutionary models that represents low-mass He-core WD stars harboring a range of H envelope thicknesses. Although there are currently nine ELMVs, here we only focus on those that exhibit more than three periods and whose periods do not show significant uncertainties. Methods. We considered g-mode adiabatic pulsation periods for low-mass He-core WD models with stellar masses in the range [0.1554–0.4352] M⊙, effective temperatures in the range [6000–10 000] K, and H envelope thicknesses in the interval −5.8 ≲ log(MH/M⋆)≲ −1.7. We explore the effects of employing different H-envelope thicknesses on the adiabatic pulsation properties of low-mass He-core WD models, and perform period-to-period fits to ELMV stars to search for a representative asteroseismological model. Results. We found that the mode-trapping effects of g modes depend sensitively on the value of MH, with the trapping cycle and trapping amplitude larger for thinner H envelopes. We also found that the asymptotic period spacing, ΔΠa, is longer for thinner H envelopes. Finally, we found asteroseismological models (when possible) for the stars under analysis, characterized by canonical (thick) and by thin H envelope. The effective temperature and stellar mass of these models are in agreement with the spectroscopic determinations. Conclusions. The fact that we have found asteroseismological solutions with H envelopes thinner than canonical gives a suggestion of the possible scenario of formation of these stars. Indeed, in the light of our results, some of these stars could have been formed by binary evolution through unstable mass loss.

scholarly journals Dynamical masses for the nearest brown dwarf binary: ε Indi Ba,b

2009 ◽  
Vol 5 (H15) ◽  
pp. 761-761
Author(s):  
C. V. Cardoso ◽  
M. J. McCaughrean ◽  
R. R. King ◽  
L. M. Close ◽  
R.-D. Scholz ◽  
...  
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Brown Dwarf ◽  
Near Ir ◽  
The Earth ◽  
Benchmark System ◽  
Model Independent ◽  
Dynamical Masses

Binary brown dwarfs are important because their dynamical masses can be determined in a model-independent way. If a main sequence star is also involved, the age and metallicity for the system can be determined, making it possible to break the sub-stellar mass-age degeneracy. The most suitable benchmark system for intermediate age T dwarfs is ε Indi Ba,b, two T dwarfs (spectral types T1 and T6; McCaughrean et al. (2004)) orbiting a K4.5V star, ε Indi A, at a projected separation of 1460AU. At a distance of 3.6224pc (HIPPARCOS distance to ε Indi A; van Leeuwen (2007)), these are the closest brown dwarfs to the Earth, and thus both components are bright and the system is well-resolved. The system has been monitored astrometrically with NACO and FORS2 on the VLT since June 2004 and August 2005, respectively, in order to determine the system and individual masses independent of evolutionary models. We have obtained a preliminary system mass of 121±1MJup. We have also analysed optical/near-IR spectra (0.6-5.0μm at a resolution up to R~5000; King et al. (2009)) allowing us to determine bolometric luminosities, compare and calibrate evolutionary and atmospheric models of T dwarfs at an age of 4-8Gyr.

scholarly journals What Do Young Brown Dwarfs Tell Us About Exoplanets?

2015 ◽  
Vol 10 (S314) ◽  
pp. 226-231
Author(s):  
Katelyn N. Allers ◽  
Michael C. Liu ◽  
Trent J. Dupuy
Keyword(s):  
Effective Temperature ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Sky Surveys ◽  
Fundamental Properties ◽  
Dust Clouds ◽  
Planetary Mass ◽  
Substellar Objects ◽  
Successes And Challenges

AbstractIn recent years, all-sky surveys have uncovered a new and interesting population of young (≈10–200 Myr), nearby substellar objects. Many of these objects have inferred masses and temperatures that overlap those of directly imaged exoplanets. These young brown dwarfs provide valuable analogs to young, dusty exoplanets in a context where detailed spectroscopic observations across a broad range of wavelengths and at high S/N are possible. How do the temperatures inferred by atmospheric models and evolutionary models compare? Can we determine the formation mechanism of a young planetary-mass object? How well do we understand the role that disequilibrium chemistry and dust clouds play in the atmospheres of these objects? We review the successes and challenges in determining the fundamental properties (mass, log(g), effective temperature) of young substellar objects, both brown dwarfs and gas-giant exoplanets.

scholarly journals The early evolution of low mass stars and brown dwarfs

2009 ◽  
Vol 5 (H15) ◽  
pp. 755-755
Author(s):  
Isabelle Baraffe
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Brown Dwarfs ◽  
Early Evolution ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass ◽  
Effects Of Rotation ◽  
Star Formation Regions

My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation regions for objects of a few Myr old.

scholarly journals Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458

2003 ◽  
Vol 402 (2) ◽  
pp. 701-712 ◽  
Author(s):  
I. Baraffe ◽  
G. Chabrier ◽  
T. S. Barman ◽  
F. Allard ◽  
P. H. Hauschildt
Keyword(s):  
Brown Dwarfs ◽  
Giant Planets ◽  
Evolutionary Models

scholarly journals Precise radial velocities of giant stars

2018 ◽  
Vol 616 ◽  
pp. A33 ◽  
Author(s):  
Stephan Stock ◽  
Sabine Reffert ◽  
Andreas Quirrenbach
Keyword(s):  
Test Sample ◽  
Evolutionary Stage ◽  
Evolutionary Models ◽  
Planetary Evolution ◽  
Giant Stars ◽  
Small Test ◽  
Red Giant ◽  
Stellar Masses ◽  
Host Stars

Context. The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method, but also for dynamical modeling of multiplanetary systems and the analysis of planetary evolution. Aims. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. Methods. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. Results. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that 81% of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only ΔM = 〈Mtrk. − MAst.〉 = 0.01 ± 0.20 M⊙. Conclusions. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.

scholarly journals Evolutionary Models for Low Mass Stars and Brown Dwarfs at Young Ages

2003 ◽  
Vol 211 ◽  
pp. 41-50 ◽  
Author(s):  
Isabelle Baraffe ◽  
Gilles Chabrier ◽  
France Allard ◽  
Peter Hauschildt
Keyword(s):  
Initial Conditions ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass

We analyse evolutionary tracks at young ages for low mass stars with masses m ≤ 1.4 M⊙ and brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages ≲ 1 Myr.

scholarly journals Orbital and spectral analysis of the benchmark brown dwarf HD 4747B

2019 ◽  
Vol 631 ◽  
pp. A107 ◽  
Author(s):  
S. Peretti ◽  
D. Ségransan ◽  
B. Lavie ◽  
S. Desidera ◽  
A.-L. Maire ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
High Contrast ◽  
Imaging Data ◽  
Velocity Measurements ◽  
Brown Dwarf ◽  
Contrast Imaging ◽  
Semi Major Axis ◽  
Dynamical Mass

Context. The study of high-contrast imaged brown dwarfs and exoplanets depends strongly on evolutionary models. To estimate the mass of a directly imaged substellar object, its extracted photometry or spectrum is used and adjusted with model spectra together with the estimated age of the system. These models still need to be properly tested and constrained. HD 4747B is a brown dwarf close to the H burning mass limit, orbiting a nearby (d = 19.25 ± 0.58 pc), solar-type star (G9V); it has been observed with the radial velocity method for over almost two decades. Its companion was also recently detected by direct imaging, allowing a complete study of this particular object. Aims. We aim to fully characterize HD 4747B by combining a well-constrained dynamical mass and a study of its observed spectral features in order to test evolutionary models for substellar objects and to characterize its atmosphere. Methods. We combined the radial velocity measurements of High Resolution Echelle Spectrometer (HIRES) and CORALIE taken over two decades and high-contrast imaging of several epochs from NACO, NIRC2, and SPHERE to obtain a dynamical mass. From the SPHERE data we obtained a low-resolution spectrum of the companion from Y to H band, and two narrow band-width photometric measurements in the K band. A study of the primary star also allowed us to constrain the age of the system and its distance. Results. Thanks to the new SPHERE epoch and NACO archival data combined with previous imaging data and high-precision radial velocity measurements, we were able to derive a well-constrained orbit. The high eccentricity (e = 0.7362 ± 0.0025) of HD 4747B is confirmed, and the inclination and the semi-major axis are derived (i = 47.3 ± 1.6°, a = 10.01 ± 0.21 au). We derive a dynamical mass of mB = 70.0 ± 1.6 MJup, which is higher than a previous study but in better agreement with the models. By comparing the object with known brown dwarfs spectra, we derive a spectral type of L9 and an effective temperature of 1350 ± 50 K. With a retrieval analysis we constrain the oxygen and carbon abundances and compare them with the values from the HR 8799 planets.

scholarly journals Modeling of Optical and IR Spectra of M and Brown Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 365-368
Author(s):  
Yakiv V. Pavlenko
Keyword(s):  
Ir Spectra ◽  
Infrared Spectra ◽  
Spectral Region ◽  
Brown Dwarfs ◽  
Young Stars ◽  
Spectral Energy ◽  
Energy Distributions ◽  
Synthetic Spectra ◽  
Substellar Objects ◽  
Stellar Masses

Procedure and results of computation of optical and infrared spectra of ultracool (1000 < Teff < 3000 K) objects are discussed. LTE synthetic spectra and spectral energy distributions in wide spectral region λλ 0.6–10 microns) are computed for model atmospheres from grids of different authors taking into account opacities provided by water and other molecules.Essential interest will be paid for problems of realization of lithium and deuterium tests which can be used for assessment of objects of sub-stellar masses and big planets and refining of scenarios of evolution of young stars and substellar objects.

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