Dwarfs In Wide Binaries Research Articles

The Mass Dependence of Hα Emission and Stellar Spindown for Fully Convective M Dwarfs

Fully convective M dwarfs typically remain rapidly rotating and magnetically active for billions of years, followed by an abrupt and mass-dependent transition to slow rotation and quiescence. A robust understanding of this process is complicated by difficulties in estimating M dwarf ages and potential dependencies on other variables such as birth environment or metallicity. To isolate the effect of mass, we consider M dwarfs in wide binaries. We identify 67 widely separated, fully convective (0.08–0.35 M ⊙) M dwarf binary systems using Gaia and measure the Hα feature for each component. We classify the pairs into three categories: systems where both components are active, systems where both are inactive, and candidate transition systems, where one component is active and the other inactive. We gather higher-resolution spectra of the candidate transition systems to verify that their behavior does not result from an unresolved third component, yielding one new triple with surprising activity levels. Neglecting this triple, we find 22 active, 36 inactive, and eight transition pairs. Our results are consistent with the epoch of spindown for these binaries being primarily determined by mass, with mild second-order effects; we place a 1σ upper limit of 0.5 Gyr or 25% on the dispersion in the mass-dependent spindown relation. Our findings suggest that the large dispersion in the spindown epoch previously observed for field stars of a given mass may stem from differences in birth environment, in addition to modest intrinsic stochasticity. We also see evidence that the wide binary population is dispersed over time due to dynamical processing.

Measuring the Mass–Radius Relation of White Dwarfs Using Wide Binaries

Measuring the mass–radius relation of individual white dwarfs is an empirically challenging task that has been performed for only a few dozen stars. We measure the white dwarf mass–radius relation using the gravitational redshifts and radii of 135 white dwarfs in wide binaries with main-sequence companions. We obtain the radial velocities of these systems using the main-sequence companion, and subtract these Doppler redshifts from the white dwarfs’ apparent motions, isolating their gravitational redshifts. We use Gaia data to calculate the surface temperatures and radii of these white dwarfs, thereby deriving an empirical gravitational redshift–radius relation. This work demonstrates the utility of low-resolution Galactic surveys to measure the white dwarf equation of state. Our results are consistent with theoretical models, and represent the largest sample of individual white dwarf gravitational redshift measurements to date.

TheGaiaDR1 mass–radius relation for white dwarfs

The Gaia Data Release 1 (DR1) sample of white dwarf parallaxes is presented, including six directly observed degenerates and 46 white dwarfs in wide binaries. This data set is combined with spectroscopic atmospheric parameters to study the white dwarf mass–radius relationship (MRR). Gaia parallaxes and G magnitudes are used to derive model atmosphere-dependent white dwarf radii, which can then be compared to the predictions of a theoretical MRR. We find a good agreement between Gaia DR1 parallaxes, published effective temperatures (Teff) and surface gravities (log g), and theoretical MRRs. As it was the case for Hipparcos, the precision of the data does not allow for the characterization of hydrogen envelope masses. The uncertainties on the spectroscopic atmospheric parameters are found to dominate the error budget and current error estimates for well-known and bright white dwarfs may be slightly optimistic. With the much larger Gaia DR2 white dwarf sample, it will be possible to explore the MRR over a much wider range of mass, Teff, and spectral types.

THE INITIAL-FINAL MASS RELATION AMONG WHITE DWARFS IN WIDE BINARIES

We present the initial-final mass relation derived from 10 white dwarfs in wide binaries that consist of a main sequence star and a white dwarf. The temperature and gravity of each white dwarf was measured by fitting theoretical model atmospheres to the observed spectrum using a $\chi^{2}$ fitting algorithm. The cooling time and mass was obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main sequence component to an uncertainty of about 0.17 dex in log \textit{t} The difference between the total age and white dwarf cooling time is taken as the main sequence lifetime of each white dwarf. The initial mass of each white dwarf was then determined using stellar evolution tracks with a corresponding metallicity derived from spectra of their main sequence companions, thus yielding the initial-final mass relation. Most of the initial masses of the white dwarf components are between 1 - 2 M$_{\odot}$. Our results suggest a correlation between the metallicity of a white dwarf's progenitor and the amount of post-main-sequence mass loss it experiences - at least among progenitors with masses in the range of 1 - 2 M$_{\odot}$. A comparison of our observations to theoretical models suggests that low mass stars preferentially lose mass on the red giant branch.

Discovery of the first wide L dwarf + giant binary system and eight other ultracool dwarfs in wide binaries

We identify 806 ultra-cool dwarfs from their SDSS riz photometry (of which 34 are newly discovered L dwarfs) and obtain proper motions through cross matching with UKIDSS and 2MASS. Proper motion and distance constraints show that nine of our ultra-cool dwarfs are members of widely separated binary systems; SDSS 0101 (K5V+M9.5V), SDSS 0207 (M1.5V+L3V), SDSS 0832 (K3III+L3.5V), SDSS 0858 (M4V+L0V), SDSS 0953 (M4V+M9.5V), SDSS 0956 (M2V+M9V), SDSS 1304 (M4.5V+L0V), SDSS 1631 (M5.5V+M8V), SDSS 1638 (M4V+L0V). One of these (SDSS 0832) is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries can provide age and metallicity constraints for any companion objects, yielding excellent benchmark objects. Eta Cancri AB is the first wide ultra-cool dwarf + giant binary system identified. We present new observations and analysis that constrain the metallicity of Eta Cancri A to be near solar, and use recent evolutionary models to constrain the age of the giant to be 2.2-6.1 Gyr. If Eta Cancri B is a single object, we estimate its physical attributes to be; mass = 63-82 M_Jup, T_eff = 1800+/-150 K, log g = 5.3-5.5, [M/H] = 0.0+/-0.1. Its colours are non typical when compared to other ultra-cool dwarfs, and we also assess the possibility that Eta Cancri B is itself an unresolved binary, showing that the combined light of an L4 + T4 system could provide a reasonable explanation for its colours.

Stellar chronology with white dwarfs in wide binaries

AbstractWhite dwarfs are the evolutionary end product of stars with low and intermediate masses. The evolution of white dwarfs can be understood as a cooling process, which is relatively well known at the moment. For this reason, wide binaries containing white dwarfs are a powerful tool to constrain stellar ages. We have studied several wide binaries containing white dwarfs with two different purposes: when the age of the companion of the white dwarf can be determined with accuracy, we use the binary to improve the knowledge about the white dwarf member. On the contrary, if the companion is a low-mass star with no age indicator available, the white dwarf member itself is used to calibrate the age of the system. In this contribution we present some results using both methodologies to constrain the ages of wide binaries.

White Dwarfs in Wide Binaries and the Age of the Galaxy

We present a photometric study of wide binaries with suspected white dwarf (WD) components. These systems were initially identified on the basis of their reduced proper motions and colors by W. J. Luyten (Proper Motion Survey with the Forty-Eight Inch Schmidt Telescope [Minneapolis: Univ. Minnesota Press, 1963–]) and H. L. Giclas et al. (Lowell Proper Motion Survey, Northern Hemisphere [Flagstaff: Lowell Obs., 1971], Lowell Proper Motion Survey, Southern Hemisphere [Flagstaff: Lowell Obs., 1978]). These systems usually contain a WD and a main-sequence star; however, a few contain more than two components. We obtained BVRI CCD images for approximately 475 of the 512 systems in our sample. These systems were determined by a concurrent low-resolution spectroscopy program to contain about 325 relatively cool WDs. We use this sample to determine the WD luminosity function (WDLF) and, by inference, the minimum age of the Galaxy. The WDLF was constructed using the 1/Vmax technique (M. Schmidt, ApJ, 151, 393 [1968]), as modified by T. Oswalt & J. A. Smith (Proc. Ninth European Workshop on White Dwarfs, ed. D. Koester & K. Werner [Berlin: Springer, 1995], p. 24) to correct for sample incompleteness. Error estimates were determined using the conservative approach used by J. Liebert, C. C. Dahn, & D. G. Monet (ApJ, 332, 891 [1988]). Of the spectroscopically identified WDs, 152 met the selection and completeness criteria for our study and were included in the final sample used to derive the WDLF. Most stars will end their lives as white dwarfs, slowly radiating their stored thermal energy and cooling to invisibility. The cooling timescale, calibrated using pulsating WDs, is on the order of 10 Gyr to cool to . This cooling log (L/L ) ≈ 5 , rate is slow enough that the remnants of the first epoch of star formation in the solar neighborhood are still visible. Comparison of the observed WDLF with age-dependent WDLFs integrated numerically by M. A. Wood (Proc. Ninth European Workshop on White Dwarfs [Berlin: Springer, 1995], p. 41) suggests a lower limit age of the local Galactic disk of Gyr. Assuming a ∼1 Gyr delay between the big bang 0.9 9.7 0.8 and galaxy formation, and allowing for main-sequence evolutionary times, this minimum Galactic disk age then implies a lower limit to the age of the universe of about 11 Gyr. Newly revised ages derived from globular cluster studies (B. Chaboyer, P. Demarque, P. J. Kernan, & L. M. Krauss, ApJ, 494, 96 [1998]) and recently derived cosmological ages, corrected for Hipparcos data (M. W. Feast & R. M. Catchpole, MNRAS, 286, L1 [1997]), now agree with our age determination to within 1 j. Furthermore, our age estimate is in accord with those derived from nuclear-cosmochronology studies (e.g., C. Sneden, J. J. Cowen, D. L. Burris, & J. W. Truran, ApJ, 496, 235 [1998]) and meteoritic sample analyses (e.g., L. R. Nittler & R. Cowsik, Phys. Rev. Lett., 78, 175 [1997]). Our data show no clear observational evidence for an increase in the WDLF at crystallization, , so there is log (L/L ) ≈ 3.8 ,

White Dwarfs in Wide Binaries - Part Two - Double Degenerates and Composite Spectra

view Abstract Citations (48) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS White dwarfs in wide binaries. II. Double degenerates and composite spectra. Greenstein, J. L. Abstract Spectrophotometry of six northern visual pairs containing two degenerate stars shows that the components are quite similar in luminosity and temperature. Presumably the two progenitors were similar and had nuclear lifetimes short compared to the subsequent cooling ages of the white dwarfs. The white dwarfs are near twins, with dispersion in radii below 14%. The mean cooling age of the pairs is 4 × l09 yr, their luminosity Mv = + 14.5 mag. One pair is relatively young, with components less similar. Study of pairs containing a white dwarf and a main-sequence star shows that a large fraction of such pairs are undiscovered. Those containing a hot white dwarf and a red main-sequence companion, discovered from the composite spectra, are quite blue and have an infrared excess. When the fluxes in pairs observed as resolved are added, the composite so synthesized is yellow or red, with a large violet or ultraviolet excess. Methods of discovery of white dwarfs leave regions of the color-color diagrams untouched. A possible technique of searching for violet excess suggested involves magnitudes in the infrared, visual, and blue. Analysis of old novae, spectroscopic binaries containing a white dwarf, and a dM star with a faint white dwarf companion displays composite spectra. Whether the large number of missing white dwarfs in noninteracting binaries exist, or whether the progenitor binaries have been dissolved, remains undecided. Publication: The Astronomical Journal Pub Date: October 1986 DOI: 10.1086/114220 Bibcode: 1986AJ.....92..867G full text sources ADS | data products SIMBAD (57) Related Materials (1) Part 1: 1986AJ.....92..859G

White dwarfs in wide binaries. I - Physical properties. II - Double degenerates and composite spectra

White dwarfs in wide binaries. I - Physical properties. II - Double degenerates and composite spectra

The outbursts of symbiotic novae

view Abstract Citations (77) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The outbursts of symbiotic novae. Kenyon, S. J. ; Truran, J. W. Abstract Possible conditions are discussed under which thermonuclear burning episodes in the hydrogen-rich envelopes of accreting white dwarfs give rise to outbursts similar in nature to those observed in the symbiotic stars Ag Peg, RT Ser, RR Tel, AS 239, V1016 Cyg, V1329 Cyg, and HM Sge. In principle, thermonuclear runaways involving low-luminosity white dwarfs accreting matter at low rates produce configurations that evolve into A-F supergiants at maximum visual light and which resemble the outbursts of Rr Tel, RT Ser, and AG Peg. Very weak, nondegenerate hydrogen shell flashes on white dwarfs accreting matter at high rates do not produce cool supergiants at maximum, and may explain the outbursts in V1016 Cyg, V1329 Cyg, and HM Sge. The extremely slow outbursts of symbiotic novae appear to be typical of accreting white dwarfs in wide binaries, which suggests that the outbursts of classical novae may be accelerated by the interaction of the expanding white dwarf envelope with its close binary companion. Publication: The Astrophysical Journal Pub Date: October 1983 DOI: 10.1086/161367 Bibcode: 1983ApJ...273..280K Keywords: Binary Stars; Bursts; Dwarf Novae; Stellar Mass Accretion; Thermonuclear Reactions; White Dwarf Stars; F Stars; Stellar Evolution; Stellar Models; Supergiant Stars; Astrophysics full text sources ADS | data products SIMBAD (7)