- ID:
- ivo://CDS.VizieR/J/ApJ/889/49
- Title:
- The ELM Survey. VIII. Final double WD binaries
- Short Name:
- J/ApJ/889/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3M_{sun}_ He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low-mass WD candidates like GD 278, which we show is a P=0.19d double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too high to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15<g_0_<20mag. The measurements are consistent with 100% of ELM WDs being 0.0089<P<1.5d double WD binaries, 35% of which belong to the Galactic halo. We infer that these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass-transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The systems with the shortest periods, such as J0651+2844, are signature LISA verification binaries that can be studied with gravitational waves and light.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/818/155
- Title:
- The ELM survey. VII. 15 new ELM white dwarf cand.
- Short Name:
- J/ApJ/818/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of 15 extremely low-mass (5<logg<7) white dwarf (WD) candidates, 9 of which are in ultra-compact double-degenerate binaries. Our targeted extremely low-mass Survey sample now includes 76 binaries. The sample has a lognormal distribution of orbital periods with a median period of 5.4hr. The velocity amplitudes imply that the binary companions have a normal distribution of mass with 0.76 M_{sun}_ mean and 0.25M_{sun}_ dispersion. Thus extremely low-mass WDs are found in binaries with a typical mass ratio of 1:4. Statistically speaking, 95% of the WD binaries have a total mass below the Chandrasekhar mass, and thus are not type Ia supernova progenitors. Yet half of the observed binaries will merge in less than 6Gyr due to gravitational wave radiation; probable outcomes include single massive WDs and stable mass transfer AM CVn binaries.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/167
- Title:
- The ELM survey. VI. 11 new ELM WD binaries
- Short Name:
- J/ApJ/812/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of 11 new double degenerate systems containing extremely low-mass white dwarfs (ELM WDs). Our radial velocity observations confirm that all of the targets have orbital periods <=1 day. We perform spectroscopic fits and provide a complete set of physical and binary parameters. We review and compare recent evolutionary calculations and estimate that the systematic uncertainty in our mass determinations due to differences in the evolutionary models is small (~0.01M_{sun}_). Five of the new systems will merge due to gravitational wave radiation within a Hubble time, bringing the total number of merger systems found in the ELM Survey to 38. We examine the ensemble properties of the current sample of ELM WD binaries, including the period distribution as a function of effective temperature, and the implications for the future evolution of these systems. We also revisit the empirical boundaries of instability strip of ELM WDs and identify new pulsating ELM WD candidates. Finally, we consider the kinematic properties of our sample of ELM WDs and estimate that a significant fraction of the WDs from the ELM Survey are members of the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/66
- Title:
- The ELM survey. V. White dwarf binaries
- Short Name:
- J/ApJ/769/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P<=1 day) binaries. Our sample includes four objects with remarkable logg=~5 surface gravities and orbital solutions that require them to be double degenerate binaries. All of the lowest surface gravity WDs have metal lines in their spectra implying long gravitational settling times or ongoing accretion. Notably, six of the WDs in our sample have binary merger times <10Gyr. Four have >~0.9M_{sun}_ companions. If the companions are massive WDs, these four binaries will evolve into stable mass transfer AM CVn systems and possibly explode as underluminous supernovae. If the companions are neutron stars, then these may be millisecond pulsar binaries. These discoveries increase the number of detached, double degenerate binaries in the Extremely low mass (ELM) Survey to 54; 31 of these binaries will merge within a Hubble time.
- ID:
- ivo://CDS.VizieR/J/AJ/157/177
- Title:
- The evolutionary status of GK subgiants
- Short Name:
- J/AJ/157/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Snowden & Young (2005ApJS..157..126S) suggested that the reason why there are GK subgiants is because they are members of binaries, which would bring them above the main sequence in an Hertzsprung-Russell (HR) diagram. They studied a sample of 30 G0-K1 IV stars and were disappointed to find only two to be spectroscopic binaries. With more accurate radial velocities I found seven binaries in their samples of subgiants and control stars; orbital elements are given for those seven. Using Hipparcos parallaxes and SIMBAD data, I found that nearly all of the G0-K1 IV stars fall on the evolutionary tracks by Girardi et al. (2000, J/A+AS/141/371) for Population I stars with masses of 0.9-1.9 M_{sun}_ and ages of up to 10^10^ yr, which are normal parameters for nearby field stars. Therefore there is no problem regarding the existence of GK subgiants.
- ID:
- ivo://CDS.VizieR/J/ApJS/215/22
- Title:
- The Extended Virgo Cluster Catalog (EVCC)
- Short Name:
- J/ApJS/215/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of galaxies in the wider region of the Virgo cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The Extended Virgo Cluster Catalog (EVCC) covers an area of 725deg^2^ or 60.1Mpc^2^. It is 5.2 times larger than the footprint of the classical Virgo Cluster Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo cluster. We selected 1324 spectroscopically targeted galaxies with radial velocities less than 3000km/s. In addition, 265 galaxies that have been overlooked in the SDSS spectroscopic survey but have available redshifts in the NASA Extragalactic Database are also included. Our selection process secured a total of 1589 galaxies, 676 of which are not included in the VCC. The certain and possible cluster members are defined by means of redshift comparison with a cluster infall model. We employed two independent and complementary galaxy classification schemes: the traditional morphological classification based on the visual inspection of optical images and a characterization of galaxies from their spectroscopic features. SDSS u, g, r, i, and z passband photometry of all EVCC galaxies was performed using Source Extractor. We compare the EVCC galaxies with the VCC in terms of morphology, spatial distribution, and luminosity function. The EVCC defines a comprehensive galaxy sample covering a wider range in galaxy density that is significantly different from the inner region of the Virgo cluster. It will be the foundation for forthcoming galaxy evolution studies in the extended Virgo cluster region, complementing ongoing and planned Virgo cluster surveys at various wavelengths.
- ID:
- ivo://CDS.VizieR/J/ApJ/845/72
- Title:
- The factory & the beehive. III. PTFEB132.707+19.810
- Short Name:
- J/ApJ/845/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical models of stars constitute the fundamental bedrock upon which much of astrophysics is built, but large swaths of model parameter space remain uncalibrated by observations. The best calibrators are eclipsing binaries in clusters, allowing measurement of masses, radii, luminosities, and temperatures for stars of known metallicity and age. We present the discovery and detailed characterization of PTFEB132.707+19.810, a P=6.0day eclipsing binary in the Praesepe cluster ({tau}~600-800Myr; [Fe/H]=0.14+/-0.04). The system contains two late-type stars (SpT_P_=M3.5+/-0.2; SpT_S_=M4.3+/-0.7) with precise masses (M_p_=0.3953+/-0.0020M_{sun}_; M_s_=0.2098+/-0.0014M_{sun}_) and radii (R_p_=0.363+/-0.008R_{sun}_; R_s_=0.272+/-0.012R_{sun}_). Neither star meets the predictions of stellar evolutionary models. The primary has the expected radius but is cooler and less luminous, while the secondary has the expected luminosity but is cooler and substantially larger (by 20%). The system is not tidally locked or circularized. Exploiting a fortuitous 4:5 commensurability between Porb and P_rot,prim_, we demonstrate that fitting errors from the unknown spot configuration only change the inferred radii by <~1%-2%. We also analyze subsets of data to test the robustness of radius measurements; the radius sum is more robust to systematic errors and preferable for model comparisons. We also test plausible changes in limb darkening and find corresponding uncertainties of ~1%. Finally, we validate our pipeline using extant data for GU Boo, finding that our independent results match previous radii to within the mutual uncertainties (2%-3%). We therefore suggest that the substantial discrepancies are astrophysical; since they are larger than those for old field stars, they may be tied to the intermediate age of PTFEB132.707+19.810.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/377
- Title:
- The globular cluster system of NGC 4636
- Short Name:
- J/ApJ/709/377
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy NGC 4636 in the Virgo Cluster. We selected target GC candidates using the Washington photometry derived from the deep CCD images taken at the KPNO 4m Telescope. Then we obtained the spectra of 164 target objects in the field of NGC 4636 using the Multi-Object Spectroscopy mode of Faint Object Camera and Spectrograph on the Subaru 8.2m Telescope. We have measured the velocities for 122 objects: 105 GCs in NGC 4636, the nucleus of NGC 4636, 11 foreground stars, two background galaxies, and three probable intracluster GCs in the Virgo Cluster. The GCs in NGC 4636 are located in the projected galactocentric radius within 10' (corresponding to 43kpc). The measured velocities for the GCs range from ~300km/s to ~1600km/s, with a mean value of 932^+25^_-22_km/s, which is in good agreement with the velocity for the nucleus of NGC 4636, 928+/-45km/s.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/31
- Title:
- The G+M eclipsing binary V530 Orionis photometry
- Short Name:
- J/ApJ/797/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report extensive photometric and spectroscopic observations of the 6.1 day period, G+M-type detached double-lined eclipsing binary V530 Ori, an important new benchmark system for testing stellar evolution models for low-mass stars. We determine accurate masses and radii for the components with errors of 0.7% and 1.3%, as follows: M_A_=1.0038+/-0.0066 M_{sun}_, M_B_=0.5955+/-0.0022 M_{sun}_, R_A_=0.980+/-0.013 R_{sun}_, and R_B_=0.5873+/-0.0067 R_{sun}_. The effective temperatures are 5890+/-100 K (G1 V) and 3880+/-120 K (M1 V), respectively. A detailed chemical analysis probing more than 20 elements in the primary spectrum shows the system to have a slightly subsolar abundance, with [Fe/H]=-0.12+/-0.08. A comparison with theory reveals that standard models underpredict the radius and overpredict the temperature of the secondary, as has been found previously for other M dwarfs. On the other hand, models from the Dartmouth series incorporating magnetic fields are able to match the observations of the secondary star at the same age as the primary (~3 Gyr) with a surface field strength of 2.1+/-0.4 kG when using a rotational dynamo prescription, or 1.3+/-0.4 kG with a turbulent dynamo approach, not far from our empirical estimate for this star of 0.83+/-0.65 kG. The observations are most consistent with magnetic fields playing only a small role in changing the global properties of the primary. The V530 Ori system thus provides an important demonstration that recent advances in modeling appear to be on the right track to explain the long-standing problem of radius inflation and temperature suppression in low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/397/463
- Title:
- The Hamburg/SAO Survey for BCGs. I.
- Short Name:
- J/A+A/397/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the description and the first results of a new project devoted to the search for extremely metal-deficient blue compact/HII-galaxies (BCGs) and to the creation of a well selected large BCG sample with strong emission lines. Such galaxies should be suitable for reliable determination of their oxygen abundance through the measurement of the faint [OIII]4363{AA} line. The goals of the project are two-fold: a) to discover a significant number of new extremely metal-poor galaxies (Z<=1/20Z_{sun}_), and b) to study the metallicity distribution of local BCGs. Selection of candidates for follow-up slit spectroscopy is performed on the database of objective prism spectra of the Hamburg Quasar Survey. The sky region is limited by {delta}>=0{deg} and b^II^<=-30{deg}. In this paper we present the results of the follow-up spectroscopy conducted with the Russian 6m telescope. The list of observed candidates contained 52 objects, of which 46 were confirmed as strong-lined BCGs (EW([OIII]5007>=100{AA}). The remaining five lower excitation ELGs include three BCGs, and two galaxies classified as SBN (Starburst Nucleus) and DANS (Dwarf Amorphous Nucleus Starburst). One object is identified as a quasar with a strong Ly_alpha emission line near {lambda}=5000{AA} (z~3). We provide a list with coordinates, measured radial velocities, B-magnitudes, equivalent widths EW([OIII]5007) and EW(H{beta}) and for the 46 strong-lined BCGs the derived oxygen abundances 12+log(O/H). The abundances range between 7.42 and 8.4 (corresponding to metallicities between 1/30 and 1/3Z_{sun}_). The sample contains four galaxies with Z<=1/20Z_{sun}_, of which three are new discoveries. This demonstrates the high efficiency of the new project to find extremely metal-deficient galaxies. The radial velocities of the strong-lined ELGs range between 500 and 19000km/s with a median value of ~6400km/s. The typical B-magnitudes of the galaxies presented are 17.0mag-18.0mag.
