The ASAS-SN catalogue of variable stars – VII. Contact binaries are different above and below the Kraft break
ABSTRACT We characterize ${\sim } 71\, 200$ W Ursae Majoris (UMa) type (EW) contact binaries, including ${\sim } 12\, 600$ new discoveries, using All-Sky Automated Survey for SuperNovae (ASAN-SN)V-band all-sky light curves along with archival data from Gaia, 2MASS, AllWISE, LAMOST, GALAH, RAVE, and APOGEE. There is a clean break in the EW period–luminosity relation at $\rm \log (\it P/{\rm d})\,{\simeq }\,{\rm -0.30}$, separating the longer period, early-type EW binaries from the shorter period, late-type systems. The two populations are even more cleanly separated in the space of period and effective temperature, by $T_{\rm eff}=6710\,{\rm K}-1760\,{\rm K}\, \log (P/0.5\,{\rm d})$. Early-type and late-type EW binaries follow opposite trends in Teff with orbital period. For longer periods, early-type EW binaries are cooler, while late-type systems are hotter. We derive period–luminosity relationships in the WJK, V, Gaia DR2 G, J, H, Ks, and W1 bands for the late-type and early-type EW binaries separated by both period and effective temperature, and by period alone. The dichotomy of contact binaries is almost certainly related to the Kraft break and the related changes in envelope structure, winds, and angular momentum loss.
Authors:
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Award ID(s):
Publication Date:
NSF-PAR ID:
10164489
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
493
Issue:
3
Page Range or eLocation-ID:
4045 to 4057
ISSN:
0035-8711
1. ABSTRACT We characterize an all-sky catalogue of ∼8400 δ Scuti variables in ASAS-SN, which includes ∼3300 new discoveries. Using distances from Gaia DR2, we derive period–luminosity relationships for both the fundamental mode and overtone pulsators in the WJK, V, Gaia DR2 G, J, H, Ks, and W1 bands. We find that the overtone pulsators have a dominant overtone mode, with many sources pulsating in the second overtone or higher order modes. The fundamental mode pulsators have metallicity-dependent periods, with log10(P) ∼ −1.1 for $\rm [Fe/H]\lt -0.3$ and log10(P) ∼ −0.9 for $\rm [Fe/H]\gt 0$, which leads to a period-dependent scale height. Stars with $P\gt 0.100\, \rm d$ are predominantly located close to the Galactic disc ($\rm |\mathit{ Z}|\lt 0.5\, kpc$). The median period at a scale height of $Z\sim 0\, \rm kpc$ also increases with the Galactocentric radius R, from log10(P) ∼ −0.94 for sources with $R\gt 9\, \rm kpc$ to log10(P) ∼ −0.85 for sources with $R\lt 7\, \rm kpc$, which is indicative of a radial metallicity gradient. To illustrate potential applications of this all-sky catalogue, we obtained 30 min cadence, image subtraction TESS light curves for a sample of 10 fundamental mode and 10 overtone δ Scuti stars discoveredmore »
ABSTRACT The All-Sky Automated Survey for Supernovae provides long baseline (∼4 yr) V-band light curves for sources brighter than V≲ 17 mag across the whole sky. We produced V-band light curves for a total of ∼61.5 million sources and systematically searched these sources for variability. We identified ∼426 000 variables, including ∼219 000 new discoveries. Most (${\sim }74{ per\ cent}$) of our discoveries are in the Southern hemisphere. Here, we use spectroscopic information from LAMOST, GALAH, RAVE, and APOGEE to study the physical and chemical properties of these variables. We find that metal-poor eclipsing binaries have orbital periods that are shorter than metal-rich systems at fixed temperature. We identified rotational variables on the main-sequence, red giant branch, and the red clump. A substantial fraction (${\gtrsim }80{ per\ cent}$) of the rotating giants have large $v$rot or large near-ultraviolet excesses also indicative of fast rotation. The rotational variables have unusual abundances suggestive of analysis problems. Semiregular variables tend to be lower metallicity ($\rm [Fe/H]{\sim }-0.5$) than most giant stars. We find that the APOGEE DR16 temperatures of oxygen-rich semiregular variables are strongly correlated with the WRP − WJK colour index for $\rm T_{eff}\lesssim 3800$ K. Using abundance measurements from APOGEE DR16, we find evidence for Mgmore »
3. ABSTRACT We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby ($d\sim 460\, \rm pc$), bright (V ≃ 8.3 mag), evolved (Teff, giant ≃ 4440 K, and Lgiant ≃ 173 L⊙) red giant in a high mass function, f(M) = 1.72 ± 0.01 M⊙, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of $87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of Mcomp = 3.04 ± 0.06 M⊙, a stellar radius of Rgiant = 24.9 ± 0.7 R⊙, and a giant mass of Mgiant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of ${\sim }63{{\ \rm per\ cent}}$ and ${\sim }24{{\ \rm per\ cent}}$, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmermore »
4. ABSTRACT As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source ASASSN-V J192114.84+624950.8 rapidly decreased in flux by $\sim 55{{\ \rm per\ cent}}$ (∼0.9 mag) in the g band. The Transiting Exoplanet Survey Satellite light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using phoebe find the binary orbit to have e = 0.79, Porb = 18.462 d, and i = 88.6°, and the ratios of the stellar radii and temperatures to be R2/R1 = 0.71 and Te,2/Te,1 = 0.82. Both stars are chromospherically active, allowing us to determine their rotational periods of P1 = 1.52 d and P2 = 1.79 d, respectively. A Large Binocular Telescope/Multi-Object Double Spectrograph spectrum shows that the primary is a late-G- or early-K-type dwarf. Fits to the spectral energy distribution show that the luminosities and temperatures of the two stars are L1 = 0.48 L⊙, $T_1= 5050\, \mathrm{K}$, L2 = 0.12 L⊙, and $T_{2} = 4190\, \mathrm{K}$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit.