Binary Fractions of G and K Dwarf Stars Based on Gaia EDR3 and LAMOST DR5: Impacts of the Chemical Abundances

Based on the large volume Gaia Early Data Release 3 and LAMOST Data Release 5 data, we estimate the bias-corrected binary fractions of the field late G and early K dwarfs. A stellar locus outlier method is used in this work, which works well for binaries of various periods and inclination angles with single-epoch data. With a well-selected, distance-limited sample of about 90,000 GK dwarfs covering wide stellar chemical abundances, it enables us to explore the binary fraction variations with different stellar populations. The average binary fraction is 0.42 ± 0.01 for the whole sample. Thin-disk stars are found to have a binary fraction of 0.39 ± 0.02, thick-disk stars have a higher one of 0.49 ± 0.02, while inner halo stars possibly have the highest binary fraction. For both the thin- and thick-disk stars, the binary fractions decrease toward higher [Fe/H], [α/H], and [M/H] abundances. However, the suppressing impacts of [Fe/H], [α/H], and [M/H] are more significant for the thin-disk stars than those for the thick-disk stars. For a given [Fe/H], a positive correlation between [α/Fe] and the binary fraction is found for the thin-disk stars. However, this tendency disappears for the thick-disk stars. We suspect that it is likely related to the different formation histories of the thin and thick disks. Our results provide new clues for theoretical works on binary formation.

The non-monotonic, strong metallicity dependence of the wide-binary fraction

The metallicity dependence of the wide-binary fraction in stellar populations plays a critical role in resolving the open question of wide binary formation. In this paper, we investigate the metallicity ([Fe/H]) and age dependence of the wide-binary fraction (binary separations between 103 and 104 AU) for field F and G dwarfs within 500 pc by combining their metallicity and radial velocity measurements from LAMOST DR5 with the astrometric information from Gaia DR2. We show that the wide-binary fraction strongly depends on the metallicity: as metallicity increases, the wide-binary fraction first increases, peaks at [Fe/H]≃ 0, and then decreases at the high metallicity end. The wide-binary fraction at [Fe/H]=0 is about two times larger than that at [Fe/H]=−1 and [Fe/H]=+0.5. This metallicity dependence is dominated by the thin-disk stars. Using stellar kinematics as a proxy of stellar age, we show that younger stars have a higher wide-binary fraction at fixed metallicity close to solar. We propose that multiple formation channels are responsible for the metallicity and age dependence. In particular, the positive metallicity correlation at [Fe/H]<0 and the age dependence may be due to the denser formation environments and higher-mass clusters at earlier times. The negative metallicity correlation at [Fe/H]>0 can be inherited from the similar metallicity dependence of close binaries, and radial migration may play a role in enhancing the wide-binary fraction around the solar metallicity.

Penitentiary pleasures: Queer understandings of prison paradoxes

Historically, prison researchers have remained disengaged with explorations of pleasure in punishment because of the risk of romanticizing imprisonment. This risk is inherent in any discussion of pleasure experienced by prisoners. In this article, I advocate for the application of queer theory as a means of deconstructing the binary formation through which pain and pleasure in prison is understood. To do that, I explore how ex-prisoners’ narratives might reveal (queer) moments of pleasure and complement existing criminological scholarship that has neglected such an issue. This exploration is framed by Foucault’s theory of pleasure as a productive force that renders it akin to power: it produces an effect. In this article, I draw on Edelman’s concept of “futurity” and Halberstam’s “failure” to bring criminology and queer theory into a productive dialogue for the purpose of analyzing the production of narratives of pleasure by ex-prisoners. In my analysis, I use Jackson and Mazzei’s “plugging in method” centered around the categories of (a) pleasure and pain, (b) pleasure and resistance, and (c) sexuality and pleasure. Drawing upon the findings, I argue that pleasure becomes a nexus of relations that exists and correlates with sexuality, power/resistance, and the feeling of pain. I conclude that a queer understanding of what is unpleasant is possible if we reconsider pleasure and pain in a spectrum as opposed to a binary formation.

Candidate LBV stars in galaxy NGC 7793 found via HST photometry + MUSE spectroscopy

ABSTRACT Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and H α luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have MV ≤ −7 and a combination of: H α with a P-Cygni profile; no [O i]$\, \lambda 6300$ emission; weak or no [O iii]$\, \lambda 5007$ emission; large [N ii]/H α relative to H ii regions; and [S ii]$\, \lambda 6716$/[S ii]$\, \lambda 6731\sim 1$. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies.

Effects of metallicity on high-mass X-ray binary formation

ABSTRACT The heating of the intergalactic medium in the early, metal-poor Universe may have been partly due to radiation from high-mass X-ray binaries (HMXBs). Previous investigations on the effect of metallicity have used galaxies of different types. To isolate the effects of metallicity on the production of HMXBs, we study a sample consisting only of 46 blue compact dwarf galaxies covering metallicity in the range 12+log(O/H) of 7.15–8.66. To test the hypothesis of metallicity dependence in the X-ray luminosity function (XLF), we fix the XLF form to that found for near-solar metallicity galaxies and use a Bayesian method to constrain the XLF normalization as a function of star formation rate for three different metallicity ranges in our sample. We find an increase by a factor of 4.45 ± 2.04 in the XLF normalization between the metallicity ranges 7.1–7.7 and 8.2–8.66 at a statistical significance of 99.79 per cent. Our results suggest that HMXB production is enhanced at low metallicity, and consequently that HMXBs may have contributed significantly to the reheating of the early Universe.

Gravitational waves from supernova mass loss and natal kicks in close binaries

ABSTRACT Some fraction of compact binaries that merge within a Hubble time may have formed from two massive stars in isolation. For this isolated-binary formation channel, binaries need to survive two supernova (SN) explosions in addition to surviving common-envelope evolution. For the SN explosions, both the mass loss and natal kicks change the orbital characteristics, producing either a bound or unbound binary. We show that gravitational waves (GWs) may be produced not only from the core-collapse SN process, but also from the SN mass loss and SN natal kick during the pre-SN to post-SN binary transition. We model the dynamical evolution of a binary at the time of the second SN explosion with an equation of motion that accounts for the finite time-scales of the SN mass loss and the SN natal kick. From the dynamical evolution of the binary, we calculate the GW burst signals associated with the SN natal kicks. We find that such GW bursts may be of interest to future mid-band GW detectors like DECIGO. We also find that the energy radiated away from the GWs emitted due to the SN mass loss and natal kick may be a significant fraction, ${\gtrsim }10{\,{\rm {per\, cent}}}$, of the post-SN binary’s orbital energy. For unbound post-SN binaries, the energy radiated away in GWs tends to be higher than that of bound binaries.