149 research outputs found
The love triangle in Gaia DR3: occurrence rates, orientations, and eccentricities of wide tertiaries around close binaries
The formation of close binaries has been an open question for decades. A
large fraction of close binaries are in triple systems, suggesting that their
formation may be associated with the Kozai-Lidov mechanism. However, this
picture remains under debate because the configurations of many observed
triples are unlikely to trigger the Kozai-Lidov mechanism. In this paper, we
use the close binary samples, including eclipsing, spectroscopic, and
astrometric binaries, from Gaia Data Release 3 to investigate the mysterious
connection between inner binaries and their wide tertiaries. We show that the
wide tertiary (at - AU) fraction increases with decreasing orbital
periods of the inner binaries. Compared to the field wide binary fraction, the
wide tertiary fraction is times higher for eclipsing binaries (a
median orbital period of day) and times lower for
astrometric binaries (a median orbital period of days). The separation
distribution of wide tertiaries is similar to wide binaries, with a tentative
excess at AU for tertiaries of eclipsing binaries. Using the -
angle distributions, we show that the wide tertiaries are consistent with
isotropic orientations with respect to the inner binaries. The inferred
eccentricity distribution of wide tertiaries is close to thermal (), similar to wide binaries at similar separations. The dynamical unfolding
scenario is disfavored because it predicts highly eccentric wide tertiaries,
which is inconsistent with our findings. For the Kozai-Lidov mechanism to be
effective for wide tertiaries at AU, the initial separations of the
inner binaries need to be AU. Future theoretical investigations are needed
to explore the parameter space at these large initial separations and large
tertiary separations.Comment: Submitted to MNRAS. Key figures are Fig.4 and Fig.7. Comments are
welcom
THE BIRTH AND THE FATE OF CLOSE AND WIDE BINARY STARS
Binary stars, where two stars are orbiting around a common center of mass, are at the core of modern astronomy. Since a significant fraction of stars are in multiple systems, binaries are now a critical component in all subfields, from star formation, to planet formation, to the reionization of the Universe shortly after the Big Bang. Close binaries are the origin of many exotic astronomical events, including type Ia supernovae which have been used to measure the accelerated expansion of the Universe. The recent detection of gravitational waves opens a new window to witness the mergers of black hole and neutron star binaries. On the other extreme, wide binaries are easily disrupted by gravitational perturbations, making them a unique tool to probe the visible and invisible Galactic structures. Therefore, a complete understanding of binary formation and evolution is critical to modern astronomy.
In my thesis, I use the revolutionary survey Gaia to reveal the birth and the fate of close and wide binary stars. Using the kinematic-dating method, I reveal the lifetime of contact binaries, providing key constraints on their formation and their death. I develop a comoving-search method to identify wide stellar companions around hot jupiter hosts, investigating the connection between the planet formation and the wide stellar companions. By combining Gaia with a cutting-edge large spectroscopic survey, I report the first known relation between metallicity and the wide binary fraction. This relation suggests that the formation of wide binaries is more complicated than what was thought before. Following this direction, I conduct a detailed wide binary search in the Milky Way halo, further ruling out several hypotheses for wide binary formation. In the end, I conclude with the prospects of binary star research
Wide binary stars formed in the turbulent interstellar medium
The ubiquitous interstellar turbulence regulates star formation and the
scaling relations between the initial velocity differences and the initial
separations of stars. We propose that the formation of wide binaries with
initial separations in the range AU is a natural consequence of star formation in the turbulent
interstellar medium. With the decrease of , the mean turbulent relative
velocity between a pair of stars decreases, while the largest
velocity at which they still may be gravitationally bound
increases. When , a wide binary can form. In this
formation scenario, we derive the eccentricity distribution of wide
binaries for an arbitrary relative velocity distribution. By adopting a
turbulent velocity distribution, we find that wide binaries at a given initial
separation generally exhibit a superthermal . This provides a natural
explanation for the observed superthermal of the wide binaries in the
Solar neighborhood.Comment: 7 pages, 4 figures, submitted to ApJ
Dynamical masses across the Hertzsprung-Russell diagram
We infer the dynamical masses of stars across the Hertzsprung-Russell (H-R)
diagram using wide binaries from the Gaia survey. Gaia's high-precision
astrometry measures the wide binaries' orbital motion, which contains the mass
information. Using wide binaries as the training sample, we measure the mass of
stars across the two-dimensional H-R diagram using the combination of
statistical inference and neural networks. Our results provide the dynamical
mass measurements for main-sequence stars from 0.1 to 2 M, unresolved
binaries and unresolved triples on the main sequence, and the mean masses of
giants and white dwarfs. Two regions in the H-R diagram show interesting
behaviors in mass, where one of them is pre-main-sequence stars, and the other
one may be related to close compact object companions like M dwarf-white dwarf
binaries. These mass measurements depend solely on Newtonian dynamics,
providing independent constraints on stellar evolutionary models and the
occurrence rate of compact objects.Comment: Fig. 5 and Fig. 12 are the key results. Submitted to MNRAS. Comments
are welcome
CSS1603+19: a low-mass polar near the cataclysmic variable period minimum
CSS1603+19 is a cataclysmic variable (CV) with an orbital period of 81.96
min, near the minimal period of cataclysmic variables. It is unusual in having
a strong mid-infrared excess inconsistent with thermal emission from a brown
dwarf companion. Here we present time-resolved multi-wavelength observations of
this system. WISE photometry indicates that the mid-infrared excess displays a
one-magnitude eclipsing-like variability during the orbit. We obtained
near-infrared and optical spectroscopy using Gemini, MDM and APO telescopes.
Near-infrared spectra show possible cyclotron features indicating that the
white dwarf has a magnetic field of about 5MG. Optical and near-infrared
spectra display double-peaked emission lines, with both components showing
strong radial velocity variations during the orbital period and with the broad
component leading the narrow component stably by about 0.2 of the orbital
phase. We construct a physical model informed by existing observations of the
system and determine that one component likely originates from the accretion
column onto the magnetized white dwarf in synchronous rotation with the orbital
motion and the other from the Roche overflow point. This allows us to constrain
the masses of the binary components to be for the white
dwarf accretor and for the donor. We classify the
system as an AM Herculis star, or a polar. It has likely completed its stint on
the period gap, but has not yet gone through the period bounce
Winds as the origin of radio emission in radio-quiet extremely red quasars
Most active galactic nuclei (AGNs) are radio-quiet, and the origin of their
radio emission is not well-understood. One hypothesis is that this radio
emission is a by-product of quasar-driven winds. In this paper, we present the
radio properties of 108 extremely red quasars (ERQs) at . ERQs are among
the most luminous quasars ( erg/s) in the Universe,
with signatures of extreme ( km/s) outflows in their
[OIII]5007 \AA\ emission, making them the best subjects to seek the
connection between radio and outflow activity. All ERQs but one are unresolved
in the radio on kpc scales, and the median radio luminosity of ERQs
is erg/s, in the radio-quiet regime, but
one to two orders of magnitude higher than that of other quasar samples. The
radio spectra are steep, with a mean spectral index . In addition, ERQs neatly follow the extrapolation of the low-redshift
correlation between radio luminosity and the velocity dispersion of
[OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent
of the bolometric luminosity, can account for all these observations. Such
winds would interact with and shock the gas around the quasar and in the host
galaxy, resulting in acceleration of relativistic particles and the consequent
synchrotron emission observed in the radio. Our observations support the
picture in which ERQs are signposts of extremely powerful episodes of quasar
feedback, and quasar-driven winds as a contributor of the radio emission in the
intermediate regime of radio luminosity erg/s.Comment: accepted by MNRA
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