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Register a new userVery wide companion fraction from Gaia DR2: a weak or no enhancement for hot jupiter hosts, and a strong enhancement for contact binaries
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There is an ongoing debate on whether hot jupiter hosts are more likely to be found in wide binaries with separations of $gtrsim 100$ AU. In this paper, we search for comoving, very wide companions with separations of $10^3-10^4$ AU for hot jupiter hosts and main-sequence contact binaries in Gaia DR2, and compare the very wide companion fractions with their object-by-object-matched field star samples. We find that $11.9pm 2.5$% of hot jupiter hosts and $14.1pm 1.0$% of contact binaries have companions at separations of $10^3-10^4$ AU. While the very wide companion fraction of hot jupiter hosts is a factor of $1.9pm0.5$ larger than their matched field star sample, it is consistent, within $sim1sigma$, with that of matched field stars if the matching is only with field stars without close companions (within $sim50$ AU) as is the case for hot jupiter hosts. The very wide companion fraction of contact binaries is a factor of $3.1pm0.5$ larger than their matched field star sample, suggesting that the formation and evolution of contact binaries are either tied to or correlated with the presence of wide companions. In contrast, the weak enhancement of very wide companion fraction for hot jupiter hosts implies that the formation of hot jupiters is not as sensitive to those environment properties. Our results also hint that the occurrence rates of dual hot jupiter hosts and dual contact binaries may be higher than the expected values from random pairing of field stars, which may be due to their underlying metallicity and age dependence.
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Transiting planets orbiting bright stars are the most favorable targets for follow-up and characterization. We report the discovery of the transiting hot Jupiter XO-7 b and of a second, massive companion on a wide orbit around a circumpolar, bright, and metal rich G0 dwarf (V = 10.52, $T_{rm eff} = 6250 pm 100 ; rm K$, $rm[Fe/H] = 0.432 pm 0.057 ; rm dex$). We conducted photometric and radial velocity follow-up with a team of amateur and professional astronomers. XO-7 b has a period of $ 2.8641424 pm 0.0000043$ days, a mass of $0.709 pm 0.034 ; rm M_{rm J}$, a radius of $1.373 pm 0.026 ; rm R_{rm J}$, a density of $0.340 pm 0.027 ; rm g , {cm}^{-3}$, and an equilibrium temperature of $1743 pm 23 ; rm K$. Its large atmospheric scale height and the brightness of the host star make it well suited to atmospheric characterization. The wide orbit companion is detected as a linear trend in radial velocities with an amplitude of $sim100 ; rm m , {s}^{-1}$ over two years, yielding a minimum mass of $4 ; rm M_{rm J}$; it could be a planet, a brown dwarf, or a low mass star. The hot Jupiter orbital parameters and the presence of the wide orbit companion point towards a high eccentricity migration for the hot Jupiter. Overall, this system will be valuable to understand the atmospheric properties and migration mechanisms of hot Jupiters and will help constrain the formation and evolution models of gas giant exoplanets.
We present an extensive search in the literature and Gaia DR2 for visual co-moving binary companions to stars hosting exoplanets and brown dwarfs within 200 pc. We found 218 planet hosts out of 938 to be part of multiple-star systems, with 10 newly discovered binaries and 2 new tertiary stellar components. This represents an overall raw multiplicity rate of 23.2$pm$1.6% for hosts to exoplanets across all spectral types, with multi-planet systems found to have a lower duplicity frequency at the 2.2$sigma$ level. We found that more massive hosts are more often in binary configurations, and that planet-bearing stars in multiple systems are predominantly the most massive component of stellar binaries. Investigations of multiplicity as a function of planet mass and separation revealed that giant planets with masses >0.1 MJup are more frequently seen in stellar binaries than small sub-Jovian planets with a 3.6$sigma$ difference, a trend enhanced for the most massive (>7 MJup) short-period (<0.5 AU) planets and brown dwarf companions. Binarity was found to have no significant effect on the demographics of low-mass planets (<0.1 MJup) or warm and cool gas giants (>0.5 AU). While stellar companion mass appears to have no impact on planet properties, binary separation seems to be an important factor in the resulting structure of planetary systems. Stellar companions on separations <1000 AU can play a role in the formation or evolution of massive close-in planets, while planets in wider binaries show similar properties to planets orbiting single stars. Finally, numerous stellar companions on separations <1-3 arcsec likely remain undiscovered to this date. Continuous efforts to complete our knowledge of stellar multiplicity on separations of tens to hundreds of AU are essential to confirm the reported trends and further our understanding of the roles played by multiplicity on exoplanets.
We present the discoveries of KELT-25b (TIC 65412605, TOI-626.01) and KELT-26b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A-stars. The transit signals were initially detected by the KELT survey, and subsequently confirmed by textit{TESS} photometry. KELT-25b is on a 4.40-day orbit around the V = 9.66 star CD-24 5016 ($T_{rm eff} = 8280^{+440}_{-180}$ K, $M_{star}$ = $2.18^{+0.12}_{-0.11}$ $M_{odot}$), while KELT-26b is on a 3.34-day orbit around the V = 9.95 star HD 134004 ($T_{rm eff}$ =$8640^{+500}_{-240}$ K, $M_{star}$ = $1.93^{+0.14}_{-0.16}$ $M_{odot}$), which is likely an Am star. We have confirmed the sub-stellar nature of both companions through detailed characterization of each system using ground-based and textit{TESS} photometry, radial velocity measurements, Doppler Tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of $R_{rm P}$ = $1.64^{+0.039}_{-0.043}$ $R_{rm J}$, and a 3-sigma upper limit on the companions mass of $sim64~M_{rm J}$. For KELT-26b, we infer a planetary mass and radius of $M_{rm P}$ = $1.41^{+0.43}_{-0.51}$ $M_{rm J}$ and $R_{rm P}$ = $1.940^{+0.060}_{-0.058}$ $R_{rm J}$. From Doppler Tomographic observations, we find KELT-26b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the textit{TESS} data. KELT-25b appears to be in a well-aligned, prograde orbit, and the system is likely a member of a cluster or moving group.
Several recent studies have shown that very wide binary stars can potentially provide an interesting test for modified-gravity theories which attempt to emulate dark matter; these systems should be almost Newtonian according to standard dark-matter theories, while the predictions for MOND-like theories are distinctly different, if the various observational issues can be overcome. Here we explore an observational application of the test from the recent GAIA DR2 data release: we select a large sample of $sim 24,000$ candidate wide binary stars with distance $< 200$ parsec and magnitudes $G < 16$ from GAIA DR2, and estimated component masses using a main-sequence mass-luminosity relation. We then compare the frequency distribution of pairwise relative projected velocity (relative to circular-orbit value) as a function of projected separation; these distributions show a clear peak at a value close to Newtonian expectations, along with a long `tail which extends to much larger velocity ratios; the `tail is considerably more numerous than in control samples constructed from DR2 with randomised positions, so its origin is unclear. Comparing the velocity histograms with simulated data, we conclude that MOND-like theories without an external field effect are strongly inconsistent with the observed data since they predict a peak-shift in clear disagreement with the data; testing MOND-like theories with an external field effect is not decisive at present, but has good prospects to become decisive in future with improved modelling or understanding of the high-velocity tail, and additional spectroscopic data.
We examine the distribution of on-sky relative velocities for wide binaries previously assembled from GAIA DR2 data and focus on the origin of the high velocity tail of apparently unbound systems which may be interpreted as evidence for non-Newtonian gravity in the weak field limit. We argue that this tail is instead explicable in terms of a population of hidden triples, i.e. cases where one of the components of the wide binary is itself a close binary unresolved in the GAIA data. In this case the motion of the photocentre of the inner pair relative to its barycentre affects the apparent relative proper motion of the wide pair and can make pairs that are in fact bound appear to be unbound. We show that the general shape of the observed distributions can be reproduced using simple observationally motivated assumptions about the population of hidden triples.
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