- ID:
- ivo://CDS.VizieR/J/A+A/616/A37
- Title:
- Close encounters to the Sun in Gaia DR2
- Short Name:
- J/A+A/616/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Passing stars may play an important role in the evolution of our solar system. We search for close stellar encounters to the Sun among all 7.2 million stars in Gaia DR2 that have six-dimensional phase space data. We characterize encounters by integrating their orbits through a Galactic potential and propagating the correlated uncertainties via a Monte Carlo resampling. After filtering to remove spurious data, we find 694 stars that have median (over uncertainties) closest encounter distances within 5pc, all occurring within 15Myr from now. 26 of these have at least a 50% chance of coming closer than 1pc (and 7 within 0.5pc), all but one of which are newly discovered here. We confirm some and refute several other previously-identified encounters, confirming suspicions about their data. The closest encounter in the sample is Gl 710, which has a 95% probability of coming closer than 0.08pc (17000AU). Taking mass estimates obtained from Gaia astrometry and multiband photometry for essentially all encounters, we find that Gl 710 also has the largest impulse on the Oort cloud. Using a Galaxy model, we compute the completeness of the Gaia DR2 encountering sample as a function of perihelion time and distance. Only 15% of encounters within 5pc occurring within +/-5Myr of now have been identified, mostly due to the lack of radial velocities for faint and/or cool stars. Accounting for the incompleteness, we infer the present rate of encounters within 1pc to be 19.7+/-2.2 per Myr, a quantity expected to scale quadratically with the encounter distance out to at least several pc. Spuriously large parallaxes in our sample from imperfect filtering would tend to inflate both the number of encounters found and this inferred rate. The magnitude of this effect is hard to quantify.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/643/A106
- Title:
- 55 close-in (P<100days) small planets list
- Short Name:
- J/A+A/643/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stars in the Milky Way thin and thick disks can be distinguished by several properties such as metallicity and kinematics. It is not clear whether the two populations also differ in the properties of planets orbiting the stars. In order to study this, a careful analysis of both the chemical composition and mass detection limits is required for a sufficiently large sample. Currently, this information is still limited only to large radial-velocity (RV) programs. Based on the recently published archival database of the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, we present a first analysis of low-mass (small) planet occurrence rates in a sample of thin- and thick-disk stars. We aim to assess the effects of stellar properties on planet occurrence rates and to obtain first estimates of planet occurrence rates in the thin and thick disks of the Galaxy. As a baseline for comparison, we also aim to provide an updated value for the small close-in planet occurrence rate and compare it with the results of previous RV and transit (Kepler) works. We used archival HARPS RV datasets to calculate detection limits of a sample of stars that were previously analysed for their elemental abundances. For stars with known planets we first subtracted the Keplerian orbit. We then used this information to calculate planet occurrence rates according to a simplified Bayesian model in different regimes of stellar and planet properties. Our results suggest that metal-poor stars and more massive stars host fewer low-mass close-in planets. We find the occurrence rates of these planets in the thin and thick disks to be comparable. In the iron-poor regimes, we find these occurrence rates to be significantly larger at the high-{alpha} region (thick-disk stars) as compared with the low-{alpha} region (thin-disk stars). In general, we find the average number of close-in small planets (2-100 days, 1-20M_{Earth}_) per star (FGK-dwarfs) to be: n^-^_p_=0.36+/-0.05, while the fraction of stars with planets is F_h_=0.23_-0.03_^+0.04^. Qualitatively, our results agree well with previous estimates based on RV and Kepler surveys. This work provides a first estimate of the close-in small planet occurrence rates in the solar neighbourhood of the thin and thick disks of the Galaxy. It is unclear whether there are other stellar properties related to the Galactic context that affect small-planet occurrence rates, or if it is only the combined effects of stellar metal content and mass. A future larger sample of stars and planets is needed to address those questions.
3473. Close pairs of galaxies
- ID:
- ivo://CDS.VizieR/J/AJ/132/197
- Title:
- Close pairs of galaxies
- Short Name:
- J/AJ/132/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study star formation in a sample of 345 galaxies in 167 pairs and compact groups drawn from the original CfA2 Redshift Survey and from a follow-up search for companions. We construct our sample with attention to including pairs with luminosity contrast |{Delta}m_R_|>=2. These 57 galaxies with |{Delta}m_R_|>=2 provide a set of nearby representative cases of minor interactions, a central feature of the hierarchical galaxy formation model. Here we report the redshifts and positions of the 345 galaxies in our sample and of 136 galaxies in apparent pairs that are superpositions.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A87
- Title:
- Close pairs of galaxies in MUSE Deep Fields
- Short Name:
- J/A+A/631/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the ILLUSTRIS cosmological simulation project, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest MUSE deep observations over the Hubble Ultra Deep Field, Hubble Deep Field South, COSMOS-Gr30 and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts (0.2<z<6) and stellar masses (10^7^-10^11^M_{sun}_). Using the stellar mass ratio between the secondary and primary galaxy as a proxy to split the sample into major, minor and very minor mergers, we found a total of 183 major, 142 minor and 47 very minor close pairs corresponding to a mass ratio range of 1:1-1:6, 1:6-1:100 and lower than 1:100, respectively. Due to completeness issues, we do not consider the very minor pairs in the analysis. Overall, the major merger fraction increases up to z~2-3 reaching 25% for pairs with the most massive galaxy with a stellar mass M*>10^9.5^M_{sun}_. Beyond this redshift, the fraction decreases down to ~5% at z~6. The major merger fraction for lower mass primary galaxies M*<10^9.5^M_{sun}_, seems to follow a more constant evolutionary trend with redshift. Thanks to the addition of new MUSE fields and new selection criteria, the increased statistics of the pair samples allow to narrow significantly the error bars compared to our previous analysis (Ventou et al., 2017A&A...608A...9V). The evolution of the minor merger fraction is roughly constant with cosmic time, with a fraction of 20% at z<3 and a slow decrease between 3<z<6 to 8-13%.
3475. Close star encounters
- ID:
- ivo://CDS.VizieR/J/A+A/575/A35
- Title:
- Close star encounters
- Short Name:
- J/A+A/575/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stars which pass close to the Sun can perturb the Oort cloud, injecting comets into the inner solar system where they may collide with the Earth. Using van Leeuwen's re-reduction of the Hipparcos data complemented by the original Hipparcos and Tycho-2 catalogues, along with recent radial velocity surveys, I integrate the orbits of over 50000 stars through the Galaxy to look for close encounters. The search uses a Monte Carlo sampling of the covariance of the data in order to properly characterize the uncertainties in the times, distances, and speeds of the encounters.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A139
- Title:
- Closest stars to the Sun within 50pc catalog
- Short Name:
- J/A+A/629/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the Galactic gravitational tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for the perturbation of the Galactic tidal field and passing stars. We base our study on three main approaches; analytic, observational, and numerical. We first construct an analytical model of stellar encounters. We find that individual perturbations do not modify the dynamics of the comets in the cloud unless very close (<0.5pc) encounters occur. Using proper motions, parallaxes, and radial velocities from Gaia DR2 and combining them with the radial velocities from other surveys, we then construct an astrometric catalogue of the 14659 stars that are within 50pc of the Sun. For all these stars we calculate the time and distance of closest approach to the Sun. We find that the cumulative effect of relatively distant (<=1pc) passing stars can perturb the comets in the Oort cloud. Finally, we study the dynamical evolution of the comets in the Oort cloud under the influence of multiple stellar encounters from stars that pass within 2.5 pc of the Sun and the Galactic tidal field over +/-10Myr. We use the Astrophysical Multipurpose Software Environment (AMUSE), and the GPU-accelerated direct N-body code ABIE. We considered two models for the Oort cloud, compact (a<=0.25pc) and extended (a<=0.5pc). We find that the cumulative effect of stellar encounters is the major perturber of the Oort cloud for a compact configuration while for the extended configuration the Galactic tidal field is the major perturber. In both cases the cumulative effect of distant stellar encounters together with the Galactic tidal field raises the semi-major axis of ~1.1% of the comets at the edge of the Oort cloud up to interstellar regions (a>0.5pc) over the 20Myr period considered. This leads to the creation of transitional interstellar comets (TICs), which might become interstellar objects due to external perturbations. This raises the question of the formation, evolution, and current status of the Oort cloud as well as the existence of a "cloud" of objects in the interstellar space that might overlap with our Oort cloud, when considering that other planetary systems should undergo similar processes leading to the ejection of comets.
- ID:
- ivo://CDS.VizieR/J/A+A/430/137
- Title:
- Close visual companions in Scorpius OB2
- Short Name:
- J/A+A/430/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a near-infrared adaptive optics survey with the aim to detect close companions to Hipparcos members in the three subgroups of the nearby OB association Sco OB2: Upper Scorpius (US), Upper Centaurus Lupus (UCL) and Lower Centaurus Crux (LCC). We have targeted 199 A-type and late B-type stars in the K_S band, and a subset also in the J and H band. We find 151 stellar components other than the target stars. A brightness criterion is used to separate these components into 77 background stars and 74 candidate physical companion stars. Out of these 74 candidate companions, 41 have not been reported before (14 in US; 13 in UCL; 14 in LCC).
- ID:
- ivo://CDS.VizieR/J/AJ/144/93
- Title:
- Close white dwarf + M dwarf binaries (WD+dM)
- Short Name:
- J/AJ/144/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf main-sequence binaries from Rebassa-Mansergas et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space. Then using the SDSS Data Release 8 spectroscopic database, we construct a sample of 1756 WD+dM high-quality pairs from our color cuts and previous catalogs. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the H{alpha} emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types <=M7. Our results show that early-type M dwarfs (<=M4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems become more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully convective stars. Using the WD components of the pairs, we find WD cooling ages to use as an additional constraint on the age-activity relation for our sample. We find that, on average, active early-type dMs tend to be younger and that active late-type dMs span a much broader age regime making them indistinguishable from the inactive late-type population. We also show that magnetic strength, as measured by H{alpha}, is comparable between paired and field M dwarfs until a spectral type of M6/M7 where M dwarf activity for stars with close companions becomes much stronger. In addition, we present 37 very close candidate pairs with fast-moving orbits that display radial velocity changes over hour timescales.
- ID:
- ivo://CDS.VizieR/J/AJ/157/101
- Title:
- Cloud Atlas: HST/WFC3 NIR spectral library
- Short Name:
- J/AJ/157/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bayesian atmospheric retrieval tools can place constraints on the properties of brown dwarfs' and hot Jupiters' atmospheres. To fully exploit these methods, high signal-to-noise spectral libraries with well-understood uncertainties are essential. We present a high signal-to-noise spectral library (1.10-1.69 {mu}m) of the thermal emission of 76 brown dwarfs and hot Jupiters. All our spectra have been acquired with the Hubble Space Telescope's Wide Field Camera 3 instrument and its G141 grism. The near-infrared spectral types of these objects range from L4 to Y1. Eight of our targets have estimated masses below the deuterium-burning limit. We analyze the database to identify peculiar objects and/or multiple systems, concluding that this sample includes two very-low-surface-gravity objects and five intermediate-surface-gravity objects. In addition, spectral indices designed to search for composite-atmosphere brown dwarfs indicate that eight objects in our sample are strong candidates to have such atmospheres. None of these objects are overluminous, so their composite atmospheres are unlikely to be companion-induced artifacts. Five of the eight confirmed candidates have been reported as photometrically variable, suggesting that composite atmospheric indices are useful in identifying brown dwarfs with strongly heterogeneous cloud covers. We compare hot Jupiters and brown dwarfs in a near-infrared color-magnitude diagram. We confirm that the coldest hot Jupiters in our sample have spectra similar to mid-L dwarfs, and the hottest hot Jupiters have spectra similar to those of M-dwarfs. Our sample provides a uniform data set of a broad range of ultracool atmospheres, allowing large-scale comparative studies and providing an HST legacy spectral library.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/109
- Title:
- Cloud decomposition & SFR measurements
- Short Name:
- J/ApJ/841/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic star formation scaling relations show increased scatter from kpc to sub-kpc scales. Investigating this scatter may hold important clues to how the star formation process evolves in time and space. Here, we combine different molecular gas tracers, different star formation indicators probing distinct populations of massive stars, and knowledge of the evolutionary state of each star-forming region to derive the star formation properties of ~150 star-forming complexes over the face of the Large Magellanic Cloud (LMC). We find that the rate of massive star formation ramps up when stellar clusters emerge and boost the formation of subsequent generations of massive stars. In addition, we reveal that the star formation efficiency of individual giant molecular clouds (GMCs) declines with increasing cloud gas mass (M_cloud_). This trend persists in Galactic star-forming regions and implies higher molecular gas depletion times for larger GMCs. We compare the star formation efficiency per freefall time ({epsilon}_ff_) with predictions from various widely used analytical star formation models. While these models can produce large dispersions in {epsilon}_ff_ similar to those in observations, the origin of the model-predicted scatter is inconsistent with observations. Moreover, all models fail to reproduce the observed decline of {epsilon}_ff_ with increasing M_cloud_ in the LMC and the Milky Way. We conclude that analytical star formation models idealizing global turbulence levels and cloud densities and assuming a stationary star formation rate (SFR) are inconsistent with observations from modern data sets tracing massive star formation on individual cloud scales. Instead, we reiterate the importance of local stellar feedback in shaping the properties of GMCs and setting their massive SFR.