Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/536/A43
- Title:
- SDSS WD main-sequence binaries. XII.
- Short Name:
- J/A+A/536/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The complexity of the common-envelope phase and of magnetic stellar wind braking currently limits our understanding of close binary evolution. Because of their intrinsically simple structure, observational population studies of white dwarf plus main sequence (WDMS) binaries can potentially test theoretical models and constrain their parameters. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we characterise in terms of orbital and stellar parameters. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy and for an additional 861 systems from the SDSS subspectra. Radial velocity variations identify 191 of these WDMS binaries as post common-envelope binaries (PCEBs). Orbital periods of 58 PCEBs were subsequently measured, predominantly from time-resolved spectroscopy, bringing the total number of SDSS PCEBs with orbital parameters to 79. Observational biases inherent to this PCEB sample were evaluated through extensive Monte Carlo simulations. We find that 21-24% of all SDSS WDMS binaries have undergone common-envelope evolution, which is in good agreement with published binary population models and high-resolution HST imaging of WDMS binaries unresolved from the ground. The bias-corrected orbital period distribution of PCEBs ranges from 1.9h to 4.3d and approximately follows a normal distribution in log(Porb), peaking at ~10.3h. There is no observational evidence for a significant population of PCEBs with periods in the range of days to weeks. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, hence to observationally constrain the evolution of all close compact binaries.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/63
- Title:
- SDSS wide double white dwarfs spectroscopy
- Short Name:
- J/ApJ/815/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observational constraints on the initial-final mass relation (IFMR) using wide double white dwarfs (DWDs). We identify 65 new candidate wide DWDs within the Sloan Digital Sky Survey, bringing the number of candidate wide DWDs to 142. We then engage in a spectroscopic follow-up campaign and collect existing spectra for these objects; using these spectra, we derive masses and cooling ages for 54 hydrogen (DA) WDs in DWDs. We also identify one new DA/DB pair, four candidate DA/DC pairs, four candidate DA/DAH pairs, and one new candidate triple degenerate system. Because wide DWDs are co-eval and evolve independently, the difference in the pre-WD lifetimes should equal the difference in the WD cooling ages. We use this to develop a Bayesian hierarchical framework and construct a likelihood function to determine the probability that any particular IFMR fits a sample of wide DWDs. We then define a parametric model for the IFMR and find the best parameters indicated by our sample of DWDs. We place robust constraints on the IFMR for initial masses of 2-4M_{sun}_. The WD masses produced by our model for stars within this mass range differ from those predicted by semi-empirical fits to open cluster WDs. Within this mass range, where there are few constraining open cluster WDs and disagreements in the cluster ages, wide DWDs may provide more reliable constraints on the IFMR. Expanding this method to the many wide DWDs expected to be discovered by Gaia may transform our understanding of the IFMR.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/89
- Title:
- Search for companions around nearby massive stars
- Short Name:
- J/ApJ/736/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study, we present high-contrast imaging of 18 nearby massive stars of which 15 are in the B2-A0 spectral-type range and provide excellent sensitivity to wide companions. By comparing our sensitivities to model predictions of disk instability based on physical criteria for fragmentation and cooling, and using Monte Carlo simulations for orbital distributions, we find that ~85% of such companions should have been detected in our images on average. Given this high degree of completeness, stringent statistical limits can be set from the null-detection result, even with the limited sample size. We find that <30% of massive stars form and retain disk instability planets, brown dwarfs, and very low mass stars of <100M_jup_ within 300AU, at 99% confidence. These results, combined with previous findings in the literature, lead to the conclusion that core accretion is likely the dominant mode of planet formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/1647
- Title:
- Search for planetary companions with Spitzer/IRAC
- Short Name:
- J/ApJ/700/1647
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fomalhaut and {epsilon} Eridani are two young, nearby stars that possess extended debris disks whose structures suggest the presence of perturbing planetary objects. With its high sensitivity and stable point-spread function, Spitzer/Infrared Array Camera (IRAC) is uniquely capable of detecting cool, Jupiter-like planetary companions whose peak emission is predicted to occur near 4.5um. We report on deep IRAC imaging of these two stars, taken at 3.6 and 4.5um using subarray mode and in all four channels in wider-field full array mode. Observations acquired at two different telescope roll angles allowed faint surrounding objects to be separated from the stellar diffraction pattern. No companion candidates were detected at the reported position of Fomalhaut b with 3{sigma} model-dependent mass upper limits of 3M_J_ (for an age of 200Myr). Around {epsilon} Eridani, we instead set a limit of 4 and <~1M_J_ (1Gyr model age) at the inner and outer edge of the submillimeter debris ring, respectively. These results are consistent with non-detections in recent near-infrared imaging searches, and set the strongest limits to date on the presence of planets outside {epsilon} Eridani submillimeter ring.
- ID:
- ivo://CDS.VizieR/VI/151
- Title:
- Search for radio emission from giant exoplanets
- Short Name:
- VI/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The intensity of Jupiter's auroral radio emission quickly gave rise to the question whether a comparable coherent emission from the magnetosphere of an exoplanet could be detectable. An exoplanetary radio emission would have to be at least 1000 times more intense than Jupiter's emission to be detectable with current radio telescopes. Theoretical models suggest that, at least in certain cases, the radio emission of giant exoplanets may indeed reach the required intensity. At the same time, in order to generate such an emission, an exoplanet would have to have a sufficiently strong intrinsic planetary magnetic field. Extrasolar planets are indeed expected to have a planetary magnetic field, but to date, their magnetic field has never been detected. We will show that the most promising technique to observe exoplanetary magnetic fields is indeed to search for the planetary auroral radio emission. The detection of such an emission would thus constitute the first unambiguous detection of an exoplanetary magnetic field. We will review recent theoretical studies and discuss their results for the two main parameters, namely the maximum emission frequency and the intensity of the radio emission. The predicted values should allow the detection using modern low-frequency radio telescopes. We will present an ongoing observation program with the Low Frequency Array (LOFAR), which has the potential to detect exoplanetary radio emission.
- ID:
- ivo://CDS.VizieR/J/AJ/155/206
- Title:
- Search for rings around Kepler planet candidates
- Short Name:
- J/AJ/155/206
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a systematic search for rings around 168 Kepler planet candidates with sufficient signal-to-noise ratios that are selected from all of the short-cadence data. We fit ringed and ringless models to their light curves and compare the fitting results to search for the signatures of planetary rings. First, we identify 29 tentative systems, for which the ringed models exhibit statistically significant improvement over the ringless models. The light curves of those systems are individually examined, but we are not able to identify any candidate that indicates evidence for rings. In turn, we find several mechanisms of false positives that would produce ringlike signals, and the null detection enables us to place upper limits on the size of the rings. Furthermore, assuming the tidal alignment between axes of the planetary rings and orbits, we conclude that the occurrence rate of rings larger than twice the planetary radius is less than 15%. Even though the majority of our targets are short-period planets, our null detection provides statistical and quantitative constraints on largely uncertain theoretical models of the origin, formation, and evolution of planetary rings.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A84
- Title:
- Search for UMa group companions
- Short Name:
- J/A+A/591/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a survey to detect low-mass companions of Ursa Major (UMa) group members, carried out in 2003-2006 with NACO at the ESO VLT. While many extra-solar planets and planetary candidates have been found in close orbits around stars by the radial velocity and the transit methods, direct detections at wider orbits are rare. The UMa group, a young nearby stellar association at an age of about 200-600Myr, has not yet been addressed as a whole although its members represent a very interesting sample to search for and characterize substellar companions by direct imaging. Our goal was to find or to provide detection limits on wide substellar companions around nearby UMa group members using high-resolution imaging. We searched for faint companions around 20 UMa group members within 30pc. The primaries were placed below a semi-transparent coronagraph, a rarely used mode of NACO, to increase the dynamic range of the images. In most cases, second epoch images of companion candidates were taken to check whether they share common proper motion with the primary.
- ID:
- ivo://CDS.VizieR/J/AJ/152/181
- Title:
- SETI observations of exoplanets with the ATA
- Short Name:
- J/AJ/152/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report radio SETI observations on a large number of known exoplanets and other nearby star systems using the Allen Telescope Array (ATA). Observations were made over about 19000hr from 2009 May to 2015 December. This search focused on narrowband radio signals from a set totaling 9293 stars, including 2015 exoplanet stars and Kepler objects of interest and an additional 65 whose planets may be close to their habitable zones. The ATA observations were made using multiple synthesized beams and an anticoincidence filter to help identify terrestrial radio interference. Stars were observed over frequencies from 1 to 9GHz in multiple bands that avoid strong terrestrial communication frequencies. Data were processed in near-real time for narrowband (0.7-100Hz) continuous and pulsed signals with transmitter/receiver relative accelerations from -0.3 to 0.3m/s^2^. A total of 1.9x10^8^ unique signals requiring immediate follow-up were detected in observations covering more than 8x10^6^ star-MHz. We detected no persistent signals from extraterrestrial technology exceeding our frequency-dependent sensitivity threshold of 180-310x10^-26^W/m^2^.
590. SHINE II
- ID:
- ivo://CDS.VizieR/J/A+A/651/A71
- Title:
- SHINE II
- Short Name:
- J/A+A/651/A71
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- In recent decades, direct imaging has confirmed the existence of substellar companions (exoplanets or brown dwarfs) on wide orbits (>10 au) around their host stars. In striving to understand their formation and evolution mechanisms, in 2015 we initiated the SPHERE infrared survey for exoplanets (SHINE), a systematic direct imaging survey of young, nearby stars that is targeted at exploring their demographics. We aim to detect and characterize the population of giant planets and brown dwarfs beyond the snow line around young, nearby stars. Combined with the survey completeness, our observations offer the opportunity to constrain the statistical properties (occurrence, mass and orbital distributions, dependency on the stellar mass) of these young giant planets. In this study, we present the observing and data analysis strategy, the ranking process of the detected candidates, and the survey performances for a subsample of 150 stars that are representative of the full SHINE sample. Observations were conducted in a homogeneous way between February 2015 and February 2017 with the dedicated ground-based VLT/SPHERE instrument equipped with the IFS integral field spectrograph and the IRDIS dual-band imager, covering a spectral range between 0.9 and 2.3m. We used coronographic, angular, and spectral differential imaging techniques to achieve the best detection performances for this study, down to the planetary mass regime. We processed, in a uniform manner, more than 300 SHINE observations and datasets to assess the survey typical sensitivity as a function of the host star and of the observing conditions. The median detection performance reached 5-contrasts of 13mag at 200mas and 14.2mag at 800mas with the IFS (YJ and YJH bands), and of 11.8mag at 200mas, 13.1mag at 800mas, and 15.8mag at 3as with IRDIS in H band, delivering one of the deepest sensitivity surveys thus far for young, nearby stars. A total of sixteen substellar companions were imaged in this first part of SHINE: seven brown dwarf companions and ten planetary-mass companions. These include two new discoveries, HIP 65426 b and HIP 64892 B, but not the planets around PDS70 that had not been originally selected for the SHINE core sample. A total of 1483 candidates were detected, mainly in the large field of view that characterizes IRDIS. The color-magnitude diagrams, low-resolution spectrum (when available with IFS), and follow-up observations enabled us to identify the nature (background contaminant or comoving companion) of about 86% of our subsample. The remaining cases are often connected to crowded-field follow-up observations that were missing. Finally, even though SHINE was not initially designed for disk searches, we imaged twelve circumstellar disks, including three new detections around the HIP 73145, HIP 86598, and HD106906 systems. Nowadays, direct imaging provides a unique opportunity to probe the outer part of exoplanetary systems beyond 10au to explore planetary architectures, as highlighted by the discoveries of: one new exoplanet, one new brown dwarf companion, and three new debris disks during this early phase of SHINE. It also offers the opportunity to explore and revisit the physical and orbital properties of these young, giant planets and brown dwarf companions (relative position, photometry, and low-resolution spectrum in near-infrared, predicted masses, and contrast in order to search for additional companions). Finally, these results highlight the importance of finalizing the SHINE systematic observation of about 500 young, nearby stars for a full exploration of their outer part to explore the demographics of young giant planets beyond 10au and to identify the most interesting systems for the next generation of high-contrast imagers on very large and extremely large telescopes.
