- ID:
- ivo://CDS.VizieR/J/A+A/602/A93
- Title:
- SN Type Ibn OGLE-2014-SN-131 lightcurves
- Short Name:
- J/A+A/602/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Type Ibn supernovae (SNe Ibn) are thought to be the core-collapse explosions of massive stars whose ejecta interact with He-rich circumstellar material (CSM). We report the discovery of a SN Ibn, with the longest rise-time ever observed, OGLE-2014-SN-131. We discuss the potential powering mechanisms and the progenitor nature of this peculiar stripped-envelope (SE), circumstellar-interacting SN. Optical photometry and spectroscopy were obtained with multiple telescopes including VLT, NTT, and GROND. We compare light curves and spectra with those of other known SNe Ibn and Ibc. CSM velocities are derived from the spectral analysis. The SN light curve is modeled under different assumptions about its powering mechanism (56Ni decay, CSM-interaction, magnetar) in order to estimate the SN progenitor parameters. OGLE-2014-SN-131 spectroscopically resembles SNe Ibn such as SN 2010al. Its peak luminosity and post-peak colors are also similar to those of other SNe Ibn. However, it shows an unprecedentedly long rise-time and a much broader light curve compared to other SNe Ibn. Its bolometric light curve can be reproduced by magnetar and CSM-interaction models, but not by a 56Ni-decay powering model. To explain the unusually long rise-time, the broad light curve, the light curve decline, and the spectra characterized by narrow emission lines, we favor a powering mechanism where the SN ejecta are interacting with a dense CSM. The progenitor of OGLE-2014-SN-131 was likely a Wolf-Rayet star with a mass greater than that of a typical SN Ibn progenitor, which expelled the CSM that the SN is interacting with.
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- ID:
- ivo://CDS.VizieR/J/AJ/160/7
- Title:
- 2019 SOAR speckle interferometry of binary stars
- Short Name:
- J/AJ/160/7
- Date:
- 09 Dec 2021
- Publisher:
- CDS
- Description:
- The results of speckle-interferometric observations at the 4.1m Southern Astrophysical Research Telescope in 2019 are given, totaling 2555 measurements of 1972 resolved pairs with separations from 15mas (median 0.21") and magnitude difference up to 6mag, and non-resolutions of 684 targets. We resolved for the first time 90 new pairs or subsystems in known binaries. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We give a list of 127 orbits computed using our latest measurements. Their quality varies from excellent (25 orbits of grades 1 and 2) to provisional (47 orbits of grades 4 and 5).
- ID:
- ivo://CDS.VizieR/J/ApJ/894/19
- Title:
- SOAR spectra of the WD EPIC 228939929
- Short Name:
- J/ApJ/894/19
- Date:
- 03 Dec 2021 00:38:57
- Publisher:
- CDS
- Description:
- We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93-023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence in K2 Campaign 10. The behavior is associated with a magnetic (B=5.0MG) spot on the stellar surface, making the 317.278s period a direct measurement of the stellar rotation rate. This object is therefore the fastest-rotating, apparently isolated (without a stellar companion) white dwarf yet discovered and the second found to exhibit chromospheric Balmer emission after GD 356, in which the emission has been attributed to a unipolar inductor mechanism driven by a possible rocky planet. We explore the properties and behavior of this object, and consider whether its evolution may hold implications for white dwarf mergers and their remnants.
- ID:
- ivo://CDS.VizieR/J/ApJS/208/7
- Title:
- Sodium excess objects. I. SDSS-DR7
- Short Name:
- J/ApJS/208/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several studies have reported the presence of sodium excess objects having neutral atomic absorption lines at 5895{AA} (Na.D) and 8190{AA} that are deeper than expected based on stellar population models that match the stellar continuum. The origin of these lines is therefore hotly debated. van Dokkum & Conroy (2010Natur.468..940V) proposed that low-mass stars (<~0.3M_{sun}_) are more prevalent in massive early-type galaxies, which may lead to a strong Na I 8190 line strength. It is necessary to test this prediction, however, against other prominent optical line indices such as Na.D, Mg b, and Fe 5270, which can be measured with a significantly higher signal-to-noise ratio than Na I 8190. We identified a new sample of roughly 1000 Na.D excess objects (NEOs; ~8% of galaxies in the sample) based on Na.D line strength in the redshift range 0.00<=z<=0.08 from the Sloan Digital Sky Survey (SDSS) DR7 through detailed analysis of galaxy spectra. We explore the properties of these new objects here. The novelty of this work is that the galaxies were carefully identified through direct visual inspection of SDSS images, and we systematically compared the properties of NEOs and those of a control sample of galaxies with normal Na.D line strengths. We note that the majority of galaxies with high velocity dispersions ({sigma}_e_>250km/s) show Na.D excesses.
- ID:
- ivo://CDS.VizieR/J/AJ/147/85
- Title:
- Solar neighborhood. XXXIII. 45 M dwarfs
- Short Name:
- J/AJ/147/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing Research Consortium On Nearby Stars photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(L_X_/L_bol_)>-3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHK_S_ photometry from the Two Micron All Sky Survey point source catalog, X-ray data from the ROSAT All-Sky Survey, and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of {beta} Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous {approx}30Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25pc of the Sun.
- ID:
- ivo://CDS.VizieR/J/AJ/147/94
- Title:
- Solar neighborhood. XXXII. L and M dwarfs
- Short Name:
- J/AJ/147/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report newly observed VRI photometry for all 63 objects and new trigonometric parallaxes for 37 objects. The remaining 26 objects have trigonometric parallaxes from the literature. We combine our optical photometry and trigonometric parallaxes with 2MASS and WISE photometry and employ a novel spectral energy distribution fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. Our uncertainties range from ~20K to ~150K in temperature, ~0.01 to ~0.06 in log (L/L_{sun}_) and ~3% to ~10% in radius. We check our methodology by comparing our calculated radii to radii directly measured via long baseline optical interferometry. We find evidence for the local minimum in the radius-temperature and radius-luminosity trends that signals the end of the stellar main sequence and the start of the brown dwarf sequence at T_eff_~2075K, log(L/L_{sun}_)~-3.9, and (R/R_{sun}_)~0.086. The existence of this local minimum is predicted by evolutionary models, but at temperatures ~400K cooler. The minimum radius happens near the locus of 2MASS J0523-1403, an L2.5 dwarf with V-K=9.42. We make qualitative arguments as to why the effects of the recent revision in solar abundances accounts for the discrepancy between our findings and the evolutionary models. We also report new color-absolute magnitude relations for optical and infrared colors which are useful for estimating photometric distances. We study the optical variability of all 63 targets and find an overall variability fraction of 36_-7_^+9^% at a threshold of 15mmag in the I band, which is in agreement with previous studies.
- ID:
- ivo://CDS.VizieR/J/AJ/154/32
- Title:
- Solar neighborhood. XXXIX. Nearby white dwarfs
- Short Name:
- J/AJ/154/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD) systems from both the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS) parallax programs. Of these, 76 parallaxes for 69 systems were measured by the CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS program. A total of 50 systems are confirmed to be within the 25-pc horizon of interest. Coupled with a spectroscopic confirmation of a common proper-motion companion to a Hipparcos star within 25pc as well as confirmation parallax determinations for two WD systems included in the recently released Tycho Gaia Astrometric Solution catalog, we add 53 new systems to the 25-pc WD sample-a 42% increase. Our sample presented here includes four strong candidate halo systems, a new metal-rich DAZ WD, a confirmation of a recently discovered nearby short-period (P=2.85hr) double degenerate, a WD with a new astrometric perturbation (long period, unconstrained with our data), and a new triple system where the WD companion main-sequence star has an astrometric perturbation (P~1.6year).
- ID:
- ivo://CDS.VizieR/J/AJ/149/5
- Title:
- Solar neighborhood. XXXV. Distances to M dwarfs
- Short Name:
- J/AJ/149/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present trigonometric, photometric, and photographic distances to 1748 southern ({delta}{<=}O{deg}) M dwarf systems with {mu}>=0.18''/yr, of which 1404 are believed to lie within 25pc of the Sun. The stars have 6.67{<=}V_J_{<=}21.38 and 3.50{<=}(V_J_-K_S_){<=}9.27, covering the entire M dwarf spectral sequence from M0.0 V through M9.5 V. This sample therefore provides a comprehensive snapshot of our current knowledge of the southern sky for the nearest M dwarfs that dominate the stellar population of the Galaxy. Roughly one-third of the 1748 systems, each of which has an M dwarf primary, have published high quality parallaxes, including 179 from the REsearch Consortium On Nearby Stars astrometry program. For the remaining systems, we offer photometric distance estimates that have well-calibrated errors. The bulk of these (~700) are based on new V_J_R_KC_I_KC_ photometry acquired at the CTIO/SMARTS 0.9m telescope, while the remaining 500 primaries have photographic plate distance estimates calculated using SuperCOSMOS B_J_R_59F_I_IVN_ photometry. Confirmed and candidate subdwarfs in the sample have been identified, and a census of companions is included.
- ID:
- ivo://CDS.VizieR/J/AJ/153/14
- Title:
- Solar neighborhood XXXVIII. Nearby M dwarf systems
- Short Name:
- J/AJ/153/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 160 new trigonometric parallaxes for 151 M dwarf systems from the REsearch Consortium On Nearby Stars (RECONS) group's long-term astrometry/photometry program at the CTIO/SMARTS 0.9m telescope. Most systems (124 or 82%) are found to lie within 25pc. The stars have 119mas/yr{<=}{mu}{<=}828mas/yr and 3.85{<=}(V-K){<=}8.47. Among these are 58 systems from the SuperCOSMOS-RECONS search, discovered via our proper motion trawls of the SuperCOSMOS digitized archival photographic plates, while the remaining stars were suspected via photometric distance estimates to lie nearby. Sixteen systems were newly discovered via astrometric perturbations to be binaries, many of which are ideal for accurate mass determinations due to their proximity and orbital periods on the order of a decade. A variability analysis of the stars presented, two-thirds of which are new results, shows six of the stars to vary by more than 20mmag. This effort brings the total number of parallaxes for M dwarf systems measured by RECONS to nearly 500 and increases by 26% the number of southern M dwarf systems with accurate trigonometric parallaxes placing them within 25pc.
- ID:
- ivo://CDS.VizieR/J/AJ/150/6
- Title:
- Solar neighborhood. XXXVI. VRI variability of M dwarfs
- Short Name:
- J/AJ/150/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of long-term photometric variability for nearby red dwarf stars at optical wavelengths. The sample consists of 264 M dwarfs south of decl.=+30 with V-K=3.96-9.16 and M_V_~~10-20, corresponding to spectral types M2V-M8V, most of which are within 25pc. The stars have been observed in the VRI filters for ~4-14yr at the CTIO/SMARTS 0.9m telescope. Of the 238 red dwarfs within 25pc, we find that only ~8% are photometrically variable by at least 20mmag (~2%) in the VRI bands. Only four stars have been found to vary by more than 50mmag, including GJ 1207 at 8.6pc, which experienced a single extraordinary flare, and GJ 2006 A, TWA 8 A, and TWA 8 B, which are all young stars beyond 25pc linked to moving groups. We find that high variability at optical wavelengths over the long term can in fact be used to identify young stars. Overall, however, the fluxes of most red dwarfs at optical wavelengths are steady to a few percent over the long term. The low overall rate of photometric variability for red dwarfs is consistent with results found in previous work on similar stars on shorter timescales, with the body of work indicating that most red dwarfs are only mildly variable. As expected, we find that the degree of photometric variability is greater in the V band than in the R or I bands, but we do not find any obvious trends in variability over the long term with red dwarf luminosity or temperature. We highlight 17 stars that show long-term changes in brightness, sometimes because of flaring activity or spots, and sometimes because of stellar cycles similar to our Sun's solar cycle. Remarkably, two targets show brightnesses that monotonically increase (G 169-029) or decrease (WT 460AB) by several percent over a decade. We also provide long-term variability measurements for seven M dwarfs within 25pc that host exoplanets, none of which vary by more than 20mmag. Both as a population, and for the specific red dwarfs with exoplanets observed here, photometric variability is therefore often not a concern for planetary environments, at least at the optical wavelengths where they emit much of their light.
