- ID:
- ivo://CDS.VizieR/J/ApJ/746/23
- Title:
- Radio observations of ultracool dwarf stars
- Short Name:
- J/ApJ/746/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new radio survey of about 100 late-M and L dwarfs undertaken with the Very Large Array. The sample was chosen to explore the role of rotation in the radio activity of ultracool dwarfs. As part of the survey we discovered radio emission from three new objects, 2MASS J0518113-310153 (M6.5), 2MASS J0952219-192431 (M7), and 2MASS J1314203+132001 (M7), and made an additional detection of LP 349-25 (M8). Combining the new sample with results from our previous studies and from the literature, we compile the largest sample to date of ultracool dwarfs with radio observations and measured rotation velocities.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/167/103
- Title:
- Radio/Optical catalog of the SSA 13 field
- Short Name:
- J/ApJS/167/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 1.4GHz catalog of 810 radio sources (560 sources in the complete sample) found in the SSA 13 field (RA=13:12, DE=42:38). The 1.4GHz radio image was obtained from a 91hr VLA integration with an rms noise level of 4.82uJy/beam at the field center. Optical images in the R band (6300{AA}) and z band (9200{AA}) with 3{sigma} detection magnitudes of 26.1 and 24.9, respectively, were obtained from three observing nights on the 8m Subaru Telescope. We find that 88%+/-2% of the radio sources are identified with an optical counterpart.
- ID:
- ivo://CDS.VizieR/J/ApJ/439/983
- Title:
- Radio & optical observation of UX Arietis
- Short Name:
- J/ApJ/439/983
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed UX Arietis at C band (6cm) for 3 weeks with four VLA antennas. The temporal coverage during the program was approximately three scans per day. A few days into the VLA program, UX Ari began a radio flaring period which lasted for at least 2 weeks. All the radio fluxes were above the system noise during this episode, but the largest values (up to 270mJy) occurred close to 0.0 phase. This phasing is confirmed by the UX Ari radio observations of Neidhoefer, Massi, & Chiuderi-Drago (1993A&A...278L..51N). Visible-band light curves of UX Ari were obtained both during and after our radio observations; the peak-to-peak variation in all filters was ~0.2mag. The light curves indicate that the maximum starspot visibility occurred very close to 0.0 phase, the same phase as the radio maxima. Closer comparison of our radio and optical light curves indicates that they are almost perfectly anticorrelated. A similar radio/optical correlation has been found by Lim et al. (1992ApJ...388L..27L) and Lim et al. (1994ApJ...430..332L) for the single K0 V star AB Dor. We make the following conclusions from our observations. First, the episodes of long-term (~hours to days) radio flaring were modulated by stellar eclipses. Second, the flares were located close to the starspot groups. Third, the sizes of the flares were comparable to sizes of the starspot groups, which is consistent with nonthermal emission of brightness temperature T_b~10^10-10^13K. Fourth, the radio emission arose only from the midlatitude starspot groups. Last, the radio flares emitted their radiation nearly normal to the stellar surface.
- ID:
- ivo://CDS.VizieR/J/ApJS/185/124
- Title:
- 58 radio sources near BNGSs
- Short Name:
- J/ApJS/185/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a preliminary survey of 58 radio sources within the isoplanatic patches (r<25") of bright (11<R<12) stars suitable for use as natural guide stars with high-order adaptive optics (AO). An optical and near-infrared imaging survey was conducted utilizing tip-tilt corrections in the optical and AO in the near-infrared. Spectral energy distributions were fit to the multi-band data for the purpose of obtaining photometric redshifts using the Hyperz code. Several of these photometric redshifts were confirmed with spectroscopy, a result that gives more confidence to the redshift distribution for the whole sample. Additional long-wavelength data from Spitzer, SCUBA, SHARC2, and VLA supplement the optical and near-infrared data. We find the sample generally follows and extends the magnitude-redshift relation found for more powerful local radio galaxies. The survey has identified several reasonably bright (H=19-20) objects at significant redshifts (z>1) that are now within the capabilities of the current generation of AO-fed integral-field spectrographs. These objects constitute a unique sample that can be used for detailed ground-based AO studies of galactic structure, evolution, and active galactic nucleus formation at high redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/121
- Title:
- Radio to UV observations of GRB 181201A
- Short Name:
- J/ApJ/884/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present comprehensive multiwavelength radio to X-ray observations of GRB 181201A spanning from ~150s to ~163days after the burst, comprising the first joint ALMA-VLA-GMRT observations of a gamma-ray burst (GRB) afterglow. The radio and millimeter-band data reveal a distinct signature at ~3.9days, which we interpret as reverse-shock (RS) emission. Our observations present the first time that a single radio- frequency spectral energy distribution can be decomposed directly into RS and forward shock (FS) components. We perform detailed modeling of the full multiwavelength data set, using Markov Chain Monte Carlo sampling to construct the joint posterior density function of the underlying physical parameters describing the RS and FS synchrotron emission. We uncover and account for all discovered degeneracies in the model parameters. The joint RS-FS modeling reveals a weakly magnetized ({sigma}~3x10^-3^), mildly relativistic RS, from which we derive an initial bulk Lorentz factor of {Gamma}_0_~103 for the GRB jet. Our results support the hypothesis that low-density environments are conducive to the observability of RS emission. We compare our observations to other events with strong RS detections and find a likely observational bias selecting for longer lasting, nonrelativistic RSs. We present and begin to address new challenges in modeling posed by the present generation of comprehensive, multifrequency data sets.
- ID:
- ivo://CDS.VizieR/J/AJ/157/63
- Title:
- Radius relations for low-metallicity M-dwarf stars
- Short Name:
- J/AJ/157/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T_eff_) and we measure bolometric luminosities (L_bol_) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T_eff_ and L_bol_ using the Stefan-Boltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of -2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
- ID:
- ivo://CDS.VizieR/J/AJ/160/73
- Title:
- R- and I-band photometry of 506 asteroids with CNEOST
- Short Name:
- J/AJ/160/73
- Date:
- 09 Mar 2022
- Publisher:
- CDS
- Description:
- We initiated the bilateral collaboration between the Lulin Observatory and the Purple Mountain Observatory to collect asteroid lightcurves using the Chinese Near-Earth Object Survey Telescope at the Xuyi Observation Station. The primary goal of this collaboration was to discover super-fast rotators (SFRs) and study their physical properties. Two campaigns have been conducted: (a) a survey of ~45{deg}^2^ using 8minute cadence during 2017 February 26-March 2, and (b) a survey of ~60{deg}^2^ using 10minute cadence during 2018 March 9-12. Our samples are mainly main-belt asteroids and some Hildas and Jupiter Trojans. Out of 4522 collected lightcurves, 506 reliable rotation periods were obtained. Among the reliable rotation periods, we found 16 candidates with a possible rotation period of <2.2hr, in which (134291) 2006 DZ6 shows a very convincing folded lightcurve and the other 15 candidates only have a likely trend. Further confirmation is needed for the rotation periods of these SFR candidates. In addition, (2280) Kunikov seems to have an eclipsing feature on its lightcurve with a relatively long rotation period suggesting that it is likely a fully synchronized binary asteroid. When the preliminary spin-rate distributions were carried out for asteroids using different sizes, no obvious difference was found.
- ID:
- ivo://CDS.VizieR/J/MNRAS/428/2824
- Title:
- Rapid optical variability in ultracool dwarfs
- Short Name:
- J/MNRAS/428/2824
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, a summary of optical time-series photometry of 125 ultracool dwarfs is given. The observing strategy was to monitor each object continuously for 2-3h in order to ascertain whether it was rapidly variable. Many of the targets were observed at multiple epochs, to follow up possible short time-scale variability, or to test for slow brightness changes on longer time-scales. The 353 data sets obtained contain nearly 22000 individual measurements. Optical (I_C_) magnitudes, accurate to roughly 0.1-0.2mag, were derived for 21 objects for which there is no optical photometry in the literature. It is shown that photometry is affected by variable seeing in a large percentage of the time-series observations. Since this could give the appearance of variability intrinsic to the objects, magnitudes are modelled as functions of both time and seeing. Several ultracool dwarfs which had not been monitored before are variable, according to certain model-fitting criteria. A number of objects with multi-epoch observations appear to be variable on longer time-scales. Since testing for variability is far from being straightforward, the time-series data are made available so that interested readers can perform their own analyses.
- ID:
- ivo://CDS.VizieR/J/A+A/294/135
- Title:
- Rapid variations of Eta Cen
- Short Name:
- J/A+A/294/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/602/A53
- Title:
- R Aqr SPHERE/ZIMPOL narrow-H{alpha} image
- Short Name:
- J/A+A/602/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). We describe SPHERE/ZIMPOL test observations of the R Aqr system taken in H{alpha} and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. We analyze the high resolution ~=25mas images from SPHERE/ZIMPOL and determine from the H{alpha} emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2"(<400AU) of R Aqr. The data are compared to simultaneous HST line filter observations. The H{alpha} fluxes and the measured sizes of the clouds yield H{alpha} emissivities for many clouds from which one can derive the mean density, mass, recombination time scale, and other cloud parameters. Our H{alpha} data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 45 mas West (position angle -89.5{deg}) of the mira. The central jet source is the strongest H{alpha} component with a flux of about 2.5x10^-12^erg/cm^2^/s. North east and south west from the central source there are many clouds with very diverse structures. Within 0.5" (100AU) we see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, at 1"-2", fainter and more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure between 0.2"-0.7" and faint perpendicular "wisps" further out. Some jet clouds are also detected in the ZIMPOL [OI] and HeI filters, as well as in the HST-WFC3 line filters for H{alpha}, [OIII], [NII], and [OI]. We determine jet cloud parameters and find a very well defined correlation Ne{prop.to}r^-1.3^ between cloud density and distance to the central binary. Densities are very high with typical values of Ne~=3x10^5^cm^-3^ for the "outer" clouds around 300AU, Ne~=3x10^6^cm^-3^ for the "inner" clouds around 50AU, and even higher for the central jet source. The high Ne of the clouds implies short recombination or variability timescales of a year or shorter. H{alpha} high resolution data provide a lot of diagnostic information for the ionized jet gas in R Aqr. Future H{alpha} observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.