- ID:
- ivo://CDS.VizieR/J/MNRAS/452/3508
- Title:
- Young stellar structures in NGC 6503
- Short Name:
- J/MNRAS/452/3508
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep Hubble Space Telescope photometry obtained with the Legacy ExtraGalactic UV Survey. We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95 percent being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviours, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ~1.7 for length-scales between ~20pc and 2.5kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5kpc. About 60 percent of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behaviour in a time-scale of ~60Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.
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- ID:
- ivo://CDS.VizieR/J/ApJ/848/97
- Title:
- Young stellar variables with KELT for K2. I.
- Short Name:
- J/ApJ/848/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the most well-studied young stellar associations, Taurus-Auriga, was observed by the extended Kepler mission, K2, in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify "dippers," aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomena on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post-K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus-Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.
- ID:
- ivo://CDS.VizieR/J/ApJ/619/270
- Title:
- Young super star clusters in the starburst of M82
- Short Name:
- J/ApJ/619/270
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent results from the Hubble Space Telescope (HST) have resolved starbursts as collections of compact young stellar clusters. Here we present a photometric catalog of the young stellar clusters in the nuclear starburst of M82, observed with the HST WFPC2 in H{alpha} (F656N) and in four optical broadband filters. We identify 197 young super stellar clusters (SSCs). The compactness and high density of the sources led us to develop specific techniques to measure their sizes. Strong extinction lanes divide the starburst into five different zones. In the catalog we include relative coordinates, radii, fluxes, luminosities, masses, equivalent widths, extinctions, and other parameters. Extinction values have been derived from the broadband images.
- ID:
- ivo://CDS.VizieR/J/A+A/494/147
- Title:
- Young T Tauri star in CB 26 molecular outflows
- Short Name:
- J/A+A/494/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming proto-star. Although jet rotation has been observed in a few objects, no rotation of molecular outflows has been unambiguously reported so far. We report new millimeter-interferometric observations of the edge-on T-Tauri-star - disk system in the isolated Bok globule CB-26. The aim of these observations was to study the disk-outflow relation in this 1Myr old low-mass young stellar object.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A57
- Title:
- Young visual M-dwarf binaries spectra
- Short Name:
- J/A+A/642/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from an integral field spectroscopy study of seven close visual binary pairs of young M-dwarf multiple systems. The target systems are part of the astrometric monitoring AstraLux program, surveying hundreds of M-dwarf systems for multiplicity and obtaining astrometric epochs for orbital constraints. Our new VLT/SINFONI data provides resolved spectral type classification in the J, H and K bands for seven of these low-mass M-dwarf binaries, which we determine by comparing them to empirical templates and examining the strength of water absorption in the K-band. The medium resolution K-band spectra also allows us to derive effective temperatures for the individual components. All targets in the survey display several signs of youth, and some have kinematics similar to young moving groups, or low surface gravities which we determine from measuring equivalent widths of gravity sensitive alkali lines in the J-band. Resolved photometry from our targets is also compared with isochrones from theoretical evolutionary models, further implying young ages. Dynamical masses will be provided from ongoing monitoring of these systems, which can be seen as emblematic binary benchmarks that may be used to calibrate evolutionary models for low-mass stars in the future.
- ID:
- ivo://CDS.VizieR/J/ApJ/457/L99
- Title:
- 25yr CaII-HK observations of F-K nearby stars
- Short Name:
- J/ApJ/457/L99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We find a significant correlation between the magnetic and rotational moments for a sample of 112 lower main-sequence stars. The rotational moment is calculated from measurements of the rotation period in most of the stars (not from the projected rotational velocity inferred from Doppler broadening). The magnetic moment is computed from a database of homogeneous measurements of the mean level of Ca II H and K emission fluxes sampled for most of the stars over an interval of 25yr. The slope connecting the logarithm of the magnetic moment and the logarithm of the rotational moment is about +0.5-0.6, with a Pearson correlation coefficient of about +0.9. The scatter of points from the mean relation has a component that is natural and caused by decade-long surface variability.
- ID:
- ivo://CDS.VizieR/J/ApJS/223/15
- Title:
- 8yr INTEGRAL/IBIS soft gamma-ray source obs.
- Short Name:
- J/ApJS/223/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we report an all-sky soft gamma-ray source catalog based on IBIS observations performed during the first 1000 orbits of INTEGRAL. The database for the construction of the source list consists of all good-quality data available, from the launch in 2002, up to the end of 2010. This corresponds to ~110Ms of scientific public observations, with a concentrated coverage on the Galactic Plane and extragalactic deep exposures. This new catalog includes 939 sources above a 4.5{sigma} significance threshold detected in the 17-100keV energy band, of which 120 sources represent previously undiscovered soft gamma-ray emitters. The source positions are determined, mean fluxes are provided in two main energy bands, and these are both reported together with the overall source exposure. Indicative levels of variability are provided, and outburst times and durations are given for transient sources. A comparison is made with previous IBIS catalogs and catalogs from other similar missions.
- ID:
- ivo://CDS.VizieR/J/ApJ/896/L19
- Title:
- 16yr LC of TXS 0506+056 from MASTER networks
- Short Name:
- J/ApJ/896/L19
- Date:
- 07 Dec 2021
- Publisher:
- CDS
- Description:
- We present the earliest astronomical observation of a high-energy neutrino error box of which the variability was discovered after high-energy-neutrino detection. The one robotic telescope of the MASTER global international networks automatically imaged the error box of the very high-energy-neutrino event IceCube-170922A. Observations were carried out in minutes after the IceCube-170922A neutrino event was detected by the IceCube observatory at the South Pole. MASTER found the blazar TXS 0506+056 to be in the off-state after one minute and then switched to the on-state no later than two hours after the event. The effect is observed at a 50{sigma} significance level. We also present own a unique 16yr light curve of blazar TXS 0506+056 (518 data set).
- ID:
- ivo://CDS.VizieR/J/ApJS/237/30
- Title:
- 6-yr light curves of 10 blazars
- Short Name:
- J/ApJS/237/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out multi-color optical monitoring of a sample of 10 blazars from 2005 to 2011. The sample contains 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. Our monitoring focused on the long-term variability and the sample included nine BL Lac objects and one flat-spectrum radio quasar (FSRQ). A total of 14,799 data points were collected. This is one of the largest optical databases for a sample of 10 blazars. All objects showed significant variability except for OT 546. Because of the low sampling on each single night, only BL Lacertae were observed to have intraday variability on 2006 November 6. Most BL Lac objects showed a bluer-when-brighter (BWB) chromatism, while the FSRQ, 3C 454.3, displayed a redder-when-brighter trend. The BWB color behaviors of most BL Lacs can be at least partly attributed to the trend of increasing variation amplitude with increasing frequency observed in these objects. The average spectral index of LBLs is around 1.5, as expected from the model dominated by synchrotron self-Compton loss. The optical emission of HBL is probably contaminated by the thermal emission from the host galaxies. Correlation analysis did not reveal any time delay between variations at different wavelengths.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/90
- Title:
- 4yr 1.3mm VLBI observations of SgrA* with EHT
- Short Name:
- J/ApJ/820/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180{deg} rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.
