- ID:
- ivo://CDS.VizieR/J/ApJS/214/10
- Title:
- Optical counterparts of Chandra GBS sources
- Short Name:
- J/ApJS/214/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical light curves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey (GBS). Using data from the Mosaic-II instrument on the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on timescales from ~2hr to 8 days over the 3/4 of the X-ray survey containing sources from the initial GBS catalog. Among the light curve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. Eighty-seven percent of X-ray sources have at least one potential optical counterpart. Twenty-seven percent of these candidate counterparts are detectably variable; a much greater fraction than expected for randomly selected field stars, which suggests that most of these variables are real counterparts. We discuss individual sources of interest, provide variability information on candidate counterparts, and discuss the characteristics of the variable population.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/899/14
- Title:
- Optical & FeII sources in Supernova remnant with HST
- Short Name:
- J/ApJ/899/14
- Date:
- 14 Mar 2022 07:07:21
- Publisher:
- CDS
- Description:
- NGC6946 is a high-star-formation-rate, face-on, spiral galaxy that has hosted 10 supernovae since 1917. Not surprisingly, a large number of supernova remnants and candidates have been identified either as optical nebulae with high [SII]:H{alpha} line ratios (147) or as compact non-thermal radio sources (35). However, there are only seven overlaps between these two samples. Here, we apply [FeII] 1.644{mu}m emission as a new diagnostic to search for supernova remnants in an attempt to resolve this discrepancy. [FeII] is expected to be relatively strong in the radiative shocks of supernova remnants and almost absent in HII regions. It is less susceptible to the effects of absorption along the line of sight than the optical lines normally used to identify remnants. Using data from the WFC3 camera on Hubble Space Telescope (HST), we identify 132 [FeII] emission nebulae in NGC6946 as likely supernova remnants. Of these, 54 align with previously known optical supernova remnants. The remaining 78 objects are new; of these 44 are visible in new HST imagery in H{alpha} and [SII]. This brings the total number of supernova remnant candidates (from optical and/or IR data) in NGC6946 to 225. A total of 14 coincidences with radio supernova remnant candidates (out of 30 in our search area) are found in this expanded list. The identification of so many new remnant candidates validates the use of [FeII] imagery for finding remnants, and suggests that previous remnant searches in other galaxies may be far from complete.
- ID:
- ivo://CDS.VizieR/J/A+A/327/1114
- Title:
- Optical flares on EV Lac in 1967-1977
- Short Name:
- J/A+A/327/1114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a large sample of homogeneous photoelectric data obtained by monitoring the red dwarf flare star EV Lac. The data were collected in 10 years (1967-77) at Catania Astrophysical Observatory on Mt. Etna. The peak luminosity, the total energy emitted, the rise and decay times were measured for each flare.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/115
- Title:
- Optical follow-up of ASAS-SN M dwarf flares
- Short Name:
- J/ApJ/876/115
- Date:
- 18 Jan 2022 15:06:46
- Publisher:
- CDS
- Description:
- The All-sky Automated Survey for Supernovae (ASAS-SN) is the only project in existence to scan the entire sky in optical light approximately every day, reaching a depth of g~18mag. Over the course of its first 4yr of transient alerts (2013-2016), ASAS-SN observed 53 events classified as likely M dwarf flares. We present follow-up photometry and spectroscopy of all 53 candidates, confirming flare events on 47 M dwarfs, one K dwarf, and one L dwarf. The remaining four objects include a previously identified T Tauri star, a young star with outbursts, and two objects too faint to confirm. A detailed examination of the 49 flare star light curves revealed an additional six flares on five stars, resulting in a total of 55 flares on 49 objects ranging in V-band contrast from {Delta}V=-1 to -10.2mag. Using an empirical flare model to estimate the unobserved portions of the flare light curve, we obtain lower limits on the V-band energy emitted during each flare, spanning log(E_V_/erg)=32-35, which are among the most energetic flares detected on M dwarfs. The ASAS-SN M dwarf flare stars show a higher fraction of H{alpha} emission, as well as stronger H{alpha} emission, compared to M dwarfs selected without reference to activity, consistent with belonging to a population of more magnetically active stars. We also examined the distribution of tangential velocities, finding that the ASAS-SN flaring M dwarfs are likely to be members of the thin disk and are neither particularly young nor old.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A132
- Title:
- Optical follow-up of Q0957+561 in 2005-2010
- Short Name:
- J/A+A/540/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The optical variability database of the two images (A and B) of the gravitationally lensed quasar Q0957+561 is based on frames taken with the Liverpool Robotic Telescope in the 2005-2010 period, as part of the Liverpool Quasar Lens Monitoring (LQLM) project (Goicoechea et al. 2010AdAst2010E..29G). A crowded-field photometry pipeline produced instrumental fluxes of both quasar images, and only frames with signal-to-noise ratio above 80 over Q0957+561A were passed through a transformation pipeline. This pipeline transformed instrumental magnitudes into SDSS magnitudes (the calibration-correction scheme is described in Appendix A of Shalyapin et al. (2008A&A...492..401S) and the main text of the paper). We also turned SDSS magnitudes into physical fluxes using suitable conversion equations (SDSS Photometric Flux Calibration 2007, http://www.sdss.org/dr7/algorithms/fluxcal.html). Table 1 contains g-band fluxes for 357 different nights, while Table 2 includes r-band fluxes for 371 observation nights.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/32
- Title:
- Optical/{gamma}-ray flares for Fermi-LAT blazars
- Short Name:
- J/ApJ/880/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Even with several thousand Fermi-Large Area Telescope (LAT) blazar detections, the {gamma}-ray emission mechanism is poorly understood. We explore correlated optical/{gamma}-ray flux variations for 178 Fermi-LAT blazars regularly monitored by the Katzman Automatic Imaging Telescope, the Small and Moderate Aperture Research Telescope System, and the Steward Observatory. Out of the 178 sources, 121 show a measurable (>1{sigma}) discrete correlation function peak. Using the derived time lags and Bayesian block light-curve decompositions, we measure the fraction of common and orphan flares between the two bands. After accounting for sampling and sensitivity limitations we quantify for the first time the true orphan flare rates of optical and {gamma}-ray flares: 54.5% of optical and 20% of {gamma}-ray flares are orphan events. Both the intraband temporal relation and the small orphan {gamma}-ray flare fraction point toward leptonic processes as the likely mechanisms for the high-energy emission. Motivated to discriminate between synchrotron self-Compton (SSC) and external-Compton dominance in individual sources, we use the flux-flux variations to determine the slope m of the log fopt-log f{gamma} dependence. The slope distribution suggests a bimodal population with high and intermediate synchrotron peak objects showing larger m than low synchrotron peak objects. We find that m is naturally decreased through pollution from the orphan (typically optical) flares and develop a method to statistically recover, given the sources' measured orphan flare rate, the intrinsic m. While source classes show composite behavior, the majority of BL Lac objects favor m=2, indicating an SSC origin for the {gamma}-rays. No preference for either m is found in flat spectrum radio quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/449/425
- Title:
- Optical identification of ROSAT-FSC sources
- Short Name:
- J/A+A/449/425
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Byurakan/Hamburg/ROSAT Catalogue (BHRC) of the optical identifications of X-ray sources is presented. The BHRC includes all 2791 sources from the ROSAT-FSC (<IX/29>) with |b|>30, DEC>0 and ROSAT count rate CR>0.04cts/s. The optical identifications were carried out by means of the Hamburg Quasar Survey (HQS) digitized spectroscopic plates, the DSS1 and DSS2 (blue, red, and IR) images, and other available data. We managed to identify 97% of sources (2696 sources) that are associated with 3202 optical objects. 2248 X-ray sources have a single optical counterpart, 144 have a double or multiple optical counterpart (binaries, galaxy groups etc.), and 304 have ambiguous identifications. The table gives all available multiwavelength data for the identified sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/401/294
- Title:
- Optical identification of XMM-LSS sources
- Short Name:
- J/MNRAS/401/294
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical spectroscopic identifications of X-ray sources in ~3deg^2^ of the XMM-Large Scale Structure survey (XMM-LSS), also covered by the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), obtained with the AAOmega instrument at the Anglo-Australian Telescope. In a flux-limited sample of 829 point-like sources in the optical band with g'<=22mag and the 0.5-2keV flux (f_0.5-2keV_)>10^-15^erg/cm^2^/s, we observed 693 objects and obtained reliable spectroscopic identification for 487 sources, approximately 59 per cent of the overall sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/329/700
- Title:
- Optical IDs of JVAS using APM
- Short Name:
- J/MNRAS/329/700
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Files list1, list2, and list3 contain the lists of flat spectrum radio sources with their optical identifications from the APM (Automated Plate Measurement Facility at Cambridge) catalogue. List1 corresponds to the sources which are part of both the complete JVAS++ (a new complete sample constructed with selection criteria similar to those of JVAS -- Jodrell Bank VLA Astrometric Survey: S_5GHz_>200mJy, {alpha}_1.4-5GHz_>-0.5), and with the use of the more accurate GB6 and NVSS surveys) and original JVAS sample, List2 corresponds to sources which are only part of JVAS++, and List3 to sources which are only part of JVAS. The combination of List1 and List2 is a complete sample with S_6cm_>200mJy.
2540. Optical imaging for S4G
- ID:
- ivo://CDS.VizieR/J/A+A/569/A91
- Title:
- Optical imaging for S4G
- Short Name:
- J/A+A/569/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Spitzer Survey for Stellar Structure in Galaxies (S4G) and its more recently approved extension will lead to a set of 3.6 and 4.5um images for 2829 galaxies, which can be used to study many different aspects of the structure and evolution of local galaxies. We have collected and re-reduced optical images of 1768 of the survey galaxies, aiming to make these available to the community as ready-to-use FITS files to be used in conjunction with the mid-IR images. Our sky-subtraction and mosaicking procedures were optimised for imaging large galaxies. We also produce false-colour images of some of these galaxies to be used for illustrative and public outreach purposes. We collected and re-processed images in five bands from the Sloan Digital Sky Survey for 1657 galaxies.
