- ID:
- ivo://CDS.VizieR/J/ApJS/216/26
- Title:
- GALEX search for T Tauri in Taurus-Auriga
- Short Name:
- J/ApJS/216/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J-K color-color diagram is ideally suited for this purpose. From an initial sample of 163313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J-K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/173/572
- Title:
- GALEX/Spitzer photometry in NGC 7331
- Short Name:
- J/ApJS/173/572
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images of NGC 7331 obtained with GALEX and Spitzer, tracing UV and IR signatures of star formation. NGC 7331's morphology at 8-850um is dominated by a central dust ring. This structure is a vigorous site of star formation (hosting one-third of the present activity) but remains inconspicuous in our GALEX UV imagery. Radial profile analysis and photometry for discrete UV- and UV+IR-selected substructures indicate a decline in UV extinction with increasing galactocentric distance, although highly attenuated star-forming regions can be found throughout the disk. UV-optical surface brightness profiles suggest a recent birthrate parameter (b_8_) that is highest in the outer part of the disk, even though the local star formation intensity peaks in the ring. Bolometric luminosity and UV attenuation are correlated in substructures on 0.4kpc scales, with a relationship similar to that established for starburst galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/60
- Title:
- GALEX Time Domain Survey I. UV variable sources
- Short Name:
- J/ApJ/766/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~40deg^2^ of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of ~3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5{sigma} level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |{Delta}m|=4.6mag and 2.9mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV<23mag and |{Delta}m|>0.2mag of ~8.0, 7.7, and 1.8deg^-2^ for quasars, active galactic nuclei, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ~15 and 52deg^-2^/yr for M dwarfs and extragalactic transients, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/185
- Title:
- GALEX ultraviolet atlas of nearby galaxies
- Short Name:
- J/ApJS/173/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its far-ultraviolet (FUV; lambda_eff_=1516{AA}) and near-ultraviolet (NUV; lambda_eff_=2267{AA}) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate [SFR]) of galaxies in the local universe.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/33
- Title:
- Gal. midplane Spitzer/IRAC candidate YSOs (SPICY)
- Short Name:
- J/ApJS/254/33
- Date:
- 19 Jan 2022 09:09:49
- Publisher:
- CDS
- Description:
- We present ~120000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l~255{deg} and 110{deg}, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO data sets to take full advantage of Spitzer's spatial resolution and sensitivity in the mid-infrared ~3-9{mu}m range. Multiwavelength color/magnitude distributions provide intuition about how the classifier separates YSOs from other red IRAC sources and validate that the sample is consistent with expectations for disk/envelope-bearing pre-main-sequence stars. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample. Most of the candidates are in regions with mid-IR nebulosity, associated with star-forming clouds, but others appear distributed in the field. Using Gaia DR2 distance estimates, we find groups of YSO candidates associated with the Local Arm, the Sagittarius-Carina Arm, and the Scutum-Centaurus Arm. Candidate YSOs visible to the Zwicky Transient Facility tend to exhibit higher variability amplitudes than randomly selected field stars of the same magnitude, with many high-amplitude variables having light-curve morphologies characteristic of YSOs. Given that no current or planned instruments will significantly exceed IRAC's spatial resolution while possessing its wide-area mapping capabilities, Spitzer-based catalogs such as ours will remain the main resources for mid-infrared YSOs in the Galactic midplane for the near future.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/135
- Title:
- Gamma-ray bright blazars spectrophotometry
- Short Name:
- J/ApJ/789/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {gamma}-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 {gamma}-ray bright blazars over 4 years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their {gamma}-ray behavior. We derive {gamma}-ray, X-ray, and optical spectral indices, {alpha}_{gamma}_, {alpha}_X_, and {alpha}_o_, respectively (F_{nu}_{prop.to}{nu}^{alpha}^), and construct spectral energy distributions during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (1) significantly steeper {gamma}-ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (2) a small difference of {alpha}_X_ within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (3) a highly peaked distribution of X-ray spectral slopes of FSRQs at ~ -0.60, but a very broad distribution of {alpha}_X_of BL Lacs during active states; (4) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change of {alpha}_o_ of BL Lacs between states; and (5) a positive correlation between optical and {gamma}-ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/51
- Title:
- {gamma}-ray to IR study of the blazar CTA 102
- Short Name:
- J/ApJ/813/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright {gamma}-ray outburst detected by the Fermi Large Area Telescope in 2012 September-October when the source reached a flux of F_>100MeV_=5.2+/-0.4x10^-6^photons/cm2/s. At the same time, the source displayed an unprecedented optical and near-infrared (near-IR) outburst. We study the evolution of the parsec-scale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43GHz, covering the observing period from 2007 June to 2014 June. We find that the {gamma}-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful {gamma}-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight ({theta}~1.2{deg}) during the ejection of the knot and the {gamma}-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of electric vector position angles (EVPAs), which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the {gamma}-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of NIR to ultraviolet photons is the probable mechanism for the {gamma}-ray production.
- ID:
- ivo://CDS.VizieR/J/MNRAS/336/879
- Title:
- G and K dwarfs UBV(RI)c and ubvy photometry
- Short Name:
- J/MNRAS/336/879
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- K dwarfs have lifetimes older than the present age of the Galactic disc, and are thus ideal stars for investigating the chemical evolution of the disc. We have developed several photometric metallicity indicators for K dwarfs, based on a sample of accurate spectroscopic metallicities for 34 disc and halo G and K dwarfs. The photometric metallicities lead us to develop a metallicity index for K dwarfs based only on their position in the colour-absolute-magnitude diagram. Metallicities have been determined for 431 single K dwarfs drawn from the Hipparcos catalogue, selecting the stars by absolute magnitude and removing multiple systems. The sample is essentially a complete reckoning of the metal content in nearby K dwarfs. We use stellar isochrones to mark the stars by mass, and select a subset of 220 of the stars, which is complete within a narrow mass interval. We fit the data with a model of the chemical evolution of the solar cylinder. We find that only a modest cosmic scatter is required to fit our age-metallicity relation. The model assumes two main infall episodes for the formation of the halo-thick disc and thin disc, respectively. The new data confirm that the solar neighbourhood formed on a long time-scale of the order of 7Gyr.
- ID:
- ivo://CDS.VizieR/J/AJ/162/57
- Title:
- g- and Ks-band flux of K2-22 with LBT
- Short Name:
- J/AJ/162/57
- Date:
- 14 Mar 2022 06:59:12
- Publisher:
- CDS
- Description:
- The disintegrating planet candidate K2-22b shows periodic and stochastic transits best explained by an escaping debris cloud. However, the mechanism that creates the debris cloud is unknown. The grain size of the debris as well as its sublimation rate can be helpful in understanding the environment that disintegrates the planet. Here, we present simultaneous photometry with the g band at 0.48{mu}m and KS band at 2.1{mu}m using the Large Binocular Telescope. During an event with very low dust activity, we put a new upper limit on the size of the planet of 0.71R{Earth} or 4500km. We also detected a medium depth transit that can be used to constrain the dust particle sizes. We find that the median particle size must be larger than about 0.5-1.0{mu}m, depending on the composition of the debris. This leads to a high mass-loss rate of about 3x108kg/s, which is consistent with hydrodynamic escape models. If they are produced by some alternate mechanism such as explosive volcanism, it would require extraordinary geological activity. Combining our upper limits on the planet size with the high mass-loss rate, we find a lifetime of the planet of less than 370Myr. This drops to just 21Myr when adopting the 0.02M{Earth} mass predicted from hydrodynamical models.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A109
- Title:
- Gas kinematics of spiral galaxies
- Short Name:
- J/A+A/520/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We trace the interaction processes of galaxies at intermediate redshift by measuring the irregularity of their ionized gas kinematics, and investigate these irregularities as a function of the environment (cluster versus field) and of morphological type (spiral versus irregular). We obtain the gas velocity fields by placing three parallel and adjacent VLT/FORS2 slits on each galaxy. To quantify irregularities in the gas kinematics, we use three indicators: the standard deviation of the kinematic position angle ({sigma}_PA_), the mean deviation of the line of sight velocity profile from the cosine form which is measured using high order Fourier terms (k_3,5_/k_1_) and the average misalignment between the kinematical and photometric major axes ({Delta}{phi}). These indicators are then examined together with some photometric and structural parameters (measured from HST and FORS2 images in the optical) such as the disk scale length, rest-frame colors, asymmetry, concentration, Gini coefficient and M20 . Our sample consists of 92 distant galaxies. 16 cluster (z~0.3 and z~0.5) and 29 field galaxies (0.10<=z<=0.91, mean z=0.44) of these have velocity fields with sufficient signal to be analyzed. To compare our sample with the local universe, we also analyze a sample from the SINGS survey.
