Our current understanding of radio-loud active galactic nuclei (AGN) comes predominantly from studies at frequencies of 5GHz and below. With the recent completion of the Australia Telescope 20GHz (AT20G) survey, we can now gain insight into the high-frequency radio properties of AGN. This paper presents supplementary information on the AT20G sources in the form of optical counterparts and redshifts. Optical counterparts were identified using the SuperCOSMOS data base and redshifts were found from either the 6dF Galaxy Survey or the literature. We also report 144 new redshifts. For AT20G sources outside the Galactic plane, 78.5% have optical identifications and 30.9% have redshift information. The optical identification rate also increases with increasing flux density. Targets which had optical spectra available were examined to obtain a spectral classification.
We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey operations. They show a general trend of slow luminosity rise lasting at least a few months. The subsequent major LRN outbursts were extensively followed in photometry and spectroscopy. The light curves present an initial short-duration peak, followed by a redder plateau phase. AT 2020kog is a moderately luminous event peaking at ~7x10^40^erg/s, while AT 2020hat is almost one order of magnitude fainter than AT 2020kog, although it is still more luminous than V838 Mon. In analogy with other LRNe, the spectra of AT 2020kog change significantly with time. They resemble those of type IIn supernovae at early phases, then they become similar to those of K-type stars during the plateau, and to M-type stars at very late phases. In contrast, AT 2020hat already shows a redder continuum at early epochs, and its spectrum shows the late appearance of molecular bands. A moderate-resolution spectrum of AT 2020hat taken at +37d after maximum shows a forest of narrow P Cygni lines of metals with velocities of 180 km/s, along with an Halpha emission with a full-width at half-maximum velocity of 250km/s. For AT 2020hat, a robust constraint on its quiescent progenitor is provided by archival images of the Hubble Space Telescope. The progenitor is clearly detected as a mid-K type star, with an absolute magnitude of M_F606W=-3.33+/-0.09mag and a colour of F606W-F814W=1.14+/-0.05mag, which are inconsistent with the expectations from a massive star that could later produce a core-collapse supernova. Although quite peculiar, the two objects nicely match the progenitor versus light curve absolute magnitude correlations discussed in the literature.
The rapidly increasing number of stellar spectra obtained by existing and future large-scale spectroscopic surveys feeds a demand for fast and efficient tools for the spectroscopic determination of fundamental stellar parameters. Such tools should not only comprise customized solutions for one particular survey or instrument, but, in order to enable cross-survey comparability, they should also be capable of dealing with spectra from a variety of spectrographs, resolutions, and wavelength coverages. To meet these ambitious specifications, we developed ATHOS (A Tool for HOmogenizing Stellar parameters), a fundamentally new analysis tool that adopts easy-to-use, computationally inexpensive analytical relations tying flux ratios (FRs) of designated wavelength regions in optical spectra to the stellar parameters effective temperature (Teff), iron abundance ([Fe/H]), and surface gravity (logg). Our Teff estimator is based on FRs from nine pairs of wavelength ranges around the Balmer lines H{beta} and H{alpha}, while for [Fe/H] and logg we provide 31 and 11 FRs, respectively, which are spread between ~4800{AA} and ~6500{AA}; a region covered by most optical surveys. The analytical relations employing these FRs were trained on N=124 real spectra of a stellar benchmark sample that covers a large parameter space of Teff~=4000 to 6500K (spectral types F to K), [Fe/H]~=-4.5 to 0.3dex, and logg~=1 to 5dex, which at the same time reflects ATHOS' range of applicability. We find accuracies of 97K for Teff, 0.16dex for [Fe/H], and 0.26dex for logg, which are merely bounded by finite uncertainties in the training sample parameters. ATHOS' internal precisions can be better by up to 70%. We tested ATHOS on six independent large surveys spanning a wide range of resolutions (R~=2000 to 52000), amongst which are the Gaia-ESO and the SDSS/SEGUE surveys. The exceptionally low execution time (<30ms per spectrum per CPU core) together with a comparison to the literature parameters showed that ATHOS can successfully achieve its main objectives, in other words fast stellar parametrization with cross-survey validity, high accuracy, and high precision. These are key to homogenize the output from future surveys, such as 4MOST or WEAVE.
The absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study support that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M_r_=13.93mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [CaII] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H{alpha} strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M_I_~8mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications.
The Asteroid Terrestrial-impact Last Alert System (ATLAS) observes most of the sky every night in search of dangerous asteroids. Its data are also used to search for photometric variability, where sensitivity to variability is limited by photometric accuracy. Since each exposure spans 7.6{deg} corner to corner, variations in atmospheric transparency in excess of 0.01mag are common, and 0.01mag photometry cannot be achieved by using a constant flat-field calibration image. We therefore have assembled an all-sky reference catalog of approximately one billion stars to m~19 from a variety of sources to calibrate each exposure's astrometry and photometry. Gaia DR2 is the source of astrometry for this ATLAS Refcat2. The sources of g, r, i, and z photometry include Pan-STARRS DR1, the ATLAS Pathfinder photometry project, ATLAS reflattened APASS data, SkyMapper DR1, APASS DR9, the Tycho-2 catalog, and the Yale Bright Star Catalog. We have attempted to make this catalog at least 99% complete to m<19, including the brightest stars in the sky. We believe that the systematic errors are no larger than 5mmag rms, although errors are as large as 20mmag in small patches near the Galactic plane.
Here we release the first version of the atlas and catalog of dark clouds derived by using the optical database Digitized Sky Survey I (DSS). Applying a traditional star-count technique to 1043 plates contained in DSS, we have produced an Av map covering the entire region in the galactic latitude range |b|=<40{deg}. The map was drawn at two different angular resolutions of 6' and 18', and is released in FITS format. Based on the Av map, we identified 2448 dark clouds and 2841 clumps located inside them. Physical parameters, such as the position, extent, and optical extinction, were measured for each of the clouds and clumps. We also searched for counterparts among already known dark clouds in the literature. The catalog of dark clouds presented here lists the cloud parameters as well as the counterparts. Printed version of the atlas and catalog was published in a special issue of Publications of the Astronomical Society of Japan (PASJ) in February 2005 (Dobashi et al., 2005, PASJ, 57, pp.S1-S386).
This paper presents an atlas and catalog of dark clouds derived based on the 2 Micron All Sky Survey Point Source Catalog (2MASS PSC). Color excess maps of E(J-H) and E(H-K_S_) as well as extinction maps of A_J_, A_H_, and A_K_S_ covering all of the sky have been produced at the 1' grid with a changing angular resolution (~1'-12'), depending on the regions in the sky. Maps drawn at the lower 15' grid with a fixed 1{deg} resolution were also derived for various sets of threshold magnitudes in the J, H, and K_S_ bands to estimate the background star colors and star densities needed to derive the color excess and extinction maps. The maps obtained in this work are presented on various scales in a series of figures that can be used as an atlas of dark clouds for general research purposes. On the basis of the E(J-H) and A_J_ maps drawn at the 1' grid, we have carried out a systematic survey for dark clouds all over the sky. In total, we identified 7614 dark clouds, and measured the coordinates, extents, and A_V_ values for each of them. We also searched for their counterparts in a previously published catalog of dark clouds based on the optical photographic plates DSS (Dobashi et al., 2005PASJ...57S...1D, Cat. VII/244). These cloud parameters, including the information of the counterparts, are compiled into a new catalog of dark clouds.
We present here the c-o colors for identified Flora, Vesta, Nysa-Polana, Themis, and Koronis family members within the historic data set (2015-2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C- and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c- and o-filters of these two families are used to demonstrate that the ATLAS c-o color is a sufficient parameter to distinguish between the C- and S-type taxonomies. The Vesta and Nysa-Polana families are known to display a mixture of taxonomies possibly due to Vesta's differentiated parent body origin and Nysa-Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.
The traditional knowledge of the mechanisms that caused the formation and evolution of early-type galaxies (ETG) in a hierarchical universe was challenged by the unexpected finding by ATLAS^3D^ that 86% of the ETGs show signs of a fast-rotating disk at their interior. This implies a common origin of most spiral galaxies, followed by a quenching phase, while only a minority of the most massive systems are slow rotators and were likely to be the products of merger events. Our aim is to improve our knowledge on the content and distribution of ionized hydrogen and their usage to form stars in a representative sample of ETGs for which the kinematics and detailed morphological classification were known from ATLAS^3D^. Methods. Using narrow-band filters centered on the redshifted H{alpha} line along with a broad-band (r-Gunn) filter to recover the stellar continuum, we observed or collected existing imaging observations for 147 ETGs (including members of the Virgo cluster) that are representative of the whole ATLAS3D survey. Fifty-five ETGs (37%) were detected in the H{alpha} line above our detection threshold, (EW(H{alpha})<=-1{AA}), and 21 harbor a strong source (EW(H{alpha})<=-5{AA}). The strong H{alpha} emitters appear associated with mostly low-mass (M*~10^10^M_{sun}_) S0 galaxies that contain conspicuous stellar and gaseous discs. These harbor significant star formation at their interior, including their nuclei. The weak H{alpha} emitters are almost one order of magnitude more massive, contain gas-poor discs and harbor an AGN at their centers. Their emissivity is dominated by [NII] and does not imply star formation. The 92 undetected ETGs constitute the majority in our sample and are gas-free systems that lack a disc and exhibit passive spectra even in their nuclei. These pieces of evidence reinforce the conclusion made previously that the evolution of ETGs followed the secular channel for the less massive systems and the dry merging channel for the most massive galaxies at the center of clusters of galaxies.
The ATLAS^3D^ project is a multiwavelength survey combined with a theoretical modelling effort. The observations span from the radio to the millimetre and optical, and provide multicolour imaging, two-dimensional kinematics of the atomic (HI), molecular (CO) and ionized gas (H{beta}, [OIII] and [NI]), together with the kinematics and population of the stars (H{beta}, Fe5015 and Mgb), for a carefully selected, volume-limited (1.16x10^5^Mpc^3^) sample of 260 early-type (elliptical E and lenticular S0) galaxies (ETGs). The models include semi-analytic, N-body binary mergers and cosmological simulations of galaxy formation. Here we present the science goals for the project and introduce the galaxy sample and the selection criteria. The sample consists of nearby (D<42Mpc, |DE-29{deg}|<35{deg}, |b|>15{deg}) morphologically selected ETGs extracted from a parent sample of 871 galaxies (8 per cent E, 22 per cent S0 and 70 per cent spirals) brighter than M_K_<-21.5mag (stellar mass M_*_>~6x10^9^M_{sun}_).
