Search

Start Over Subject spectroscopy Content Level Research
791. Follow-up photometry & spectroscopy of PTF14jg
ID:
ivo://CDS.VizieR/J/ApJ/874/82
Title:
Follow-up photometry & spectroscopy of PTF14jg
Short Name:
J/ApJ/874/82
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the outbursting source PTF 14jg, which, prior to the onset of its late 2013 eruption, was a faint, unstudied, and virtually uncataloged star. The salient features of the PTF 14jg outburst are (i) projected location near the W4 HII region and radial velocity consistent with physical association; (ii) a light curve that underwent an ~6-7mag optical (R-band) through mid-infrared (L-band) brightening on a timescale of a few months, peaked and then faded by ~3mag, but plateaued still >3.5mag above quiescence by ~8 months post-peak, lasting to at least 4yr after eruption; (iii) strong outflow signatures with velocities reaching -530km/s; (iv) a low-gravity and broad (~100-150km/s FWHM) optical absorption-line spectrum that systematically changes its spectral type with wavelength; (v) lithium; and (vi) ultraviolet and infrared excess. We tentatively identify the outburst as exhibiting characteristics of a young star FU Ori event. However, the burst would be unusually hot, with an absorption spectrum exhibiting high-excitation (~11000-15000K) lines in the optical and no evidence of CO in the near-infrared, in addition to exhibiting an unusual light curve. We thus also consider alternative scenarios-including various forms of novae, nuclear-burning instabilities, massive star events, and mergers-finding them all inferior to the atypically hot FU Ori star classification. The source eventually may be interpreted as a new category of young star outburst with a larger amplitude and shorter rise time than most FU Ori-like events.
792. Follow-up spectroscopy of Ly{alpha} 3<z<7 emitters
ID:
ivo://CDS.VizieR/J/ApJ/815/57
Title:
Follow-up spectroscopy of Ly{alpha} 3<z<7 emitters
Short Name:
J/ApJ/815/57
Date:
21 Oct 2021
Publisher:
CDS
Description:
We explore the relationship between the spectral shape of the Ly{alpha} emission and the UV morphology of the host galaxy using a sample of 304 Ly{alpha}-emitting BVi-dropouts at 3<z<7 in the Great Observatories Origins Deep Survey and Cosmic Evolution Survey fields. Using our extensive reservoir of high-quality Keck DEIMOS spectra combined with Hubble Space Telescope WFC3 data, we measure the Ly{alpha} line asymmetries for individual galaxies and compare them to axial ratios measured from observed J- and H-band (restframe UV) images. We find that the Ly{alpha} skewness exhibits a large scatter at small elongation (a/b<2), and this scatter decreases as the axial ratio increases. Comparison of this trend to radiative transfer models and various results from the literature suggests that these high-redshift Ly{alpha} emitters are not likely to be intrinsically round and symmetric disks, but they probably host galactic outflows traced by Ly{alpha} emitting clouds. The ionizing sources are centrally located, and the optical depth is a good indicator of the absorption and scattering events on the escape path of Ly{alpha} photons from the source. Our results find no evidence of evolution in Ly{alpha} asymmetry or axial ratio with look-back time.
793. Follow-up spectroscopy of SDSS changing-look QSOs
ID:
ivo://CDS.VizieR/J/ApJ/874/8
Title:
Follow-up spectroscopy of SDSS changing-look QSOs
Short Name:
J/ApJ/874/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, changing-look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow-line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full Sloan Digital Sky Survey (SDSS) footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude (|{Delta}g|>1mag, |{Delta}r|>0.5mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted signal-to-noise ratio threshold on variability of broad H{beta} emission, we find 17 new CLQs, yielding a confirmation rate of >~20%. These candidates are at lower Eddington ratio relative to the overall quasar population, which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420{AA} increases from 1.5 to 6. We release a catalog of more than 200 highly variable candidates to facilitate future CLQ searches.
794. Follow-up study of gal. & AGNs in z>1 clusters
ID:
ivo://CDS.VizieR/J/ApJ/825/72
Title:
Follow-up study of gal. & AGNs in z>1 clusters
Short Name:
J/ApJ/825/72
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed, multi-wavelength study of star formation (SF) and active galactic nucleus (AGN) activity in 11 near-infrared (IR) selected, spectroscopically confirmed massive (>~10^14^M_{sun}_) galaxy clusters at 1<z<1.75. Using new deep Herschel/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGNs through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs) and specific SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at z>~1.4 is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores (r<0.5Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by z~1. Enhanced SFRs are found in lower mass (10.1<logM_*_/M_{sun}_<10.8) cluster galaxies. We find significant variation in SF from cluster to cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGNs in clusters from z=0.5-2, finding an excess AGN fraction at z>~1, suggesting environmental triggering of AGNs during this epoch. We argue that our results --a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGNs-- are consistent with a co-evolution between SF and AGNs in clusters and an increased merger rate in massive halos at high redshift.
795. Foreground galaxies toward FRB 190608 from SDSS
ID:
ivo://CDS.VizieR/J/ApJ/901/134
Title:
Foreground galaxies toward FRB 190608 from SDSS
Short Name:
J/ApJ/901/134
Date:
21 Feb 2022 09:50:38
Publisher:
CDS
Description:
Fast radio burst (FRB) 190608 was detected by the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to a spiral galaxy at z_host_=0.11778 in the Sloan Digital Sky Survey (SDSS) footprint. The burst has a large dispersion measure (DM_FRB_=339.8pc/cm^3^) compared to the expected cosmic average at its redshift. It also has a large rotation measure (RM_FRB_=353rad/m^2^) and scattering timescale ({tau}=3.3ms at 1.28GHz). Chittidi+ (2021ApJ...922..173C) perform a detailed analysis of the ultraviolet and optical emission of the host galaxy and estimate the host DM contribution to be 110+/-37pc/cm^3^. This work complements theirs and reports the analysis of the optical data of galaxies in the foreground of FRB 190608 in order to explore their contributions to the FRB signal. Together, the two studies delineate an observationally driven, end-to-end study of matter distribution along an FRB sightline, the first study of its kind. Combining our Keck Cosmic Web Imager (KCWI) observations and public SDSS data, we estimate the expected cosmic dispersion measure DM_cosmic along the sightline to FRB 190608. We first estimate the contribution of hot, ionized gas in intervening virialized halos (DM_halos_~7-28pc/cm^3^). Then, using the Monte Carlo Physarum Machine methodology, we produce a 3D map of ionized gas in cosmic web filaments and compute the DM contribution from matter outside halos (DM_IGM_~91-126pc/cm^3^). This implies that a greater fraction of ionized gas along this sightline is extant outside virialized halos. We also investigate whether the intervening halos can account for the large FRB rotation measure and pulse width and conclude that it is implausible. Both the pulse broadening and the large Faraday rotation likely arise from the progenitor environment or the host galaxy.
796. Formamide detection with ASAI-IRAM
ID:
ivo://CDS.VizieR/J/MNRAS/449/2438
Title:
Formamide detection with ASAI-IRAM
Short Name:
J/MNRAS/449/2438
Date:
21 Oct 2021
Publisher:
CDS
Description:
Formamide (NH_2_CHO) has been proposed as a pre-biotic precursor with a key role in the emergence of life on Earth. While this molecule has been observed in space, most of its detections correspond to high-mass star-forming regions. Motivated by this lack of investigation in the low-mass regime, we searched for formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass pre-stellar and protostellar objects. The present work is part of the IRAM Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of unbiased broad-band spectral surveys at millimetre wavelengths. We detected HNCO in all the sources and NH_2_CHO in five of them. We derived their abundances and analysed them together with those reported in the literature for high-mass sources. For those sources with formamide detection, we found a tight and almost linear correlation between HNCO and NH_2_CHO abundances, with their ratio being roughly constant - between 3 and 10 - across 6 orders of magnitude in luminosity. This suggests the two species are chemically related. The sources without formamide detection, which are also the coldest and devoid of hot corinos, fall well off the correlation, displaying a much larger amount of HNCO relative to NH_2_CHO. Our results suggest that, while HNCO can be formed in the gas-phase during the cold stages of star formation, NH_2_CHO forms most efficiently on the mantles of dust grains at these temperatures, where it remains frozen until the temperature rises enough to sublimate the icy grain mantles. We propose hydrogenation of HNCO as a likely formation route leading to NH_2_CHO.
797. Formation of MW halo and its dwarf satellites
ID:
ivo://CDS.VizieR/J/A+A/604/A129
Title:
Formation of MW halo and its dwarf satellites
Short Name:
J/A+A/604/A129
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a homogeneous set of accurate atmospheric parameters for a complete sample of very and extremely metal-poor stars in the dwarf spheroidal galaxies (dSphs) Sculptor, Ursa Minor, Sextans, Fornax, Bootes I, Ursa Major II, and Leo IV. We also deliver a Milky Way (MW) comparison sample of giant stars covering the -4<[Fe/H]<-1.7 metallicity range. We show that, in the [Fe/H]=>-3.7 regime, the non-local thermodynamic equilibrium (NLTE) calculations with non-spectroscopic effective temperature (Teff) and surface gravity (log g) based on the photometric methods and known distance provide consistent abundances of the FeI and FeII lines. This justifies the FeI/FeII ionisation equilibrium method to determine log g for the MW halo giants with unknown distance. The atmospheric parameters of the dSphs and MW stars were checked with independent methods. In the [Fe/H]>-3.5 regime, the TiI/TiII ionisation equilibrium is fulfilled in the NLTE calculations. In the logg-Teff plane, all the stars sit on the giant branch of the evolutionary tracks corresponding to [Fe/H]=-2 to -4, in line with their metallicities. For some of the most metal-poor stars of our sample, we hardly achieve consistent NLTE abundances from the two ionisation stages for both iron and titanium. We suggest that this is a consequence of the uncertainty in the Teff-colour relation at those metallicities. The results of these work provide the base for a detailed abundance analysis presented in a companion paper.
798. FORS1 catalogue of stellar magnetic fields
ID:
ivo://CDS.VizieR/J/A+A/583/A115
Title:
FORS1 catalogue of stellar magnetic fields
Short Name:
J/A+A/583/A115
Date:
21 Oct 2021
Publisher:
CDS
Description:
The FORS1 instrument of the ESO Very Large Telescope was used to obtain low resolution circular polarized spectra of nearly a thousand of different stars, with the aim of measuring their mean longitudinal magnetic fields. Magnetic fields were measured by different authors, and using different methods and software tools. A catalogue of FORS1 magnetic measurements would provide a valuable resource with which to better understand the strengths and limitations of this instrument and of similar low-dispersion, Cassegrain spectropolarimeters. However, FORS1 data reduction has been carried out by a number of different groups using a variety of reduction and analysis techniques. Both our understanding of the instrument and our data reduction techniques have improved over time. A full re-analysis of FORS1 archive data using a consistent and fully documented algorithm would optimise the accuracy and usefulness of a catalogue of field measurements. Based on ESO FORS pipeline, we have developed a semi-automatic procedure for magnetic field determinations, which includes self-consistent checks for field detection reliability. We have applied our procedure to the full content of circular spectropolarimetric measurements of the FORS1 archive. We have produced a catalogue of spectro-polarimetric observations and magnetic field measurements for 1400 observations of 850 different objects. The spectral type of each object has been accurately classified. We have also been able to test different methods for data reduction is a systematic way. The resulting catalogue has been used to produce an estimator for an upper limit to the uncertainty in a field strength measurement of an early type star as a function of the signal-to-noise ratio of the observation. While FORS1 is not necessarily an optimal instrument for the discovery of weak magnetic fields, it is very useful for the systematic study of larger fields, such as those found in Ap/Bp stars and in white dwarfs.
799. FORS spectroscopy of HDFS galaxies
ID:
ivo://CDS.VizieR/J/A+A/440/61
Title:
FORS spectroscopy of HDFS galaxies
Short Name:
J/A+A/440/61
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present low resolution multi-object spectroscopy of an I-band magnitude limited (I_AB_~23-23.5) sample of galaxies located in an area centered on the Hubble Deep Field-South (HDFS). The observations were obtained using the Focal Reducer/low dispersion Spectrograph (FORS) on the ESO Very Large Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were supplemented with galaxies detected in the Infrared Space Observatory's survey of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100 galaxies for spectroscopic observations. Based on detections of several emission lines, such as [OII]3727, H{beta} and [OIII]5007, or of other spectroscopic features, we measured accurate redshifts for 50 objects in the central HDFS and flanking fields. The redshift range of the current sample of galaxies is 0.6-1.2, with a median redshift of 1.13 (at I~23.5 not corrected for completeness). The sample is dominated by starburst galaxies with only a small fraction of ellipticals (~10%). For the emission line objects, the extinction corrected [OII]3727 line strengths yield estimates of star formation rates in the range 0.5-30M_{sun}_/yr. We used the present data to derive the [OII]3727 luminosity function up to redshift of 1.2. When combined with [OII]3727 luminosity densities for the local and high redshift Universe, our results confirm the steep rise in the star formation rate (SFR) to z~1.3.
800. FORS2 transmission spectroscopy of WASP-17b
ID:
ivo://CDS.VizieR/J/A+A/596/A47
Title:
FORS2 transmission spectroscopy of WASP-17b
Short Name:
J/A+A/596/A47
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present FORS2 (attached to ESO's Very Large Telescope) observations of the exoplanet WASP-17b during its primary transit, for the purpose of differential spectrophotometry analysis. We use the instrument in its Mask eXchange Unit (MXU) mode to simultaneously obtain low resolution spectra of the planet hosting star, as well as several reference stars in the field of view. The integration of these spectra within broadband and smaller 100{AA} bins provides us with 'white' and spectrophotometric light curves, from 5700 to 8000{AA}. Through modelling the white light curve, we obtain refined bulk and transit parameters of the planet, as well as wavelength-dependent variations of the planetary radius from smaller spectral bins through which the transmission spectrum is obtained. The inference of transit parameters, as well as the noise statistics, is performed using a Gaussian Process model. We achieve a typical precision in the transit depth of a few hundred parts per million from various transit light curves. From the transmission spectra we rule out a flat spectrum at >3{sigma} and detect marginal presence of the pressure-broadened sodium wings. Furthermore, we detect the wing of the potassium absorption line in the upper atmosphere of the planet with 3-{sigma} confidence, both facts pointing to a relatively shallow temperature gradient in the atmosphere. These conclusions are mostly consistent with previous studies of this exo-atmosphere, although previous potassium measurements have been inconclusive.

Limit your search

more »

more »

more »

more »