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1901. Optical and UV follow-up of 1ES 1927+654
ID:
ivo://CDS.VizieR/J/ApJ/883/94
Title:
Optical and UV follow-up of 1ES 1927+654
Short Name:
J/ApJ/883/94
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the sudden optical and ultraviolet (UV) brightening of 1ES1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of "true Type-2" AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broadline emission region in (persistent) broadline AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., CIV{lambda}1549, CIII]{lambda}1909, MgII{lambda}2798), probably owing to dust in the broadline emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broadline emission of a "changing look" AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication.
1902. Optical and UV Spectrum of KQ Pup
ID:
ivo://CDS.VizieR/J/A+AS/92/685
Title:
Optical and UV Spectrum of KQ Pup
Short Name:
J/A+AS/92/685
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
1903. Optical chromospheric activity of V711 Tau
ID:
ivo://CDS.VizieR/J/MNRAS/449/1380
Title:
Optical chromospheric activity of V711 Tau
Short Name:
J/MNRAS/449/1380
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present long-term high-resolution spectroscopic observations of the very active RS Canum Venaticorum-type star V711 Tau, obtained during several observing runs from 1998 to 2004, and study its chromospheric activity. Using the spectral subtraction technique, several optical chromospheric activity indicators [including the He I D_3_, Na I D_1_, D_2_, H{alpha} and Ca II infrared triplet (IRT) lines] formed at different atmospheric heights are analysed. Strong chromospheric emission supports earlier results that indicate that V711 Tau is a very active system. Two large optical flares were detected during our observations. The results suggest that the main part of chromospheric emission is attributed to the primary star of the system. The secondary also presents weak emission but is less active. The ratios of EW_8542_/EW_8498_ indicate that CaII IRT emission arises predominantly from plage-like regions. We have found rotational modulation of chromospheric activity in the H{alpha} and CaII IRT lines, which suggests the presence of the chromospheric active longitudes over the surface of V711 Tau. Two active longitudes separated by about 180{deg} were observed to dominate the activity, and the so-called flip-flop phenomenon was seen during our observations. Moreover, the chromospheric activity level shows a long-term variation that gradually increases from a deep minimum near the year 2002. A close spatial connection of photospheric spots and chromospheric active regions in both short and long timescales was found for V711 Tau.
1904. Optical classification of southern ULIRGs
ID:
ivo://CDS.VizieR/J/MNRAS/414/702
Title:
Optical classification of southern ULIRGs
Short Name:
J/MNRAS/414/702
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the optical spectral properties of 115 ultraluminous infrared galaxies (ULIRGs) in the southern sky. Using the optical spectra obtained at the Cerro Tololo Inter-American Observatory (CTIO) 4m telescope and provided by the Two-degree Field (2dF) Galaxy Redshift Survey and the Six-degree Field (6dF) Galaxy Survey, we measure emission linewidths and fluxes for spectral classification.
1905. Optical constants of H_2_O-ice
ID:
ivo://CDS.VizieR/J/ApJ/701/1347
Title:
Optical constants of H_2_O-ice
Short Name:
J/ApJ/701/1347
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using new laboratory spectra, we have calculated the real and imaginary parts of the index of refraction of amorphous and crystalline H_2_O-ice from 20-150K in the wavelength range 2.5-22um (4000-455cm^-1^) and joined these results with previous measurement from 1.25 to 2.5um. These optical constants improve on previous measurements by having better temperature and spectral resolution and can be used to create model spectra for comparison to spectra of solar system objects and interstellar materials. In this wavelength range, the infrared band shapes and positions of amorphous H_2_O-ice are strongly dependent on deposition temperature. Amorphous and crystalline H_2_O-ice have distinctive spectral bands at all wavelengths in this region with bands weakening and shifting to shorter wavelength in amorphous H_2_O-ice compared to crystalline H_2_O-ice. Some notable exceptions are the band near 6um, which is stronger in amorphous H2O-ice, and the bands near 4.5um and 12.5um, which shift to longer wavelength in amorphous H_2_O-ice.
1906. Optical depths in 19 QSOs
ID:
ivo://CDS.VizieR/J/ApJ/596/768
Title:
Optical depths in 19 QSOs
Short Name:
J/ApJ/596/768
Date:
21 Oct 2021
Publisher:
CDS
Description:
We measure the distribution of carbon in the intergalactic medium as a function of redshift z and overdensity {delta}. Using a hydrodynamical simulation to link the H I absorption to the density and temperature of the absorbing gas, and a model for the UV background radiation, we convert ratios of C IV to H I pixel optical depths into carbon abundances. For the median metallicity this technique was described and tested in Paper I (Aguirre et al., 2002ApJ...576....1A) of this series. Here we generalize it to reconstruct the full probability distribution of the carbon abundance and apply it to 19 high-quality quasar absorption spectra.
1907. Optical follow-up of ASAS-SN M dwarf flares
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.
1908. Optical imaging and spectra of 3C 58
ID:
ivo://CDS.VizieR/J/ApJS/174/379
Title:
Optical imaging and spectra of 3C 58
Short Name:
J/ApJS/174/379
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive imaging and spectroscopic survey of optical emission knots associated with the young Galactic supernova remnant 3C 58. H{alpha} images show hundreds of clumpy filaments and knots arranged in a complex structure covering a nearly circular area roughly 400" in diameter. A quite different emission structure is seen in [OIII], where the brightest features are less clumpy and largely confined to the remnant's northwest quadrant. Measured radial velocities of over 450 knots reveal two distinct kinematic populations; one with average and peak expansion velocities of 770 and 1100km/s, respectively, forming a thick shell, and the other showing |v|<=250km/s. High-velocity knots (|v|>=500km/s) exhibit a strong bipolar expansion pattern with redshifted and blueshifted knots located in northeastern and southwestern regions, respectively. These knots also show strong [NII]/H{alpha} line emission ratios, suggesting enhanced N/H. In contrast, the slower expanding knot population shows much lower [NII]/H{alpha} line ratios and likely represents circumstellar mass loss material from the 3C 58 progenitor. Proper-motion estimates using images spanning a 28yr time interval suggest positional shifts of between 0.5" and 2.0", implying proper motions of 0.02-0.07"/yr. These values agree with previous estimates but are much less than the ~0.2"/yr expected if 3C 58 were associated with historic guest star of 1181 CE.
1909. Optical LCs & spectrum of the RCB star ZTF18abhjrcf
ID:
ivo://CDS.VizieR/J/AJ/159/61
Title:
Optical LCs & spectrum of the RCB star ZTF18abhjrcf
Short Name:
J/AJ/159/61
Date:
07 Mar 2022 07:17:25
Publisher:
CDS
Description:
R Coronae Borealis stars (RCBs) constitute a rare class of stars that are hydrogen depleted and carbon enriched, possibly from white dwarf mergers. RCBs are identified by their stochastic dimming with photometric variations of as much as eight magnitudes. Hence, the discoveries of RCBs were heavily biased to the limited regions monitored by long-term microlensing experiments. However, recent studies of galactic RCBs have shown that they exhibit distinct mid-infrared colors originating from their cool circumstellar shells. The all-sky Wide-field Infrared Survey Explorer (WISE) survey thus facilitates the identification of RCB candidates. Therefore, combining the WISE colors with large-area time-domain surveys will enable us to discover more RCBs. Here we present the results of a first attempt to identify RCBs in the public Zwicky Transient Facility (ZTF) alert stream, using the alert broker ANTARES. We identify a candidate RCB using the infrared color selection by Tisserand+, 2013A&A...551A..77T and large light curve variations in the optical from ZTF. We then conduct subsequent observations using the FLOYDS spectrograph at the Las Cumbres Observatory and confirm ZTF18abhjrcf as a bona fide RCB. This demonstrates the potential to discover uncharted RCBs as ZTF and other time-domain surveys continue to operate.
1910. Optically thin CIII absorbers at z~2.5
ID:
ivo://CDS.VizieR/J/MNRAS/456/3509
Title:
Optically thin CIII absorbers at z~2.5
Short Name:
J/MNRAS/456/3509
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the Voigt profile analysis of 132 intervening CIV+CIII components associated with optically thin HI absorbers at 2.1<z<3.4 in the 19 high-quality UVES/VLT and HIRES/Keck QSO spectra. For logN_CIV_ in [11.7, 14.1], N_CIII_{propto}N_CIV_^1.42+/-0.11^ and <N_CIII}/N_CIV>=1.0+/-0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at logN_HI_ in [12.2, 16.0] and logN_CIV_ in [11.8, 13.8], the gas temperature T_b_ estimated from absorption line widths is well approximated to a Gaussian peaking at logT_b_~4.4+/-0.3 for logT_b_ in [3.5, 5.5], with a negligible non-thermal contribution. For 32 of 54 tied HI+CIV pairs, also tied with CIII at logN_CIII_ in [11.7, 13.8], we ran both photoionization equilibrium (PIE) and non-PIE (using a fixed temperature T_b_) cloudy models for the Haardt-Madau QSOs+galaxies 2012 UV background. We find evidence of bimodality in observed and derived physical properties. High-metallicity branch absorbers have a carbon abundance [C/H]temp>=-1.0, a line-of-sight length L_temp_<=20kpc and a total (neutral and ionized) hydrogen volume density logn_H,temp_ in [-4.5, -3.3] and logT_b_ in [3.9, 4.5]. Low-metallicity branch absorbers have [C/H]temp<=-1.0, L_temp_ in [20, 480]kpc and logn_H,temp_ in [-5.2, -4.3] and logT_b_~ 4.5. High-metallicity branch absorbers seem to be originated from extended discs, inner haloes or outflowing gas of intervening galaxies, while low-metallicity absorbers are produced by galactic haloes or the surrounding intergalactic medium filament.

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