- ID:
- ivo://CDS.VizieR/J/MNRAS/418/114
- Title:
- Opacity-sampling models of Mira variables
- Short Name:
- J/MNRAS/418/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present four model series of the CODEX dynamical opacity-sampling models of Mira variables with solar abundances, designed to have parameters similar to {omicron} Cet, R Leo and R Cas. We demonstrate that the CODEX models provide a clear physical basis for the molecular shell scenario used to explain interferometric observations of Mira variables. We show that these models generally provide a good match to photometry and interferometry at wavelengths between the near-infrared and the radio, and make the model outputs publicly available. These models also demonstrate that, in order to match visible and infrared observations, the Fe-poor silicate grains that form within 3 continuum radii must have small grain radii and therefore cannot drive the winds from O-rich Mira variables.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/733/L8
- Title:
- Optical and IR photometry of [KOS94] HA11
- Short Name:
- J/ApJ/733/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a long-term optical photometric and spectroscopic monitoring of the strongly variable, accreting young sun-like star [KOS94] HA11, associated with the dark cloud Lynds 1340 that exhibited large amplitude (5-6mag in the I_C_ band) brightness variations on 2-3 years timescales, flat spectral energy distribution (SED), and extremely strong (300<~EW/{AA}<~900) H{alpha} emission. In this Letter we describe the basic properties of the star, derived from our observations between 1999 and 2011, and put into context the observed phenomena. The observed variations in the emission spectra, near-infrared colors, and SED suggest that [KOS94] HA11 (spectral type: K7-M0) is an eruptive young star, possibly similar in nature to V1647 Ori: its large-scale photometric variations are governed by variable accretion rate, associated with variations in the inner disk structure. The star recently has undergone strong and rapid brightness variations, thus its further observations may offer a rare opportunity for studying structural and chemical rearrangements of the inner disk, induced by variable central luminosity.
- ID:
- ivo://CDS.VizieR/J/AJ/145/59
- Title:
- Optical and mid-IR photometry of PTF 10nvg
- Short Name:
- J/AJ/145/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report extensive new photometry and spectroscopy of the highly variable young stellar object PTF 10nvg (also known as IRAS 20496+4354 and V2492 Cyg), including optical and near-infrared time-series data as well as mid-infrared and millimeter data. Following the previously reported 2010 rise to R_PTF_<~13.5^m^ and subsequent fade, during 2011 and 2012 the source underwent additional episodes of brightening, followed by several magnitude dimming events including prolonged faint states at R_PTF_>~20^m^. The observed high-amplitude variations are largely consistent with extinction changes ({Delta}A_V_ up to 30mag) having a ~220day quasi-periodic signal. However, photometry measured when the source was near maximum brightness in mid-2010 as well as in late-2012 does not phase well to this period. Spectral evolution includes not only changes in the spectral slope but also correlated variation in the prominence of TiO/VO/CO bands and atomic line emission, as well as anti-correlated variation in forbidden line emission which, along with H_2_, dominates optical and infrared spectra at faint epochs. Notably, night-to-night variations in several forbidden doublet strengths and ratios are observed. High-dispersion spectra were obtained in a variety of photometric states and reveal time-variable line profiles. Neutral and singly ionized atomic species are likely formed in an accretion flow and/or impact while the origin of zero-velocity atomic LiI{lambda}6707 in emission is unknown. Forbidden lines, including several rare species, exhibit blueshifted emission profiles and likely arise from an outflow/jet. Several of these lines are also seen spatially offset from the continuum source position, presumably in a shocked region of an extended jet. Blueshifted absorption components of the NaI D doublet, KI{lambda}{lambda}7665,7669 doublet, and the OI 7774 triplet, as well as blueshifted absorption components seen against the broad H{alpha} and CaII triplet emission lines, similarly are formed in the outflow. CARMA maps resolve on larger scales a spatially extended outflow in millimeter-wavelength CO. We attribute the recently observed photometric and spectroscopic behavior to rotating circumstellar disk material located at separation a~0.7(M_*_/M_{sun}_)^1/3^AU from the continuum source, causing the semi-periodic dimming. Occultation of the central star as well as the bright inner disk and the accretion/outflow zones renders shocked gas in the inner part of the jet amenable to observation at the faint epochs. We discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or GM Cep) high-amplitude variability phenomena.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A42
- Title:
- Optical counterparts of ROSAT X-ray in 2 fields
- Short Name:
- J/A+A/575/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The optical identification of large number of X-ray sources such as those from the ROSAT All-Sky Survey is challenging with conventional spectroscopic follow-up observations. We investigate two ROSAT All-Sky Survey fields of size 10{deg}x10{deg} each, one at galactic latitude b=83{deg} (26 Com), the other at b=-5{deg} (gamma Sge), in order to optically identify the majority of sources. We used optical variability, among other more standard methods, as a means of identifying a large number of ROSAT All- Sky Survey sources. All objects fainter than about 12mag and brighter than about 17mag, in or near the error circle of the ROSAT positions, were tested for optical variability on hundreds of archival plates of the Sonneberg field patrol.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/431/779
- Title:
- Optical/near-IR atlas of OH/IR stars
- Short Name:
- J/A+A/431/779
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present optical and near-infrared finding charts, accurate astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS sources, 96% of those included in the so-called "Arecibo sample of OH/IR stars" (Eder et al., 1988ApJS...66..183E; Lewis et al., 1990ApJ...362..634L; Chengalur et al., 1993, Cat. <J/ApJS/89/189>). The main photometric properties of the stars in the sample are presented and discussed as well as the problems found during the process of identification of the optical/near-infrared counterparts. In addition, we also identify suitable reference stars in each field to be used for differential photometry purposes in the future.
- ID:
- ivo://CDS.VizieR/J/AZh/84/714
- Title:
- Optical spectral variability of BD+48 1220
- Short Name:
- J/AZh/84/714
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on high-resolution observations (R=60000 and 75000), we have studied the optical spectral variability of the star BD+48 1220, identified with the IR-source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 to 6760{AA}, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature Teff=7900K, surface gravity log g=0.0, microturbulence velocity xi_t_=6.0, and the abundances for 16 elements. The star's metallicity differs little from the solar value: [Fe/H]=-0.10dex. The main peculiarity of the chemical composition of the star is a large He-excess, derived from the HeI 5876{AA} absorption, [He/H]=+1.04, and the equally large O-excess, [O/Fe]=+0.72dex. The C-excess is small, [C/Fe]=+0.09dex, and the ratio [C/O]<=1. We obtained a revised relation for the light-metal abundances: [Na/Fe]=+0.87 with [Mg/Fe]=-0.31. The barium abundance is low, [Ba/Fe]=-0.84. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V_{sun}_=-(7-15)km/s. Time variable differential line shifts have been revealed. The entire set of available data (the luminosity Mv~-5mag, velocity V_lsr_~-20km/s, metallicity [Fe/H]=-0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD+48 1220 as a post-AGB star with He- and O-excesses belonging to the Galactic disk.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A88
- Title:
- Optical spectra of 12 Miras
- Short Name:
- J/A+A/531/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Miras are long-period variables thought to be in the asymptotic giant branch (AGB) phase of evolution. In about one percent of known Miras, the pulsation period is changing. It has been speculated that this changing period is the consequence of a recent thermal pulse in these stars. We aim to clarify the evolutionary state of these stars, and to determine in particular whether or not they are in the thermally-pulsing (TP-)AGB phase. One important piece of information that has been neglected so far when determining the evolutionary state is the presence of the radio-active s-process element technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio optical spectra of a dozen prominent Mira variables with changing pulsation period to search for this indicator of TPs and dredge-up. We also use the spectra to measure lithium (Li) abundances. Furthermore, we establish the evolutionary states of our sample stars by means of their present-day periods and luminosities. Among the twelve sample stars observed in this programme, five were found to show absorption lines of Tc. BH Cru is found to be a carbon-star, its period increase in the past decades possibly having stopped by now. We report a possible switch in the pulsation mode of T UMi from Mira-like to semi-regular variability in the past two years. R Nor, on the other hand, is probably a fairly massive AGB star, which could be true for all meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with properties very similar to the short-period, metal-poor Miras. We conclude that there is no clear correlation between period change type and Tc presence. The stars that are most likely to have experienced a recent TP are BH Cru and R Hya, although their rates of period change are quite different.
