- ID:
- ivo://CDS.VizieR/J/ApJ/900/11
- Title:
- Spectra of SN 2017eaw 545 & 900 days after explosion
- Short Name:
- J/ApJ/900/11
- Date:
- 14 Mar 2022 07:13:15
- Publisher:
- CDS
- Description:
- SN 2017eaw, the tenth supernova observed in NGC6946, was a normal Type II-P supernova with an estimated 11-13M{sun} red supergiant progenitor. Here we present nebular-phase spectra of SN 2017eaw at +545 and +900days post-max, extending approximately 50-400days past the epochs of previously published spectra. While the +545day spectrum is similar to spectra taken between days +400 and +493, the +900day spectrum shows dramatic changes both in spectral features and emission-line profiles. The H{alpha} emission is flat-topped and boxlike with sharp blue and red profile velocities of ~-8000 and +7500km/s. These late-time spectral changes indicate strong circumstellar interaction with a mass-loss shell, expelled ~1700yr before explosion. SN 2017eaw's +900day spectrum is similar to those seen for SN2004et and SN2013ej observed 2-3yr after explosion. We discuss the importance of late-time monitoring of bright SNeII-P and the nature of presupernova mass-loss events for SNII-P evolution.
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- ID:
- ivo://CDS.VizieR/J/A+A/414/699
- Title:
- Spectra of southern late-type dwarfs
- Short Name:
- J/A+A/414/699
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Echelle spectra of 91 late-type dwarfs, of spectral types from F to M and of different levels of chromospheric activity, obtained with the 2.15-m telescope of the CASLEO Observatory located in the Argentinean Andes. Our observations range from 3890 to 6690{AA}, at a spectral resolution from 0.141 to 0.249{AA} per pixel (R={lambda}/{delta}{lambda}~26400). The observations were flux calibrated with the aid of long slit spectra (R~1050-2070), also available.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/115
- Title:
- Spectra of 28 stars in Price-Whelan 1 association
- Short Name:
- J/ApJ/887/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report spectroscopic measurements of stars in the recently discovered young stellar association Price-Whelan 1 (PW1), which was found in the vicinity of the Leading Arm (LA) of the Magellanic Stream (MS). We obtained Magellan+MIKE high-resolution spectra of the 28 brightest stars in PW 1 and used The Cannon to determine their stellar parameters. We find that the mean metallicity of PW1 is [Fe/H]=-1.23 with a small scatter of 0.06dex and the mean RV is V_hel_=276.7km/s with a dispersion of 11.0km/s. Our results are consistent in T_eff_, logg, and [Fe/H] with the young and metal-poor characteristics (116Myr and [Fe/H]=-1.1) determined for PW1 from our discovery paper. We find a strong correlation between the spatial pattern of the PW1 stars and the LA II gas with an offset of -10.15{deg} in L_MS_ and +1.55{deg} in B_MS_. The similarity in metallicity, velocity, and spatial patterns indicates that PW1 likely originated in LA II. We find that the spatial and kinematic separation between LA II and PW1 can be explained by ram pressure from Milky Way (MW) gas. Using orbit integrations that account for the LMC and MW halo and outer disk gas, we constrain the halo gas density at the orbital pericenter of PW1 to be n_halo_(17kpc)=2.7_-2.0_^+3.4^x10^-3^atoms/cm^3^ and the disk gas density at the midplane at 20kpc to be n_disk_(20kpc,0)=6.0_-2.0_^+1.5^x10^-2^atoms/cm^3^. We, therefore, conclude that PW 1 formed from the LA II of the MS, making it a powerful constraint on the MW-Magellanic interaction.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A75
- Title:
- Spectra of 8 supergiants in nearby galaxies
- Short Name:
- J/A+A/562/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The role of episodic mass loss in massive star evolution is one of the outstanding questions of current stellar evolution theory. Episodic mass loss produces dust and therefore causes evolved massive stars to be very luminous in the mid-infrared and dim at optical wavelengths. We aim to increase the number of investigated luminous mid-IR sources to shed light on the late stages of these objects. To achieve this we explore mid-IR selection criteria to identity dusty evolved massive stars in two nearby galaxies. The method is based on mid-IR colors, using 3.6um and 4.5um photometry from archival Spitzer Space Telescope images of nearby galaxies and J-band from 2MASS. We apply our criteria to two nearby star-forming dwarf-irregular galaxies: Sextans A and IC 1613, selecting 8 targets, which we follow up with spectroscopy. Our spectral classification and analysis yielded the discovery of 2 M-type supergiants in IC 1613, 3 K-type supergiants and 1 candidate F-type giant in Sextans A, and 2 foreground M giants. We show that the proposed criteria provide an independent way for identifying dusty evolved massive stars, which can be extended to all nearby galaxies with available Spitzer/IRAC images at 3.6um and 4.5um.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A101
- Title:
- Spectra of 29 Swift/BAT optical counterparts
- Short Name:
- J/A+A/545/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Through an optical campaign performed at four telescopes located in the northern and the southern hemispheres, plus archival data from two on-line sky surveys, we obtained optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/Burst Alert Telescope (BAT) and listed in the 39 month Palermo catalogue. All these objects also have observations taken with Swift/X-ray Telescope (XRT) or XMM-European Photon Imaging Camera (EPIC) which not only allow us to pinpoint their optical counterpart, but also study their X-ray spectral properties (column density, power law photon index, and F2-10keV flux).
- ID:
- ivo://CDS.VizieR/J/ApJ/836/15
- Title:
- Spectra of the post-AGB star J005252.87-722842.9
- Short Name:
- J/ApJ/836/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Post-asymptotic giant branch (post-AGB) stars are known to be chemically diverse. In this paper we present the first observational evidence of a star that has failed the third dredge-up (TDU). J005252.87-722842.9 is an A-type (T_eff_=8250+/-250K) luminous (8200+/-700L_{sun}_) metal-poor ([Fe/H]=-1.18+/-0.10) low-mass (M_initial_~1.5-2.0M_{sun}_) post-AGB star in the Small Magellanic Cloud. Through a systematic abundance study, using high-resolution optical spectra from UVES, we found that this likely post-AGB object shows an intriguing photospheric composition with no confirmed carbon-enhancement (upper limit of [C/Fe]<0.50) nor enrichment of s-process elements. We derived an oxygen abundance of [O/Fe]=0.29+/-0.1. For Fe and O, we took the effects of nonlocal thermodynamic equilibrium into account. We could not derive an upper limit for the nitrogen abundance as there are no useful nitrogen lines within our spectral coverage. The chemical pattern displayed by this object has not been observed in single or binary post-AGBs. Based on its derived stellar parameters and inferred evolutionary state, single-star nucleosynthesis models predict that this star should have undergone TDU episodes while on the AGB, and it should be carbon enriched. However, our observations are in contrast with these predictions. We identify two possible Galactic analogs that are likely to be post-AGB stars, but the lack of accurate distances (hence luminosities) to these objects does not allow us to confirm their post-AGB status. If they have low luminosities, then they are likely to be dusty post-RGB stars. The discovery of J005252.87-722842.9 reveals a new stellar evolutionary channel whereby a star evolves without any TDU episodes.
- ID:
- ivo://CDS.VizieR/J/A+A/557/L6
- Title:
- Spectra of the Titan haze at 1-5 micron
- Short Name:
- J/A+A/557/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We retrieved optical-depth spectra of the Titanian haze in the range 1-5um from solar occultation data obtained by the Cassini/Visual Infrared Mapping Spectrometer (VIMS) at altitudes of 59-502km. Only limited wavelength intervals within this spectral range have been analyzed before. The haze spectra we retrieved are mostly similar to those of alkane particles (or powders), with three major absorption peaks typical of alkane powders at 2.3, 3.4, and 4.3um.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/1964
- Title:
- Spectra of three nearby star-forming regions
- Short Name:
- J/ApJ/703/1964
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1-2Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31um and the equivalent width of the 10um silicate emission feature to identify objects whose disk configuration departs from that of a continuous, optically thick accretion disk. Based on their medians and fraction of evolved disks, T Tauri stars in Taurus and Chamaeleon I are very alike.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A58
- Title:
- Spectra of two mid-L subdwarfs
- Short Name:
- J/A+A/579/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained low- to intermediate-resolution (R~2500-9000) optical (~560-770nm) spectra of two mid-L subdwarfs, SDSS J125637.13-022452.4 (SDSS1256; sdL3.5) and 2MASS J162620.14+392519.5 (2MASS1626; sdL4). We report the presence of a feature at the nominal position of the lithium absorption doublet at 6707.8{AA} in the spectrum of SDSS1256, with an equivalent width of 66+/-27{AA} at 2.4{sigma}, which we identify as arising from a CaH molecular transition based on atmosphere models. We do not see any feature at the position of the lithium feature in the spectrum of 2MASS1626. The existence of overlapping molecular absorption sets a confusion detection limit of [Li/H]=-3 for equivalently-typed L subdwarfs. We provided improved radial velocity measurements of -126+/-10km/s and -239+/-12km/s for SDSS1256 and 2MASS1626, respectively, as well as revised Galactic orbits. We implemented adjusting factors for the CaH molecule in combination with the NextGen atmosphere models to fit the optical spectrum of SDSS1256 in the 6200-7300{AA} range. We also estimate the expected Li abundance from interstellar accretion ([Li/H]=-5), place limits on circumstellar accretion (10^9^g/yr), and discuss the prospects of Li searches in cooler L and T subdwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A142
- Title:
- Spectra of 5 Type II supernovae
- Short Name:
- J/A+A/555/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Core-collapse Supernovae (CC-SNe) descend from progenitors more massive than about 8M_{sun}_. Because of the young age of the progenitors, the ejecta may eventually interact with the circumstellar medium (CSM) via highly energetic processes detectable in the radio, X-ray, ultraviolet (UV) and, sometimes, in the optical domains. In this paper we present ultraviolet, optical and near infrared observations of five type II SNe, namely SNe 2009dd, 2007pk, 2010aj, 1995ad, and 1996W. Together with few other SNe they form a group of moderately luminous type II events. We investigate the photometric similarities and differences among these bright objects. We also attempt to characterise them by analysing the spectral evolutions, in order to find some traces of CSM-ejecta interaction. We collected photometry and spectroscopy with several telescopes in order to construct well-sampled light curves and spectral evolutions from the photospheric to the nebular phases. Both photometry and spectroscopy indicate a degree of heterogeneity in this sample. Modelling the data of SNe 2009dd, 2010aj and 1995ad allows us to constrain the explosion parameters and the properties of the progenitor stars. The light curves have luminous peak magnitudes (-16.95<M_B}_-18.70). The ejected masses of ^56^Ni for three SNe span a wide range of values (2.8x10^-2^M_{sun}<M(^56^Ni)<1.4x10^-1^M_{sun}_), while for a fourth (SN2010aj) we could determine a stringent upper limit (7x10^-3^M_{sun}_). Clues of interaction, such as the presence of high velocity (HV) features of the Balmer lines, are visible in the photospheric spectra of SNe 2009dd and 1996W. For SN2007pk we observe a spectral transition from a type IIn to a standard type II SN. Modelling the observations of SNe 2009dd, 2010aj and 1995ad with radiation hydrodynamics codes, we infer kinetic plus thermal energies of about 0.2-0.5 foe, initial radii of 2-5x10^13^cm and ejected masses of ~5.0-9.5M_{sun}_. These values suggest moderate-mass, super-asymptotic giant branch (SAGB) or red super-giants (RSG) stars as SN precursors, in analogy with other luminous type IIP SNe 2007od and 2009bw.
