- ID:
- ivo://CDS.VizieR/J/ApJS/99/173
- Title:
- Synthetic UV spectra of massive stars
- Short Name:
- J/ApJS/99/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An atlas of synthetic ultraviolet spectra of a population of massive stars is presented. The spectra are based on a stellar library of IUE high-dispersion spectra of O and Wolf-Rayet stars, coupled to an evolutionary synthesis code. Later spectral types are included via low-dispersion spectra. Line profiles of N V lambda 1240, Si IV lambda 1400, C IV lambda 1550, He II lambda 1640, and N IV lambda 1720 have been computed for star-formation histories and initial mass functions typically found in starburst regions. It is found that the lines are sensitive indicators for the presence or absence of massive stars. C IV lambda 1550 is the strongest stellar line in the ultraviolet spectrum of a typical starburst. If O stars with zero-age main-sequence masses above 50M_{sun}_ are present, C IV always shows a P Cygni profile. In the absence of such stars, only a blue-shifted absorption is present. During later epochs of the starburst, when late-O/early-B stars dominate, an unshifted photospheric absorption appears. Si IV lambda 1400 shows a conspicuous wind profile when luminous O supergiants are present. A strong P Cygni profile is found only for an instantaneous burst observed at 3 to 5Myr, which has a top-heavy IMF. The velocity of the blueshifted absorption is strongly correlated with the age and the upper cutoff mass (or slope) of the IMF. N V lambda 1240 traces the most massive stars and behaves rather similar to Si IV lambda 1400. Its usefulness as an indicator of very massive stars is limited due to the strong blending effect of the nearby Ly-alpha line. Nevertheless, strong N V lambda 1240 emission in a starburst suggests the presence of stars with masses in excess of 60M_{sun}_. He II lambda 1640 and N IV lambda 1720 are produced by very hot and luminous O and Wolf-Rayet stars. Both lines can have weak absorption or emission in a typical starburst but are predicted to be observable only under rare circumstances, such as in an instantaneous burst at t{approx.}3Myr. The profiles presented in the atlas can be compared to high-quality ultraviolet observations of galaxies with active star formation in order to constrain the massive star population. The atlas is published in its entirety in computer-readable form in the AAS CD-ROM series, Vol. 5.
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- ID:
- ivo://CDS.VizieR/J/A+A/650/A73
- Title:
- Synthetic XUV spectra of GJ 3470
- Short Name:
- J/A+A/650/A73
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Neptune-size exoplanets seem particularly sensitive to atmospheric evaporation, making it essential to characterize the stellar high-energy radiation that drives this mechanism. This is particularly important with M dwarfs, which emit a large and variable fraction of their luminosity in the ultraviolet and can display strong flaring behavior. The warm Neptune GJ 3470b, hosted by an M2 dwarf, was found to harbor a giant exosphere of neutral hydrogen thanks to three transits observed with the Hubble Space Telescope Imaging Spectrograph (HST/STIS). Here we report on three additional transit observations from the Panchromatic Comparative Exoplanet Treasury program, obtained with the HST Cosmic Origin Spectrograph. These data confirm the absorption signature from GJ 3470b's exosphere in the stellar Lyman-{alpha} line and demonstrate its stability over time. No planetary signatures are detected in other stellar lines, setting a 3{sigma} limit on GJ 3470b's far-ultraviolet (FUV) radius at 1.3 times its Roche lobe radius. We detect three flares from GJ 3470. They show different spectral energy distributions but peak consistently in the SiIII line, which traces intermediate-temperature layers in the transition region. These layers appear to play a particular role in GJ 3470's activity as emission lines that form at lower or higher temperatures than SiIII evolved differently over the long term. Based on the measured emission lines, we derive synthetic X-ray and extreme-ultraviolet (X+EUV, or XUV) spectra for the six observed quiescent phases, covering one year, as well as for the three flaring episodes. Our results suggest that most of GJ 3470's quiescent high-energy emission comes from the EUV domain, with flares amplifying the FUV emission more strongly. The neutral hydrogen photoionization lifetimes and mass loss derived for GJ 3470b show little variation over the epochs, in agreement with the stability of the exosphere. Simulations informed by our XUV spectra are required to understand the atmospheric structure and evolution of GJ 3470b and the role played by evaporation in the formation of the hot-Neptune desert.
- ID:
- ivo://CDS.VizieR/J/A+AS/110/553
- Title:
- Teff for B, A and F main sequence stars
- Short Name:
- J/A+AS/110/553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A method of determination of the effective temperature of B, A and F main sequence stars is proposed, using the slope of the continuum between 3200A and 3600A. We have determined the Balmer jump and the effective temperatures for 235 main sequence stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/728/70
- Title:
- The abundance of boron in diffuse clouds
- Short Name:
- J/ApJ/728/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive survey of boron abundances in diffuse interstellar clouds from observations made with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Space Telescope. Our sample of 56 Galactic sight lines is the result of a complete search of archival STIS data for the BII{lambda}1362 resonance line, with each detection confirmed by the presence of absorption from OI{lambda}1355, CuII{lambda}1358, and GaII{lambda}1414 (when available) at the same velocity. Five previous measurements of interstellar BII from Goddard High Resolution Spectrograph (GHRS) observations are incorporated in our analysis, yielding a combined sample that more than quadruples the number of sight lines with significant boron detections. Our survey also constitutes the first extensive analysis of interstellar gallium from STIS spectra and expands on previously published results for oxygen and copper. The observations probe both high- and low-density diffuse environments, allowing the density-dependent effects of interstellar depletion to be clearly identified in the gas-phase abundance data for each element.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A127
- Title:
- The C^+^ ion photofragment spectra
- Short Name:
- J/A+A/647/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon monoxide (CO) is one of the most abundant molecular species in comets. Its photodissociation by the solar radiation in the vacuum ultraviolet (VUV) region produces excited atomic fragments C(^1^D), C(^1^S), and O(^1^D), which radiate at characteristic wavelengths when they decay to lower states. The fractional rate constants for generating these fragments from CO photodissociation under the entire range of the solar radiation field are key input values in modelling the observed atomic emission intensities from comets. In this study, the branching ratios of the four lowest dissociation channels C(^3^P)+O(^3^P), C(^1^D)+O(^3^P), C(^3^P)+O(^1^D), and C(^1^S)+O(^3^P) of the ^12^C^16^O photodissociation are measured in the VUV energy range between the threshold of producing the C(^1^S)+O(^3^P) channel (~110500cm^-1^) and the ionisation energy (IE) of ^12^C^16^O (~113045cm^-1^). We measured these ratios using the VUV time-slice velocity-map ion imaging apparatus. We observe a number of high Rydberg states in the aforementioned energy range, with most of them mainly producing ground C(^3^P) and O(^3^P) atomic fragments, and only a few of them producing a significant amount of excited C(^1^D) or O(^1^D) fragments. We also observe the excited C(^1^S) fragment from CO photodissociation and measured its branching ratio for the first time. Based on the photodissociation branching ratios measured in the current and previous studies, we are able to estimate the relative percentages of the excited atomic fragments C(^1^D), C(^1^S), and O(^1^D) from the solar photolysis of ^12^C^16^O below its IE. We discuss the implications for the photochemical modelling of the CO-dominated comet C/2016 R2 (Pan-STARRS).
- ID:
- ivo://CDS.VizieR/J/ApJ/872/81
- Title:
- The COS CGM Compendium (CCC). II. Lyman limit syst.
- Short Name:
- J/ApJ/872/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from our COS circumgalactic medium (CGM) compendium (CCC), a survey of the CGM at z<~1 using HI-selected absorbers with 15<logN_HI_<19. We focus here on 82 partial Lyman limit systems (pLLSs, 16.2<=logN_HI_<17.2) and 29 LLSs (17.2<=logN_HI_<19). Using Bayesian techniques and Markov Chain Monte Carlo sampling of a grid of photoionization models, we derive the posterior probability distribution functions (PDFs) for the metallicity of each absorber in CCC. We show that the combined pLLS metallicity PDF at z<~1 has two main peaks at [X/H]~-1.7 and -0.4, with a strong dip at [X/H]~-1. The metallicity PDF of the LLSs might be more complicated than a unimodal or bimodal distribution. The pLLSs and LLSs probe a similar range of metallicities -3<~[X/H]<~+0.4, but the fraction of very metal-poor absorbers with [X/H]<~-1.4 is much larger for the pLLSs than the LLSs. In contrast, absorbers with logN_HI_>=19 have mostly -1<~[X/H]<~0 at z<~1. The metal-enriched gas probed by pLLSs and LLSs confirms that galaxies that have been enriching their CGM over billions of years. Surprisingly, despite this enrichment, there is also abundant metal-poor CGM gas (41%-59% of the pLLSs have [X/H]<~-1.4), representing a reservoir of near-pristine gas around z<~1 galaxies. We compare our empirical results to recent cosmological zoom simulations, finding some discrepancies, including an overabundance of metal- enriched CGM gas in simulations.
- ID:
- ivo://CDS.VizieR/J/ApJ/866/33
- Title:
- The COS CGM compendium. I. Initial results
- Short Name:
- J/ApJ/866/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15<logN_HI_<19 at z<~1 using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity distribution of these absorbers. Our sample consists of 224 absorbers selected on the basis of their HI absorption strength. Here we discuss the properties of our survey and the immediate empirical results. We find singly and doubly ionized metal species, and HI typically have similar velocity profiles, implying they probe gas in the same or similar environments. The ionic ratios (e.g., N_CII_/N_CIII_, N_OI_/N_CII_) indicate that the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled N_HI_ range. The Doppler parameters of the HI imply T<~5x10^4^K on average, consistent with the gas being photoionized. The MgII column densities span >2 orders of magnitude at any given N_HI_, indicating a wide range of metallicities (from solar to <1/100 solar). In the range of 16.2<~logN_HI_<~17, there is a gap in the N_MgII_ distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying that truly pristine gas at z<~1 is uncommon. We find <[FeII/MgII]>=-0.4+/-0.3, and since {alpha}-enhancement can affect this ratio, dust depletion is extremely mild.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/163
- Title:
- The first Swift UV-Opt GRB afterglow catalog
- Short Name:
- J/ApJ/690/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first Swift Ultraviolet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog. The catalog contains data from over 64000 independent UVOT image observations of 229 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The catalog covers GRBs occurring during the period from 2005 January 17 to 2007 June 16 and includes ~86% of the bursts detected by the Swift Burst Alert Telescope (BAT). The catalog provides detailed burst positional, temporal, and photometric information extracted from each of the UVOT images. Positions for bursts detected at the 3{sigma} level are provided with a nominal accuracy, relative to the USNO-B1 catalog, of ~0.25". Photometry for each burst is given in three UV bands, three optical bands, and a "white" or open filter. Upper limits for magnitudes are reported for sources detected below 3{sigma}. General properties of the burst sample and light curves, including the filter-dependent temporal slopes, are also provided.
- ID:
- ivo://CDS.VizieR/VI/129
- Title:
- The FUSE Observation Log
- Short Name:
- VI/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Funded by NASA as part of its Origins program, FUSE was developed in collaboration with the space agencies of Canada and France, and is being operated for NASA by the Johns Hopkins University. FUSE was launched into orbit aboard a Delta II rocket on June 24, 1999 for at least three years of operations. FUSE (Far Ultraviolet Spectroscopic Explorer) provides spectra in the far ultraviolet portion of the electromagnetic spectrum (range 905-1180 Angstroems, or 90.5-118nm) with a high resolution of about 20000 (one point each 5pm).
- ID:
- ivo://CDS.VizieR/J/A+A/579/A29
- Title:
- The GUViCS FUV diffuse emission
- Short Name:
- J/A+A/579/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Virgo direction has been observed at many wavelengths in recent years, in particular in the ultraviolet with GALEX. The far ultraviolet (FUV) diffuse light detected by GALEX offers interesting information on the large scale distribution of Galactic dust, owing to the GALEX FUV band sensitivity and resolution. We aim to characterise the ultraviolet large scale distribution of diffuse emission in the Virgo direction. A map of this emission may become useful for various studies by identifying regions where dust affects observations by either scattering light or absorbing radiation.
