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Start Over Subject ultraviolet astronomy
191. HST far-UV survey of H2 emission of T Tau stars
ID:
ivo://CDS.VizieR/J/ApJ/756/171
Title:
HST far-UV survey of H2 emission of T Tau stars
Short Name:
J/ApJ/756/171
Date:
21 Oct 2021
Publisher:
CDS
Description:
The formation timescale and final architecture of exoplanetary systems are closely related to the properties of the molecular disks from which they form. Observations of the spatial distribution and lifetime of the molecular gas at planet-forming radii (a<10AU) are important for understanding the formation and evolution of exoplanetary systems. Toward this end, we present the largest spectrally resolved survey of H_2_ emission around low-mass pre-main-sequence stars compiled to date. We use a combination of new and archival far-ultraviolet spectra from the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph instruments on the Hubble Space Telescope to sample 34 T Tauri stars (27 actively accreting Classical T Tauri Stars and 7 non-accreting Weak-lined T Tauri Stars) with ages ranging from ~1 to 10Myr. We observe fluorescent H_2_emission, excited by Ly{alpha} photons, in 100% of the accreting sources, including all of the transitional disks in our sample (CS Cha, DM Tau, GM Aur, UX Tau A, LkCa 15, HD 135344B, and TW Hya). The spatial distribution of the emitting gas is inferred from spectrally resolved H_2_ line profiles. Some of the emitting gas is produced in outflowing material, but the majority of H_2_ emission appears to originate in a rotating disk. For the disk-dominated targets, the H_2_ emission originates predominately at a<~3AU. The emission line widths and inner molecular radii are found to be roughly consistent with those measured from mid-IR CO spectra.
192. HST FOS spectral atlas
ID:
ivo://CDS.VizieR/J/ApJS/140/143
Title:
HST FOS spectral atlas
Short Name:
J/ApJS/140/143
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyzed the absorption line spectra of all quasars observed with the high-resolution gratings of the Faint Object Spectrograph on board the Hubble Space Telescope. We examined 788 spectra for 334 quasars and present line lists and identifications of absorption lines in the spectra of 271 of them. Analysis of the statistics of the Ly{alpha} and metal absorption systems are presented in companion papers. The data and several analysis products are available on the authors' Web site, http://lithops.as.arizona.edu/~jill/QuasarSpectra .
193. HST & Keck spectroscopy of bright CEMP-s stars
ID:
ivo://CDS.VizieR/J/ApJ/812/109
Title:
HST & Keck spectroscopy of bright CEMP-s stars
Short Name:
J/ApJ/812/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD 196944 (V=8.40, [Fe/H]=-2.41) and HD 201626 (V=8.16, [Fe/H]=-1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. HD 196944 has been well-studied in the optical region, but we add abundance results for six species (Ge, Nb, Mo, Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide the first determination of its orbital period, P=1325 days. HD 201626 has only a limited number of abundance results based on previous optical work --here we add five new species from the NUV, including Pb. We compare these results with models of binary-system evolution and s-process element production in stars on the asymptotic giant branch, with the goal of explaining their origin and evolution. Our best-fitting models for HD 196944 (M_1,i_=0.9M_{sun}_, M_2,i_=0.86M_{sun}_, for [Fe/H]=-2.2), and HD 201626 (M_1,i_=0.9M_{sun}_, M_2,i_=0.76M_{sun}_ for [Fe/H]=-2.2; M_1,i_=1.6M_{sun}_, M_2,i_=0.59M_{sun}_ for [Fe/H]=-1.5) are consistent with the current accepted scenario for the formation of CEMP-s stars.
194. HST observations of carbon in spiral galaxies
ID:
ivo://CDS.VizieR/J/ApJ/513/168
Title:
HST observations of carbon in spiral galaxies
Short Name:
J/ApJ/513/168
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present measurements of the gas-phase abundance ratio C/O in six H II regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope. The ratios of C to O increase systematically with O/H in both galaxies, from log(C/O){~=}-0.8 at log(O/H){~=}-4.0 to log(C/O){~=}-0.1 at log(O/H){~=}-3.4. C/N shows no correlation with O/H. The rate of increase of C/O is somewhat uncertain because of uncertainty as to the appropriate UV reddening law and uncertainty in the metallicity dependence on grain depletions. However, the trend of increasing C/O with O/H is clear, confirming and extending the trend in C/O indicated previously from observations of irregular galaxies. Our data indicate that the radial gradients in C/H across spiral galaxies are steeper than the gradients in O/H. Comparing the data to chemical-evolution models for spiral galaxies shows that models in which the massive star yields do not vary with metallicity predict radial C/O gradients that are much flatter than the observed gradients.
195. HST observations of QSOs with medium spectra
ID:
ivo://CDS.VizieR/J/ApJ/818/113
Title:
HST observations of QSOs with medium spectra
Short Name:
J/ApJ/818/113
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly{alpha} absorbers (DLAs) at low redshift (z<1.6). Our statistical sample includes 463 quasars with spectral coverage spanning a total redshift path {Delta}z=123.3 or an absorption path {Delta}X=229.7. Within this survey path, we identify 4 DLAs defined as absorbers with HI column density N_HI_>=10^20.3^/cm2, which implies an incidence per absorption length lDLA(X)=0.017_-0.008_^+0.014^ at a median survey path redshift of z=0.623. While our estimate of l_DLA_(X) is lower than earlier estimates at z~0 from HI 21cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the N_HI_ frequency distribution function f(N_HI_,X), but the observed distribution agrees with previous estimates at z>2. Adopting the z>2 shape of f(N_HI_, X), we infer an HI mass density at z~0.6 of {rho}_HI_^DLA^=0.25_-0.12_^+0.20^. This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z HI 21cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10Gyr.
196. HST photometry in 6 dwarf galaxies
ID:
ivo://CDS.VizieR/J/AJ/143/74
Title:
HST photometry in 6 dwarf galaxies
Short Name:
J/AJ/143/74
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to IR to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 10^7^ years in Sextans A, Sextans B, NGC 6822, and WLM, ~10^8^yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of ~3 between Sextans A, WLM, and Sextans B, which have similar M_V_. Extinction properties are also derived.
197. HST QSO Catalog
ID:
ivo://CDS.VizieR/J/ApJ/736/42
Title:
HST QSO Catalog
Short Name:
J/ApJ/736/42
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a survey for optically thick Lyman limit absorbers at z<2.6 using archival Hubble Space Telescope observations with the Faint Object Spectrograph and Space Telescope Imaging Spectrograph. We identify 206 Lyman limit systems (LLSs), increasing the number of cataloged LLSs at z<2.6 by a factor of ~10.
198. HST spectral light curve of HAT-P-41
ID:
ivo://CDS.VizieR/J/AJ/161/51
Title:
HST spectral light curve of HAT-P-41
Short Name:
J/AJ/161/51
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive analysis of the 0.3-5{mu}m transit spectrum for the inflated hot Jupiter HAT-P-41b. The planet was observed in transit with Hubble STIS and WFC3 as part of the Hubble Panchromatic Comparative Exoplanet Treasury (PanCET) program, and we combine those data with warm Spitzer transit observations. We extract transit depths from each of the data sets, presenting the STIS transit spectrum (0.29-0.93{mu}m) for the first time. We retrieve the transit spectrum both with a free-chemistry retrieval suite (AURA) and a complementary chemical equilibrium retrieval suite (PLATON) to constrain the atmospheric properties at the day-night terminator. Both methods provide an excellent fit to the observed spectrum. Both AURA and PLATON retrieve a metal-rich atmosphere for almost all model assumptions (most likely O/H ratio of log_10_Z/Z{odot}=1.46_-0.68_^+0.53^ and log_10_Z/Z{odot}=2.33_-0.25_^+0.23^, respectively); this is driven by a 4.9{sigma} detection of H_2_O as well as evidence of gas absorption in the optical (>2.7{sigma} detection) due to Na, AlO, and/or VO/TiO, though no individual species is strongly detected. Both retrievals determine the transit spectrum to be consistent with a clear atmosphere, with no evidence of haze or high-altitude clouds. Interior modeling constraints on the maximum atmospheric metallicity (log_10_Z/Z{odot}<1.7) favor the AURA results. The inferred elemental oxygen abundance suggests that HAT-P-41b has one of the most metal-rich atmospheres of any hot Jupiters known to date. Overall, the inferred high metallicity and high inflation make HAT-P-41b an interesting test case for planet formation theories.
199. HST/STIS FUV spectra of K2-18
ID:
ivo://CDS.VizieR/J/A+A/634/L4
Title:
HST/STIS FUV spectra of K2-18
Short Name:
J/A+A/634/L4
Date:
21 Oct 2021
Publisher:
CDS
Description:
K2-18 b is a transiting mini-Neptune that orbits a nearby (38pc), cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-{alpha} transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of fluxes of the stellar Lyman-{alpha} emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by 67%+/-18% during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-{alpha} emission of K2-18, we estimate an EUV irradiation in the range 10^1^-10^2^erg/s/cm^2^ and a total escape rate on the order of 10^8^g/s. The inferred escape rate suggests that the planet will lose only a small fraction (<1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption, and better assess the atmospheric escape and high-energy environment of K2-18 b.
200. HST/STIS near-UV spectrum of {eta} Telescopii
ID:
ivo://CDS.VizieR/J/AJ/162/235
Title:
HST/STIS near-UV spectrum of {eta} Telescopii
Short Name:
J/AJ/162/235
Date:
14 Mar 2022 07:38:34
Publisher:
CDS
Description:
We present far- and near-ultraviolet absorption spectroscopy of the ~23Myr edge-on debris disk surrounding the A0V star {eta}Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from CI, CII, OI, MgII, AlII, SiII, SII, MnII, FeII, and marginally NI. The lines show two clear absorption components at -22.7{+/-}0.5km/s and -17.8{+/-}0.7km/s, which we attribute to circumstellar (CS) and interstellar gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by -16.9{+/-}2.6km/s in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the {eta}Tel CS gas is significantly higher than the solar ratio, as is the case in the {beta}Pic and 49Cet debris disks. Unlike those disks, however, the measured C/O ratio in the {eta}Tel CS gas is consistent with the solar value. Our analysis shows that because {eta}Tel is an earlier type star than {beta}Pic and 49Cet, with more substantial radiation pressure at the dominant CII transitions, this species cannot bind the CS gas disk to the star as it does for {beta}Pic and 49Cet, resulting in the disk wind.