Search

Start Over Subject spectroscopy Content Level Research
2171. Reduced spectra of NGC 6528 stars
ID:
ivo://CDS.VizieR/J/A+A/601/A31
Title:
Reduced spectra of NGC 6528 stars
Short Name:
J/A+A/601/A31
Date:
21 Oct 2021
Publisher:
CDS
Description:
Here we explore robust ways of determining the iron content of metal-rich giant stars. We aim to understand what biases and shortcomings the widely applied methods suffer from. In this study we were mainly concerned with standard methods of analysing stellar spectra. These include the analysis of individual lines to determine stellar parameters, and analysis of the broad wings of certain lines (e.g. Halpha and calcium lines) to determine effective temperature and surface gravity for the stars. For NGC 6528 we find that [Fe/H]=+0.04dex with a scatter of 0.07dex, which gives an error in the derived mean abundance of 0.02dex. Our work has two important conclusions for analysis of metal-rich red giant branch stars. Firstly, for spectra with S/N of below about 35 per reduced pixel, [Fe/H] becomes too high. Secondly, determination of Teff using the wings of the H{alpha} line results in [Fe/H] values about 0.1dex higher than if excitational equilibrium is used. The last conclusion is perhaps unsurprising, as we expect the NLTE effect to become more prominent in cooler stars and we can not use the the wings of the H{alpha} line to determine Teff for the cool stars in our sample. We therefore recommend that in studies of metal-rich red giant stars care should be taken to obtain sufficient calibration data to enable use of the cooler stars.
2172. Reduced X-shooter spectra of GRB 190114A
ID:
ivo://CDS.VizieR/J/A+A/629/A131
Title:
Reduced X-shooter spectra of GRB 190114A
Short Name:
J/A+A/629/A131
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the detections of molecular hydrogen (H_2_), vibrationally-excited H_2_ (H_2_*), and neutral atomic carbon (CI), an efficient tracer of molecular gas, in two new afterglow spectra of GRBs 181020A (z=2.938) and 190114A (z=3.376), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman-alpha absorbers (DLAs) and substantial amounts of molecular hydrogen with logN(HI,H_2_)=22.20+/-0.05, 20.40+/-0.04 (GRB 181020A) and logN(HI, H_2_)=22.15+/-0.05, 19.44+/-0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with [Zn/H]=-1.57+/-0.06, [Zn/Fe]=0.67+/-0.03, and AV=0.27+/-0.02mag (GRB 181020A) and [Zn/H]=-1.23+/-0.07, [Zn/Fe]=1.06+/-0.08, and AV=0.36+/-0.02mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe CI and H_2_*. We confirm that H2 is detected in all CI- and H2*-bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of f_H2_>~10^-3^ is required for CI to be detected. The defining characteristic for H_2_* to be present is less clear, though a large H_2_ column density is an essential factor. We also find that the observed line profiles of the molecular-gas tracers are kinematically "cold", with small velocity offsets of {delta}v<20km/s from the bulk of the neutral absorbing gas. We then derive the H_2_ excitation temperatures of the molecular gas and find that they are relatively low with Tex~=100-300K, however, there could be evidence of warmer components populating the high-J H_2_ levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H_2_ absorbers from identification. CI and H_2_* could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.
2173. Reduction of integral-field spectrograph code P3D
ID:
ivo://CDS.VizieR/J/A+A/515/A35
Title:
Reduction of integral-field spectrograph code P3D
Short Name:
J/A+A/515/A35
Date:
21 Oct 2021
Publisher:
CDS
Description:
The reduction of integral-field spectrograph (IFS) data is demanding work. Many repetitive operations are required to convert raw data into, typically, a large number of spectra. This effort can be markedly simplified through the use of a tool or pipeline, which is designed to complete many of the repetitive operations without human interaction. Here we present our semi-automatic data-reduction tool P3D, which is designed to be used with fiber-fed IFSs. Important components of P3D include a novel algorithm for automatic finding and tracing of spectra on the detector and two methods of optimal spectrum extraction in addition to standard aperture extraction. P3D also provides tools to combine several images, perform wavelength calibration and flat field data. P3D is at the moment configured for four IFSs. To evaluate its performance, we tested the different components of the tool. For these tests we used both simulated and observational data. We demonstrate that a correction for so-called cross-talk due to overlapping spectra on the detector is required for three of the IFSs. Without such a correction, spectra will be inaccurate, in particular if there is a significant intensity gradient across the object. Our tests showed that P3D is able to produce accurate results. P3D is a highly general and freely available tool. It is easily extended to include improved algorithms, new visualization tools, and support for additional instruments. The program code can be downloaded from the P3D-project web site http://p3d.sourceforge.net.
2174. Reflectance spectra of 12 Trojans and Hildas
ID:
ivo://CDS.VizieR/J/A+A/568/L7
Title:
Reflectance spectra of 12 Trojans and Hildas
Short Name:
J/A+A/568/L7
Date:
21 Oct 2021
Publisher:
CDS
Description:
Hilda asteroids and Jupiter Trojans are two low-albedo (p_v_~0.07) populations for which the Nice model predicts an origin in the primordial Kuiper Belt region. However, recent surveys by WISE and the Spitzer Space Telescope (SST) have revealed that ~2% of these objects possess high albedos (p_v_>=0.15), which might indicate interlopers --that is, objects not formed in the Kuiper Belt-- among these two populations. Here, we report spectroscopic observations in the visible and/or near-infrared spectral ranges of twelve high-albedo (p_v_>0.15) Hilda asteroids and Jupiter Trojans. These twelve objects have spectral properties similar to those of the low-albedo population, which suggests a similar composition and hence a similar origin for low- and high-albedo Hilda asteroids and Jupiter Trojans. We therefore propose that most high albedos probably result from statistical bias or uncertainties that affect the WISE and SST measurements. However, some of the high albedos may be true and the outcome of some collision-induced resurfacing by a brighter material that could include water ice. Future work should attempt to investigate the nature of this supposedly bright material. The lack of interlopers in our sample allows us to set an upper limit of 0.4% at a confidence level of 99.7% on the abundance of interlopers with unexpected taxonomic classes (e.g., A-, S-, V-type asteroids) among these two populations.
2175. Refraction of corundum, spinel, {alpha}-quartz
ID:
ivo://CDS.VizieR/J/A+A/553/A81
Title:
Refraction of corundum, spinel, {alpha}-quartz
Short Name:
J/A+A/553/A81
Date:
21 Oct 2021
Publisher:
CDS
Description:
Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum ({alpha}-Al_2_O_3_), spinel (MgAl_2_O_4_), and {alpha}-quartz (SiO_2_), temperature-dependent optical constants were measured from 300K up to more than 900K. Small particle spectra were also calculated from these data.
2176. Refractive index for silicon carbide (SiC)
ID:
ivo://CDS.VizieR/J/A+A/483/661
Title:
Refractive index for silicon carbide (SiC)
Short Name:
J/A+A/483/661
Date:
21 Oct 2021
Publisher:
CDS
Description:
The SiC optical constants are fundamental inputs for radiative transfer (RT) models of astrophysical dust environments. However, previously published values contain errors and do not adequately represent the bulk physical properties of the cubic ({beta}) SiC polytype usually found around carbon stars. We provide new, uncompromised optical constants for {beta}- and {alpha}-SiC derived from single-crystal reflectance spectra and investigate quantitatively (i) whether there is any difference between {alpha}- and {beta}-SiC that can be seen in infrared (IR) spectra and optical functions and (ii) whether weak features from {lambda}~12.5-13.0{mu}m need to be fitted. We measured mid- and far-IR reflectance spectra for two samples of 3C ({beta}-)SiC and four samples of 6H ({alpha}-)SiC. For the latter group, we acquired polarized data (E{perpendicular.to}c, E{parallel.to}c orientations). We calculated the real and imaginary parts of the complex refractive index (n({lambda})+ik({lambda})) and the ideal absorption coefficients via classical dispersion fits to our reflectance spectra.
2177. Relations between spectra and colors of SNe Ia
ID:
ivo://CDS.VizieR/J/ApJ/742/89
Title:
Relations between spectra and colors of SNe Ia
Short Name:
J/ApJ/742/89
Date:
21 Oct 2021
Publisher:
CDS
Description:
To understand how best to use observations of Type Ia supernovae (SNe Ia) to obtain precise and accurate distances, we investigate the relations between spectra of SNe Ia and their intrinsic colors. Using a sample of 1630 optical spectra of 255 SNe, based primarily on data from the CfA Supernova Program, we examine how the velocity evolution and line strengths of SiII(6355) and CaII H&K are related to the B-V color at peak brightness. We find that the maximum-light velocity of SiII6355 and CaII H&K and the maximum-light pseudo-equivalent width of SiII6355 are correlated with intrinsic color, with intrinsic color having a linear relation with the SiII6355 measurements. CaII H&K does not have a linear relation with intrinsic color, but lower-velocity SNe tend to be intrinsically bluer. Combining the spectroscopic measurements does not improve intrinsic color inference. The intrinsic color scatter is larger for higher-velocity SNe Ia - even after removing a linear trend with velocity - indicating that lower-velocity SNe Ia are more "standard crayons". Employing information derived from SN Ia spectra has the potential to improve the measurements of extragalactic distances and the cosmological properties inferred from them.
2178. REQUIEM survey. I. Ly{alpha} halos around QSOs
ID:
ivo://CDS.VizieR/J/ApJ/887/196
Title:
REQUIEM survey. I. Ly{alpha} halos around QSOs
Short Name:
J/ApJ/887/196
Date:
21 Oct 2021
Publisher:
CDS
Description:
The discovery of quasars a few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes as well as galaxy formation and evolution. Quasars' luminosity is produced by extreme gas accretion onto black holes, which have already reached masses of M_BH_>10^9^M_{sun}_ by z~6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources, we started a Very Large Telescope/Multi-Unit Spectroscopic Explorer (MUSE) effort aimed at characterizing the surroundings of a sample of 5.7<z<6.6 quasars, which we have dubbed the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Ly{alpha} halos around the first 31 targets observed as part of this program. Reaching 5{sigma} surface brightness limits of 0.1-1.1x10^-17^erg/s/cm^2^/arcsec^2^ over a 1arcsec^2^ aperture, we were able to unveil the presence of 12 Ly{alpha} nebulae, eight of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8x10^42^ to 2x10^44^erg/s, FWHMs between 300 and 1700km/s, sizes <30pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circumgalactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3Gyr of the universe. A comparison with the extended Ly{alpha} emission observed around bright (M_1450_<~-25mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z~6 to z~3, followed by a decline in the average surface brightness down to z~2.
2179. Resolved IR spectra of pure CO2 ice (15-75K)
ID:
ivo://CDS.VizieR/J/A+A/555/A85
Title:
Resolved IR spectra of pure CO2 ice (15-75K)
Short Name:
J/A+A/555/A85
Date:
21 Oct 2021
Publisher:
CDS
Description:
The v2 bending mode of pure CO_2_ ice around 15.2um exhibits a fine double-peak structure that offers a sensitive probe to study the physical and chemical properties of solid CO_2_ in space. Current laboratory spectra do not fully resolve the CO_2_ ice features. To improve the fitting of the observed CO_2_ features, high-resolution solid-state infrared spectra of pure CO_2_ ice are recorded in the laboratory for a series of astronomically relevant temperatures and at an unprecedented level of detail. The infrared spectra of pure CO_2_ ice were recorded in the 4000 to 400cm^-1^ (2.5-25um) region at a resolution of 0.1cm^-1^ using Fourier transform infrared spectroscopy. Accurate band positions and band widths (FWHM) of pure CO_2_ ice are presented for temperatures of 15, 30, 45, 60, and 75K. The focus of this spectroscopic work is on the CO_2_ (v2) bending mode, but more accurate data are also reported for the ^12^CO_2_ and ^13^CO_2_ (v3) stretching mode, and CO_2_ (v1+v3) and (2v2+v3) combination bands.
2180. RESOLVE survey: 21cm obs. with GBT & Arecibo
ID:
ivo://CDS.VizieR/J/ApJ/832/126
Title:
RESOLVE survey: 21cm obs. with GBT & Arecibo
Short Name:
J/ApJ/832/126
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the HI mass inventory for the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey, a volume-limited, multi-wavelength census of >1500 z=0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of ~10^9^M_{sun}_. This first 21cm data release provides robust detections or strong upper limits (1.4M_HI_<5%-10% of stellar mass M*) for ~94% of RESOLVE. We examine global atomic gas-to-stellar mass ratios (G/S) in relation to galaxy environment using several metrics: group dark matter halo mass M_h_, central/satellite designation, relative mass density of the cosmic web, and distance to the nearest massive group. We find that at fixed M*, satellites have decreasing G/S with increasing M_h_ starting clearly at M_h_~10^12^M_{sun}_, suggesting the presence of starvation and/or stripping mechanisms associated with halo gas heating in intermediate-mass groups. The analogous relationship for centrals is uncertain because halo abundance matching builds in relationships between central G/S, stellar mass, and halo mass, which depend on the integrated group property used as a proxy for halo mass (stellar or baryonic mass). On larger scales G/S trends are less sensitive to the abundance matching method. At fixed M_h_<=10^12^M_{sun}_, the fraction of gas-poor centrals increases with large-scale structure density. In overdense regions, we identify a rare population of gas-poor centrals in low-mass (M_h_<10^11.4^M_{sun}_) halos primarily located within ~1.5x the virial radius of more massive (M_h_>10^12^M_{sun}_) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias.

Limit your search

more »

more »

more »

more »