- ID:
- ivo://CDS.VizieR/J/A+A/641/A35
- Title:
- Dark dust and single-cloud sightlines in ISM
- Short Name:
- J/A+A/641/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as KI, that show at a resolving power of {lambda}{Delta}{lambda}~75000 one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH^+^ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH^+^>1) clouds, but {is frequently absent} in warm clouds. We inspected the WISE (3-22um) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar CaII distance scale, and compared these two distance estimates with GAIA parallaxes. These distance estimates scatter by ~40%. By comparing spectral type-luminosity distances with those of GAIA, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This dark dust is populated by >~ 1um large grains and predominately appears in the field of the cold interstellar medium.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/898/161
- Title:
- 500days of ASASSN-18pg multiwavelength obs.
- Short Name:
- J/ApJ/898/161
- Date:
- 16 Mar 2022 00:55:51
- Publisher:
- CDS
- Description:
- We present nearly 500 days of observations of the tidal disruption event (TDE) ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our data set includes X-ray, UV, and optical photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d=78.6Mpc; with a peak UV magnitude of m~14, it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of L~2.4x10^44^erg/s, and its late-time evolution is shallower than a flux {propto}t^-5/3^ power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak, which remained detectable for roughly 225days after peak. Analysis of the two-component H{alpha} profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between ~10 and ~60 lt-days from the black hole. No X-ray emission is detected from the TDE, and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations indicate that the projected emission region is likely not significantly aspherical, with the projected emission region having an axis ratio of >~0.65.
- ID:
- ivo://CDS.VizieR/J/A+A/363/1040
- Title:
- DB white dwarfs from the Hamburg/ESO survey
- Short Name:
- J/A+A/363/1040
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 40 cool helium-rich white dwarfs found in the Hamburg/ESO survey. They were selected for follow-up spectroscopy because of their U-B colour below -0.18, the absence of strong absorption lines, and a continuum shape similar to that of a quasar. Effective temperatures for individual stars were determined by fitting model atmospheres of nearly pure helium with a small admixture of hydrogen. As a consequence of the selection criteria all but one sample stars have T_eff_ below 20000K. Four stars clearly show helium and hydrogen lines in their spectra. In the spectra of another three, helium, hydrogen, and metal lines can be detected. For these stars hydrogen and metal abundances were also determined by fitting appropriate model atmospheres containing these elements. Seven sample stars most likely have helium-rich atmospheres but do not show any helium lines. They either have featureless spectra or show calcium lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/106
- Title:
- DB white dwarfs with SDSS and Gaia data
- Short Name:
- J/ApJ/882/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of DB white dwarfs drawn from the Sloan Digital Sky Survey, based on model fits to ugriz photometry and medium-resolution spectroscopy from the Sloan Digital Sky Survey. We also take advantage of the exquisite trigonometric parallax measurements recently obtained by the Gaia mission. Using the so-called photometric and spectroscopic techniques, we measure the atmospheric and physical parameters of each object in our sample (Teff, logg, H/He, Ca/He, R, M), and compare the values obtained from both techniques in order to assess the precision and accuracy of each method. We then explore in great detail the surface gravity, stellar mass, and hydrogen abundance distributions of DB white dwarfs as a function of effective temperature. We present some clear evidence for a large population of unresolved double-degenerate binaries composed of DB+DB and even DB+DA white dwarfs. In the light of our results, we finally discuss the spectral evolution of DB white dwarfs, in particular the evolution of the DB-to-DA ratio as a function of Teff, and we revisit the question of the origin of hydrogen in DBA white dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/597
- Title:
- Debris disks in NGC 2232
- Short Name:
- J/ApJ/688/597
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe Spitzer IRAC and MIPS observations of the nearby 25Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24um indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8um excesses and 8 early-type stars with definite 24um excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24um excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/2606
- Title:
- Deep echelle spectrophotometry of NGC3918
- Short Name:
- J/MNRAS/452/2606
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical content of the planetary nebula NGC 3918 is investigated through deep, high-resolution (R~40000) UVES (Ultraviolet-Visual Echelle Spectrograph) at VLT (Very Large Telescope) spectrophotometric data. We identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in NGC 3918 progenitor star. We find that Kr is strongly enriched in NGC 3918 and that Se is less enriched than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC 3918 as is Kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity asymptotic giant branch (AGB) stars. A clear correlation is found when representing [Kr/O] versus log(C/O) for NGC 3918 and other objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought to the surface of AGB stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. We also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C, N, O, and Ne. We compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to the high ionization of NGC 3918 we detect a large number of recombination lines of multiple ionization stages of C, N, O and Ne. The abundances obtained for these elements by using recently determined state-of-the-art ionization correction factor (ICF) schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent ICF scheme for high-ionization planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/135
- Title:
- DEEP2 galaxies with UV spectra in the EGS
- Short Name:
- J/ApJ/758/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering Si II, C IV, Fe II, Mg II, and Mg I lines in the rest-frame ultraviolet. Using Galaxy Evolution Explorer (GALEX), Hubble Space Telescope (HST), and Spitzer imaging available for the Extended Groth Strip, we examine galaxies on a per-object basis in order to better understand both the prevalence of galactic outflows at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of Fe II interstellar absorption lines, are found to span the interval [-217,+155]km/s. We find that ~40% (10%) of the sample exhibits blueshifted Fe II lines at the 1{sigma} (3{sigma}) level. We also measure maximal outflow velocities using the profiles of the Fe II and Mg II lines; we find that Mg II frequently traces higher velocity gas than Fe II. Using quantitative morphological parameters derived from the HST imaging, we find that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. In light of clumpy galaxy morphologies, we develop a new physically motivated technique for estimating areas corresponding to star formation. We use these area measurements in tandem with GALEX-derived star formation rates (SFRs) to calculate SFR surface densities. At least 70% of the sample exceeds an SFR surface density of 0.1M_{sun}_/yr/kpc2, the threshold necessary for driving an outflow in local starbursts. At the same time, the outflow detection fraction of only 40% in Fe II absorption provides further evidence for an outflow geometry that is not spherically symmetric. We see a ~3{sigma} trend between outflow velocity and SFR surface density, but no significant trend between outflow velocity and SFR. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both SFR and SFR surface density predicted by theory.
- ID:
- ivo://CDS.VizieR/J/ApJS/193/14
- Title:
- DEEP3 Galaxy Redshift Survey: GOODS-N field
- Short Name:
- J/ApJS/193/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectroscopic observations in the GOODS-N field completed using DEIMOS on the Keck II telescope as part of the DEEP3 Galaxy Redshift Survey (M. C. Cooper et al. 2011, in preparation). Observations of 370 unique targets down to a limiting magnitude of R_AB_=24.4 yielded 156 secure redshifts. In addition to redshift information, we provide sky-subtracted one- and two-dimensional spectra of each target. Observations were conducted following the procedures of the Team Keck Redshift Survey (TKRS, Cat. J/AJ/127/3121), thereby producing spectra that augment the TKRS sample while maintaining the uniformity of its spectral database.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/152
- Title:
- Deep NIR spectrum of the Orion Bar PDR
- Short Name:
- J/ApJ/838/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R~45000) and instantaneous broad wavelength coverage (1.45-2.45{mu}m), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H_2_) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H_2_ and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T=50-250K, n_H_=10^5^-10^7^cm^-3^) embedded in a warmer lower density medium (T=250-1000K, n_H_=10^4^-10^5^cm^-3^). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H_2_ level populations well, to constrain the temperature to a range of 600-650 K and the density to n_H_=2.5x10^3^-10^4^cm^-3^. The best-fit model gives T=625K and n_H_=5x10^3^cm^-3^. This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/115
- Title:
- Deep spectroscopy in the GOODS fields
- Short Name:
- J/ApJ/741/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new measures of the evolving scaling relations between stellar mass, luminosity and rotational velocity for a morphologically inclusive sample of 129 disk-like galaxies with z_AB_<22.5 in the redshift range 0.2<z<1.3, based on spectra from DEep Imaging Multi-Object Spectrograph on the Keck II telescope, multi-color Hubble Space Telescope (HST) Advanced Camera for Surveys photometry, and ground-based Ks-band imaging. A unique feature of our survey is the extended spectroscopic integration times, leading to significant improvements in determining characteristic rotational velocities for each galaxy. Rotation curves are reliably traced to the radius where they begin to flatten for ~90% of our sample, and we model the HST-resolved bulge and disk components in order to accurately de-project our measured velocities, accounting for seeing and dispersion. We demonstrate the merit of these advances by recovering an intrinsic scatter on the stellar mass Tully-Fisher relation a factor of two to three less than in previous studies at intermediate redshift and comparable to that of locally determined relations. With our increased precision, we find that the relation is well established by <z>~1, with no significant evolution to <z>~0.3, {Delta}M_*_~0.04+/-0.07dex. A clearer trend of evolution is seen in the B-band Tully-Fisher relation corresponding to a decline in luminosity of {Delta}M_B_~0.85+/-0.28 magnitudes at fixed velocity over the same redshift range, reflecting the changes in star formation over this period. As an illustration of the opportunities possible when gas masses are available for a sample such as ours, we show how our dynamical and stellar mass data can be used to evaluate the likely contributions of baryons and dark matter to the assembly history of spiral galaxies.
