- ID:
- ivo://CDS.VizieR/J/ApJ/735/26
- Title:
- Chandra observations of M81
- Short Name:
- J/ApJ/735/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 15 Chandra observations of the nearby spiral galaxy M81 taken over the course of six weeks in 2005 May-July. Each observation reaches a sensitivity of ~10^37^erg/s. With these observations and one previous deeper Chandra observation, we compile a master source list of 265 point sources, extract and fit their spectra, and differentiate basic populations of sources through their colors. We also carry out variability analyses of individual point sources and of X-ray luminosity functions (XLFs) in multiple regions of M81 on timescales of days, months, and years. We find that, despite measuring significant variability in a considerable fraction of sources, snapshot observations provide a consistent determination of the XLF of M81. We also fit the XLFs for multiple regions of M81 and, using common parameterizations, compare these luminosity functions to those of two other spiral galaxies, M31 and the Milky Way.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/655/A109
- Title:
- Chandra view of the LX-LUV relation in quasars
- Short Name:
- J/A+A/655/A109
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey DR14 with the latest Chandra Source Catalog 2.0 (2332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500{AA}, LUV) and the X-ray (at 2keV, LX) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of Chandra, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the LX-LUV relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, z~=0.5-4. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of 0.6 over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are 'standardisable candles', that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/L84
- Title:
- Changes in Titan's atmosphere from Cassini
- Short Name:
- J/ApJ/724/L84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a six-year data set (2004-2010) of mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer to search for seasonal variations in Titan's atmospheric temperature and composition. During most of Cassini's mission Titan's northern hemisphere has been in winter, with an intense stratospheric polar vortex highly enriched in trace gases, and a single south-to-north circulation cell. Following northern spring equinox in mid-2009, dramatic changes in atmospheric temperature and composition were expected, but until now the temporal coverage of polar latitudes has been too sparse to discern trends. Here, we show that during equinox and post-equinox periods, abundances of trace gases at both poles have begun to increase. We propose that increases in north polar trace gases are due to a seasonal reduction in gas depletion by horizontal mixing across the vortex boundary. A simultaneous south polar abundance increase suggests that Titan is now entering, or is about to enter, a transitional circulation regime with two branches, rather than the single branch circulation pattern previously observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/893/96
- Title:
- CHAOS IV: NGC3184 LBT obs. & 3 other gal. abundances
- Short Name:
- J/ApJ/893/96
- Date:
- 07 Mar 2022 07:28:28
- Publisher:
- CDS
- Description:
- The chemical abundances of spiral galaxies, as probed by HII regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 HII regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual HII regions. We find that the dispersion in T_e_-T_e_ relationships is dependent on ionization, as characterized by F_{lambda}5007_/F_{lambda}3727_, and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [NII] and [SIII] provide the most robust measures of electron temperature in low-ionization zones, while [OIII] provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of {alpha}_N/O_=-0.33dex/R_e_ with {sigma}_tot._=0.08 for R_g_/R_e_<2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich HII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/L7
- Title:
- CH_3_CH_2_SH detection in Orion KL
- Short Name:
- J/ApJ/784/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New laboratory data of ethyl mercaptan, CH_3_CH_2_SH, in the millimeter- and submillimeter-wave domains (up to 880GHz) provided very precise values of the spectroscopic constants that allowed the detection of gauche-CH_3_CH_2_ SH toward Orion KL. This identification is supported by 77 unblended or slightly blended lines plus no missing transitions in the range 80-280GHz. A detection of methyl mercaptan, CH_3_SH, in the spectral survey of Orion KL is reported as well. Our column density results indicate that methyl mercaptan is {=~}5 times more abundant than ethyl mercaptan in the hot core of Orion KL.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A104
- Title:
- Chemical abundance analysis of HD 20
- Short Name:
- J/A+A/635/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal-poor stars with available detailed information about their chemical inventory pose powerful empirical benchmarks for nuclear astrophysics. Here we present our spectroscopic chemical abundance investigation of the metal-poor ([Fe/H]=-1.60dex), r-process-enriched ([Eu/Fe]=0.73dex) halo star HD 20 using novel and archival high-resolution data at outstanding signal-to-noise ratios (up to 1000 per Angstroem). By combining one of the first asteroseismic gravity measurements in the metal-poor regime from a TESS light curve with the spectroscopic analysis of iron lines under non-local thermodynamic equilibrium conditions, we derive a set of highly accurate and precise stellar parameters. These allow us to delineate a reliable chemical pattern that is comprised of solid detections of 48 elements, including 28 neutron-capture elements. Hence, we establish HD 20 among the few benchmark stars that have almost complete patterns and possess low systematic dependencies on the stellar parameters. Our light-element (Z<30) abundances are representative of other, similarly metal-poor stars in the Galactic halo with contributions from core-collapse supernovae of type II. In the realm of the neutron-capture elements, our comparison to the scaled solar r-pattern shows that the lighter neutron-capture elements (Z<60) are poorly matched. In particular, we find imprints of the weak r-process acting at low metallicities. Nonetheless, by comparing our detailed abundances to the observed metal-poor star BD +17 3248, we find a persistent residual pattern involving mainly the elements Sr, Y, Zr, Ba, and La. These are indicative of enrichment contributions from the s-process and we show that mixing with material from predicted yields of massive, rotating AGB stars at low metallicity considerably improves the fit. Based on a solar ratio of heavy- to light-s elements -- at odds with model predictions for the i-process -- and a missing clear residual pattern with respect to other stars with claimed contributions from this process, we refute (strong) contributions from such astrophysical sites providing intermediate neutron densities. Finally, nuclear cosmochronology is used to tie our detection of the radioactive element Th to an age estimate for HD 20 of 11.0+/-3.8Gyr.
- ID:
- ivo://CDS.VizieR/J/AZh/88/284
- Title:
- Chemical abundance of Hercules moving group
- Short Name:
- J/AZh/88/284
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a comparative analysis of the kinematics, ages, and elemental abundances for 17 red giants in the Hercules moving group are presented. Model atmospheres are used to determine the parameters of the stellar atmospheres and the abundances of about 20 elements. The masses and ages of the stars are estimated, and the components of their Galactic velocities and the elements of their Galactic orbits are calculated. Our analysis demonstrates that the Hercules stream is a heterogeneous group of objects from the thin and thick disks.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A12
- Title:
- Chemical abundances in Galactic PNe
- Short Name:
- J/A+A/567/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new low-resolution (R~800) optical spectra of 22 Galactic PNe with Spitzer spectra. These data are combined with recent optical spectroscopic data available in the literature to construct representative samples of compact (and presumably young) Galactic disc and bulge PNe with Spitzer spectra. Attending to the nature of the dust features seen in their Spitzer spectra, Galactic disc and bulge PNe are classified according to four major dust types (oxygen chemistry or OC, carbon chemistry or CC, double chemistry or DC, featureless or F) and subtypes (amorphous and crystalline, and aliphatic and aromatic). Nebular gas abundances of He, N, O, Ne, S, Cl, and Ar, as well as plasma parameters (e.g. Ne, Te) are homogeneously derived and we study the median chemical abundances and nebular properties in Galactic disc and bulge PNe depending on their Spitzer dust types and subtypes. A comparison of the derived median abundance patterns with AGB nucleosynthesis predictions show mainly that i) DC PNe, both with amorphous and crystalline silicates, display high-metallicity (solar/supra-solar) and the highest He abundances and N/O ratios, suggesting relatively massive (~3-5M_{sun}_) hot bottom burning AGB stars as progenitors; ii) PNe with O-rich and C-rich unevolved dust (amorphous and aliphatic) seem to evolve from subsolar metallicity (z~0.008) and lower mass (<3M_{sun}_) AGB stars; iii) a few O-rich PNe and a significant fraction of C-rich PNe with more evolved dust (crystalline and aromatic, respectively) display chemical abundances similar to DC PNe, suggesting that they are related objects. A comparison of the derived nebular properties with predictions from models combining the theoretical central star evolution with a simple nebular model is also presented. Finally, a possible link between the Spitzer dust properties, chemical abundances, and evolutionary status is discussed.
- ID:
- ivo://CDS.VizieR/J/AJ/161/183
- Title:
- Chemical abundances in 52 M-giant stars
- Short Name:
- J/AJ/161/183
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We measured ^35^Cl abundances in 52-M giants with metallicities in the range -0.5<[Fe/H]<0.12. Abundances and atmospheric parameters were derived using infrared spectra from CSHELL on the NASA Infrared Telescope Facility and from optical echelle spectra. We measured Cl abundances by fitting a H^35^Cl molecular feature at 3.6985{mu}m with synthetic spectra. We also measured the abundances of O, Ca, Ti, and Fe using atomic absorption lines. We find that the [Cl/Fe] ratio for our stars agrees with chemical evolution models of Cl, and the [Cl/Ca] ratio is broadly consistent with the solar ratio over our metallicity range. Both indicate that Cl is primarily made in core-collapse supernovae with some contributions from Type Ia supernovae. We suggest that other potential nucleosynthesis processes, such as the {nu}-process, are not significant producers of Cl. Finally, we also find our Cl abundances are consistent with HII and planetary nebular abundances at a given oxygen abundance, although there is scatter in the data.
- ID:
- ivo://CDS.VizieR/J/AJ/160/181
- Title:
- Chemical abundances in red giants with Magellan
- Short Name:
- J/AJ/160/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution Magellan/MIKE spectroscopy of 42 red giant stars in seven stellar streams confirmed by the Southern Stellar Stream Spectroscopic Survey (S5): ATLAS, Aliqa Uma, Chenab, Elqui, Indus, Jhelum, and Phoenix. Abundances of 30 elements have been derived from over 10000 individual line measurements or upper limits using photometric stellar parameters and a standard LTE analysis. This is currently the most extensive set of element abundances for stars in stellar streams. Three streams (ATLAS, Aliqa Uma, and Phoenix) are disrupted metal-poor globular clusters, although only weak evidence is seen for the light-element anticorrelations commonly observed in globular clusters. Four streams (Chenab, Elqui, Indus, and Jhelum) are disrupted dwarf galaxies, and their stars display abundance signatures that suggest progenitors with stellar masses ranging from 106 to 107M{sun}. Extensive description is provided for the analysis methods, including the derivation of a new method for including the effect of stellar parameter correlations on each star's abundance and uncertainty. This paper includes data gathered with the 6.5m Magellan Telescopes located at Las Campanas Observatory, Chile.
