- ID:
- ivo://CDS.VizieR/J/A+A/635/A33
- Title:
- Galactic classical Cepheids Per-Lbol-Rad
- Short Name:
- J/A+A/635/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral energy distributions (SEDs) were constructed for a sample of 477 classical cepheids (CCs); including stars that have been classified in the literature as such but are probably not. The SEDs were fitted with a dust radiative transfer code. Four stars showed a large mid- or far-infrared excess and the fitting then included a dust component. These comprise the well-known case of RS Pup, and three stars that are (likely) Type-II cepheids (T2Cs), AU Peg, QQ Per, and FQ Lac. The infrared (IR) excess in FQ Lac is reported for the first time in this work. The remainder of the sample was fitted with a stellar photosphere to derive the best-fitting luminosity and effective temperature. Distance and reddening were taken from the literature. The stars were plotted in a Hertzsprung-Russell diagram (HRD) and compared to evolutionary tracks for cepheids and theoretical instability strips. For the large majority of stars, the position in the HRD is consistent with the instability strip for a CC or T2C. About 5% of the stars are outliers in the sense that they are much hotter or cooler than expected. A comparison to effective temperatures derived from spectroscopy suggests in some cases that the photometrically derived temperature is not correct and that this is likely linked to an incorrectly adopted reddening. Two three-dimensional reddening models have been used to derive alternative estimates of the reddening for the sample. There are significant systematic differences between the two estimates with a non-negligible scatter. In this work the presence of a small near-infrared (NIR) excess, as has been proposed in the literature for a few well-known cepheids, is investigated. Firstly, this was done by using a sample of about a dozen stars for which a mid-infrared spectrum is available. This data is particularly con straining as the shape of the observed spectrum should match that of the photosphere and any dust spectrum, both dust continuum and any spectral features of, for example, silicates or aluminium oxide. This comparison provides constraints on the dust composition, in agreement with a previous work in the literature. Secondly, the SEDs of all stars were fitted with a dust model to see if a statistically significant better fit could be obtained. The results were compared to recent work. Eight new candidates for exhibiting a NIR excess are proposed, solely based on the photometric SEDs. Obtaining mid-infrared spectra would be needed to confirm this excess. Finally, period-bolometric luminosity and period-radius relations are presented for samples of over 370 fundamental-mode CCs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/PAZh/39/942
- Title:
- Galactic classical Cepheids properties
- Short Name:
- J/PAZh/39/942
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on our compiled catalogue of positions, velocities, ages, and abundances of nine chemical elements for 221 classical Cepheids, we analyze the dependences of the relative abundances of alpha-elements as well as rapid and slow neutron capture elements on metallicity, space velocity components, and Galactocentric distance.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A92
- Title:
- Galactic Cold Cores. IV. Cold sub-mm sources
- Short Name:
- J/A+A/584/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the project Galactic cold cores, Herschel photometric observations were carried out as a follow-up of cold regions of interstellar clouds previously identified with the Planck satellite. The aim of the project is to derive the physical properties of the population of cold sources and to study its connection to ongoing and future star formation. We build a catalogue of cold sources within the clouds in 116 fields observed with the Herschel PACS and SPIRE instruments. We wish to determine the general physical characteristics of the cold sources and to examine the correlations with their host cloud properties. From Herschel data, we compute colour temperature and column density maps of the fields. We estimate the distance to the target clouds and provide both uncertainties and reliability flags for the distances. The getsources multi-wavelength source extraction algorithm is employed to build a catalogue of several thousands of cold sources. Mid-infrared data are used along with a colour and position criteria to separate starless and protostellar sources. We also propose another classification method based on sub-millimetre temperature profiles. We analyse the statistical distributions of the physical properties of the source samples. We provide a catalogue of ~4000 cold sources within or near star forming clouds, most of which are located either in nearby molecular complexes (<1kpc) or in star forming regions of the nearby galactic arms (~2kpc). About 70% of the sources have a size compatible with an individual core, and 35% of those sources are likely gravitationally bound. Significant statistical differences in physical properties are found between starless and protostellar sources, in column density - dust temperature, mass - size, and mass - dust temperature diagrams. The core mass functions are very similar to those previously reported for other regions. On statistical grounds we find that gravitationally bound sources have higher background column densities (median N_bg_(H_2_)~5x10^21^cm-2) than unbound sources (median N_bg_(H_2_)~3x10^21^cm-2). These values of N_bg_(H_2_) are higher for larger dust temperature of the external layers of the parent cloud. However, only in few cases do we find clear N_bg_(H_2_) thresholds for the presence of cores. The dust temperature of cloud external layers shows clear variations with galactic location, as possibly do the source temperatures. Our data support a more complex view of star formation than in the simple idea of a column density threshold. They show a clear influence of the surrounding UV-visible radiation on how cores distribute in their host clouds, with possible variations on the Galactic scale.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A93
- Title:
- Galactic cold cores. V. Dust opacity
- Short Name:
- J/A+A/584/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Galactic Cold Cores has carried out Herschel photometric observations of interstellar clouds where Planck satellite survey has located cold and compact clumps. The sources represent different stages of cloud evolution from starless clumps to protostellar cores and are located in different Galactic environments. We examine this sample of 116 Herschel fields to estimate the submillimetre dust opacity and to look for variations that could be attributed to the evolutionary stage of the sources or to environmental factors, including the location within the Galaxy. The submillimetre dust opacity is derived from Herschel data and near-infrared observations of the reddening of background stars are converted to near-infrared optical depth. We investigate the systematic errors affecting these parameters and use modelling to make corrections for the expected biases. The ratio of 250{mu}m and J band opacities is correlated with the Galactic location and the star formation activity. Local variations in the ratio {tau}(250{mu}m)/{tau}(J) are searched using the correlation plots and maps of the opacity ratio. We find a median ratio of {tau}(250{mu}m)/{mu}(J)=(1.6+/-0.2)*10^-3^, which is more than three times the mean value reported for the diffuse medium. Assuming an opacity spectral index {beta}=1.8 instead of {beta}=2.0, the value would be smaller by ~30%. No significant systematic variation is detected with Galactocentric distance or with Galactic height. Examination of the {tau}(250{mu}m)/{tau}(J) maps reveals half a dozen fields with clear indications of local increase of submillimetre opacity, up to {tau}(250{mu}m)/{tau}(J)~4*10^-3^, towards the densest clumps. These are all nearby fields with spatially resolved clumps of high column density. We interpret the increase in the far-infrared opacity as a sign of grain growth in the densest and coldest regions of interstellar clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A94
- Title:
- Galactic cold cores. VI. List of Herschel fields
- Short Name:
- J/A+A/584/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Cold Cores project has carried out Herschel photometric observations of 116 fields where the Planck survey has found signs of cold dust emission. The fields contain sources in different environments and different phases of star formation. Previous studies have revealed variations in their dust submillimetre opacity. The aim is to measure the value of dust opacity spectral index and to understand its variations spatially and with respect to other parameters, such as temperature, column density, and Galactic location. The dust opacity spectral index {beta} and the dust colour temperature T are derived using Herschel and Planck data. The relation between {beta} and T is examined for the whole sample and inside individual fields.
6716. Galactic CO maps
- ID:
- ivo://CDS.VizieR/J/A+A/655/A64
- Title:
- Galactic CO maps
- Short Name:
- J/A+A/655/A64
- Date:
- 10 Mar 2022 07:19:13
- Publisher:
- CDS
- Description:
- Carbon monoxide (CO) is the best tracer of Galactic molecular hydrogen H_2_. Its lowest rotational emission lines are in the radio regime, and thanks to Galactic rotation, emission at different distances is Doppler shifted. For a given gas flow model, the observed spectra can thus be deprojected along the line of sight to infer the gas distribution. We used the CO-line survey of Dame et al. (2001ApJ...547..792D) to reconstruct the three-dimensional density of H_2_. We considered the deprojection as a Bayesian variational inference problem. The posterior distribution of the gas densities allowed us to estimate the mean and uncertainty of the reconstructed density. Unlike most of the previous attempts, we took the correlations of gas on a variety of scales into account, which allowed us to correct for some of the well-known pathologies, such as finger-of-god effects. The two gas flow models that we adopted incorporate a Galactic bar that induces radial motions in the inner few kiloparsecs and thus offers spectral resolution towards the Galactic centre. We compared our gas maps with those of earlier studies and characterise their statistical properties, for instance the radial profile of the average surface mass density. We have made our three-dimensional gas maps and their uncertainties available to the community here and at https://dx.doi.org/10.5281/zenodo.5501196.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/3408
- Title:
- Galactic disc RR Lyrae stars
- Short Name:
- J/MNRAS/492/3408
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a kinematical study of 314 RR Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and Gaia DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR Lyrae stars in the solar neighbourhood at a pericentre distance of between 5 and 9kpc from the Galactic Centre. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=-0.60dex and v_theta_=241km/s, respectively. From the distribution of the Galactocentric spherical velocity components, we find that these 22 disc-like RR Lyrae variables are not consistent with the Gaia Sausage (Gaia-Enceladus), unlike almost half of the local RR Lyrae stars. Chemical information from the literature shows that the majority of the selected pericentre-peak RR Lyrae variables are alpha-poor, a property shared by typically much younger stars in the thin disc. Using the available photometry, we rule out a possible misclassification with the known classical and anomalous Cepheids. The similar kinematic, chemical, and pulsation properties of these disc RR Lyrae stars suggest they share a common origin. In contrast, we find that the RR Lyrae stars associated with the Gaia- Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population (approximately 1dex).
- ID:
- ivo://CDS.VizieR/J/A+A/418/551
- Title:
- Galactic disk stars abundances and velocities
- Short Name:
- J/A+A/418/551
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed the detailed analysis of 174 high-resolution spectra of FGK dwarfs obtained with the ELODIE echelle spectrograph at the Observatoire de Haute-Provence. Abundances of Fe, Si and Ni have been determined from equivalent widths under LTE approximation, whereas abundances of Mg have been determined under NLTE approximation using equivalent widths of 4 lines and profiles of 5 lines. Spatial velocities with an accuracy better than 1kms, as well as orbits, have been computed for all stars.
- ID:
- ivo://CDS.VizieR/J/A+A/480/91
- Title:
- Galactic disk stars vertical distribution. IV.
- Short Name:
- J/A+A/480/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the parameters of 891 stars, mostly clump giants, including atmospheric parameters, distances, absolute magnitudes, spatial velocities, galactic orbits and ages. One part of this sample consists of local giants, within 100pc, with atmospheric parameters either estimated from our spectroscopic observations at high resolution and high signal-to-noise ratio, or retrieved from the literature. The other part of the sample includes 523 distant stars, spanning distances up to 1 kpc in the direction of the North Galactic Pole, for which we have estimated atmospheric parameters from high resolution but low signal-to-noise Echelle spectra. This new sample is kinematically unbiased, with well-defined boundaries in magnitude and colours. We revisit the basic properties of the Galactic thin disk as traced by clump giants. We find the metallicity distribution to be different from that of dwarfs, with fewer metal-rich stars. We find evidence for a vertical metallicity gradient of -0.31dex/kpc and for a transition at 4-5Gyr in both the metallicity and velocities. The age - metallicity relation (AMR), which exhibits a very low dispersion, increases smoothly from 10 to 4Gyr, with a steeper increase for younger stars. The age-velocity relation (AVR) is characterized by the saturation of the V and W dispersions at 5Gyr, and continuous heating in U.
- ID:
- ivo://CDS.VizieR/J/A+A/493/785
- Title:
- Galactic disk stellar populations from ISOGAL
- Short Name:
- J/A+A/493/785
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify the stellar populations (mostly red giants and young stars) detected in the ISOGAL survey at 7 and 15um towards a field (LN45) in the direction l=-45, b=0.0. The sources detected in the survey of the Galactic plane by the Infrared Space Observatory were characterised based on colour-colour and colour-magnitude diagrams. We combine the ISOGAL catalogue with the data from surveys such as 2MASS and GLIMPSE. Interstellar extinction and distance were estimated using the red clump stars detected by 2MASS in combination with the isochrones for the AGB/RGB branch. Absolute magnitudes were thus derived and the stellar populations identified from their absolute magnitudes and their infrared excess. A standard approach to analysing the ISOGAL disc observations has been established. We identify several hundred RGB/AGB stars and 22 candidate young stellar objects in the direction of this field in an area of 0.16deg^2^. An overdensity of stellar sources is found at distances corresponding to the distance of the Scutum-Crux spiral arm. In addition, we determined mass-loss rates of AGB-stars using dust radiative transfer models from the literature.