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691. Methane partition function
ID:
ivo://CDS.VizieR/J/ApJ/789/2
Title:
Methane partition function
Short Name:
J/ApJ/789/2
Date:
21 Oct 2021
Publisher:
CDS
Description:
The paper describes the construction of complete sets of hot methane lines based on accurate ab initio potential and dipole moment surfaces and extensive first-principle calculations. Four line lists spanning the [0-5000]/cm infrared region were built at T = 500, 1000, 1500, and 2000 K. For each of these four temperatures, we have constructed two versions of line lists: a version for high-resolution applications containing strong and medium lines and a full version appropriate for low-resolution opacity calculations. A comparison with available empirical databases is discussed in detail for both cold and hot bands giving a very good agreement for line positions, typically <0.1-0.5/cm and ~5% for intensities of strong lines. Together with numerical tests using various basis sets, this confirms the computational convergence of our results for the most important lines, which is the major issue for theoretical spectra predictions. We showed that transitions with lower state energies up to 14,000/cm could give significant contributions to the methane opacity and have to be systematically taken into account. Our list at 2000 K calculated up to J = 50 contains 11.5 billion transitions for I > 10^-29^ cm/mol. These new lists are expected to be quantitatively accurate with respect to the precision of available and currently planned observations of astrophysical objects with improved spectral resolution.
692. Methanol masers towards IRAS sources
ID:
ivo://CDS.VizieR/J/A+AS/110/81
Title:
Methanol masers towards IRAS sources
Short Name:
J/A+AS/110/81
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of our second search for 6.7-GHz methanol masers towards colour-selected IRAS sources. Five hundred and twenty IRAS sources that meet the far-infrared colour criteria set by Wood & Churchwell (1989ApJ...340..265W) for ultra-compact HII regions were searched for 6.7-GHz methanol maser emission, to a sensitivity limit of 5Jy. Thirty one new maser sources were detected. We also compare the FIR colours of the newly detected maser sources with those detected by Schutte et al. (1993MNRAS.261..783S) and the IRAS counterparts of sources that have both methanol and hydroxyl maser emission. It was found that the average flux distribution of the newly detected sources differs significantly from that of all other known 6.7-GHz methanol maser sources. It is argued that the differences may be due either to intrinsic differences between the three groups of sources or to interstellar extinction. An analysis of the relation between the 6.7-GHz maser and IRAS flux densities shows that the maser flux density is always less than the 100{mu}m flux density while only three sources have a maser flux density greater than the 60{mu}m flux density. Far-infrared pumping of the 6.7-GHz methanol masers is therefore in principle viable although it was found that the apparent maser efficiency will exceed 10 per cent for a significant number of sources in the case of FIR pumping by photons between 50 and 100{mu}m. The overall detection rates on the IRAS [25-12] vs [60-12] two-colour diagram are also presented. Possible new search strategies for masers in colour-selected IRAS sources are discussed.
693. M8, G333.6-0.2 and NGC6357 young stars
ID:
ivo://CDS.VizieR/J/A+A/633/A155
Title:
M8, G333.6-0.2 and NGC6357 young stars
Short Name:
J/A+A/633/A155
Date:
21 Oct 2021
Publisher:
CDS
Description:
The identification and characterisation of populations of young massive stars in (giant) HII regions provides important constraints on i) the formation process of massive stars and their early feedback on the environment, and ii) the initial conditions for population synthesis models predicting the evolution of ensembles of stars. We identify and characterise the stellar populations of the following young giant HII regions: M8, G333.6-0.2, and NGC6357. We have acquired H- and K-band spectra of around 200 stars using The K-band Multi Object Spectrograph (KMOS) on the ESO Very Large Telescope. The targets for M8 and NGC6357 were selected from the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX), which combines X-ray observations with near-infrared and mid-infrared data. For G333.6-0.2, the sample selection is based on the near-infrared colours combined with X-ray data. We introduce an automatic spectral classification method in order to obtain temperatures and luminosities for the observed stars. We analysed the stellar populations using their photometric, astrometric, and spectroscopic properties and compared the position of the stars in the Hertzprung-Russell diagram with stellar evolution models to constrain their ages and mass ranges. We confirm the presence of candidate ionising sources in the three regions and report new ones, including the first spectroscopically identified O stars in G333.6-0.2. In M8 and NGC6357, two populations are identified: (i) OB main-sequence stars (M>5M_{sun}_) and (ii) pre-main sequence stars (M~=0.5-5M_{sun}_). The ages of the clusters are ~1-3Myr, <3Myr, and 0.5-3Myr for M8, G333.6-0.2, and NGC6357, respectively. We show that MYStIX selected targets have >90% probability of being members of the HII region, whereas a selection based on near infrared (NIR) colours leads to a membership probability of only 70%.
694. ~420MHz uGMRT obs. of MIR selected radio-loud AGN
ID:
ivo://CDS.VizieR/J/ApJS/255/28
Title:
~420MHz uGMRT obs. of MIR selected radio-loud AGN
Short Name:
J/ApJS/255/28
Date:
11 Mar 2022
Publisher:
CDS
Description:
We present results from a spectroscopically blind search for associated and intervening HI 21cm and OH 18cm absorption lines toward 88 active galactic nuclei (AGN) at 2<z<5 using the uGMRT. The sample of AGN with 1.4GHz spectral luminosity in the range 10^27-29.3^W/Hz is selected using mid-infrared colors and closely resembles the distribution of the underlying quasar population. The search for associated or proximate absorption, defined to be within 3000km/s of the AGN redshift, led to one HI 21cm absorption detection (M1540-1453; z_abs_=2.1139). This is only the fourth known absorption at z>2. The detection rate (1.6_-1.4_^+3.8^%) suggests a low covering factor of the cold neutral medium (CNM; T~100K) associated with these powerful AGN. The intervening absorption line search, with a sensitivity to detect the CNM in damped Ly{alpha} systems (DLAs), has comoving absorption path lengths of {Delta}X=130.1 and 167.7 for HI and OH, respectively. The corresponding number of absorbers per unit comoving path length are <=0.014 and <=0.011, respectively. The former is at least 4.5 times lower than that of DLAs and consistent with the CNM cross section estimated using H_2_ and CI absorbers at z>2. Our AGN sample is optically fainter compared to the quasars used to search for DLAs in the past. In our optical spectra obtained using SALT and NOT, we detect five intervening (redshift path ~9.3) and two proximate DLAs. This is slightly excessive compared to the statistics based on optically selected quasars. The nondetection of HI 21cm absorption from these DLAs suggests a small CNM covering fraction around galaxies at z>2.
695. 2-35 micron point source IR sky model
ID:
ivo://CDS.VizieR/J/AJ/105/1860
Title:
2-35 micron point source IR sky model
Short Name:
J/AJ/105/1860
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Point Source Infrared Sky Model of Wainscoat et al. [ApJS, 83, 111 (1992)] is extended to make predictions for any filter lying wholly within the range 2.0 to 35.0 microns. The development of a library of complete 2-35micron low-resolution spectra (with 0.1micron step size) that represent the 87 categories of Galactic object and four types of extragalactic source implicit in the Model supports this extension. This library is based upon the "spectral template" technique whereby existing spectral fragments for individual sources (from ground-based, airborne, and satellite-borne instruments) are combined into complete spectra. Templates provide a natural way to represent the complete spectral energy distributions of celestial sources for which only infrared photometry and/or partial spectroscopy are available. Consequently, templates bear upon the important general problem of establishing midinfrared calibration sources. The new Model is validated by comparison with broadband K (2.2micron) source counts.
696. 1-1.4 micron spectral atlas of stars
ID:
ivo://CDS.VizieR/J/ApJS/142/79
Title:
1-1.4 micron spectral atlas of stars
Short Name:
J/ApJS/142/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of J-band (1.08 to 1.35{mu}m) stellar spectra at low resolution (R~400). The targets consist of 105 stars ranging in spectral type from O9.5 to M7 and luminosity classes I through V. The relatively featureless spectra of hot stars, earlier than A4, can be used to remove the atmospheric features which dominate ground-based J-band spectroscopy. We measure equivalent widths for three absorption lines and nine blended features which we identify in the spectra. Using detailed comparison with higher resolution spectra, we demonstrate that low-resolution data can be used for stellar classification, since several features depend on the effective temperature and gravity. For example, the CN index (1.096-1.104{mu}m) decreases with temperature, but the strength of a blended feature at 1.28{mu}m (consisting of primarily P{beta}) increases. The slope of a star's spectrum can also be used to estimate its effective temperature. The luminosity class of a star correlates with the ratio of the MgI (1.1831{mu}m) line to a blend of several species at 1.16{mu}m. Using these indicators, a star can be classified to within several subclasses. Fifteen stars with particularly high and low metal abundances are included in the catalog, and some spectral dependence on metal abundance is also found.
697. 100-Micron Survey of the Galactic Plane
ID:
ivo://CDS.VizieR/II/56
Title:
100-Micron Survey of the Galactic Plane
Short Name:
II/56
Date:
21 Oct 2021
Publisher:
CDS
Description:
The catalog represents a survey of a portion of the galactic plane at a wavelength of 100 micrometers with a balloon-borne, stabilized, 12-inch infrared telescope having a sensitivity of 10(-22) W/m2/Hz. The survey covers 750 square degrees of the sky, including most of the galactic plane between galactic longitudes of 335 and 88 degrees, plus a number of other selected areas of interest. Seventy-two sources have been detected, 60 of which are identified with continuum radio sources, bright nebulae, dark nebulae, and infrared stars. The catalog includes right ascension and declination (B1950.0), galactic coordinates, 100-micrometer peak flux densities, sizes of sources, and identifications.
698. Microquasar candidates
ID:
ivo://CDS.VizieR/J/A+A/477/125
Title:
Microquasar candidates
Short Name:
J/A+A/477/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
Microquasars are ideal natural laboratories for understanding accretion/ejection processes, studying the physics of relativistic jets, and testing gravitational phenomena. Nevertheless, these objects are difficult to find in our Galaxy. The main goal of this work is to increase the number of known systems of this kind, which should allow better testing of high-energy phenomena and more realistic statistical studies of this galactic population to be made. We have developed an improved search strategy based on positional cross-identification with very restrictive selection criteria to find new MQs, taking advantage of more sensitive modern X-ray data. To do this, we made combined use of the radio, infrared, and X-ray properties of the sources, using different available catalogs.
699. MIDI atlas of low- and intermediate-mass YSOs
ID:
ivo://CDS.VizieR/J/A+A/617/A83
Title:
MIDI atlas of low- and intermediate-mass YSOs
Short Name:
J/A+A/617/A83
Date:
21 Oct 2021
Publisher:
CDS
Description:
Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Archival mid-infrared interferometric data from the MIDI instrument on the Very Large Telescope Interferometer are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size-luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (r<~1au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming Multi-AperTure mid- Infrared SpectroScopic Experiment (MATISSE) instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
700. Mid-infrared diameter of 4 AGBs
ID:
ivo://CDS.VizieR/J/A+A/545/A56
Title:
Mid-infrared diameter of 4 AGBs
Short Name:
J/A+A/545/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
Asymptotic giant branch (AGB) stars are one of the largest distributors of dust into the interstellar medium. However, the wind formation mechanism and dust condensation sequence leading to the observed high mass-loss rates have not yet been constrained well observationally, in particular for oxygen-rich AGB stars. The immediate objective in this work is to identify molecules and dust species which are present in the layers above the photosphere, and which have emission and absorption features in the mid-infrared (IR), causing the diameter to vary across the N- band, and are potentially relevant for the wind formation. Mid-IR (8-13 micron) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbon-rich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 micron and gradually increases at wavelengths longer than 10 micron. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 micron. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H2O, and the gradual increase longward of 10 micron can be most likely attributed to the contribution of a close Al2O3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al2O3 in oxygen-rich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism. Future modeling with hydrostatic and self-consistent dynamical stellar atmospheric models will be required for a more certain understanding.