- ID:
- ivo://CDS.VizieR/J/A+A/552/A40
- Title:
- MSX high-contrast IRDCs with NH_3_
- Short Name:
- J/A+A/552/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 220 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15K, are turbulent (with line width FWHMs around 2km/s), have ammonia column densities on the order of 10^14^cm^-2^ and molecular hydrogen column densities on the order of 10^22^cm^-2^. Their virial masses are between 100 and a few 1000M_{sun}_. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/876/23
- Title:
- Multiple populations of extrasolar gas giants
- Short Name:
- J/ApJ/876/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There are two planetary formation scenarios: core accretion and gravitational disk instability. Based on the fact that gaseous objects are preferentially observed around metal-rich host stars, most extrasolar gaseous objects discovered to date are thought to have been formed by core accretion. Here, we present 569 samples of gaseous planets and brown dwarfs found in 485 planetary systems that span three mass regimes with boundary values at 4 and 25 Jupiter-mass masses through performing cluster analyses of these samples regarding the host-star metallicity, after minimizing the impact of the selection effect of radial-velocity measurement on the cluster analysis. The larger mass is thought to be the upper mass limit of the objects that were formed during the planetary formation processes. In contrast, the lower mass limit appears to reflect the difference between planetary formation processes around early-type and G-type stars; disk instability plays a greater role in the planetary formation process around early-type stars than that around G-type stars. Populations with masses between 4 and 25 Jupiter masses that orbit early-type stars comprise planets formed not only via the core-accretion process but also via gravitational disk instability because the population preferentially orbits metal-poor stars or is independent of the host-star metallicity. Therefore, it is essential to have a hybrid scenario for the planetary formation of the diverse systems.
- ID:
- ivo://CDS.VizieR/J/AJ/154/184
- Title:
- Multiplicity of RV exoplanet host stars
- Short Name:
- J/AJ/154/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Given the frequency of stellar multiplicity in the solar neighborhood, it is important to study the impacts this can have on exoplanet properties and orbital dynamics. There have been numerous imaging survey projects established to detect possible low-mass stellar companions to exoplanet host stars. Here, we provide the results from a systematic speckle imaging survey of known exoplanet host stars. In total, 71 stars were observed at 692 and 880 nm bands using the Differential Speckle Survey Instrument at the Gemini-north Observatory. Our results show that all but two of the stars included in this sample have no evidence of stellar companions with luminosities down to the detection and projected separation limits of our instrumentation. The mass-luminosity relationship is used to estimate the maximum mass a stellar companion can have without being detected. These results are used to discuss the potential for further radial velocity follow-up and interpretation of companion signals.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/77
- Title:
- MW halo. III. Statistical chemical abundances
- Short Name:
- J/ApJ/749/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We find that the relative contribution of satellite galaxies accreted at high redshift to the stellar population of the Milky Way's smooth halo increases with distance, becoming observable relative to the classical smooth halo about 15 kpc from the Galactic center. In particular, we determine line-of-sight-averaged [Fe/H] and [{alpha}/Fe] in the metal-poor main-sequence turnoff (MPMSTO) population along every Sloan Extension for Galactic Understanding and Exploration (SEGUE) spectroscopic line of sight. Restricting our sample to those lines of sight along which we do not detect elements of cold halo substructure (ECHOS), we compile the largest spectroscopic sample of stars in the smooth component of the halo ever observed in situ beyond 10 kpc. We find significant spatial autocorrelation in [Fe/H] in the MPMSTO population in the distant half of our sample beyond about 15 kpc from the Galactic center. Inside of 15 kpc however, we find no significant spatial autocorrelation in [Fe/H]. At the same time, we perform SEGUE-like observations of N-body simulations of Milky Way analog formation. While we find that halos formed entirely by accreted satellite galaxies provide a poor match to our observations of the halo within 15 kpc of the Galactic center, we do observe spatial autocorrelation in [Fe/H] in the simulations at larger distances. This observation is an example of statistical chemical tagging and indicates that spatial autocorrelation in metallicity is a generic feature of stellar halos formed from accreted satellite galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A115
- Title:
- Na and Al abundances of 1303 stars
- Short Name:
- J/A+A/589/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~1.5-2.0M_{aun}_. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. We re-address both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters and ii) low- and intermediate-mass clump giants in six open clusters. Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A54
- Title:
- NaI and CaII interstellar absorption
- Short Name:
- J/A+A/510/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high resolution (R>50000) absorption measurements of the NaI doublet (5889-5895{AA}) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933{AA}) absorption line. We have combined these new data with previously reported measurements to produce a catalog of absorptions towards a total of 1857 early-type stars located within 800pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized interstellar gas density within a distance-cube of 300pc from the Sun.
957. NaI in Local Bubble
- ID:
- ivo://CDS.VizieR/J/A+A/346/785
- Title:
- NaI in Local Bubble
- Short Name:
- J/A+A/346/785
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present preliminary results form a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, taking advantage of Hipparcos stellar distances. Equivalent width of the NaI D-line doublet at 5890{AA} are presented for the lines-of-sight towards some 143 new target stars lying within 300pc of the Sun.
- ID:
- ivo://CDS.VizieR/III/25A
- Title:
- Na, Mg, Ca abundances in K-type giants
- Short Name:
- III/25A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Narrow-band photometric measures of the strengths of the Mg b, Ca triplet, and Na D lines on 312 G and K type giant stars have been analysed with a model atmosphere technique to determine abundances of Mg, Ca and Na.
- ID:
- ivo://CDS.VizieR/J/A+A/517/A81
- Title:
- 2nd and 3d parameters of HB of globular clusters
- Short Name:
- J/A+A/517/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second parameter (the first being metallicity) defining the distribution of stars on the horizontal branch (HB) of globular clusters (GCs) has long been one of the major open issues in our understanding of the evolution of normal stars. Large photometric and spectroscopic databases are now available: they include large and homogeneous sets of colour-magnitude diagrams, cluster ages, and homogeneous data about chemical compositions from our FLAMES survey. We use these databases to re-examine this issue. Methods. We use the photometric data to derive median and extreme (i.e., the values including 90% of the distribution) colours and magnitudes of stars along the HB for about a hundred GCs. We transform these into median and extreme masses of stars on the HB, using the models developed by the Pisa group, and taking into account evolutionary effects. We compare these masses with those expected at the tip of the red giant branch (RGB) to derive the total mass lost by the stars.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A143
- Title:
- Nearby B-stars stellar parameters and abundances
- Short Name:
- J/A+A/539/A143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or HII regions. A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established.
