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- ID:
- ivo://CDS.VizieR/J/A+A/622/A99
- Title:
- Starless MDCs of NGC6334 molecular spectra
- Short Name:
- J/A+A/622/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of high-mass stars remains unknown in many aspects. Two families of models compete to explain the formation of high-mass stars. On the one hand, quasi-static models predict the existence of high-mass pre-stellar cores sustained by a high degree of turbulence. On the other hand competitive accretion models predict that high-mass proto-stellar cores evolve from low/intermediate mass proto-stellar cores in dynamic environments. The aim of the present work is to bring observational constraints at the scale of high-mass cores (~0.03pc). We targeted with ALMA and MOPRA a sample of 9 starless massive dense cores (MDCs) discovered in a recent Herschel/HOBYS study. Their mass and size (~110M_{sun}_ and r=0.1pc, respectively) are similar to the initial conditions used in the quasi-static family of models explaining for the formation of high-mass stars.We present ALMA 1.4mm continuum observations that resolve the Jeans length ({lambda}_Jeans_~0.03pc) and that are sensitive to the Jeans mass (M_Jeans_~0.65M_{sun}_) in the 9 starless MDCs, together with ALMA-^12^CO(2-1) emission line observations. We also present HCO^+^(1-0), H^13^CO+(1-0) and N_2_H^+^(1-0) molecular lines from the MOPRA telescope for 8 of the 9 MDCs. The 9 starless MDCs have the mass reservoir to form high-mass stars according to the criteria by Baldeschi et al. (2017MNRAS.466.3682B). Three of the starless MDCs are subvirialized with {alpha}_vir_~0.35, and 4 MDCs show sign of collapse from their molecular emission lines. ALMA observations show very little fragmentation within the MDCs. Only two of the starless MDCs host compact continuum sources, whose fluxes correspond to <3M_{sun}_ fragments. Therefore the mass reservoir of the MDCs has not yet been accreted onto compact objects, and most of the emission is filtered out by the interferometer. These observations do not support the quasi-static models for high-mass star formation since no high-mass pre-stellar core is found in NGC6334. The competitive accretion models, on the other hand, predict a level of fragmentation much higher than what we observe
17883. Starlight polarization
- ID:
- ivo://CDS.VizieR/J/A+A/624/L8
- Title:
- Starlight polarization
- Short Name:
- J/A+A/624/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic dust emission is polarized at unexpectedly high levels, as revealed by Planck. The origin of the observed 20% polarization fractions can be identified by characterizing the properties of optical starlight polarization in a region with maximally polarized dust emission. We measure the R-band linear polarization of 22 stars in a region with a submillimeter polarization fraction of 20%. A subset of 6 stars is also measured in the B, V, and I bands to investigate the wavelength dependence of polarization. We find that starlight is polarized at correspondingly high levels. Through multiband polarimetry we find that the high polarization fractions are unlikely to arise from unusual dust properties, such as enhanced grain alignment. Instead, a favorable magnetic field geometry is the most likely explanation, and is supported by observational probes of the magnetic field morphology. The observed starlight polarization exceeds the classical upper limit of [pV/E(B-V]_{max}_=9%/mag and is at least as high as 13%/mag, as inferred from a joint analysis of Planck data, starlight polarization and reddening measurements. Thus, we confirm that the intrinsic polarizing ability of dust grains at optical wavelengths has long been underestimated.
- ID:
- ivo://CDS.VizieR/J/AJ/137/3245
- Title:
- STARMIND MK standard's database
- Short Name:
- J/AJ/137/3245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrophysics is evolving toward a more rational use of costly observational data by intelligently exploiting the large terrestrial and spatial astronomical databases. In this paper, we present a study showing the suitability of an expert system to perform the classification of stellar spectra in the Morgan and Keenan (MK) system. Using the formalism of artificial intelligence for the development of such a system, we propose a rules' base that contains classification criteria and confidence grades, all integrated in an inference engine that emulates human reasoning by means of a hierarchical decision rules tree that also considers the uncertainty factors associated with rules. Our main objective is to illustrate the formulation and development of such a system for an astrophysical classification problem. An extensive spectral database of MK standard spectra has been collected and used as a reference to determine the spectral indexes that are suitable for classification in the MK system. It is shown that by considering 30 spectral indexes and associating them with uncertainty factors, we can find an accurate diagnose in MK types of a particular spectrum. The system was evaluated against the NOAO-INDO-US spectral catalog.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/44
- Title:
- Star motions in the nuclear cluster of the MW
- Short Name:
- J/ApJ/821/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain the basic properties of the nuclear cluster of the Milky Way. First, we investigate the structural properties by constructing a stellar density map of the central 1000" using extinction-corrected old star counts from VISTA, WFC3/IR, and VLT/NACO data. We describe the data using two components. The inner, slightly flattened (axis ratio of q=0.80+/-0.04) component is the nuclear cluster, while the outer component corresponds to the stellar component of the circumnuclear zone. For the nuclear cluster, we measure a half-light radius of 178+/-51"~7+/-2pc and a luminosity of M_Ks_=-16.0+/-0.5. Second, we measure detailed dynamics out to 4pc. We obtain 10351 proper motions from AO data, and 2513 radial velocities from VLT/SINFONI data. We determine the cluster mass by means of isotropic spherical Jeans modeling. We fix the distance to the Galactic Center and the mass of the supermassive black hole. We model the cluster either with a constant M/L or with a power law. For the latter case, we obtain a slope of 1.18+/-0.06. We get a cluster mass within 100" of M_100"_=(6.09+/-0.53|_fixR_0_+/-0.97|_R_0_)x10^6^M_{sun}_ for both modeling approaches. A model which includes the observed flattening gives a 47% larger mass (see Chatzopoulos et al. 2015MNRAS.447..948C). Our results slightly favor a core over a cusp in the mass profile. By minimizing the number of unbound stars within 8", we obtain a distance of R_0_=8.53_-0.15_^+0.21^kpc when using an R0 supermassive black hole mass relation from stellar orbits. Combining our results, we obtain M/L=0.51+/-0.12M_{sun}/L_{sun},Ks_, which is roughly consistent with a Chabrier IMF.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/71
- Title:
- Star polarization in the Galactic plane
- Short Name:
- J/ApJ/749/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work combines new observations of NIR starlight linear polarimetry with previously simulated observations in order to constrain dynamo models of the Galactic magnetic field. Polarimetric observations were obtained with the Mimir instrument on the Perkins Telescope in Flagstaff, AZ, along a line of constant Galactic longitude ({ell}=150{deg}) with 17 pointings of the 10'x10' field of view between -75{deg}<b<10{deg}, with more frequent pointings toward the Galactic midplane. A total of 10962 stars were photometrically measured and 1116 had usable polarizations. The observed distribution of polarization position angles with Galactic latitude and the cumulative distribution function of the measured polarizations are compared to predicted values. While the predictions lack the effects of turbulence and are therefore idealized, this comparison allows significant rejection of A0-type magnetic field models. S0 and disk-even halo-odd magnetic field geometries are also rejected by the observations, but at lower significance. New predictions of spiral-type, axisymmetric magnetic fields, when combined with these new NIR observations, constrain the Galactic magnetic field spiral pitch angle to -6{deg}+/-2{deg}.
- ID:
- ivo://CDS.VizieR/J/A+AS/53/181
- Title:
- Star positions in 14 southern galactic clusters
- Short Name:
- J/A+AS/53/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Positions for a total of 3487 stars, scattered over 14 regions, have been determined using the Danish 1.5-m telescope at La Silla. The 14 regions are centred on one of the southern galactic clusters NGC 1981, 2287, 2437, 2451, 2516, 2546, 2547, 2548, 3114, 3532, IC 2391, 2395, 2602 and Trumpler 10. Combining the Ritchey-Chretien reflector optics with a single element Schmidt-type corrector, gives a considerably enlarged flat field (radius about 25 minutes of arc, or 95mm) with stellar images of excellent definition. With the exception of distortion, which can be allowed for, the effect of the primary aberrations is negligible. A frame of reference has been established for each region using ESO Schmidt plates centred on the clusters, each plate containing from 20 to 35 measurable Perth 70 stars. These objects have served for determining positions of some 200 to 400 fainter stars within a central field of 25 minutes of arc radius, covering the corresponding 1.5-m plates. The fainter stars serve as a secondary standard. Based on three 1.5-m plates for each region, taken on different nights, an internal mean error in one plate position in the range 0.030 to 0.048 seconds of arc has been derived.
- ID:
- ivo://CDS.VizieR/J/AN/283/109
- Title:
- Star positions in the region of alpha Per
- Short Name:
- J/AN/283/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This file contains 1221 stars observed for spectral type in the field of the alpha Persei cluster. The types were published in the well known proper-motion survey by Heckmann et al. (1956AN....283..109H), and were determined by Wachmann with the equipment and methods used for the Bergedorf selected areas surveys (BSD). In general the brighter HD stars were not observed for spectral type, but most of these have been classified on the MK system by Roman & Morgan (1950ApJ...111..426R) and in later work. Nearly all the stars are included in SIMBAD with the source positions, and most also appear in WEBDA with these data as well. The positions below are nearly all from UCAC2 (for both epoch and equinox J2000), and thus differ by a few arcsec mainly from proper motion, but also from the systematic shift between the FK3 to the ICRS. In general the spectral types are not present in SIMBAD or WEBDA. I worked from Alain Fresneau's compilation for the field, which is based largely on the Heckmann data (Cat. <I/68>). I ran those coordinates into VizieR looking at UCAC2, Tycho-2, and the Fabricius Tycho double-star catalogue (Cat. <I/276>). Coordinates for two crowded stars were obtained from 2MASS. With one exception all the stars were found quite close to the predicted positions. Close pairs are indicated in the notes, as are stars with substantial proper motion (>>0.1"/year).
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/3393
- Title:
- Stars and globulars in NGC4494
- Short Name:
- J/MNRAS/415/3393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of the spatial, kinematic and chemical properties of stars and globular clusters (GCs) in the 'ordinary' elliptical galaxy NGC 4494 using data from the Keck and Subaru telescopes. We derive galaxy surface brightness and colour profiles out to large galactocentric radii. We compare the latter to metallicities derived using the near-infrared Calcium Triplet. We obtain stellar kinematics out to ~3.5 effective radii.
- ID:
- ivo://CDS.VizieR/J/A+A/521/A61
- Title:
- Stars associated to Eagle Nebula (M16=NGC6611)
- Short Name:
- J/A+A/521/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive star-forming regions are characterized by intense ionizing fluxes, strong stellar winds and, occasionally, supernovae explosions, all of which have important effects on the surrounding media, on the star-formation process and on the evolution of young stars and their circumstellar disks. We present a multiband study of the massive young cluster NGC 6611 and its parental cloud (the Eagle Nebula) with the aim of studying how OB stars affect the early stellar evolution and the formation of other stars. We search for evidence of triggering of star formation by the massive stars inside NGC 6611 on a large spatial scale (~10 parsec) and ongoing disk photoevaporation in NGC 6611 and how its efficiency depends on the mass of the central stars.