The large Coalsack dark cloud is one of the most prominent southern starless clouds, which is even visible to the naked eye. Furthermore, it is one of the rare molecular clouds without clear signs of star formation. We investigate the dynamical properties of the gas within the Coalsack. The two highest extinction regions were mapped with the APEX telescope in ^13^CO(2-1) comprising a region of ~1 square degree.
We examine the stellar velocity dispersions ({sigma}) of a sample of 48 galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants, the {sigma} derived from the near-infrared CO band heads is smaller than that measured from optical lines, while no discrepancy between these measurements is found for early-type galaxies. No such studies are available for spiral galaxies - the subject of this paper. We used cross-dispersed spectroscopic data obtained with the Gemini Near-Infrared Spectrograph, with spectral coverage from 0.85 to 2.5{mu}m, to obtain {sigma} measurements from the 2.29{mu}m CO band heads ({sigma}CO) and the 0.85{mu}m calcium triplet ({sigma}_CaT_). For the spiral galaxies in the sample, we found that {sigma}_CO_ is smaller than {sigma}_CaT_, with a mean fractional difference of 14.3 per cent. The best fit to the data is given by {sigma}_opt_=(46.0+/-18.1)+(0.85+/-0.12){sigma}_CO_. This '{sigma}-discrepancy' may be related to the presence of warm dust, as suggested by a slight correlation between the discrepancy and the infrared luminosity. This is consistent with studies that have found no {sigma}-discrepancy in dust-poor early-type galaxies, and a much larger discrepancy in dusty merger remnants and ULIRGs. That {sigma}_CO_ is lower than {sigma}opt may also indicate the presence of a dynamically cold stellar population component. This would agree with the spatial correspondence between low-{sigma}_CO_ and young/intermediate-age stellar populations that has been observed in spatially resolved spectroscopy of a handful of galaxies.
We seek to investigate the ^17^O/^18^O ratio for a sample of AGB stars containing M-, S-, and C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period. Circumstellar ^13^C^16^O, ^12^C^17^O, and ^12^C^18^O line observations were obtained for a sample of nine stars with various singledish long-wavelength facilities. Line intensity ratios are shown to relate directly to the surface ^17^O/^18^O abundance ratio. Stellar evolution models predict the ^17^O/^18^O ratio to be a sensitive function of initial mass and to remain constant throughout the entire TP-AGB phase for stars initially less massive than 5 solar masses. This makes the measured ratio a probe of the initial stellar mass. Observed ^17^O/^18^O ratios are found to be well in the range predicted by stellar evolution models that do not consider convective overshooting. From this, accurate initial mass estimates are calculated for seven sources. For the remaining two sources, there are two mass solutions, although there is a larger probability that the low-mass solution is correct. Finally, we present hints at a possible separation between M/S- and C-type stars when comparing the ^17^O/^18^O ratio to the stellar pulsation period.
CO and HCN observations of circumstellar envelopes
Short Name:
J/A+AS/99/291
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have searched the literature for all observations of the ^12^CO(1-0), ^12^CO(2-1), and HCN(1-0) lines in circumstellar envelopes of late type stars published between January 1985 and September 1992. We report data for 1361 observations (stellar velocity, expansion velocity, peak intensity, integrated area, noise level). This CO-HCN sample now contains 444 sources. 184 are identified as oxygen-rich, 205 as carbon-rich, and there are 9 S stars. About 85% of the sources are AGB stars. There are 32 planetary nebulae and about thirty post-AGB stars candidates. Besides results of millimeter observations, we also list identifications, coordinates, IRAS data, chemical and spectral types for every source. For AGB stars, we have estimated (or compiled) bolometric fluxes and distances for 349 sources, and mass loss rates deduced from CO results for 324 sources, taking into account the influence of the CO photodissociation radius. We also list mass loss rates derived from detailed models of CO emission which we could find in the literature.
Using SEST, the Parkes antenna and the Australia Telescope Compact Array, we have made a survey of the ^12^CO(1-0) and HI emission of an optically-selected sample of =~60 southern interacting and merging galaxies. In this paper we present the data and determine global masses of neutral gas (in molecular and atomic form) for the observed galaxies. We have detected HI in 26 systems and found that these galaxies have less than 15% of their gas in molecular form.
The carbon-to-oxygen ratio in a protoplanetary disk can have a dramatic influence on the compositions of any terrestrial planets formed. In regions of high C/O, planets form primarily from carbonates, and in regions of low C/O, the ratio of magnesium to silicon determines the types of silicates that dominate the compositions. We present C/O and Mg/Si ratios for 852 F, G, and K dwarfs in the solar neighborhood. We find that the frequency of carbon-rich dwarfs in the solar neighborhood is <0.13% and that 156 known planet hosts in the sample follow a similar distribution as all of the stars as a whole. The cosmic distribution of Mg/Si for these same stars is broader than the C/O distribution and peaks near 1.0, with ~60% of systems having 1<=Mg/Si<2, leading to rocky planet compositions similar to the Earth. This leaves 40% of systems that can have planets that are silicate-rich and that may have very different compositions than our own.
Core condensation is a critical step in the star-formation process, but it is still poorly characterized observationally. We have studied the 10pc-long L1495/B213 complex in Taurus to investigate how dense cores have condensed out of the lower density cloud material. We observed L1495/B213 in C^18^O(1-0), N_2_H^+^(1-0), and SO(J_N_=3_2_-2_1_) with the 14m FCRAO telescope, and complemented the data with dust continuum observations using APEX (870um) and IRAM 30m (1200um).
Based on the high resolution infrared spectra observed with the Fourier Transform Spectrometer (FTS) at the 4m telescope of the Kitt Peak National Observatory (KPNO), ro-vibrational lines of ^12^C^16^O, ^13^C^16^O, ^12^C^17^O, and ^16^OH were measured. Some details of the observed spectra including the resolution, S/N ratio, and data of observation are given in table2. The spectroscopic and equivalent width data are given in table3 for 23 red giant stars. The resulting data are used to investigate the nature of the infrared spectra of K-M giant stars. It is found that only the weak lines (log(W/nu)<-4.75) carry the information on the photosphere and hence can be used to extract the nature of the photosphere such as the stellar abundances. The intermediate-strength (-4.75<log(W/nu)<-4.40) as well as the strong (log(W/nu)>-4.4) lines are badly disturbed by the lines of non-photospheric origin. In other words, most lines dominating the infrared spectra, except for the weak lines, are actually hybrid of at least two different kinds of lines originating in the photosphere and in an extra molecular layers outside of photosphere. The nature of the extra layers is not known well, but it may be related to the molecular envelope producing H_2_O lines, not only in late M but also in early M giants as well. Also, the intermediate-strength lines include those with LEP as high as 2eV and hence the extra molecular layer should be quite warm. For the reason outlined above, we determine C, O, and their isotopic abundances using only the weak lines, but we listed the measured data not only of the weak lines but also of the stronger lines as well in table3, with the hope that these data can be of some use to clarify the nature of the warm extra molecular layers.
In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 Planck Galactic cold clumps (PGCCs) in the second quadrant of the Milky Way. Using the ^13^CO and C^18^O J=1-0 lines and 850{mu}m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the ^13^CO line and 850{mu}m continuum maps, respectively. We made use of the Bayesian distance calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of m~r^1.67^. At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency (~3.0%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850{mu}m cores are more turbulent, more optically thick, and denser than the ^13^CO clumps for star formation candidates, suggesting that the 850{mu}m cores are likely more appropriate future star formation candidates than the ^13^CO clumps.
The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of ^56^Ni to ^56^Co at early times, and the decay of ^56^Co to ^56^Fe from ~60 d after explosion. We examine the evolution of the [CoIII] {lambda}5893 emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of ^56^Co as a function of time. This result indicates both efficient local energy deposition from positrons produced in ^56^Co decay and long-term stability of the ionization state of the nebula. We compile SN Ia nebular spectra from the literature and present 21 new late-phase spectra of 7 SNe Ia, including SN 2014J. From these we measure the flux in the [CoIII] {lambda}5893 line and remove its well-behaved time dependence to infer the initial mass of ^56^Ni (M_Ni_) produced in the explosion. We then examine ^56^Ni yields for different SN Ia ejected masses (M_ej_ - calculated using the relation between light-curve width and ejected mass) and find that the ^56^Ni masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s~0.7-0.9), M_Ni_ is clustered near M_Ni_~0.4M_{sun}_ and shows a shallow increase as M_ej_ increases from ~1 to 1.4M_{sun}_; at high stretch, M_ej_ clusters at the Chandrasekhar mass (1.4M_{sun}_) while M_Ni_ spans a broad range from 0.6 to 1.2M_{sun}_. This could constitute evidence for two distinct SN Ia explosion mechanisms.