- ID:
- ivo://CDS.VizieR/J/A+A/538/A119
- Title:
- Spectrum of ^18^O-methyl formate (HCO^18^OCH_3_)
- Short Name:
- J/A+A/538/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range of organic molecules in order to be able to identify them. Very accurate spectroscopic constants are obtained in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict with very high precision the frequencies of transitions that have not been measured in the laboratory. In this work, an experimental study and its theoretical analysis is presented for two ^18^O-methyl formate isotopologues in order to detect for the first time both isotopologues in Orion KL. The experimental spectra of both isotopologues of methyl formate have been recorded in the microwave and sub-mm energy range from 1 to 660GHz. Both spectra have been analysed by using the Rho-Axis Method (RAM) which takes into account the CH3 internal rotation. Spectroscopic constants of both ^18^O-methyl formate have been obtained with high accuracy. Thousands of transitions were assigned and others predicted, which allowed us to detect both species in the IRAM 30m line survey of Orion KL for the first time in the space.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/605/A76
- Title:
- Spectrum of Orion KL between 41.5 and 50GHz
- Short Name:
- J/A+A/605/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We resent a sensitive spectral survey of Orion KL in Q-band (7mm), made with one of the 34m antennas of the Madrid Deep Space Communications Complex in Robledo de Chavela, Spain.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1560
- Title:
- Spitzer c2d small clouds and cores
- Short Name:
- J/AJ/133/1560
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a submillimeter survey of 53 low-mass dense cores with the Submillimeter High Angular Resolution Camera II (SHARC-II). The survey is a follow-up project to the Spitzer Legacy Program "From Molecular Cores to Planet-Forming Disks," with the purpose of creating a complete data set of nearby low-mass dense cores from the infrared to the millimeter. We present maps of 52 cores at 350um and three cores at 450um, two of which were observed at both wavelengths. Of these 52 cores, 41 were detected by SHARC-II; 32 contained one submillimeter source, while 9 contained multiple sources. For each submillimeter source detected, we report various source properties including source position, fluxes in various apertures, size, aspect ratio, and position angle.
- ID:
- ivo://CDS.VizieR/J/MNRAS/438/426
- Title:
- Spitzer interstellar bubbles
- Short Name:
- J/MNRAS/438/426
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The expansion of interstellar bubbles is suggested to be an important mechanism of triggering material accumulation and star formation. In this work, we investigate the gaseous environment of a large sample of interstellar bubbles identified by the Spitzer space telescope, aiming to explore the possible evidence of triggered gas accumulation and star formation in a statistical sense. By cross-matching 6124 Spitzer interstellar bubbles from the Milky Way Project (MWP) and more than 2500 Galactic HII regions collected by us, we obtain the velocity information for 818 MWP bubbles. To study the gaseous environment of the interstellar bubbles and get rid of the projection effect as much as possible, we constrain the velocity difference between the bubbles and the ^13^CO(1-0) emission extracted from the Galactic Ring Survey (GRS). Three methods: the mean azimuthally averaged radial profile of ^13^CO emission, the surface number density of molecular clumps and the angular cross-correlation function of MWP bubbles and the GRS molecular clumps are adopted. Significant over density of molecular gas is found to be close to the bubble rims. 60 percent of the studied bubbles were found to have associated molecular clumps. By comparing the clump-associated and the clump-unassociated MWP interstellar bubbles, we reveal that the bubbles in associations tend to be larger and thicker in physical sizes. From the different properties shown by the bubble-associated and bubble-unassociated clumps, we speculate that some of the bubble-associated clumps result from the expansion of bubbles. The fraction of the molecular clumps associated with the MWP bubbles is estimated to be about 20 percent after considering the projection effect. For the bubble-clump complexes, we found that the bubbles in the complexes with associated massive young stellar object(s) (MYSO(s)) have larger physical sizes, hence the complexes tend to be older. We propose that an evolutionary sequence might exist between the relatively younger MYSO-unassociated bubble-clump complexes and the MYSO-associated complexes.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/147
- Title:
- Spitzer-IRAC photometry of jets in Vela-D
- Short Name:
- J/ApJ/767/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of H_2_ jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer-IRAC data between 3.6 {mu}m and 8.0 {mu}m. Our search has led to the identification of 15 jets (two new discoveries) and about 70 well-aligned knots within 1.2 deg^2^. We compare the Infrared Array Camera (IRAC) maps with observations of the H_2_ 1-0 S(1) line at 2.12 {mu}m, with a Spitzer-MIPS map at 24 {mu}m and 70 {mu}m, and with a map of the dust continuum emission at 1.2 mm. From such a comparison, we find a tight association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the young stellar objects of VMR-D. In particular, we searched for all the sources of Class II or (preferentially) earlier which are located close to the jet center and aligned with it. Furthermore, the association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets, for which two alternative candidates are given. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 {mu}m, suggesting that they are very young protostars. Three of them are also associated with the most compact jets (projected length<~0.1 pc). The exciting source spectral energy distributions (SEDs) have been constructed and modeled by means of all the available photometric data between 1.2 {mu}m and 1.2 mm. From SEDs fits, we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24]-[70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.
816. Spitzer IRDCs
- ID:
- ivo://CDS.VizieR/J/ApJ/698/324
- Title:
- Spitzer IRDCs
- Short Name:
- J/ApJ/698/324
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a survey of a sample of infrared-dark clouds (IRDCs) with the Spitzer Space Telescope in order to explore their mass distribution. We present a method for tracing mass using dust absorption against the bright Galactic background at 8um. The IRDCs in this sample are comprised of tens of clumps, ranging in sizes from 0.02 to 0.3pc in diameter and masses from 0.5 to a few 10^3^M_{sun}_, the broadest dynamic range in any clump mass spectrum study to date.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/59
- Title:
- Spitzer/IRS observations of the Galactic Center
- Short Name:
- J/ApJ/857/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of HII regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal HII regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, HII region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/140
- Title:
- Stacked spectra of SDSS star forming galaxies
- Short Name:
- J/ApJ/765/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation between galaxy stellar mass and gas-phase metallicity is a sensitive diagnostic of the main processes that drive galaxy evolution, namely cosmological gas inflow, metal production in stars, and gas outflow via galactic winds. We employed the direct method to measure the metallicities of ~200000 star-forming galaxies from the Sloan Digital Sky Survey that were stacked in bins of (1) stellar mass and (2) both stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak [OIII]{lambda}4363 and [OII]{lambda}{lambda}7320,7330 auroral lines required to apply the direct method. These metallicity measurements span three decades in stellar mass from log(M_*_/M_{sun}_)=7.4-10.5, which allows the direct method mass-metallicity relation to simultaneously capture the high-mass turnover and extend a full decade lower in mass than previous studies that employed more uncertain strong line methods. The direct method mass-metallicity relation rises steeply at low mass (O/H{prop.to}M_*_^1/2^) until it turns over at log(M_*_/M_{sun}_)=8.9 and asymptotes to 12+log(O/H)=8.8 at high mass. The direct method mass-metallicity relation has a steeper slope, a lower turnover mass, and a factor of two to three greater dependence on SFR than strong line mass-metallicity relations. Furthermore, the SFR-dependence appears monotonic with stellar mass, unlike strong line mass-metallicity relations. We also measure the N/O abundance ratio, an important tracer of star formation history, and find the clear signature of primary and secondary nitrogen enrichment. N/O correlates tightly with oxygen abundance, and even more so with stellar mass.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A29
- Title:
- Star formation in massive clumps in Milky Way
- Short Name:
- J/A+A/588/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. A sample of 24 micron based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 micron dust continuum emission and NH_3_ line emission. Linear correlations are identified between the star formation rate surface density, Sigma_SFR and the quantities Sigma_H2/tau_ff and Sigma_H2/tau_cross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 micron saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2M_{sun}_) stars with emergent 24 micron fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified.
- ID:
- ivo://CDS.VizieR/J/ApJ/619/L95
- Title:
- Star formation in Stephan's Quintet
- Short Name:
- J/ApJ/619/L95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first Galaxy Evolution Explorer (GALEX) UV images of the well-known interacting group of galaxies, Stephan's Quintet (SQ). We detect widespread UV emission throughout the group. However, there is no consistent coincidence between UV structure and emission in the optical, H{alpha}, or HI. Excluding the foreground galaxy NGC 7320 (Sd), most of the UV emission is found in regions associated with the two spiral members of the group, NGC 7319 and NGC 7318b, and the intragroup medium starburst SQ-A. The extinction-corrected UV data are analyzed to investigate the overall star formation activity in SQ.