- ID:
- ivo://CDS.VizieR/J/ApJ/843/33
- Title:
- SOFIA Massive (SOMA) Star Formation Survey. I.
- Short Name:
- J/ApJ/843/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ~10 to 40{mu}m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid- infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m*~10-50M_{sun}_ accreting at ~10^-4^-10^-3^M_{sun}_/yr inside cores of initial masses Mc~30-500M_{sun}_ embedded in clumps with mass surface densities {Sigma}_cl_~0.1-3g/cm^2^. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ~100x smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/874/16
- Title:
- SOFIA Massive Star Formation Survey. II. 7 protostars
- Short Name:
- J/ApJ/874/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multiwavelength images observed with SOFIA-FORCAST from ~10 to 40{mu}m of seven high luminosity massive protostars, as part of the SOFIA Massive Star Formation Survey. Source morphologies at these wavelengths appear to be influenced by outflow cavities and extinction from dense gas surrounding the protostars. Using these images, we build spectral energy distributions (SEDs) of the protostars, also including archival data from Spitzer, Herschel, and other facilities. Radiative transfer (RT) models of Zhang & Tan (2018ApJ...853...18Z), based on Turbulent Core Accretion theory, are then fit to the SEDs to estimate key properties of the protostars. Considering the best five models fit to each source, the protostars have masses m*~12-64M_{sun}_ accreting at rates of dm/dt_*_~10^-4^-10^-3^M_{sun}_/yr inside cores of initial masses M_c_~100-500M_{sun}_ embedded in clumps with mass surface densities {Sigma}_cl_~0.1-3g/cm^2^ and span a luminosity range of 10^4^-10^6^L_{sun}_. Compared with the first eight protostars in Paper I (De Buizer+ 2017ApJ...843...33D), the sources analyzed here are more luminous and, thus, likely to be more massive protostars. They are often in a clustered environment or have a companion protostar relatively nearby. From the range of parameter space of the models, we do not see any evidence that {Sigma}cl needs to be high to form these massive stars. For most sources, the RT models provide reasonable fits to the SEDs, though the cold clump material often influences the long wavelength fitting. However, for sources in very clustered environments, the model SEDs may not be such a good description of the data, indicating potential limitations of the models for these regions.
- ID:
- ivo://CDS.VizieR/J/ApJS/210/12
- Title:
- Solar photoionization rates
- Short Name:
- J/ApJS/210/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extreme UV (EUV) spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment are used to infer photoionization rates in the inner heliosphere. Relating these rates to various proxies describing the solar EUV radiation, we construct a multi-linear model which allows us to extrapolate ionization rates back to periods when no routine measurements of the solar EUV spectral distribution have been available. Such information is important, e.g., for comparing conditions of the interstellar neutral particles in the inner heliosphere at the time of Ulysses/GAS observations with conditions during the more recent observations of the Interstellar Boundary Explorer. From a period of 11 yr when detailed spectra from both TIMED and three proxies -- Solar and Heliospheric Observatory/CELIAS/SEM-rates, F10.7 radio flux, and Mg II core-to-wing indices -- have been available, we conclude that the simple model is able to reproduce the photoionization rates with an uncertainty of typically 5%.
- ID:
- ivo://CDS.VizieR/J/A+A/605/L3
- Title:
- SOLIS. II. L1157-B1 NH_2_CHO image
- Short Name:
- J/A+A/605/L3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Modern versions of the Miller-Urey experiment claim that formamide (NH_2_CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming Solar-type stars as well as in external galaxies. How NH_2_CHO is formed has been a puzzle for decades: our goal is to contribute to the hotly debated question of whether formamide is mostly formed via gas-phase or grain surface chemistry. We used the NOEMA interferometer to image NH_2_CHO towards the L1157-B1 blue-shifted shock, a well known interstellar laboratory, to study how the components of dust mantles and cores released into the gas phase triggers the formation of formamide. Results. We report the first spatially resolved image (size ~9", ~2300AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM~=5km/s. A column density of N(NH_2_CHO)=8x10^12^cm^-1^, and an abundance (with respect to H-nuclei) of 4x10^-9^ are derived. We show a spatial segregation of formamide with respect to other organic species. Our observations, coupled with a chemical modelling analysis, indicate that the formamide observed in L1157-B1 is formed by gas-phase chemical process, and not on grain surfaces as previously suggested. The SOLIS interferometric observations of formamide provide direct evidence that this potentially crucial brick of life is efficiently formed in the gas-phase around Sun-like protostars.
- ID:
- ivo://CDS.VizieR/J/A+A/605/A57
- Title:
- SOLIS. I. OMC2-FIR4 HC_3_N and HC_5_N images
- Short Name:
- J/A+A/605/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, meaning that they could be excellent reservoirs of carbon. The simplest member, HC_3_N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects them, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC_3_N and HC_5_N, in the protocluster OMC-2 FIR4. Because our Sun is thought to be born in a rich cluster, OMC-2 FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC_3_N/HC_5_N abundance ratio across the source in the range ~1-30, with the smallest values (<10) in FIR5 and in the Eastern region of FIR4. The ratios <=10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate z is ~4x10^-14^s^-1^; (2) the gaseous elemental ratio C/O is close to unity; and (3) oxygen and carbon are largely depleted. The large z is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (>10MeV) particles from embedded sources. We suggest that these sources could lie East of FIR4 and FIR5.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A75
- Title:
- SOLIS. X. NGC 1333 IRAS 4A images
- Short Name:
- J/A+A/640/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar complex organic molecules (iCOMs) are C-bearing molecules containing at least six atoms; two main proposals for their formation are suggested: a direct formation in the icy mantle of the dust grains and formation through the reaction in gas phase of released grain mantle species. The shocked gas along outflows driven by low-mass protostars is a unique environment to study how the iCOMs can be formed as the composition of the dust mantles is sputtered into the gas phase. The chemical richness in shocked material associated with low-mass protostellar outflows has been so far studied in the prototypical L1157 blue-shifted outflow to investigate the iCOM formation routes. To understand whether the case of L1157-B1 is unique, we imaged and studied the IRAS 4A outflows in the NGC 1333 star forming region. We used the NOrthern Extended Millimeter Array (NOEMA) interferometer as part of the IRAM Seeds Of Life in Space (SOLIS) Large Program to image the large-scale bipolar outflows driven by the IRAS 4A system in the 3 mm band, and we compared the observation with the GRAINOBLE+ astrochemical model. We report the first detection, in the IRAS 4A outflows, of several iCOMs: six lines of methanol (CH_3_OH), eight of acetaldehyde (CH_3_CHO), one of formamide (NH_2_CHO), and four of dimethyl ether (CH_3_OCH_3_), all sampling upper excitation energy up to 30K. We found a significant chemical differentiation between the southeast outflow driven by the IRAS 4A1 protostar, showing a richer molecular content, and the north-southwest one driven by the IRAS 4A2 hot corino. The CH_3_OH/CH_3_CHO abundance ratio is lower by a factor of 4 in the former; furthermore, the ratio in the IRAS 4A outflows is lower by a factor of 10 with respect to the values found in different hot corinos. After L1157-B1, the IRAS 4A outflow is now the second outflow to show an evident chemical complexity. Given that CH_3_OH is a grain surface species, the astrochemical gas-phase model run with GRAINOBLE+ reproduced our observation assuming that acetaldehyde is formed mainly through the gas-phase reaction of the ethyl radical (CH_3_CH_2_) and atomic oxygen. Furthermore, the chemical differentiation between the two outflows suggests that the IRAS 4A1 outflow is likely younger than that of the IRAS 4A2. Further investigation is needed to constrain the age of the outflow. In addition, observation of even younger shocks are necessary. In order to provide strong constraints on the CH_3_CHO formation mechanisms it would be interesting to observe CH_3_CH_2_, but given that its frequencies are not known, future spectroscopic studies on this species are needed.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A146
- Title:
- Southern Hemisphere ISM FORS2 spectropolarimetry
- Short Name:
- J/A+A/608/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/176
- Title:
- 19 species in 14 super stars clusters in NGC 253
- Short Name:
- J/ApJ/897/176
- Date:
- 14 Mar 2022 07:03:40
- Publisher:
- CDS
- Description:
- We present submillimeter spectra of the (proto-)super star cluster (SSC) candidates in the starbursting center of the nearby galaxy NGC 253 identified by Leroy et al. The 2.5pc resolution of our Atacama Large Millimeter/submillimeter Array cycle 3 observations approaches the size of the SSCs and allows for the study of physical and chemical properties of the molecular gas in these sources. In the 14 SSC sources and in the frequency ranges 342.0-345.8GHz and 353.9-357.7GHz, we detect 55 lines belonging to 19 different chemical species. The SSCs differ significantly in chemical complexity, with the richest clusters showing 19 species and the least complex showing four species. We detect HCN isotopologues and isomers (H13CN, HC15N, H15NC), abundant HC3N, SO and S18O, SO2, and H2CS. The gas ratios CO/HCN, CO/HCO+ are low, ~1-10, implying high dense gas fractions in the SSCs. Line ratio analyses suggests chemistry consistent with photon-dominated regions and mechanical heating. None of the SSCs near the galaxy center show line ratios that imply an X-ray-dominated region, suggesting that heating by any (still unknown) active galactic nucleus does not play a major role. The gas temperatures are high in most sources, with an average rotational temperature of ~130K in SO2. The widespread existence of vibrationally excited HCN and HC3N transitions implies strong infrared radiation fields, potentially trapped by a greenhouse effect due to high continuum opacities.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A37
- Title:
- Spectral cube toward NGC 6334 I and I(N)
- Short Name:
- J/A+A/593/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HF molecule has been proposed as a sensitive tracer of diffuse interstellar gas, while at higher densities its abundance could be influenced heavily by freeze-out onto dust grains. We investigate the spatial distribution of a collection of absorbing gas clouds, some associated with the dense, massive star-forming core NGC 6334 I, and others with diffuse foreground clouds elsewhere along the line of sight. For the former category, we aim to study the dynamical properties of the clouds in order to assess their potential to feed the accreting protostellar cores. We use far-infrared spectral imaging from the Herschel SPIRE iFTS to construct a map of HF absorption at 243um in a 6'x3.5' region surrounding NGC 6334 I and I(N).
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/3842
- Title:
- Spectral line survey of two LOSs
- Short Name:
- J/MNRAS/446/3842
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of two Mopra 3-mm spectral line surveys of the lines of sight (LOS) towards the Galactic Centre (GC) molecular complexes Sgr B2 (LOS+0.693) and Sgr A (LOS-0.11). The spectra covered the frequency ranges of ~77-93 GHz and ~105-113 GHz. We have detected 38 molecular species and 25 isotopologues. The isotopic ratios derived from column density ratios are consistent with the canonical values, indicating that chemical isotopic fractionation and/or selective photodissociation can be considered negligible (<10 percent) for the GC physical conditions. The derived abundances and rotational temperatures are very similar for both LOSs, indicating very similar chemical and excitation conditions for the molecular gas in the GC. The excitation conditions are also very similar to those found for the nucleus of the starburst galaxy NGC 253. We report for the first time the detection of HCO and HOC^+^ emission in LOS+0.693. Our comparison of the abundance ratios between CS, HCO, HOC^+^ and HCO^+^ found in the two LOSs with those in typical Galactic photodissociation regions (PDRs) and starbursts galaxies does not show any clear trend to distinguish between ultraviolet- and X-ray-induced chemistries. We propose that the CS/HOC^+^ ratio could be used as a tracer of the PDR components in the molecular clouds in the nuclei of galaxies.
