Discovery of Broad Molecular lines and of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, Spitzer and SOFIA Observations

We report a discovery of shocked gas from the supernova remnant (SNR) G357.7+0.3. Our millimeter and submillimeter observations reveal broad molecular lines of CO(2-1), CO(3-2), CO(4-3), 13CO (2-1) and 13CO (3-2), HCO^+ and HCN using HHSMT, Arizona 12-Meter Telescope, APEX and MOPRA Telescope. The widths of the broad lines are 15-30 kms, and the detection of such broad lines is unambiguous, dynamic evidence showing that the SNR G357.7+0.3 is interacting with molecular clouds. The broad lines appear in extended regions (>4.5'x5'). We also present detection of shocked H2 emission in mid-infrared but lacking ionic lines using the Spitzer IRS observations to map a few arcmin area. The H2 excitation diagram shows a best-fit with a two-temperature LTE model with the temperatures of ~200 and 660 K. We observed [C II] at 158um and high-J CO(11-10) with the GREAT on SOFIA. The GREAT spectrum of [C II], a 3 sigma detection, shows a broad line profile with a width of 15.7 km/s that is similar to those of broad CO molecular lines. The line width of [C~II] implies that ionic lines can come from a low-velocity C-shock. Comparison of H2 emission with shock models shows that a combination of two C-shock models is favored over a combination of C- and J-shocks or a single shock. We estimate the CO density, column density, and temperature using a RADEX model. The best-fit model with n(H2) = 1.7x10^{4} cm^{-3}, N(CO) = 5.6x10^{16} cm^{-2}, and T = 75 K can reproduce the observed millimeter CO brightnesses.Comment: 19 pages, 22 figure

The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds: III. The Serpens Cloud in CO J=2-1 and 13CO J=2-1 Emission

We mapped 12CO and 13CO J = 2-1 emission over 1.04 square deg of the Serpens molecular cloud with 38 arcsec spatial and 0.3 km/s spectral resolution using the Arizona Radio Observatory Heinrich Hertz Submillimeter telescope. Our maps resolve kinematic properties for the entire Serpens cloud. We also compare our velocity moment maps with known positions of Young Stellar Objects (YSOs) and 1.1 mm continuum emission. We find that 12CO is self-absorbed and 13CO is optically thick in the Serpens core. Outside of the Serpens core, gas appears in filamentary structures having LSR velocities which are blue-shifted by up to 2 km/s relative to the 8 km/s systemic velocity of the Serpens cloud. We show that the known Class I, Flat, and Class II YSOs in the Serpens core most likely formed at the same spatial location and have since drifted apart. The spatial and velocity structure of the 12CO line ratios implies that a detailed 3-dimensional radiative transfer model of the cloud will be necessary for full interpretation of our spectral data. The starless cores region of the cloud is likely to be the next site of star formation in Serpens.Comment: 41 pages, 15 figure

The abundance of HCN in circumstellar envelopes of AGB stars of different chemical types

A multi-transition survey of HCN (sub-) millimeter line emission from a large sample of AGB stars of different chemical type is presented. The data are analysed and circumstellar HCN abundances are estimated. The sample stars span a large range of properties such as mass-loss rate and photospheric C/O-ratio. The analysis of the new data allows for more accurate estimates of the circumstellar HCN abundances and puts new constraints on chemical models. In order to constrain the circumstellar HCN abundance distribution a detailed non-LTE excitation analysis, based on the Monte Carlo method, is performed. Effects of line overlaps and radiative excitation from dust grains are included. The median values for the derived abundances of HCN (with respect to H2) are 3x10-5, 7x10-7 and 10-7 for carbon stars (25 stars), S-type AGB stars (19 stars) and M-type AGB stars (25 stars), respectively. The estimated sizes of the HCN envelopes are similar to those obtained in the case of SiO for the same sample of sources and agree well with previous results from interferometric observations, when these are available. We find that there is a clear dependence of the derived circumstellar HCN abundance on the C/O-ratio of the star, in that carbon stars have about two orders of magnitude higher abundances than M-type AGB stars, on average. The derived HCN abundances of the S-type AGB stars have a larger spread and typically fall in between those of the two other types, however, slightly closer to the values for the M-type AGB stars. For the M-type stars, the estimated abundances are much higher than what would be expected if HCN is formed in thermal equilibrium. However, the results are also in contrast to predictions from recent non-LTE chemical models, where very little difference is expected in the HCN abundances between the various types of AGB stars.Comment: Accepted for publication in A&

Star formation in the S233 region

The main objective of this paper is to study the possibility of triggered star formation on the border of the HII region S233, which is formed by a B-star. Using high-resolution spectra we determine the spectral class of the ionizing star as B0.5 V and the radial velocity of the star to be -17.5(1.4) km/s. This value is consistent with the velocity of gas in a wide field across the S233 region, suggesting that the ionizing star was formed from a parent cloud belonging to the S233 region. By studying spatial-kinematic structure of the molecular cloud in the S233 region, we detected an isolated clump of gas producing CO emission red-shifted relative to the parent cloud. In the UKIDSS and WISE images, the clump of gas coincides with the infrared source containing a compact object and bright-rimmed structure. The bright-rimmed structure is perpendicular to the direction of the ionizing star. The compact source coincides in position with IRAS source 05351+3549. All these features indicate a possibility of triggering formation of a next-generation star in the S233 region. Within the framework of a theoretical one-dimensional model we conclude that the "collect-and-collapse" process is not likely to take place in the S233 region. The presence of the bright-rimmed structure and the compact infrared source suggest that the "collapse of the pre-existing clump" process is taking place.Comment: 12 pages, 10 figure

Observational Constraints on Submillimeter Dust Opacity

Infrared extinction maps and submillimeter dust continuum maps are powerful probes of the density structure in the envelope of star-forming cores. We make a direct comparison between infrared and submillimeter dust continuum observations of the low-mass Class 0 core, B335, to constrain the ratio of submillimeter to infrared opacity (κ_(smm)/κ_(ir)) and the submillimeter opacity power-law index (κ ∝ λ–β). Using the average value of theoretical dust opacity models at 2.2 μm, we constrain the dust opacity at 850 and 450 μm. Using new dust continuum models based upon the broken power-law density structure derived from interferometric observations of B335 and the infall model derived from molecular line observations of B335, we find that the opacity ratios are ^κ_(850)_κ_(2.2) = (3.21 - 4.80)^(+0.44)_(-0.30) x 10^(-4) ^κ_(450)_κ(2.0) = (12.8-24.8)^(+2.4)_(-1.3) x 10^(-4) with a submillimeter opacity power-law index of β_(smm) = (2.18-2.58)^(+0.30)_(–0.30). The range of quoted values is determined from the uncertainty in the physical model for B335. For an average 2.2 μm opacity of 3800 ± 700 cm^2 g^(–1), we find a dust opacity at 850 and 450 μm of κ_(850) = (1.18-1.77)^9+0.36)_(–0.24) and κ_(450) = (4.72-9.13)^(+1.9)_(–0.98) cm^2 g^(–1) of dust. These opacities are from (0.65-0.97)κ^(OH5)_(850) of the widely used theoretical opacities of Ossenkopf and Henning for coagulated ice grains with thin mantles at 850 μm

Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback

One of the key questions in the field of star formation is the role of stellar feedback on subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the stellar winds of the massive stars in W4. AFGL333 is a ~10^4 Msun cloud within W3. This paper presents a study of the star formation activity within AFGL333 using deep JHKs photometry obtained from the NOAO Extremely Wide-Field Infrared Imager combined with Spitzer-IRAC-MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects in the complex, of which 99 are classified as Class I and 713 are classified as Class II sources. The stellar density analysis of young stellar objects reveals three major stellar aggregates within AFGL333, named here AFGL333-main, AFGL333-NW1 and AFGL333-NW2. The disk fraction within AFGL333 is estimated to be ~50-60%. We use the extinction map made from the H-Ks colors of the background stars to understand the cloud structure and to estimate the cloud mass. The CO-derived extinction map corroborates the cloud structure and mass estimates from NIR color method. From the stellar mass and cloud mass associated with AFGL333, we infer that the region is currently forming stars with an efficiency of ~4.5% and at a rate of ~2 - 3 Msun Myr-1pc-2. In general, the star formation activity within AFGL333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL333 region.Comment: 17 pages, 9 figures, Accepted for publication in Ap

First interferometric observations with arc-sec. resolution of solar radio bursts at millimeter wavelengths

The Berkeley-Maryland-Illinois Array (BIMA) is briefly described in the context of solar observations. Specific areas of research that could be performed using BIMA during the Solar Maximum Mission (SMM) in 1991 are outlined. Some preliminary results of flare observations during March 1989 are presented

Gas-phase CO depletion and N2H+ abundances in starless cores

Seven isolated, nearby low-mass starless molecular cloud cores have been observed as part of the Herschel key program Earliest Phases of Star formation (EPoS). By applying a ray-tracing technique to the obtained continuum emission and complementary (sub)mm emission maps, we derive the physical structure (density, dust temperature) of these cloud cores. We present observations of the 12CO, 13CO, and C18O (2-1) and N2H+ (1-0) transitions towards the same cores. Based on the density and temperature profiles, we apply time-dependent chemical and line-radiative transfer modeling and compare the modeled to the observed molecular emission profiles. CO is frozen onto the grains in the center of all cores in our sample. The level of CO depletion increases with hydrogen density and ranges from 46% up to more than 95% in the core centers in the core centers in the three cores with the highest hydrogen density. The average hydrogen density at which 50% of CO is frozen onto the grains is 1.1+-0.4 10^5 cm^-3. At about this density, the cores typically have the highest relative abundance of N2H+. The cores with higher central densities show depletion of N2H+ at levels of 13% to 55%. The chemical ages for the individual species are on average 2+-1 10^5 yr for 13CO, 6+-3 10^4 yr for C18O, and 9+-2 10^4 yr for N2H+. Chemical modeling indirectly suggests that the gas and dust temperatures decouple in the envelopes and that the dust grains are not yet significantly coagulated. We observationally confirm chemical models of CO-freezeout and nitrogen chemistry. We find clear correlations between the hydrogen density and CO depletion and the emergence of N2H+. The chemical ages indicate a core lifetime of less than 1 Myr.Comment: 24 pages, 25 figures, Accepted for publication in Astronomy and Astrophysic