Mid- and high-J CO observations towards UCHIIs

A study of 12 ultracompact HII regions was conducted to probe the physical conditions and kinematics in the inner envelopes of the molecular clumps harboring them. The APEX telescope was used to observe the sources in the CO (4-3) and 13CO (8-7) lines. Line intensities were modeled with the RATRAN radiative transfer code using power laws for the density and temperature to describe the physical structure of the clumps. All sources were detected in both lines. The optically thick CO (4-3) line shows predominantly blue skewed profiles reminiscent of infall. Line intensities can be reproduced well using the physical structure of the clumps taken from the literature. The optically thick line profiles show that CO is a sensitive tracer of ongoing infall in the outer envelopes of clumps harboring ultracompact HII regions and hot molecular cores.Comment: APEX A&A special issue, accepte

The kinematics of molecular clumps surrounding hot cores in G29.96-0.02 and G31.41+0.31

We present high angular resolution interferometric observations of the 3 and 1.3mm continuum emission, and HCO+(1-0) and SiO(2-1)v=0 lines, obtained with the Owens Valley Radio Observatory millimeter-wave array, toward two hot cores (HCs) associated with two well known ultracompact (UC) HII regions: G29.96-0.02 and G31.41+0.31. These HCs are believed to host young forming massive stars which have been suggested to be surrounded by massive rotating accretion disks. The aim of these new observations is to study the structure and kinematics of the molecular clumps surrounding the HCs and nearby UCHII regions at moderately high angular resolution. Our observations reveal that the clumps within which the HCs and UCHII regions are embedded have a complex kinematical structure. The total mass of the clumps is estimated to be in the range 1000-3000 Msun, consistent with previous findings. Our observations also show compelling evidence that the clump in G29.96-0.02 is contracting onto the HC position, suggesting that the accretion process onto the massive young stellar object embedded in the HC is still ongoing. In these objects the kinematical structure that we observe is also compatible with the presence of a massive rotating disk within the HC, even though we cannot prove this suggestion with our data. The case of G31.41+0.31 is more complicated, and our data, although consistent with the presence of an inner disk and an infalling envelope around it, do not have the required spatial resolution to resolve the different structures.Comment: 13 pages, 15 figs, A&A in pres

VLBA imaging of a periodic 12.2 GHz methanol maser flare in G9.62+0.20E

The class II methanol maser source G9.62+0.20E undergoes periodic flares at both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven epochs over three months using the VLBA at 12.2 GHz. High angular resolution images (beam size $\sim$ 1.7 x 0.6 mas) were obtained, enabling us to observe changes in 16 individual maser components. It was found that while existing maser spots increased in flux density, no new spots developed and no changes in morphology were observed. This rules out any mechanism which disturbs the masing region itself, implying that the flares are caused by a change in either the seed or pump photon levels. A time delay of 1--2 weeks was observed between groups of maser features. These delays can be explained by light travel time between maser groups. The regularity of the flares can possibly be explained by a binary system.Comment: 11 pages, accepted for publication in MNRA

X-Ray Emission from Young Stars in the Massive Star Forming Region IRAS 20126+4104

We present a $40\,$ks Chandra observation of the IRAS$\,$20126+4104 core region. In the inner $6^{\prime\prime}$ two X-ray sources were detected, which are coincident with the radio jet source I20S and the variable radio source I20Var. No X-ray emission was detected from the nearby massive protostar I20N. The spectra of both detected sources are hard and highly absorbed, with no emission below $3\,$keV. For I20S, the measured $0.5-8\,$keV count rate was $4.3\,$cts$\,$ks$^{-1}$. The X-ray spectrum was fit with an absorbed 1T APEC model with an energy of kT$\,=10\,$keV and an absorbing column of N$_H = 1.2\times 10^{23}\,$cm$^{-2}$. An unabsorbed X-ray luminosity of about $1.4\times 10^{32}\,$erg$\,$s$^{-1}$ was estimated. The spectrum shows broad line emission between 6.4 and 6.7\, keV, indicative of emission from both neutral and highly ionized iron. The X-ray lightcurve indicates that I20S is marginally variable; however, no flare emission was observed. The variable radio source I20Var was detected with a count rate of $0.9\,$cts$\,$ks$^{-1}$ but there was no evidence of X-ray variability. The best fit spectral model is a 1T APEC model with an absorbing hydrogen column of N$_H = 1.1\times 10^{23}\,$cm$^{-2}$ and a plasma energy of kT = 6.0$\,$keV. The unabsorbed X-ray luminosity is about $3\times 10^{31}\,$erg$\,$s$^{-1}$.Comment: 17pages, 4 figures to appear in Astronomical Journa

Carbon recombination lines in the Orion Bar

We have carried out VLA D-array observations of the C91alpha carbon recombination line as well as Effelsberg 100-m observations of the C65alpha line in a 5 arcmin square region centered between the Bar and the Trapezium stars in the Orion Nebula with spatial resolutions of 10 arcsec and 40 arcsec, respectively. The results show the ionized carbon in the PDR associated with the Orion Bar to be in a thin, clumpy layer sandwiched between the ionization front and the molecular gas. From the observed line widths we get an upper limit on the temperature in the C+ layer of 1500 K and from the line intensity a hydrogen density between 5 10^4 and 2.5 10^5 cm-3 for a homogeneous medium. The observed carbon level population is not consistent with predictions of hydrogenic recombination theory but could be explained by dielectronic recombination. The layer of ionized carbon seen in C91alpha is found to be essentially coincident with emission in the v=1-0 S(1) line of vibrationally excited molecular hydrogen. This is surprising in the light of current PDR models and some possible explanations of the discrepancy are discussed.Comment: 9 pages, 3 Postscript figures, uses aaspp4 and psfig, To Appear in ApJ Letters (accepted Jul. 24, 1997

Long-term Variability of H2_2CO Masers in Star-forming Regions

We present results of a multi-epoch monitoring program on variability of 6$\,$cm formaldehyde (H$_2$CO) masers in the massive star forming region NGC$\,$7538$\,$IRS$\,$1 from 2008 to 2015 conducted with the GBT, WSRT, and VLA. We found that the similar variability behaviors of the two formaldehyde maser velocity components in NGC$\,$7538$\,$IRS$\,$1 (which was pointed out by Araya and collaborators in 2007) have continued. The possibility that the variability is caused by changes in the maser amplification path in regions with similar morphology and kinematics is discussed. We also observed 12.2$\,$GHz methanol and 22.2$\,$GHz water masers toward NGC$\,$7538$\,$IRS$\,$1. The brightest maser components of CH$_3$OH and H$_2$O species show a decrease in flux density as a function of time. The brightest H$_2$CO maser component also shows a decrease in flux density and has a similar LSR velocity to the brightest H$_2$O and 12.2$\,$GHz CH$_3$OH masers. The line parameters of radio recombination lines and the 20.17 and 20.97$\,$GHz CH$_3$OH transitions in NGC$\,$7538$\,$IRS$\,$1 are also reported. In addition, we observed five other 6$\,$cm formaldehyde maser regions. We found no evidence of significant variability of the 6$\,$cm masers in these regions with respect to previous observations, the only possible exception being the maser in G29.96$-$0.02. All six sources were also observed in the H$_2^{13}$CO isotopologue transition of the 6$\,$cm H$_2$CO line; H$_2^{13}$CO absorption was detected in five of the sources. Estimated column density ratios [H$_2^{12}$CO]/[H$_2^{13}$CO] are reported.Comment: 29 pages, 9 figure

A Search for Formaldehyde 6 cm Emission toward Young Stellar Objects. II. H2CO and H110α Observations

We report the results of our second survey for Galactic H2CO maser emission toward young stellar objects. Using the GBT and the VLA in the A configuration we observed 58 star-forming regions and discovered the fifth H2CO 6 cm maser region in the Galaxy (G23.71-0.20). We have discussed the detection toward G23.71-0.20 in a previous paper. Here we present all the other results from our survey, including detection of H2CO absorption features toward 48 sources, detection of the H110α recombination line toward 29 sources, detection (including tentative detections) of the carbon recombination line C110α toward 14 sources, subarcsecond angular resolution images of 6 cm continuum emission toward five sources, and observations of the H2CO masers in IRAS 18566+0408 and NGC 7538. In the case of NGC 7538, we detected the two main H2CO maser components, and our observations confirm variability of the blueshifted component recently reported by Hoffman et al. The variability of both maser components in NGC 7538 could be caused by a shock wave that reached the redshifted component approximately 14 yr before reaching the blueshifted component. If that were the case, we would expect to detect an increase in the flux density rate of change of the blueshifted component sometime after the year 2009. Our data also support the use of H2CO/H110α observations as a tool to resolve the kinematic distance ambiguity of massive star-forming regions in the Galaxy

Mira's wind explored in scattering infrared CO lines

We have observed the intermediate regions of the circumstellar envelope of Mira (o Ceti) in photospheric light scattered by three vibration-rotation transitions of the fundamental band of CO, from low-excited rotational levels of the ground vibrational state, at an angular distance of beta = 2"-7" away from the star. The data were obtained with the Phoenix spectrometer mounted on the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately 0.5" and seeing limited. Our observations provide absolute fluxes, leading to an independent new estimate of the mass-loss rate of approximately 3e-7 Msun/yr, as derived from a simple analytic wind model. We find that the scattered intensity from the wind of Mira for 2" < beta < 7" decreases as beta^-3, which suggests a time constant mass-loss rate, when averaged over 100 years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa