Spitzer--IRAC Imagery and Photometry of Ultracompact HII Regions With Extended Emission
E. de la Fuente, A. Porras, J. M. C. Grave, M. S. N. Kumar, M. A. Trinidad, S. Kurtz, S. Kemp, J. Franco, G. Quevedo
备注：
9 pages, 5 Figures, To be published in "A Long Walk Through Astronomy: A Celebration of Luis Carrasco's 60th Birthday", proceedings, Rev, Mex. AA SC. Work based in de la Fuente Ph. D. Thesis, 2007, University of Guadalajara, México
We present the results of a morphological study performed to a sample of Ultracompact (UC) HII regions with Extended Emission (EE) using Spitzer--IRAC imagery and 3.6 cm VLA conf. D radio-continuum (RC) maps. Some examples of the comparison between maps and images are presented. Usually there is an IR point source counterpart to the peak(s) of RC emission, at the position of the UC source. We find that the predominant EE morphology is the cometary, and in most cases is coincident with IR emission at 8.0 $μ$m. Preliminary results of Spitzer--IRAC photometry of a sub-sample of 13 UC HII regions with EE based on GLIMPSE legacy data are also presented. Besides, individual IRAC photometry was performed to 19 UC sources within these 13 regions. We show that UC sources lie on specific locus, both in IRAC color-color and AM-product diagnostic diagrams. Counts of young stellar sources are presented for each region, and we conclude that a proportion of ~ 2%, ~10%, and ~88% of sources in the UC HII regions with EE are, in average, Class I, II, and III, respectively.
We review some recent observational results on the properties of ultracompact HII regions, in particular the presence of extended continuum emission surrounding ultracompact sources and the discovery of a new class of so-called ``Hypercompact'' HII regions. In addition, we discuss recent attempts to probe the density structure within UC HII regions using the technique of spectral index analysis.
We have observed extended emission physically associated with 15 out of 16 UC HII regions with large ratios of single-dish to VLA fluxes. We discuss their implications for the age problem of UC HII regions and the evolution of HII regions.
The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) has been used to observe 78 of the IRAS point sources identified by Bronfman et al. (1996) as likely ultracompact HII regions. Results for the CO(4-3) line at 461.041GHz are presented. The 74 sources detected are bright and in many cases compact, making them potentially suitable as pointing calibrators for single dish submillimeter telescopes.
Here we present a brief overview of UC HII regions with EE (UC HII+EE) including our most recent effort aimed at searching for UC HII regions associated with extended emission.
Cometary ultracompact HII regions have been modelled as the interaction of the hypersonic wind from a moving star with the molecular cloud which surrounds the star. We here show that a similar morphology can ensue even if the star is stationary with respect to the cloud material. We assume that the HII region is within a stellar wind bubble which is strongly mass loaded: the cometary shape results from a gradient in the distribution of mass loading sources. This model circumvents problems associated with the necessarily high spatial velocities of stars in the moving star models.
The microwave spectral energy distribution of the dusty, diffuse H II region LPH 201.663+1.643 has been interpreted by others as tentative evidence for microwave emission from spinning dust grains. We present an alternative interpretation for that particular object; specifically, that an ultracompact H II region embedded within the dust cloud would explain the available observations as well or better than spinning dust. Parameters for the size, surface brightness, and flux density of the putative ultracompact HII region, derived from the microwave observations, are within known ranges. A possi…
The dynamical evolution of HII regions with and without stellar motion in dense, structured molecular clouds is studied. Clouds are modeled in hydrostatic equilibrium, with gaussian central cores and external halos that obey r**-2 and r**-3 density power laws. The cloud gravity is included as a time-independent, external force. Stellar velocities of 0, 2, 8, and 12 km/s are considered. When stellar motion is included, stars move from the central core to the edge of the cloud, producing transitions from ultracompact to extended HII regions as the stars move into lower density regions. The oppos…
We propose that a significant fraction of the ultracompact HII regions found in massive star-forming clouds are the result of the interaction of the wind and ionizing radiation from a young massive star with the clumpy molecular cloud gas in its neighbourhood. Distributed mass loading in the flow allows the compact nebulae to be long-lived. In this paper, we discuss a particularly simple case, in which the flow in the HII region is everywhere supersonic. The line profiles predicted for this model are highly characteristic, for the case of uniform mass loading. We discuss briefly other observat…
We have obtained the first classification spectrum and present the first direct spectral classification of the ionizing star of an ultracompact HII region. The ultracompact HII region is G29.96-0.02, a well-studied object with roughly twice solar metallicity. The near infrared K-band spectrum of the ionizing star exhibits CIV and NIII emission and HeII absorption, but lines of HI and HeI are obliterated by nebular emission. We determine that the star has a spectral type of O5 to O7 or possibly O8. We critically evaluate limits on the properties of the star and find that it is compatible with z…
We present a survey in the 6_{16}-5_{23} rotational water transition toward 33 galactic ultracompact HII regions. Maser emission is detected toward 18 of these sources; two are new detections. High quality spectra are provided for all 18 sources. We discuss the detection rate of this survey and the correlation of various maser properties with other physical parameters. In addition, we report wide-bandwidth (316 km/s), moderate-resolution (~ 3'') water maser observations of the HH80-81 region. We report the first detection of water maser emission at the approximate velocity of the molecular cor…
We report the first detection of the reactive ions CO+ and HOC+ towards ultracompact (UC) HII regions, particularly in Mon R2 and G29.96-0.02. We have observed two positions in Mon R2, namely the peak of the UC HII region and a position in the high density molecular cloud which bounds it. CO+ and HOC+ were detected at the UC HII region but not at the molecular cloud, as expected if the CO$^+$ and HOC$^+$ emissions arise in the PDR surrounding the \uch. The measured CO$^+$ and HOC$^+$ column densities are of the order of 10$^{11}$ cm$^{-2}$ in both sources, which yields a strikingly low [HCO$^+…
We present the first results of a study of the kinematics and morphology of ultracompact HII regions using a new observational technique. We used very high spatial (1.5") and spectral (3.4 km/s)resolution observations of the [NeII] line at 12.8 microns to study the ionized gas in Monoceros R2. The [NeII] emission shows an HII region with highest emission measure in a ~24" shell. Line widths are as narrow as 8 km/s at some positions. In places where the lines are complex and broader, the additional width is most likely due to overlap of narrower features along the line of sight. The global kine…
We present infrared imaging and spectroscopic data of the complex massive star-forming region G10.47+0.03. The detection of seven mid-infrared (MIR) sources in our field combined with a sensitive Ks/ISAAC image allows to establish a very accurate astrometry, at the level of 0.3". Two MIR sources are found to be coincident with two ultracompact HII regions (UCHIIs) within our astrometric accuracy. Another MIR source lies very close to three other UCHII regions and to the hot molecular core (HMC) in G10.47+0.03. Spectroscopy of two of the most interesting MIR sources allows to identify the locat…
This review discussed near- and mid- infrared observations of ultracompact (UC) HII regions. The importance of ISO mid-IR fine-structure nebular lines is emphasised since only a small fraction of UCHII regions are observed directly in the near-IR. The reliability of contemporary atmospheric models for such indirect diagnostics is discussed, whilst a revised Spectral Type-Temperature calibration is presented for Galactic O3 to B3 dwarfs. In particular, fine-structure line derived properties of G29.96-0.02 differ from the direct near-IR spectroscopic result and represents a serious discrepancy w…
We present high resolution (0.''12 x 0.''079) observations of the ultracompact HII region G10.6-0.4 in 23 GHz radio continuum and the NH3(3,3) line. Our data show that the infall in the molecular material is largely spherical, and does not flatten into a molecular disk at radii as small as 0.03 pc. The spherical infall in the molecular gas matches in location and velocity the infall seen in the ionized gas. We use a non-detection to place a stringent upper limit on the mass of an expanding molecular shell associated with pressure driven expansion of the HII region. These data support a scenari…
In recent years, a number of extragalactic massive star clusters that are still deeply embedded in their birth material have been discovered. These objects represent the youngest stage of massive star cluster evolution yet observed, and the most massive and dense of these may be proto globular clusters. Their properties appear to be similar to those of ultracompact HII regions in the Galaxy, but scaled up in total mass and luminosity. In many cases, these clusters are only visible at mid-IR to radio wavelengths, and they have typically been detected as ``inverted'' spectrum radio sources. Howe…
We carried out 13CO J=1-0, CS, and C34S J=2-1 and J=3-2 line observations of molecular clouds associated with 16 ultracompact (UC) HII regions with extended envelopes. The molecular clouds are the ones that give birth to rich stellar clusters and/or very massive (O7-O4) stars. Our data show that the clouds are very clumpy and of irregular morphology. They usually have much larger masses, velocity dispersions, and fractions of dense gas than molecular clouds that form early B or late O stars. This is compatible with earlier findings that more massive stars form in more massive cores. 13CO cores…
We present a SCUBA submillimetre (450 & 850 micron) survey of the environment of 105 IRAS point sources, selected from the Wood & Churchwell (1989a) and Kurtz, Churchwell & Wood (1994) radio ultracompact (UC) HII region surveys. We detected a total of 155 sub-mm clumps associated with the IRAS point sources and identified three distinct types of object: ultracompact cm-wave sources that are not associated with any sub-mm emission (sub-mm quiet objects), sub-mm clumps that are associated with ultracompact cm-wave sources (radio-loud clumps); and sub-mm clumps that are not associated with any kn…
We have modelled ultracompact HII regions (UCHIIR) in terms of steady subsonic ionized flows in a clumpy medium. Mass loss from neutral clumps allows the regions to be long-lived. We examine the form of global flows for different dependences of the volume mass injection rate, $\dot{q}$, on radius and Mach number, and describe the solutions in detail. We find that three observed UCHIIR morphologies are reproduced with these models. Mach number independent flows that include a radial variation can give centre- brightened core--halo morphologies. Mach number dependent flows reproduce naturally th…
We present mid-IR 21micron images of a sample of radio selected Ultracompact HII (UCHII) regions, obtained with the Midcourse Space Experiment (MSX). All, with one possible exception, are detected at mid-IR wavelengths, sampling the warm dust emission of the cocoons of the OB star central exciting sources. Many of the UCHII regions have nearby (up to a few pc distant) companion dust emission sources, which represent other potential star birth sites. In some objects the companion dominates the IRAS point source catalogue entry for the UCHII region. We compare the mid- and far-IR dust emission, …
We have used Very Large Array (VLA) observations of the massive star forming regions W49A and Sgr B2, obtained with resolutions from 2\farcs0 to 0\farcs04, to classify the morphologies of nearly 100 ultracompact HII regions. These high resolution, multi-frequency, multi-configuration VLA observations motivate several modifications of the existing morphological classification scheme for UC HII regions. In this work, we describe the modified morphology scheme and the criteria used in source classification. In particular, we drop the ``core-halo'' classification, add a ``bipolar'' classification,…
We present complete, low resolution IJHK spectroscopy of the ultracompact HII region, G45.12+0.13. From the observed HI line strengths, we derive a near infrared extinction law that is slightly steeper than the average. After correction with this extinction law, we find good agreement between the observed line ratios of HeI, Fe+, Fe++, S+ and S++ and the available atomic data. Our data show that the density within the core of G45.12+0.13 must be at least 10^4/cm^3. This is consistent with the known radio structure of the HII region and in considerable disagreement with previous work using mid …
The published properties of M1-78 are discussed with the purpose to resolve the object's classification as either a planetary nebula or an ultracompact HII region. A classification as a planetary nebula is rejected primarily because of the high luminosity of the object, but because of the chemical composition and expansion velocity of the nebula, a novel classification is proposed instead: that of an ultracompact HII region with a post-main sequence central star (possibly a WN star). It must therefore follow that observable ultracompact HII regions persist beyond the main sequence lifetimes of…
We investigate the diffuse absolute calibration of the InfraRed Array Camera on the Spitzer Space Telescope at 8.0microns using a sample of 43 HII regions with a wide range of morphologies near GLON=312deg. For each region we carefully measure sky-subtracted,point-source- subtracted, areally-integrated IRAC 8.0-micron fluxes and compare these with Midcourse Space eXperiment (MSX) 8.3-micron images at two different spatial resolutions, and with radio continuum maps. We determine an accurate median ratio of IRAC 8.0-micron/MSX\8.3-micron fluxes, of 1.55+/-0.15. From robust spectral energy distri…
A high quality, medium-resolution K-band spectrum has been obtained of the ultracompact HII region G29.96-0.02 with the Very Large Telescope (VLT). The slit was positioned along the symmetry axis of the cometary shaped nebula. Besides the spectrum of the embedded ionizing O star, the long-slit observation revealed the rich emission-line spectrum produced by the ionized nebula with sub-arcsec spatial resolution. The nebular spectrum includes Br$γ$, several helium emission lines and a molecular hydrogen line. A detailed analysis is presented of the variation in strength, velocity and width of th…
We present a multiwavelength study of the ultra compact HII region associated with IRAS 20178+4046. This enables us to probe the different components associated with this massive star forming region. The radio emission from the ionized gas was mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India. We have used 2MASS $J H K_{s}$ data to study the nature of the embedded sources associated with IRAS 20178+4046. Submillimetre emission from the cold dust at 450 and 850 $μ$m was studied using JCMT-SCUBA. The high-resolution radio continuum maps at 610 and 1280 MHz displa…
We report on the detection of optically thick free-free radio sources in the galaxies M33, NGC 253, and NGC 6946 using data in the literature. We interpret these sources as being young, embedded star birth regions, which are likely to be clusters of ultracompact HII regions. All 35 of the sources presented in this article have positive radio spectral indices alpha>0 suggesting an optically thick thermal bremsstrahlung emission arising in the HII region surrounding hot stars. Energy requirements indicate a range of a several to >500 O7V star equivalents powering each HII region. Assuming a Salp…
We present the first subarcsecond submillimeter images of the enigmatic ultracompact HII region (UCHII) G5.89-0.39. Observed with the SMA, the 875 micron continuum emission exhibits a shell-like morphology similar to longer wavelengths. By using images with comparable angular resolution at five frequencies obtained from the VLA archive and CARMA, we have removed the free-free component from the 875 micron image. We find five sources of dust emission: two compact warm objects (SMA1 and SMA2) along the periphery of the shell, and three additional regions further out. There is no dust emission in…
Ultracompact HII regions are signposts of massive star formation and their properties provide diagnostics for the characteristics of very young O stars embedded in molecular clouds. While radio observations have given us a good picture of the morphology of these regions, they have not provided clear information about the kinematics. Using high spectral resolution observations of the 12.8 micron [NeII] line, it has been possible for the first time to trace the internal kinematics of several ultracompact HII regions. We find that the motions in the cometary ultracompact HII regions MonR2 and G29…
The James Clerk Maxwell Telescope has been used to obtain submillimeter and millimeter continuum photometry of a sample of 30 IRAS sources previously studied in molecular lines and centimeter radio continuum. All the sources have IRAS colours typical of very young stellar objects (YSOs) and are associated with dense gas. In spite of their high luminosities (L>10000 solar units), only ten of these sources are also associated with a radio counterpart. In 17 cases we could identify a clear peak of millimeter emission associated with the IRAS source, while in 9 sources the millimeter emission was …
We have observed seven ultracompact HII regions in hydrogen recombination lines in the millimeter band. Toward four of these regions, there is a high velocity (full width to half maximum 60-80 km/s) component in the line profiles. The high velocity gas accounts for 35-70% of the emission measure within the beam. We compare these objects to an additional seven similar sources we have found in the literature. The broad recombination line objects (BRLOs) make up about 30% of all sources in complexes containing ultracompact HII regions. Comparison of spectral line and continuum data implies that t…
We have carried out 21 cm radio continuum, H76_αradio recombination line, and various (CO, ^13CO, CS, & C^34S) molecular line observations of the W31 complex. Our radio continuum data show that W31 is composed of two extended HII regions, G10.2-0.3 and G10.3-0.1, each of which comprises an ultracompact HII region, two or more compact components, and diffuse envelope. The W31 cloud appears as an incomplete shell on the whole and consists of southern spherical and northern flat components, which are associated with G10.2-0.3 and G10.3-0.1, respectively. We detect two large and massive CS-emittin…
We present $K$-band spectra of the near infrared counterparts to IRS2E and IRS2W which is associated with the ultracompact HII region W51d, both of them embedded sources in the Galactic compact HII region W51 IRS2. The high spatial resolution observations were obtained with the laser guide star facility and Near infrared Integral Field Spectrograph (NIFS) mounted at the Gemini North observatory. The spectrum of the ionizing source of W51d shows the photospheric features NIII (21155 Å) in emission and HeII (21897 Å) in absorption which lead us to classify it as an young O3 type star. We detecte…
W75N is a star-forming region containing various ultracompact HII regions and OH, water, and methanol maser emission. Our VLBA map shows that the OH masers are located in a thin disk rotating around an O-star which is the exciting star of the ultracompact HII region VLA1. A separate set of maser spots is connected with the ultracompact HII region VLA2. The radial velocity of OH maser spots varies across the disk from 3.7 km/s to 10.9 km/s. The diameter of the disk is 4000 A.U. All maser spots are strongly polarized. This are the first OH masers showing nearly 100 per cent linear polarization i…
Velocity shifts and differential broadening of radio recombination lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact HII regions. These small HII regions are thought to be at their earliest evolutionary phase and associated with the youngest massive stars. The observations suggest that these HII regions are characterized by high densities, supersonic flows and steep density gradients, consistent with accretion and outflows that would be associated with the formation of massive stars.
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…
We present Spitzer/IRAC photometry on the star-forming HII region N 90, related to the young stellar association NGC 602 in the Small Magellanic Cloud. Our photometry revealed bright mid-infrared sources, which we classify with the use of a scheme based on templates and models of red sources in the Milky Way, and criteria recently developed from the Spitzer Survey of the SMC for the selection of candidate Young Stellar Objects (YSOs). We detected 57 sources in all four IRAC channels in a 6.2' x 4.8' field-of-view centered on N 90; 22 of these sources are classified as candidate YSOs. We compar…
We present observations of the giant HII region complex N159 in the LMC using IRAC on the {\it Spitzer Space Telescope}. One of the two objects previously identified as protostars in N159 has an SED consistent with classification as a Class I young stellar object (YSO) and the other is probably a Class I YSO as well, making these two stars the youngest stars known outside the Milky Way. We identify two other sources that may also be Class I YSOs. One component, N159AN, is completely hidden at optical wavelengths, but is very prominent in the infrared. The integrated luminosity of the entire co…
This review covers the dynamic processes that are important in the evolution and structure of galactic HII regions, concentrating on an elementary presentation of the physical concepts and recent numerical simulations of HII region evolution in a non-uniform medium. The contents are as follows: (1) The equations (Euler equations; Radiative transfer; Rate equations; How to avoid the dynamics; How to avoid the atomic physics). (2) Physical concepts (Static photoionization equilibrium; Ionization front propagation; Structure of a D-type front; Photoablation flows; Other ingredients - Stellar wind…
High resolution 7 mm observations of the W49N massive star forming region have detected recombination line emission from the individual ultracompact (UC) HII regions on 50 milliarcsecond (600 AU) scales. These line observations, combined with multifrequency, high-resolution continuum imaging of the region at 7 mm (VLA) and at 3 mm and 1 mm (BIMA), indicate that five to seven of the eighteen ultracompact sources in W49N are broad recombination line objects (BRLOs) as described by Jaffe & Martin-Pintado (1999). BRLOs have both broad radio recombination lines ($Δ$V$>$60 \kms) and rising spectra (…
We present a study of the mid-infrared properties and dust content of a sample of 27 HII ``blobs'', a rare class of compact HII regions in the Magellanic Clouds. A unique feature of this sample is that even though these HII regions are of high and low excitation they have nearly the same physical sizes ~1.5-3 pc. We base our analysis on archival 3-8 microns infrared imagery obtained with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope. We find that despite their youth, sub-solar metallicity and varied degrees of excitation, the mid-infrared colors of these regions are sim…
We present Spitzer-IRAC, NOAO 2.1meter-Flamingos, Keck-NIRC, and FCRAO-SEQUOIA observations of the massive star forming complex S254-S258, covering an area of 25x20 arc-minutes. Using a combination of the IRAC and NIR data, we identify and classify the young stellar objects (YSO) in the complex. We detect 510 sources with near or mid IR-excess, and we classify 87 Class I, and 165 Class II sources. The YSO are found in clusters surrounded by isolated YSO in a low-density distributed population. The ratio of clustered to total YSO is 0.8. We identify six new clusters in the complex. One of them,…
The hypothesis that massive stars form by accretion can be investigated by simple analytical calculations that describe the effect that the formation of a massive star has on its own accretion flow. Within a simple accretion model that includes angular momentum, that of gas flow on ballistic trajectories around a star, the increasing ionization of a massive star growing by accretion produces a three-stage evolutionary sequence. The ionization first forms a small quasi-spherical HII region gravitationally trapped within the accretion flow. At this stage the flow of ionized gas is entirely inwar…
We present a systematic survey for ultracompact HII (UCHII) regions in the Magellanic Clouds. Understanding the physics of massive star formation (MSF) is a critical astrophysical problem. The study of MSF began in our galaxy with surveys of UCHII regions, but before now this has not been done for other galaxies. We selected candidates based on their Infrared Astronomical Satellite (IRAS) colors and imaged them at 3 and 6 cm with the Australia Telescope Compact Array (ATCA). Nearly all of the observed regions contain compact radio sources consistent with thermal emission. Many of the sources a…
We have carried out 21 cm radio continuum observations of 16 UC HII regions using the VLA (D-array) in search of associated extended emission. We have also observed H76$_α$ recombination line towards all the sources and He76$_α$ line at the positions with strong H76$_α$ line emission. The UC HII regions have simple morphologies and large (>10) ratios of single-dish to VLA fluxes. Extended emission was detected towards all the sources. The extended emission consists of one to several compact components and a diffuse extended envelope. All the UC HII regions but two are located in the compact co…
Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact UC HII regions toward the high-mass star forming region G19.61--0.23. In addition, we performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the VLA archive data base. The newly obtained 3 mm image brings information on a cluster of high-mass (proto)stars located in the innermost and densest part of the parsec scale clump detected in the 1.2 mm continuum. We identify a total of 10 high-mass young stellar objects: one hot core (HC…
We present evidence for anomalous microwave emission in the RCW175 \hii region. Motivated by 33 GHz $13\arcmin$ resolution data from the Very Small Array (VSA), we observed RCW175 at 31 GHz with the Cosmic Background Imager (CBI) at a resolution of $4\arcmin$. The region consists of two distinct components, G29.0-0.6 and G29.1-0.7, which are detected at high signal-to-noise ratio. The integrated flux density is $5.97\pm0.30$ Jy at 31 GHz, in good agreement with the VSA. The 31 GHz flux density is $3.28\pm0.38$ Jy ($8.6σ$) above the expected value from optically thin free-free emission based on…
We present an analysis of wind-blown, parsec-sized, mid-infrared bubbles and associated star-formation using GLIMPSE/IRAC, MIPSGAL/MIPS and MAGPIS/VLA surveys. Three bubbles from the Churchwell et al. (2006) catalog were selected. The relative distribution of the ionized gas (based on 20 cm emission), PAH emission (based on 8 um, 5.8 um and lack of 4.5 um emission) and hot dust (24 um emission) are compared. At the center of each bubble there is a region containing ionized gas and hot dust, surrounded by PAHs. We identify the likely source(s) of the stellar wind and ionizing flux producing eac…
The HII regions Sh 217 and Sh 219 are textbook examples of a Stromgren sphere surrounded by an annular photodissociation region (PDR). The annular PDR is observed in both the 21 cm atomic hydrogen emission and the dust (PAH) emission near 8 micron (MSX Survey). An ultracompact radio continuum source is observed in the direction of the annular PDR, in both Sh 217 and Sh 219. JHKobservations show the presence of highly reddened stellar clusters (AV ~ 20 mag) in the directions of these radio sources. These clusters are also IRAS sources, of luminosities 22700 Lo for Sh 217 and 5900 Lo for Sh 219.…
We present a ground-based optical spectroscopic and HST U, V, I photometric study of the blue compact dwarf (BCD) galaxy Pox 186. It is found that the emission of the low-surface brightness (LSB) component in Pox 186 at radii < 3'' (< 270 pc in linear scale) is mainly gaseous in origin. We detect Halpha emission out to radii as large as 6''. At radii > 3'' the light of the LSB component is contaminated by the emission of background galaxies complicating the study of the outermost regions. The surface brightness distribution in the LSB component can be approximated by an exponential law with a …
The Spitzer-GLIMPSE point source catalog and images have been used to study a sample of 381 massive protostellar candidates. IRAC-Point source photometry was used to analyse colours, magnitudes and spectral indicies of the infrared counterparts (IRCs) of massive protostellar objects and a bonafide sample of 50 point sources was obtained. Spectral energy distributions (SEDs) of these 50 sources was extended to the near-infrared and millimeter range by using 2MASS and millimeter data from the literature. An online SED fitter tool based on Monte-Carlo radiative transfer of an accretion model invo…
We have observed the ultracompact HII region G29.96-0.02 in the near infrared J, H, and K bands and in the Br-gamma line. By comparison with radio observations, we determine that the extinction to the nebula is AK = 2.14 with a 3 sigma uncertainty of 0.25. We identify the ionizing star and determine its intrinsic K magnitude. The star does not have an infrared excess and so appears to be no longer accreting. The K magnitude and the bolometric luminosity allow us to place limits on the location of the ionizing star in the HR diagram. The 3 sigma upper limit on the effective temperature of the i…
Context. Massive-star formation triggered by the expansion of HII regions. Aims. To understand if sequential star formation is taking place at the periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results. In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000\msol …
We compare H-alpha, radio continuum, and Spitzer Space Telescope (SST) images of 58 planetary nebulae (PNe) recently discovered by the Macquarie-AAO-Strasbo- urg H-alpha PN Project (MASH) of the SuperCOSMOS H-alpha Survey. Using InfraRed Array Camera (IRAC) data we define the IR colors of PNe and demonstrate good isolation between these colors and those of many other types of astronomical object. The only substantive contamination of PNe in the color-color plane we illustrate is due to YSOs. However, this ambiguity is readily resolved by the unique optical characteristics of PNe and their envi…
We have mapped the ultracompact HII region, G5.89-0.39, and its molecular surroundings with the Submillimeter Array at 2".8 x 1".8 angular resolution in 1.3 mm continuum, SiO(5-4), and eight other molecular lines. We have resolved for the first time the highly energetic molecular outflow in this region. At this resolution, the outflow is definitely bipolar and appears to originate in a 1.3 mm continuum source. The continuum source peaks in the center of the HII region. The axis of the outflow lines up with a recently discovered O5V star.
We summarize the status of our program of near-infrared adaptive optics observations of ultracompact HII regions. By means of selected results we demonstrate the usefulness of this technique for disentangling the complexity of massive star-forming regions. The primary scientific aims of our study are the identification of the ionizing stars, the characterization of the stellar population, the clarification of the role of dust for the excitation of the HII region and, last but not least, the search for circumstellar disks surrounding high-mass stars. We present results obtained by adaptive opti…
We present initial results of an ongoing search for interferometric calibrators at submillimeter (sub-mm) wavelengths with the Submillimeter Array (SMA). Powerful radio galaxies are commonly used as calibrators at centimeter and millimeter wavelengths, but many are not strong enough to serve as calibrators at sub-mm wavelengths because of their rapidly declining flux densities toward shorter wavelengths. The inability to find a calibrator close to the target source may limit or even prevent us from imaging many interesting sources at sub-mm wavelengths. Here, we investigate whether high-mass p…
UltraCompact HII regions are signposts of high mass star formation. Since high-mass star formation occurs in clusters, one expects to find even earlier phases of massive star formation in the vicinity of UltraCompact HII regions. Here, we study the amount of deuteration and depletion toward pre/protocluster clumps found in a wide-field (10 X 10 arcmin) census of clouds in 32 massive star-forming regions that are known to harbour UCHII regions. We find that 65% of the observed sources have strong NH2D emission and more than 50% of the sources exhibit a high degree of deuteration, (0.1 < NH2D/NH…
We present new Spitzer Space Telescope observations of the region NGC 2467, and use these observations to determine how the environment of an HII region affects the process of star formation. Our observations comprise IRAC (3.6, 4.5, 5.8, and 8.0 um) and MIPS (24 um) maps of the region, covering approximately 400 square arcminutes. The images show a region of ionized gas pushing out into the surrounding molecular cloud, powered by an O6V star and two clusters of massive stars in the region. We have identified as candidate Young Stellar Objects (YSOs) 45 sources in NGC 2467 with infrared excess…
