HCO+ survey of unassociated compact molecular clouds in the IRAS Point Source Catalog

Richards, P. J.; Little, L. T.; Toriseva, M.; Heaton, B. D.

doi:10.1093/mnras/228.1.43

Cited by 33 publications

(31 citation statements)

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“…4, whose position is coincident with that of the ultracompact HII region IRAS 20220+3728. This object appears in numerous studies of molecular line and radio continuum emission, having been detected in NH 3 (Molinari et al 1996) and HCO + (Richards et al 1987); see Chan et al (1996) for a compilation of data. Moderate-velocity 12 CO emission is detected by Shepherd & Churchwell (1996).…”

Section: Ecx6-11mentioning

confidence: 92%

Near-infrared imaging of compact HII regions in Cygnus X

Comerón

Torra

2001

A&A

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Abstract. We present a near-infrared imaging survey of compact HII regions in the direction of the Cygnus X complex, for which no previous observations at those wavelengths have been published so far. The targets have been selected from a catalog of sources in that region having a thermal spectral energy distribution between 408 and 4800 MHz (Wendker et al. 1991), and an inferred angular size smaller than 5 arcmin across. We present images in the JHK filters, color-magnitude, and color-color diagrams for each region. We also suggest and apply a method for estimating the distance by comparing the dereddened H-band flux from all the stars in the area of the HII region and the radio-continuum flux. Many of the regions imaged are clearly associated with stellar aggregates with different degrees of concentration, whose components show varying amounts of extinction. Some objects are often found in the region of the (J − H), (H − K) diagram indicating excess emission of circumstellar nature. A detailed discussion on each object is provided in the context of existing published observations at different wavelengths, in particular regarding the existence of ultracompact components. A number of ultracompact HII regions are found to have clearly visible unresolved or nearly unresolved K-band counterparts characterized by very red H − K colors, suggesting that the extinction may be low enough in their direction so as to allow the direct observation of the star ionizing the ultracompact component.

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Section: Ecx6-11mentioning

confidence: 92%

Near-infrared imaging of compact HII regions in Cygnus X

Comerón

Torra

2001

A&A

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“…The 1.2 mm emission is likely associated with the HCO + emission (Richards et al 1987) and the CO emission detected in the region (Wouterloot & Brand 1989). SCUBA maps at 850 and 450 μm (Di Francesco et al 2008) show condensations associated with the 1.2 mm peaks (see Fig.…”

Section: Iras 22187+5559mentioning

confidence: 93%

“…Garay et al (2006) find a similar case of a cluster of centimeter sources in IRAS 15502−5302, but with the millimeter emission still associated with the centimeter sources. HCO + and HCN emission has been detected toward Jenness et al (1995), and NGC 7538-IRS9 1.3 mm map from Sandell & Sievers (2004 : 4, 6, 14, 17, 29, 30;I04579: 7, 17, 27, 28, 29, 30;I18171: 4, 17, 19, 26;I19045: 3, 4;I20293: 17, 19;I22187: 7, 9, 19, 20, 29;I22198: 7, 8, 10, 12, 15, 17, 19, 23, 24, 25, 27, 29, 30, 32;NGC 7538-9: 2, 11, 13, 16, 21, 31;I23448: 5, 7, 18, 19, 20, 28, 29. References: (1) Bachiller et al (1990); (2) Hasegawa & Mitchell (1995); (12) Jenness et al (1995); (13) Kameya et al (1990); (14) Kim & Kurtz (2006); (15) Larionov et al (1999); (16) Mitchell & Hasegawa (1991); (17) Molinari et al (1996); (18) I23448 (Richards et al 1987) as has CO emission (Wouterloot & Brand 1989). …”

Section: Iras 23448+6010mentioning

confidence: 99%

Survey of intermediate/high mass star-forming regions at centimeter and millimeter wavelengths

Sánchez-Monge¹,

Palau

Estalella³

et al. 2008

A&A

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Aims. The goal of this work is to characterize the millimeter and centimeter properties of intermediate/high mass young stellar objects (YSOs) to search for any evolutionary trends. Methods. We carried out observations at 1.2 mm with the IRAM 30 m telescope, and at 3.6 and 1.3 cm with the VLA toward a sample of 11 luminous (>10 3 L ) IRAS sources classified as high mass protostellar object candidates. The most promising regions additionally were observed at 7 mm with the VLA. Results. The 1.2 mm emission, tracing the dust core in which the massive YSO is forming, shows a clear peak surrounded by some substructure in most cases, while in others it is very extended and weak. The masses from the 1.2 mm data range from 10 to 140 M . For all (but one) of the sources, we detected centimeter emission associated with the IRAS source, with spectral indices between 3.6 and 1.3 cm typical of optically thin emission, and deconvolved sizes from <0.01 to 0.3 pc, suggesting that the emission comes from compact or ultra-compact (UC) H ii regions. The physical parameters of the UCH ii regions indicate that the ionizing stars are early B-type. The 7 mm emission is partially resolved for the four regions observed at this wavelength, and we estimated the contribution of the dust emission to the 7 mm flux density, ranging from negligible to 45%. By combining our data with infrared surveys, we built the spectral energy distribution and fitted a modified blackbody law. We found dust temperatures between 25 and 35 K, dust emissivity indices between 1.5 and 2.2, and masses similar to the masses derived from the 1.2 mm continuum emission. In addition, we found a correlation between the degree of disruption of the natal cloud, estimated from the fraction of dust emission associated with the centimeter source relative to the total amount of dust in its surroundings, and the size of the centimeter source. Conclusions. From the correlation found, we established an evolutionary sequence in which sources with compact millimeter emission clearly associated with compact centimeter emission are younger than sources with the millimeter emission dispersed and with the centimeter emission extended. Such a sequence is consistent with the evolutionary stage expected from maser/outflow/dense gas emission reported in the literature, and with the infrared excess of the 2MASS sources associated with the centimeter source.

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“…A sample of 260 objects was selected from the IPSC, based on their FIR emission properties (for details see Palla et al 1991). In particular, the IRAS colour criteria by Richards et al (1987) were applied, which identify compact molecular clouds. This sample was then split into two sub-samples, based on their colour indices.…”

Section: The Search For Massive Protostarsmentioning

confidence: 99%

A molecular-line study of clumps with embedded high-mass protostar candidates

Brand

Cesaroni

Palla

et al. 2001

A&A

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Abstract. We present molecular line observations made with the IRAM 30-m telecopes of the immediate surroundings of a sample of 11 candidate high-mass protostars. These observations are part of an effort to clarify the evolutionary status of a set of objects which we consider to be precursors of UC Hii regions. In a preceding series of papers we have studied a sample of objects, which on the basis of their IR colours are likely to be associated with compact molecular clouds. The original sample of 260 objects was divided approximately evenly into a High group, with IR colour indices [25−12] ≥ 0.57 and [60−12] ≥ 1.3, and a Low group with complementary colours. The FIR luminosity of the Low sources, their distribution in the IR colour-colour diagram, and their lower detection rate in H2O maser emission compared to the High sources, led to the hypothesis that the majority of these objects represent an earlier stage in the evolution than the members of the High group, which are mostly identifiable with UC Hii regions. Subsequent observations led to the selection of 12 Low sources that have FIR luminosities indicating the presence of B2.5 to O8.5 V0 stars, are associated with dense gas and dust, have (sub-)mm continuum spectra indicating temperatures of ∼30 K, and have no detectable radio continuum emission. One of these sources has been proposed by us to be a good candidate for the high-mass equivalent of a Class 0 object. In the present paper we present observations of the molecular environment of 11 of these 12 objects, with the aim to derive the physical parameters of the gas in which they are embedded, and to find further evidence in support of our hypothesis that these sources are the precursors to UC Hii regions. We find that the data are consistent with such an interpretation. All observed sources are associated with well-defined molecular clumps. Masses, sizes, and other parameters depend on the tracer used, but typically the cores have average diameters of ∼0.5-1 pc (with a range of 0.2 to 2.2 pc), and masses of a few tens to a few thousand solar masses. Compared to a similar analysis of High sources, the present sample has molecular clumps that are more massive, larger, cooler, and less turbulent. They also tend to have a smaller ratio of virial-to-luminous mass, indicating they are less dynamically stable than their counterparts in which the High sources are embedded. The large sizes suggest these clumps should still undergo substantial contraction (their densities are ∼10 times smaller than those of the High sources). The lower temperatures and small linewidths are also expected in objects in an earlier evolutionary state. In various sources indications are found for outflowing gas, though its detection is hampered by the presence of multiple emission components in the line spectra. There are also signs of self-absorption, especially in the spectra of 13 CO and HCO + . We find that the masses of the molecular clumps associated with our objects increase with L fir (M clump ∝ L 1.17 fir ), and that there i...

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HCO+ survey of unassociated compact molecular clouds in the IRAS Point Source Catalog

Cited by 33 publications

References 0 publications

Near-infrared imaging of compact HII regions in Cygnus X

Near-infrared imaging of compact HII regions in Cygnus X

Survey of intermediate/high mass star-forming regions at centimeter and millimeter wavelengths

A molecular-line study of clumps with embedded high-mass protostar candidates

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