HCO+ emission in the HH7–11 region: the slowest component of the outflow?

Viti

et al. 2010

A&A

Context. Some well-studied Herbig Haro objects have one or more cold, dense and quiescent clumps of gas associated with them. We propose that such clumps near an HH object can be used as a general measure of clumpiness in the molecular cloud that contains that HH object. Aims. Our aim is to survey clumps around a sample of HH objects and to use the results to estimate the clumpiness in molecular clouds. Methods. All known cold, dense and quiescent clumps near HH objects are anomalously strong HCO + emitters. Our method is, therefore, to search for strong HCO + emission as an indicator of a clump near an HH object. The searches were made using JCMT (for Northern hemisphere objects) and SEST (for Southern hemisphere objects) in the HCO + (3-2) and also (for SEST observations) H 13 CO + (1-0) lines, with some additional searches for methanol and sulphur monoxide lines. The selected sources were a sample of 22 HH objects in which no previous HCO + emission had been detected. Results. We find that half of the HH objects have clumps detected in the HCO + (3-2) line and that all searches in H 13 CO + 1-0 lines show evidence of clumpiness. All condensations have narrow linewidths and are evidently unaffected dynamically by the HH jet shock. Conclusions. We conclude that the molecular clouds in which these HH objects are found must be highly heterogeneous on scales of less than 0.1 pc. An approximate calculation based on these results suggests that the area filling factor of clumps affected by HH objects is of ∼10%. These clumps have gas number densities of > ∼ 3 × 10 4 cm −2 .

Section: Introductionmentioning

confidence: 99%

The clumpiness of molecular clouds: HCO⁺(3–2) survey near Herbig-Haro objects

Whyatt

Viti

et al. 2010

A&A

“…Several HH objects are found to have associated quiescent dense clumps ahead of them: HH 1/2 (see references below), HH 7-11 (Rudolph & Welch 1988;Dent et al 1993;Rudolph et al 2001), HH 34 (Rudolph & Welch 1992), NGC 2264G (Girart et al 2000), HH 80N (Girart et al 1994(Girart et al , 1998(Girart et al , 2001). Most of them have high excitation knots, i.e., with strong high excitation lines, such as [OIII] and Hα, strong UV lines and significant UV continuum radiation (e.g., Reipurth & Bally 2001).…”

Section: Introductionmentioning

confidence: 99%

“…Herbig-Haro (HH) objects, which trace shock-excited plasma, are signposts of the intense outflow phenomena associated with star formation (e. g., Reipurth & Bally 2001). Several HH objects are found to have associated quiescent dense clumps ahead of them: HH 1/2 (see references below), HH 7-11 (Rudolph & Welch 1988;Dent et al 1993;Rudolph et al 2001), HH 34 (Rudolph & Welch 1992), NGC 2264G (Girart et al 2000), HH 80N (Girart et al 1994(Girart et al , 2001Girart, Estalella & Ho 1998). Most of them have high excitation knots, i. e., with strong high excitation lines, such as [OIII] and Hα, strong UV lines and significant UV continuum radiation (e. g., Send offprint requests to: J.M.…”

Section: Introductionmentioning

confidence: 99%

The molecular condensations ahead of Herbig-Haro objects

Viti

Williams

et al. 2002

A&A

Abstract. We present a CSO and BIMA molecular line survey of the dense, quiescent molecular environment ahead of HH 2. The molecular gas is cold, 13 K, and moderately dense, 3 ×10 5 cm −3 . A total of 14 species has been detected (including different isotopes and deuterated species). The relative abundances of the clump are compared with other dense molecular environments, including quiescent dark clouds, and active low and high mass star forming regions. This comparison confirms the peculiar chemical composition of the quiescent gas irradiated by the HH objects. Thus, from this comparison, we found that the HCO + , CH3OH and H2CO are strongly enhanced. SO and SO2 are weakly enhanced, whereas HCN and CS are underabundant. The CN abundance is within the range of values found in starless dark clouds, but it is low with respect to high mass star forming regions. Finally, the chemical composition of HH 2 confirms the qualitative results of the Viti & Williams (1999) complex chemical model that follows the chemical behavior of a molecular clump irradiated by a HH object.

“…From the dust observations Chini et al (2001) derive that the total mass of the quiescent gas around HH 8-10 is 4.0 M . From the study of the HCO + 3-2 emission, Dent et al (1993) suggest that the dense molecular gas and dust around HH 8-11 is the densest, slowest component of the outflow. This is somewhat similar to the picture of the molecular gas ahead of HH 2 .…”

Section: Observationsmentioning

confidence: 99%

“…We selected three positions, two of them, HH 7-11 A and B, toward the HCO + 1-0 clumps (Rudolph et al 1988) and one, HH 7-11 X, toward a HCO + 3-2 emission peak southwest of HH 8 (Dent et al 1993). Note that the 3 mm beams of our 3 positions (A, X and B) intersect (see Fig.…”

Section: Observationsmentioning

confidence: 99%

An observational survey of molecular emission ahead of Herbig-Haro objects

Viti¹,

Hatchell

2006

A&A

Context. A molecular survey recently performed ahead of HH 2 supports the idea that the observed molecular enhancement is due to UV radiation from the HH object. Aims. The aim of the present work is to determine whether all HH objects with enhanced HCO + emission ahead of them also exhibit the same enhanced chemistry as HH 2. We thus observed several molecular lines at several positions ahead of five Herbig-Haro objects where enhanced HCO + emission was previously observed. Methods. We mapped the five Herbig-Haro objects using the IRAM-30 m. For each position we searched for more than one molecular species, and where possible for more than one transition per species. We then estimated the averaged beam column densities for all species observed and also performed LVG analyses to constrain the physical properties of the gas. Results. The chemically richest quiescent gas is found ahead of the HH 7-11 complex, in particular at the HH 7-11 A position. In some regions we also detected a high velocity gas component. We find that the gas densities are always higher than those typical of a molecular cloud while the derived temperatures are always quite low, ranging from 10 to 25 K. The emission of most species seems to be enhanced with respect to that of a typical dense clump, probably due to the exposure to a high UV radiation from the HH objects. Chemical differentiation among the positions is also observed. We attempt a very simple chemical analysis to explain such differentiation.