Universität zu Köln

Cesaroni, R., Sanchez-Monge, A., Beltran, M. T., Johnston, K. G., Maud, L. T., Moscadelli, L., Mottram, J. C., Ahmadi, A., Allen, V., Beuther, H., Csengeri, T., Etoka, S., Fuller, G. A., Galli, D., Galvan-Madrid, R., Goddi, C., Henning, T., Hoare, M. G., Klaassen, P. D., Kuiper, R., Kumar, M. S. N., Lumsden, S., Peters, T., Rivilla, V. M., Schilke, P., Testi, L., van der Tak, F., Vig, S., Walmsley, C. M. and Zinnecker, H. (2017). Chasing discs around O-type (proto)stars: Evidence from ALMA observations. Astron. Astrophys., 602. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Circumstellar discs around massive stars could mediate the accretion onto the star from the infalling envelope, and could minimize the e ff ects of radiation pressure. Despite such a crucial role, only a few convincing candidates have been provided for discs around deeply embedded O-type (proto) stars. Aims. In order to establish whether disc-mediated accretion is the formation mechanism for the most massive stars, we have searched for circumstellar, rotating discs around a limited sample of six luminous (>10(5) L-circle dot) young stellar objects. These objects were selected on the basis of their IR and radio properties in order to maximize the likelihood of association with disc + jet systems. Methods. We used ALMA with similar to 0.'' 2 resolution to observe a large number of molecular lines typical of hot molecular cores. In this paper we limit our analysis to two disc tracers (methyl cyanide, CH3CN, and its isotopologue, (CH3CN)-C-13), and an outflow tracer (silicon monoxide, SiO). Results. We reveal many cores, although their number depends dramatically on the target. We focus on the cores that present prominent molecular line emission. In six of these a velocity gradient is seen across the core, three of which show evidence of Keplerian-like rotation. The SiO data reveal clear but poorly collimated bipolar outflow signatures towards two objects only. This can be explained if real jets are rare (perhaps short-lived) in very massive objects and /or if stellar multiplicity significantly a ff ects the outflow structure. For all cores with velocity gradients, the velocity field is analysed through position-velocity plots to establish whether the gas is undergoing rotation with nu(rot) proportional to R-alpha, as expected for Keplerian-like discs. Conclusions. Our results suggest that in three objects we are observing rotation in circumstellar discs, with three more tentative cases, and one core where no evidence for rotation is found. In all cases but one, we find that the gas mass is less than the mass of any embedded O-type star, consistent with the (putative) discs undergoing Keplerian-like rotation. With the caveat of low number statistics, we conclude that the disc detection rate could be sensitive to the evolutionary stage of the young stellar object. In young, deeply embedded sources, the evidence for discs could be weak because of confusion with the surrounding envelope, while in the most evolved sources the molecular component of the disc could have already been dispersed. Only in those objects that are at an intermediate stage of the evolution would the molecular disc be su ffi ciently prominent and relatively less embedded to be detectable by mm /submm observations.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Cesaroni, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sanchez-Monge, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Beltran, M. T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Johnston, K. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Maud, L. T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Moscadelli, L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Mottram, J. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ahmadi, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Allen, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Beuther, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Csengeri, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Etoka, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fuller, G. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Galli, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Galvan-Madrid, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Goddi, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Henning, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoare, M. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Klaassen, P. D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kuiper, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kumar, M. S. N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Lumsden, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Peters, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Rivilla, V. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schilke, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Testi, L. UNSPECIFIED UNSPECIFIED UNSPECIFIED van der Tak, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Vig, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Walmsley, C. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Zinnecker, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-229548
DOI:	10.1051/0004-6361/201630184
Journal or Publication Title:	Astron. Astrophys.
Volume:	602
Date:	2017
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HOT MOLECULAR CORE; YOUNG STELLAR OBJECTS; H II REGIONS; HYPERCOMPACT HII-REGIONS; DISTANCE-LIMITED SAMPLE; CANDIDATE MASSIVE YSOS; GALACTIC PLANE SURVEY; STAR-FORMING REGIONS; MSX SOURCE SURVEY; RMS SURVEY Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/22954