The Mass Distribution in the Galactic Centre Estimated from OH/IR stars

Aims.A pilot project has been carried out to measure circumstellar CO emission from three OH/IR stars close to the Galactic centre. The intention was to find out whether it would be possible to conduct a large-scale survey for mass-loss rates using, for example, the Atacama large millimeter array (ALMA). Such a survey would increase our understanding of the evolution of the Galactic bulge. Methods. Two millimetre-wave instruments were used: the Nobeyama Millimeter Array at 115 GHz and the Submillimeter Array at 230 GHz. An interferometer is necessary as a "spatial filter" in this region of space because of the confusion with interstellar CO emission.Results. Towards two of the stars, CO emission was detected with positions and radial velocities coinciding within the statistical errors with the corresponding data of the associated OH sources. However, for one of the stars the line profile is not what one expects for an unresolved expanding circumstellar envelope. We believe that this CO envelope is partially resolved and that this star therefore is a foreground star not belonging to the bulge. Conclusions. The results of the observations have shown that it is possible to detect line profiles of circumstellar CO from late-type stars both within and in the direction of the Galactic bulge. ALMA will be able to detect CO emission in short integrations with sensitivity sufficient to estimate mass-loss rates from a large number of such stars.

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“…Sevenster et al (1997); 3. Lindqvist et al (1992). late-type stars in the Galactic bulge using the Atacama large millimeter array (ALMA).…”

Section: Introductionmentioning

confidence: 99%

CO in OH/IR stars close to the Galactic centre

Winnberg¹,

Deguchi

Reid

et al. 2009

A&A

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“…H 2 O masers have been detected in both star forming regions (Elitzur et al 1989) and envelopes of AGB stars (Sjouwerman & van Langevelde 1996). We compared them with the AGB star catalogues in e.g., Lindqvist et al (1992), Sevenster et al (1997), and Sjouwerman et al (1998Sjouwerman et al ( , 2002, and excluded three masers with known AGB star counterparts in the following analyses. In two of the clouds, the 20 km s −1 cloud and Sgr C, we found clusters (more than 10 within 1 pc) of strong H 2 O masers (fluxes>1 Jy) that may trace active star formation.…”

Section: Resultsmentioning

confidence: 99%

Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H₂O Masers and Dense Cores

Zhang

Kauffmann

et al. 2016

Proc. IAU

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Abstract. The Central Molecular Zone (CMZ), usually referring to the inner 500 pc of the Galaxy, contains a dozen of massive (∼10 5 M⊙) molecular clouds. Are these clouds going to actively form stars like Sgr B2? How are they affected by the extreme physical conditions in the CMZ, such as strong turbulence? Here we present a first step towards answering these questions. Using high-sensitivity, high angular resolution radio and (sub)millimeter observations, we studied deeply embedded star formation in six massive clouds in the CMZ, including the 20 and 50 km s −1 clouds, Sgr B1 off (as known as dust ridge clouds e/f), Sgr C, Sgr D, and G0.253−0.016. The VLA water maser observations suggest a population of deeply embedded protostellar candidates, many of which are new detections. The SMA 1.3 mm continuum observations reveal peaks in dust emission associated with the masers, suggesting the existence of dense cores. While our findings confirm that clouds such as G0.253−0.016 lack internal compact substructures and are quiescent in terms of star formation, two clouds (the 20 km s −1 cloud and Sgr C) stand out with clusters of water masers with associated dense cores which may suggest a population of deeply embedded protostars at early evolutionary phases. Follow-up observations with VLA and ALMA are necessary to confirm their protostellar nature.

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“…Using the VLA in two different sets of observations, we searched for radio continuum emission from a sample of the population of OH/IR stars (Lindqvist et al 1992;te Lintel Hekkert et al 1991). A more detailed account of the observations will be given elsewhere.…”

Section: Observations and Resultsmentioning

confidence: 99%

“…2 2.5 ϫ 10 9 ͑Ṁ Ϫ5 ͒ Ϫ4 photons cm Ϫ2 s Ϫ1 (1) (Serabyn et al 1991), where an outflow velocity of v ϭ 10.2 km s Ϫ1 has been taken from the OH observations (Lindqvist et al 1992), ␣ (2) 2 3 ϫ 10 Ϫ13 cm 3 s Ϫ1 is the recombination coefficient excluding captures to the ground energy level, and Ṁ Ϫ5 is the mass-loss rate in units of 10 Ϫ5 M J yr Ϫ1 . Assuming that ionizing photons are produced close to the Galactic center at a rate of 2 ϫ 10 50 s Ϫ1 , the expected UV flux incident on the envelope is F UV 2 1.7 ϫ 10 10 (d 10 ) Ϫ2 cm Ϫ2 s Ϫ1 , where d 10 is the distance from the Galactic center in units of 10 pc.…”

Section: Observations and Resultsmentioning

confidence: 99%

“…Motivated by the detection of externally ionized gas associated with IRS 7, we have begun a program to probe the nature of the UV radiation field in the inner Galaxy by searching for radio continuum emission from the outer envelope of the population of OH/IR stars that are known to lie in the Galactic center region (Lindqvist et al 1992). The strength of the free-free emission from the ionized surfaces of the stellar envelopes depends on the value of the ambient UV flux.…”

Section: Introductionmentioning

confidence: 99%

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Detection of Ionized Gas toward an OH/IR Star: A Measure of the UV Radiation Field near the Galactic Center

Yusef‐Zadeh

Wardle

Roberts

1996

The Astrophysical Journal

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The nature of the ionizing UV radiation field in the inner Galaxy is investigated by searching for radio continuum emission from the outer envelope of the population of OH/IR stars toward the Galactic center region. Radio continuum observations of a sample of OH/IR stars have been made at 3.6 cm using the VLA in its A, B, and DnC configurations. A highly scattered OH/IR star has been detected with a flux density of 11 mJy, which suggests that the star is photoionized by an external radiation field. The UV flux responsible for ionization is estimated to be 2.5 ϫ 10 9 (Ṁ Ϫ5 ) Ϫ4 photons cm Ϫ2 s Ϫ1 , where Ṁ Ϫ5 is the mass-loss rate in units of 10 Ϫ5 M J yr Ϫ1 . We note that the continuum emission should become optically thick below a few hundred megahertz and that measurements at these frequencies will be able to determine both the UV flux and Ṁ .

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The Mass Distribution in the Galactic Centre Estimated from OH/IR stars

Cited by 26 publications

References 11 publications

CO in OH/IR stars close to the Galactic centre

CO in OH/IR stars close to the Galactic centre

Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H₂O Masers and Dense Cores

Detection of Ionized Gas toward an OH/IR Star: A Measure of the UV Radiation Field near the Galactic Center

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The Mass Distribution in the Galactic Centre Estimated from OH/IR stars

Cited by 26 publications

References 11 publications

CO in OH/IR stars close to the Galactic centre

CO in OH/IR stars close to the Galactic centre

Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H2O Masers and Dense Cores

Detection of Ionized Gas toward an OH/IR Star: A Measure of the UV Radiation Field near the Galactic Center

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Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H₂O Masers and Dense Cores