Universität zu Köln

Shahzamanian, B., Eckart, A., Zajacek, M., Valencia-S, M., Sabha, N., Moser, L., Parsa, M., Peissker, F. and Straubmeier, C. (2016). Polarized near-infrared light of the Dusty S-cluster Object (DSO/G2) at the Galactic center. Astron. Astrophys., 593. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

We investigate an infrared-excess source called G2 or Dusty S-cluster Object (DSO), which moves on a highly eccentric orbit around the Galaxy's central black hole, Sgr A*. We use, for the first time, near-infrared polarimetric imaging data to determine the nature and properties of the DSO and obtain an improved Ks-band identification of this source in median polarimetry images of di ff erent observing years. The source started to deviate from the stellar confusion in 2008, and it does not show any flux density variability over the years we analyzed it. We measured the polarization degree and angle of the DSO between 2008 and 2012 and conclude, based on the significance analysis on polarization parameters, that it is an intrinsically polarized source (> 20%) with a varying polarization angle as it approaches the position of Sgr A*. The DSO shows a near-infrared excess of Ks L' > 3 that remains compact close to the pericenter of its orbit. Its observed parameters and the significant polarization obtained in this work show that the DSO might be a dust-enshrouded young star, forming a bow shock as it approaches the super massive black hole. The significantly high measured polarization degree indicates that it has a non-spherical geometry, and it can be modeled as a combination of a bow shock with a bipolar wind of the star. We used a 3D radiative transfer model that can reproduce the observed properties of the source such as the total flux density and the polarization degree. We obtain that the change of the polarization angle can be due to an intrinsic change in the source structure. Accretion disk precession of the young star in the gravitational field of the black hole can lead to the change of the bipolar outflow and therefore the polarization angle variation. It might also be the result of the source interaction with the ambient medium.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Shahzamanian, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Eckart, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Zajacek, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Valencia-S, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sabha, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Moser, L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Parsa, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Peissker, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Straubmeier, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-263567
DOI:	10.1051/0004-6361/201628994
Journal or Publication Title:	Astron. Astrophys.
Volume:	593
Date:	2016
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 SGR A-ASTERISK; CENTER SOURCE G2; CENTER CLOUD G2; PROPER MOTIONS; BLACK-HOLE; GAS CLOUD; STAR; DISKS; SIMULATIONS; POLARIMETRY Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/26356