2011A&A...534A.117B

Query : 2011A&A...534A.117B

2011A&A...534A.117B - Astronomy and Astrophysics, volume 534A, 117-117 (2011/10-1)

Adaptive-optics assisted near-infrared polarization measurements of sources in the Galactic Center.

BUCHHOLZ R.M., WITZEL G., SCHOEDEL R., ECKART A., BREMER M. and MUZIC K.

Abstract (from CDS):

The Galactic center offers unique opportunities to study stellar and bow-shock polarization effects in a dusty environment. The goals of this work are to provide near-infrared (NIR) polarimetry of the stellar sources in the central parsec at the resolution of an 8m telescope for the first time, along with new insights into the nature of the known bright bow-shock sources. We use adaptive-optics assisted observations obtained at the ESO VLT in the H- and Ks-band, applying both high-precision photometric methods specifically developed for crowded fields and a newly established polarimetric calibration for NACO to produce polarization maps of the central 3''x19'', in addition to spatially resolved polarimetry and a flux variability analysis on the extended sources in this region.We find foreground polarization mainly parallel to the Galactic plane, with average values of (4.6±0.6)% at 26°±6° (Ks-band) and (9.3±1.3)% at 20° ±6° (H-band) in the center of the field-of-view (FOV). Farther away from the center, we find higher polarization degrees and steeper polarization angles: (7.5±1.0)% at 11°±6° (Ks-band) and (12.1±2.1)% at 13°±6° (H-band). pH/pKs peaks at 1.9±0.4, corresponding to a power law index for the wavelength dependency of α=2.4±0.7. These values also vary over the FOV, with higher values in the center. This is indicative of the influence of local effects on the total polarization, possibly dichroic extinction by Northern Arm dust. The two extended sources IRS 21 and 1W show similar intrinsic polarization degrees of 6.1 resp. 7.8% (Ks) and 6.9 (H, only 1W) at polarization angles coincident with previous NIR and mid-infrared (MIR) findings, both in total and spatially resolved. The spatial polarization pattern of both sources points to scattering on aligned elongated dust grains as the major source of intrinsic polarization, and matches the known orientation of the magnetic field. Our data also allow us to separate the bow shock of IRS 21 from the central source for the first time in the Ks-band, finding the apex north of the central source and determining a standoff distance of ∼400AU, which matches previous estimates. This source also shows a ∼50% increase in flux in the NIR over several years.

Abstract Copyright: ∼

Journal keyword(s): Galaxy: center - polarization - dust, extinction - infrared: stars

VizieR on-line data: <Available at CDS (J/A+A/534/A117): pollist.dat>

Status at CDS : All or part of tables of objects will not be ingested in SIMBAD.

Simbad objects: 1

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Number of rows : 1
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14407 0

Query : 2011A&A...534A.117B

Basic data :
NAME Galactic Center -- Region defined in the Sky
Origin of the objects types :

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    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
ICRS coord. (ep=J2000) : 		17 45 39.60213 -29 00 22.0000 (Gamma-ray) [ ] E 2018A&A...612A...1H
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
FK4 coord. (ep=B1950 eq=1950) : 		17 42 28.87566 -28 59 12.3570 [ ]
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
Gal coord. (ep=J2000) : 		359.94487501 -00.04391769 [ ]
SIMBAD within arcmin
', {sourceSize:12, color:'#30a090'})); aladin.on('objectClicked', function(object) { var objName=object.data.MAIN_ID; aladin.showPopup(object.ra,object.dec,'',''+ objName+''); });" title="Show Simbad objects"> Overlay Simbad points in this preview
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NAME Gal Centre HESS J1745-290 NAME Gal Center TeV J1745-290
GAL 000.0+00.0 NAME Galactic Centre NAME Galactic Center VER J1745-290

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