J/A+A/649/L8 Extreme adaptive optics astrometry of R136 (Khorrami+, 2021)
Extreme adaptive optics astrometry of R136: Search for high proper motion stars.
Khorrami Z., Langlois M., Vakili F., Clark P.C., Buckner A.S.M.,
Gonzalez M., Crowther P., Wunsch R., Palous J., Boccaletti A., Lumsden S.,
Moraux E.
<Astron. Astrophys. 649, L8 (2021)>
=2021A&A...649L...8K 2021A&A...649L...8K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Photometry, infrared
Keywords: galaxies: star clusters: individual: R136 - astrometry -
proper motions - instrumentation: high angular resolution -
instrumentation: adaptive optics
Abstract:
We compared high-contrast near-infrared images of the core of R136
taken by VLT/SPHERE, in two epochs separated by 3.06 years. For the
first time we monitored the dynamics of the detected sources in the
core of R136 from a ground-based telescope with adaptive optics. The
aim of these observations was to search for High prOper Motion
cAndidates (HOMAs) in the central region of R136 (r<6") where it has
been challenging for other instruments. Two bright sources (K<15mag
and V<16mag) are located near R136a1 and R136c (massive WR stars) and
have been identified as potential HOMAs. These sources have
significantly shifted in the images with respect to the mean shift of
all reliable detected sources and their neighbours, and six times
their own astrometric errors. We calculate their proper motions to be
1.36±0.22mas/yr2 (321±52km/s) and 1.15±0.11mas/yr2
(273±26km/s). We discuss different possible scenarios to explain the
magnitude of such extreme proper motions, and argue for the necessity
to conduct future observations to conclude on the nature of HOMAs in
the core of R136.
Description:
We used two sets of imaging data over a field of view (FOV) of 11"x12"
centred on the core of R136 in the K band in 2015 (2015-09-22, ID
095.D-0309) and 2018 (2018-10-10, ID 0102.D-0271). These two sets of
epoch data were recorded using the classical imaging mode of IRDIS.
Using the data taken with the same instrument and exactly the same
configuration, 3.06 yr apart, enabled us to study the dynamics of the
core of R136 with the highest angular resolution to date.
Photometry is carried out on the two images (left and right) from each
epoch.
We analysed the movement (shift) of each source locally, by
superimposing its neighbours located within the radius of 50pix.
The 141 sources that have consistent PMs between these data sets are
presented in catalog.dat.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
05 38 42.40 -69 06 03.4 R136 = RMC 136
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 240 141 Catalogue
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See also:
J/ApJ/448/179 : HST photometry in R136 (Hunter+ 1995)
J/A+A/602/A56 : R136 JKs photometry from VLT/SPHERE EAO (Khorrami+, 2017)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/580] Star identification, this paper
5- 13 F9.5 pix Xpos Star X position, this paper
15- 23 F9.5 pix Ypos Star Y position, this paper
25- 31 F7.4 mag Kmag Star magnitude in SPHERE/IRDIS/Ks filter,
this paper
33- 39 F7.4 mag Hmag Star magnitude in SPHERE/IRDIS/H filter,
this paper
41- 45 F5.2 mag Kmag15 Star magnitude in SPHERE/IRDIS/Ks filter
from Khorrami et al. (2017,
Cat. J/A+A/602/A56)
47- 51 F5.2 mag Jmag15 Star magnitude in SPHERE/IRDIS/J filter
from Khorrami et al. (2017,
Cat. J/A+A/602/A56)
53- 56 I4 --- [HSH95] Star identification from Hunter et al.
(1995, Cat. J/ApJ/448/179)
58- 62 F5.2 mag Umag ?=99.99 Star magnitude in HST/WFPC2/F336W
filter from Hunter et al.
(1995, Cat. J/ApJ/448/179)
64- 68 F5.2 mag Vmag Star magnitude in HST/WFPC2/F555W filter
from Hunter et al.
(1995, Cat. J/ApJ/448/179)
70- 74 F5.2 mag Imag Star magnitude in HST/WFPC2/F884W filter
from Hunter et al.
(1995, Cat. J/ApJ/448/179)
76- 83 F8.5 pix shiftLx Star PM in X direction in Lefts data-sets
85- 92 F8.5 pix shiftLy Star PM in Y direction in Lefts data-sets
94-101 F8.5 pix shiftRx Stars PM in X direction in Rights data-sets
103-110 F8.5 pix shiftRy Stars PM in Y direction in Rights data-sets
112-118 F7.5 pix sigmaLx Stars PM error in X direction from LCT
analysis in Left data-sets
120-126 F7.5 pix sigmaLy Stars PM error in Y direction from LCT
analysis in Left data-sets
128-134 F7.5 pix sigmaRx Star PM error in X direction from LCT
analysis in Rights data-sets
136-142 F7.5 pix sigmaRy Star PM error in Y direction from LCT
analysis in Rights data-sets
144-158 F15.13 pix totSigmaL Error on the PM of Star in Lefts
(combination of LCT errors and photometric
errors on the position of stars)
160-174 F15.13 pix totSigmaR Error on the PM of Star in Rights
(combination of LCT errors and photometric
errors on the position of stars)
176-190 F15.13 pix AveShiftLnei Average value of the shift of the
neighbours within 50pix radius in Lefts
192-206 F15.13 pix AveShiftRnei Average value of the shift of the
neighbours within 50pix radius in Rights
208-222 F15.13 pix Errtot Total amount of error on the PM of Star
averaged between Lefts and Rights using
standard deviation
224-240 F17.15 pix Errphot Part of Errtot that just comes from
photometry
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Acknowledgements:
Zeinab Khorrami, khorramiuz(at)cardiff.ac.uk
(End) Patricia Vannier [CDS] 23-Apr-2021