J/A+A/287/769 UV photometry of NGC 6397 (Burgarella+ 1994)
HST observations of the core of globular cluster NGC 6397
Burgarella D., Paresce F., Meylan G., King I.R., Greenfield P.,
Baxter D., Jedrzejewski R., Nota A., Albrecht R., Barbieri C.,
Blades J.C., Boksenberg A., Crane P., Deharveng J.M., Disney M.J.,
Jakobsen P., Kamperman T.M., Macchetto F., Mackay C.D., Weigelt G.
<Astron. Astrophys. 287, 769 (1994)>
=1994A&A...287..769B 1994A&A...287..769B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, blue ; Photometry, ultraviolet
Mission_Name: HST
Keywords: stars: binaries: close - stars: blue stragglers -
stars: population II - globular clusters: individual: NGC 6397 -
ultraviolet: stars - stars: kinematics
Description:
The core of the nearby and very concentrated globular cluster NGC 6397
has been imaged through the f/96-F140W, f/48-F140W, f/96-F210M and
f/48-F220W ultraviolet filters of the Faint Object Camera on board the
Hubble Space Telescope down to an ultraviolet limiting magnitude of
∼19. The most interesting objects in the field of view are six very
bright centrally concentrated, blue stragglers observed for the first
time in the UV. Using these and other data from ground-based
observations, we have been able to deduce from a comparison with
Kurucz's atmosphere models, temperatures of ∼10000K and masses of
∼1.6M☉ for the four brightest ones, which is remarkably close to
twice the turn-off mass of NGC 6397. This finding supports the idea
that two-star mechanisms (collisions, mergers) are at the origin of
the blue stragglers in the core of NGC 6397. Since the central density
is very high, collisions between main sequence stars are frequent,
therefore providing the best formation mechanism. We have computed the
number of such collisions in the core of NGC 6397 and found it to be
of the same order as the number of bright blue stragglers observed
there. Thanks to the HST resolution, we have also been able to resolve
one object, previously classified as a yellow straggler, into a blend
of a blue straggler and three redder stars.
Objects:
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RA (2000) DE Designation(s)
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17 40.9 -53 41 NGC 6397
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2 66 179 Positions, magnitudes and colors for the 179
objects detected in NGC 6397
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Byte-by-byte Description of file: table2
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Bytes Format Units Label Explanations
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1- 3 I3 --- Id Identification number
5- 10 F6.2 arcsec Xpos X position
12- 17 F6.2 arcsec Ypos Y position
21- 25 F5.2 mag m140a ? f/48 camera m140w magnitude
28- 32 F5.2 mag m140-m220 ? f/48 camera m140w-m220w colour
35- 39 F5.2 mag m140b ? f/96 camera m140w magnitude
41- 45 F5.2 mag m140-m210 ? f/96 camera m200w-m210w colour
48- 52 F5.2 mag Vmag ? V magnitude
55- 58 F4.2 mag B-V ? B-V color index
60- 66 A7 --- Note Notes (1)
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Note (1): BSS: Blue stragglers star with an identification number for stars
detected by Lauzeral et al. (1992A&A...262...63L 1992A&A...262...63L)
BHB: Blue horizontal branch star
YSS: Yellow stragglers star
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History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 08-Nov-1996