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Deep near-IR observations of the globular cluster M4: hunting for brown dwarfs

Deep near-IR observations of the globular cluster M4: hunting for brown dwarfs
Deep near-IR observations of the globular cluster M4: hunting for brown dwarfs
We present an analysis of deep Hubble Space Telescope (HST)/Wide Field Camera 3 near-IR (NIR) imaging data of the globular cluster (GC) M4. The best-photometry NIR color–magnitude diagram (CMD) clearly shows the main sequence extending toward the expected end of the hydrogen-burning limit and going beyond this point toward fainter sources. The white dwarf (WD) sequence can be identified. As such, this is the deepest NIR CMD of a GC to date. Archival HST optical data were used for proper-motion cleaning of the CMD and for distinguishing the WDs from brown dwarf (BD) candidates. Detection limits in the NIR are around F110W ≈ 26.5 mag and F160W ≈ 27 mag, and in the optical around F775W ≈ 28 mag. Comparing our observed CMDs with theoretical models, we conclude that we have reached beyond the H-burning limit in our NIR CMD and are probably just above or around this limit in our optical–NIR CMDs. Thus, any faint NIR sources that have no optical counterpart are potential BD candidates, since the optical data are not deep enough to detect them. We visually inspected the positions of NIR sources that are fainter than the H-burning limit in F110W and for which the optical photometry did not return a counterpart. We found in total five sources for which we did not get an optical measurement. For four of these five sources, a faint optical counterpart could be visually identified, and an upper optical magnitude was estimated. Based on these upper optical magnitude limits, we conclude that one source is likely a WD, one source could be either a WD or BD candidate, and the remaining two sources agree with being BD candidates. No optical counterpart could be detected for just one source, which makes this source a good BD candidate. We conclude that we found in total four good BD candidates.
brown dwarfs, globular clusters: general, globular clusters: individual: M4, stars: low-mass
0004-637X
Dieball, A.
5f595453-aa6b-4067-a3e1-026867fb9f7a
Bedin, L.R.
e5bc5fc4-4bb0-4889-8a8e-f800eee960bd
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Rich, R.M.
ef2a92bd-15a6-4203-8d1b-fb7b368fe385
Allard, F.
4fa90735-a010-4ec6-aaa4-c4ad5230ceb3
Dotter, A.
1c1815ba-06ff-4255-8f8f-cef5325e7523
Richer, H.
d1418450-81a8-466c-a5db-e6dbd0474a7a
Zurek, D.
0de59032-c43c-4c8f-89a2-b451488b86db
Dieball, A.
5f595453-aa6b-4067-a3e1-026867fb9f7a
Bedin, L.R.
e5bc5fc4-4bb0-4889-8a8e-f800eee960bd
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Rich, R.M.
ef2a92bd-15a6-4203-8d1b-fb7b368fe385
Allard, F.
4fa90735-a010-4ec6-aaa4-c4ad5230ceb3
Dotter, A.
1c1815ba-06ff-4255-8f8f-cef5325e7523
Richer, H.
d1418450-81a8-466c-a5db-e6dbd0474a7a
Zurek, D.
0de59032-c43c-4c8f-89a2-b451488b86db

Dieball, A., Bedin, L.R., Knigge, C., Rich, R.M., Allard, F., Dotter, A., Richer, H. and Zurek, D. (2016) Deep near-IR observations of the globular cluster M4: hunting for brown dwarfs. The Astrophysical Journal, 817 (1), [38005476]. (doi:10.3847/0004-637X/817/1/48).

Record type: Article

Abstract

We present an analysis of deep Hubble Space Telescope (HST)/Wide Field Camera 3 near-IR (NIR) imaging data of the globular cluster (GC) M4. The best-photometry NIR color–magnitude diagram (CMD) clearly shows the main sequence extending toward the expected end of the hydrogen-burning limit and going beyond this point toward fainter sources. The white dwarf (WD) sequence can be identified. As such, this is the deepest NIR CMD of a GC to date. Archival HST optical data were used for proper-motion cleaning of the CMD and for distinguishing the WDs from brown dwarf (BD) candidates. Detection limits in the NIR are around F110W ≈ 26.5 mag and F160W ≈ 27 mag, and in the optical around F775W ≈ 28 mag. Comparing our observed CMDs with theoretical models, we conclude that we have reached beyond the H-burning limit in our NIR CMD and are probably just above or around this limit in our optical–NIR CMDs. Thus, any faint NIR sources that have no optical counterpart are potential BD candidates, since the optical data are not deep enough to detect them. We visually inspected the positions of NIR sources that are fainter than the H-burning limit in F110W and for which the optical photometry did not return a counterpart. We found in total five sources for which we did not get an optical measurement. For four of these five sources, a faint optical counterpart could be visually identified, and an upper optical magnitude was estimated. Based on these upper optical magnitude limits, we conclude that one source is likely a WD, one source could be either a WD or BD candidate, and the remaining two sources agree with being BD candidates. No optical counterpart could be detected for just one source, which makes this source a good BD candidate. We conclude that we found in total four good BD candidates.

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arXiv:1506.01400v3 - Author's Original
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Published date: 20 January 2016
Keywords: brown dwarfs, globular clusters: general, globular clusters: individual: M4, stars: low-mass

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Local EPrints ID: 429994
URI: http://eprints.soton.ac.uk/id/eprint/429994
ISSN: 0004-637X
PURE UUID: 14018ac7-0fdc-4b9e-a5b5-fb220b386baf

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Date deposited: 09 Apr 2019 16:30
Last modified: 21 Nov 2021 16:05

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Contributors

Author: A. Dieball
Author: L.R. Bedin
Author: C. Knigge
Author: R.M. Rich
Author: F. Allard
Author: A. Dotter
Author: H. Richer
Author: D. Zurek

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