J/ApJ/857/132 gri photometry of NGC 796 cluster (Kalari+, 2018)
The Magellanic Bridge cluster NGC 796: deep optical AO imaging reveals the
stellar content and initial mass function of a massive open cluster.
Kalari V.M., Carraro G., Evans C.J., Rubio M.
<Astrophys. J., 857, 132-132 (2018)>
=2018ApJ...857..132K 2018ApJ...857..132K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open; Magellanic Clouds; Photometry, ugriz
Keywords: galaxies: star clusters: individual: NGC 796;
Hertzsprung-Russell and C-M diagrams; Magellanic Clouds;
stars: emission-line, Be; stars: formation;
stars: luminosity function, mass function
Abstract:
NGC 796 is a massive young cluster located 59kpc from us in the
diffuse intergalactic medium of the 1/5-1/10Z☉ Magellanic
Bridge, allowing us to probe variations in star formation and stellar
evolution processes as a function of metallicity in a resolved
fashion, and providing a link between resolved studies of nearby
solar-metallicity and unresolved distant metal-poor clusters located
in high-redshift galaxies. In this paper, we present adaptive optics
griHα imaging of NGC 796 (at 0.5", which is ∼0.14pc at the
cluster distance) along with optical spectroscopy of two bright
members to quantify the cluster properties. Our aim is to explore
whether star formation and stellar evolution vary as a function of
metallicity by comparing the properties of NGC 796 to
higher-metallicity clusters. We find an age of 20-5+12Myr from
isochronal fitting of the cluster main sequence in the color-magnitude
diagram. Based on the cluster luminosity function, we derive a
top-heavy stellar initial mass function (IMF) with a slope
α=1.99±0.2, hinting at a metallicity and/or environmental
dependence of the IMF, which may lead to a top-heavy IMF in the early
universe. Study of the Hα emission-line stars reveals that
classical Be stars constitute a higher fraction of the total B-type
stars when compared with similar clusters at greater metallicity,
providing some support to the chemically homogeneous theory of stellar
evolution. Overall, NGC 796 has a total estimated mass of
990±200M☉, and a core radius of 1.4±0.3pc, which classifies
it as a massive young open cluster, unique in the diffuse interstellar
medium of the Magellanic Bridge.
Description:
NGC 796 was observed using the SAM (SOAR AO module) imager mounted on
the 4.1m SOAR (Southern Astrophysical Research) telescope located at
Cerro Pachon, Chile.
We utilized the g' r' i' filters along with an Hα filter for our
observations. These filters closely resemble the United States Naval
Observatory (USNO) u'g'r'i'z' filter set, rather than the Sloan
Digital Sky Survey (SDSS) ugriz filters.
Observations were conducted in a closed loop during the night of 2016
October 10, centered on RAJ2000=01:56:44, DEJ2000=-74:13:12.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 137 429 4.1m SOAR telescope gri photometry of all stars
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See also:
II/288 : IRSF Magellanic Clouds Point Source Catalog (Kato+ 2007)
J/other/Sci/359.69 : Massive stars in 30 Dor (Schneider+, 2018)
J/MNRAS/453/1026 : Lagoon Nebula M8 T tauri accretion rates (Kalari+, 2015)
J/MNRAS/440/2036 : VPHAS+ survey synthetic colours (Drew+, 2014)
J/ApJ/795/108 : Stellar populations in Magellanic bridge (Skowron+, 2014)
J/ApJ/785/162 : YSO candidates in the Magellanic Bridge (Chen+, 2014)
J/A+A/551/A78 : The Magellanic Bridge Catalog of Stars (Bagheri+, 2013)
J/MNRAS/426/2427 : Structural param. of M33 star clusters (San Roman+, 2012)
J/AJ/142/48 : LMC star clusters structural parameters (Werchan+, 2011)
J/MNRAS/415/103 : IPHAS T Tauri candidates in IC 1396 (Barentsen+, 2011)
J/AJ/140/416 : IR photometry of massive stars in the SMC (Bonanos+, 2010)
J/A+A/509/A11 : Ha emission-line objects in SMC clusters (Martayan+, 2010)
J/ApJ/707/1347 : HST F160W photometry in RMC 136 (Andersen+, 2009)
J/MNRAS/382/1203 : CT1 photometry of 5 SMC star clusters (Piatti+, 2007)
J/A+A/471/625 : VLT-FLAMES survey of massive stars (Trundle+, 2007)
J/ApJ/658/358 : Ae/Be stars of Magellanic Bridge in JHKs (Nishiyama+, 2007)
J/ApJ/658/345 : CRIc photometry of Magellanic Bridge Fields (Harris, 2007)
J/A+A/430/941 : Star formation region NGC 6530 (Prisinzano+, 2005)
J/MNRAS/353/601 : 2dF survey of the Small Magellanic Cloud (Evans+, 2004)
J/AJ/114/2644 : UBVRIHa photometry of NGC2264 (Sung+, 1997)
J/ApJS/101/41 : SMC and Bridge extended catalog (Bica+ 1995)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [KCE2018] [1/577] Identification number
5- 6 I2 h RAh [1] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [56/57] Minute of Right Ascension (J2000)
11- 15 F5.2 s RAs Second of Right Ascension (J2000)
17 A1 --- DE- [-] Sign of the Declination (J2000)
18- 19 I2 deg DEd [74] Degree of Declination (J2000)
21- 22 I2 arcmin DEm [11/14] Arcminute of Declination (J2000)
24- 27 F4.1 arcsec DEs Arcsecond of Declination (J2000)
29- 33 F5.2 mag gmag [13.7/25.4] g band magnitude
35- 38 F4.2 mag e_gmag [0.02/0.5] Uncertainty in gmag
40- 44 F5.2 mag rmag [14/24] r band magnitude
46- 49 F4.2 mag e_rmag [0.02/0.2] Uncertainty in rmag
51- 55 F5.2 mag imag [14.3/24] i band magnitude
57- 60 F4.2 mag e_imag [0.04/0.2] Uncertainty in imag
62-137 A76 --- Comm Additional comments (1)
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Note (1):
(a) = From Kato et al. (2007PASJ...59..615K 2007PASJ...59..615K ; see II/288).
(b) = From Nishiyama et al. (2007; J/ApJ/658/358).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 06-Mar-2019