J/ApJ/764/172 UBVRI photometry of stars toward NGC 1931 (Pandey+, 2013)
Optical photometric and polarimetric investigation of NGC 1931.
Pandey A.K., Eswaraiah C., Sharma S., Samal M.R., Chauhan N., Chen W.P.,
Jose J., Ojha D.K., Yadav R.K., Chandola H.C.
<Astrophys. J., 764, 172 (2013)>
=2013ApJ...764..172P 2013ApJ...764..172P
ADC_Keywords: Photometry, UBVRI ; Polarization ; Clusters, open ; YSOs ;
Stars, ages
Keywords: dust, extinction; ISM: magnetic fields;
open clusters and associations: individual: NGC 1931;
polarization; stars: formation;
stars: luminosity function, mass function; stars: pre-main sequence
Abstract:
We present optical photometric and polarimetric observations of stars
toward NGC 1931 with the aim of deriving cluster parameters such as
distance, reddening, age, and luminosity/mass function as well as
understanding dust properties and star formation in the region. The
distance to the cluster is found to be 2.3±0.3kpc and the reddening
E(B-V) in the region is found to be variable. The stellar density
contours reveal two clusters in the region. The observations suggest a
differing reddening law within the cluster region. Polarization
efficiency of the dust grains toward the direction of the cluster is
found to be less than that for the general diffuse interstellar medium
(ISM). The slope of the mass function (-0.98±0.22) in the southern
region in the mass range of 0.8<M/M☉<9.8 is found to be
shallower in comparison to that in the northern region (-1.26±0.23),
which is comparable to the Salpeter value (-1.35). The K-band
luminosity function (KLF) of the region is found to be comparable to
the average value of the slope (∼0.4) for young clusters obtained by
Lada & Lada (2003ARA&A..41...57L 2003ARA&A..41...57L); however, the slope of the KLF is
steeper in the northern region as compared to the southern region. The
region is probably ionized by two B2 main-sequence-type stars. The
mean age of the young stellar objects (YSOs) is found to be 2±1Myr,
which suggests that the identified YSOs could be younger than the
ionizing sources of the region. The morphology of the region, the
distribution and ages of the YSOs, and ionizing sources indicate a
triggered star formation in the region.
Description:
The photometric data were acquired on 2005 December 31, 2006 January
22, 23, and 2006 February 24 using the CCD camera mounted on the 104cm
Sampurnanand Telescope at the Aryabhatta Research Institute of
Observational Sciences (ARIES) in Nainital, India. The entire chip
covers a field of ∼13x13arcmin2 on the sky. The FWHM of the star
images was ∼2"-3".
The Spitzer/IRAC MIR observations (3.6 and 4.5um) for the NGC 1931
region are also available and NIR JHKs data for point sources in the
NGC 1931 region have been obtained from 2MASS (Cutri+, 2003, II/246).
Polarimetric observations were carried out on two nights (2010
November 12 and December 13) using the ARIES Imaging Polarimeter
(AIMPOL) mounted on the Cassegrain focus of the 104cm Sampurnanand
Telescope at ARIES in Nainital, India. The details of the AIMPOL are
given in our earlier works (Eswaraiah+, 2011MNRAS.411.1418E 2011MNRAS.411.1418E;
Eswaraiah+, 2012MNRAS.419.2587E 2012MNRAS.419.2587E). The observations were carried out in
the V, Rc, and Ic photometric bands.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 99 1579 UBV(RI)c photometric data
table6.dat 126 62 Observed polarization, polarization angles, and
estimated Serkowski parameters
table9.dat 22 41 *Age and mass of YSOs obtained in the present study
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Note on table9.dat: The age and mass of each YSO have been estimated using the
V/(V-I) CMD, as discussed by Pandey et al. (2008, J/MNRAS/383/1241) and
Chauhan et al. (2009, J/MNRAS/396/964).
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/MNRAS/396/964 : T Tauri in and around bright-rimmed clouds (Chauhan+, 2009)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/MNRAS/383/1241 : UBVIc photometry of cluster Berkeley 59 (Pandey+, 2008)
J/AJ/132/1669 : Wide-field CCD phot. around 9 open clusters (Sharma+, 2006)
J/PAZh/25/10 : Young open clusters space-age distribution (Dambis, 1999)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/1579] Star running sequence number
6- 6 I1 h RAh [5] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [30/32] Minute of Right Ascension (J2000)
11- 16 F6.3 s RAs Second of Right Ascension (J2000)
18 A1 --- DE- [+] Sign of Declination (J2000)
19- 20 I2 deg DEd [34] Degree of Declination (J2000)
22- 23 I2 arcmin DEm [5/20] Arcminute of Declination (J2000)
25- 29 F5.2 arcsec DEs Arcsecond of Declination (J2000)
31- 36 F6.3 mag Umag ?=99.999 The U band magnitude
38- 43 F6.4 mag e_Umag ?=9.9999 The 1σ uncertainty in Umag
45- 50 F6.3 mag Bmag ?=99.999 The B band magnitude
52- 57 F6.4 mag e_Bmag ?=9.9999 The 1σ uncertainty in Bmag
59- 64 F6.3 mag Vmag [10.7/21.8] The V band magnitude
66- 71 F6.4 mag e_Vmag [0.001/0.1] The 1σ uncertainty in Vmag
73- 78 F6.3 mag Rmag ?=99.999 The RC band magnitude
80- 85 F6.4 mag e_Rmag ?=9.9999 The 1σ uncertainty in Rmag
87- 92 F6.3 mag Imag [9.3/20.4] The IC band magnitude
94- 99 F6.4 mag e_Imag [0.001/0.9] The 1σ uncertainty in Imag
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1 A1 --- n_Seq Note on Seq (1)
3- 6 I4 --- Seq [1/2003] Star identification number
8 A1 --- f_Seq [a] Optical data not available (2)
10 I1 h RAh [5] Hour of right ascension (J2000)
12- 13 I2 min RAm Minute of right ascension (J2000)
15- 20 F6.3 s RAs Second of right ascension (J2000)
22 A1 --- DE- [+] Sign of declination (J2000)
23- 24 I2 deg DEd Degree of declination (J2000)
26- 27 I2 arcmin DEm Arcminute of declination (J2000)
29- 34 F6.3 arcsec DEs Arcsecond of declination (J2000)
36- 39 F4.2 % Vpol [0.3/8.7]? Degree of polarization in V-band
41- 44 F4.2 % e_Vpol [0.08/1.1]? Vpol uncertainty
46- 50 F5.1 deg Vpa [6.1/173]? V-band polarization angle
52- 55 F4.1 deg e_Vpa [1.1/11]? Vpa uncertainty
57- 60 F4.2 % Rpol [0.3/6.4]? Rc-band polarization degree
62- 65 F4.2 % e_Rpol [0.08/0.8]? Rpol uncertainty
67- 71 F5.1 deg Rpa [2.7/180]? Rc-band polarization angle
73- 75 F3.1 deg e_Rpa [0.9/9]? Rpa ncertainty
77- 80 F4.2 % Ipol [0.3/6.9]? Ic-band polarization degree
82- 85 F4.2 % e_Ipol [0.05/0.7]? Ipol uncertainty
87- 91 F5.1 deg Ipa [-3.3/175]? Ic-band polarization angle
93- 95 F3.1 deg e_Ipa [0.8/9]? Ipa uncertainty
97-100 F4.2 % Pmax [0.4/8.3]? Peak polarization occurring at
wavelength λmax (3)
102-105 F4.2 % e_Pmax [0.06/1]? Pmax uncertainty
107-110 F4.2 um lam.m [0.3/0.9]? Wavelength λmax (3)
112-115 F4.2 um e_lam.m [0.04/0.3]? lam.m uncertainty
117-120 F4.2 --- sig1 [0.05/3.2]? σ1 parameter (4)
122-126 F5.2 --- eps [0.06/14]? <ε> parameter (5)
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Note (1): Note as follows:
p = Stars with V(RI)c passband data
e = Stars embedded in the nebulosity
d = Stars with either single or double band data
Note (2):
a = Optical data are not available for the three stars, namely, 2001, 2002,
and 2003. Their IDs are given arbitrarily.
Note (3): Pλ=Pmaxexp[-K.ln2(λmax/λ)]
The λmax depends on the optical properties and characteristic
particle size distribution of aligned grains (Serkowski et al.
1975ApJ...196..261S 1975ApJ...196..261S; McMillan 1978ApJ...225..880M 1978ApJ...225..880M), whereas the value
of Pmax is dictated by the chemical composition, shape, size, column
density, and alignment efficiency of the dust grains. See section 5.4.
Note (4): The parameter σ1 (the unit weight error of the fit for
each star) quantifies the departure of the data from the standard
Serkowski's law. See section 5.4.
Note (5): <ε> is the dispersion of the polarization angle
for each star normalized by the average of the polarization angle
errors (cf. Marraco et al. 1993AJ....105..258M 1993AJ....105..258M). See section 5.4.
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Byte-by-byte Description of file: table9.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [32/1575] Star number
6 A1 --- l_Age Limit flag on Age
8- 10 F3.1 Myr Age [0.4/5] Age
12- 14 F3.1 Myr e_Age [0.1/1.5]? Age uncertainty
16- 18 F3.1 Msun Mass [0.3/3.5] Mass
20- 22 F3.1 Msun e_Mass [0.1/0.3] Mass uncertainty
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Oct-2014