J/ApJ/875/64 Polarization & photom. of stars toward LDN1225 (Eswaraiah+, 2019)
Polarimetric and photometric investigation of the dark globule LDN 1225:
distance, extinction law, and magnetic fields.
Eswaraiah C., Lai S.-P., Ma Y., Pandey A.K., Jose J., Chen Z., Samal M.R.,
Wang J.-W., Sharma S., Ojha D.K.
<Astrophys. J., 875, 64 (2019)>
=2019ApJ...875...64E 2019ApJ...875...64E
ADC_Keywords: Polarization; Photometry, UBVRI; Extinction; Molecular clouds
Keywords: dust, extinction ; ISM: clouds ; local interstellar matter ;
magnetic fields ; polarization
Abstract:
We present results based on the optical R-band observations of the
polarization of 280 stars distributed toward the dark globule LDN1225.
Parallaxes from Gaia data release 2 along with the polarization data
of ∼200 stars have been used to (a) constrain the distance of LDN 1225
as 830±83pc, (b) determine the contribution of interstellar
polarization, and (c) characterize the dust properties and delineate
the magnetic field (B-field) morphology of LDN 1225. We find that
B-fields are more organized and exhibit a small dispersion of 12°.
Using the 12CO molecular line data from the Purple Mountain
Observatory, along with the column density and dispersion in B-fields,
we estimate the B-field strength to be ∼56±10µG, the ratio of
magnetic to turbulent pressure to be ∼3±2, and the ratio of mass to
magnetic flux (in units of the critical value) to be <1. These results
indicate the dominant role of B-fields in comparison to turbulence and
gravity in rendering the cloud support. B-fields are aligned parallel
to the low-density parts (traced by a 12CO map) of the cloud; in
contrast, they are neither parallel nor perpendicular to the
high-density core structures (traced by 13CO and C18O maps).
LDN1225 hosts two 70µm sources, which seem to be low-mass Class 0
sources. The ratio of total to selective extinction derived using
optical and near-infrared photometric data is found to be anomalous
(RV=3.4), suggesting the growth of dust grains in LDN 1225. The
polarization efficiency of dust grains follows a power law with an
index of -0.7, implying that optical polarimetry traces B-fields in
the outer parts of the cloud.
Description:
Polarimetric observations of LDN 1225 were carried out on five nights
(2010 November 12 and 13, 2010 December 14, and 2013 November 1 and 2)
using the ARIES Imaging Polarimeter (AIMPOL) mounted at the Cassegrain
focus of the 104cm Sampurnanand telescope of the Aryabhatta Research
Institute of Observational Sciences (ARIES), Nainital, India. The
observations were carried out in the Rc (λRceff=0.670um)
photometric band. See Section 2.1.
To understand whether the large-scale B-fields of CepOB3 are preserved
and have any effect on the small scales of LDN 1225, we also observed
19 additional fields covering different parts of CepOB3 using various
polarimeters. Three fields with FOV of 8' diameter were observed in
the R-band with AIMPOL on 2016 October 29.
Eight fields with FOV of 4' diameter were observed in the R-band on
five nights (2014 November 19, 20, 25, 26, and 27) using the 2m
telescope of the Inter University Center for Astronomy and
Astrophysics (IUCAA), Girawali Observatory, India, with the IUCAA
Faint Object Spectrograph and Camera (IFOSC) in the polarimetric mode.
Eight fields with FOV of 4'x4' were observed on 2015 October 13 with
the Triple Range Imager and Polarimeter (TRIPOL) mounted on the Lulin
One-meter Telescope (LOT) at Lulin observatory, Taiwan (S. Sato et al.
2019, in preparation). See Section 2.2.
Optical photometric observations toward LDN 1225 were performed on
2013 September 6 and 7 using the Himalaya Faint Object Spectrograph
and Camera (HFOSC) of the 2m Himalayan Chandra Telescope (HCT) of the
Indian Astronomical Observatory (IAO), Hanle, operated by Indian
Institute of Astrophysics (IIA), India. Photometric observations in
BVRI bands were performed toward four fields around LDN 1225.
See Section 2.4.
In order to study the gas kinematics of the cloud LDN 1225, we used
the 12CO(1-0), 13CO (1-0), and C18O (1-0) molecular line data
from the Milky Way Imaging Scroll Painting (MWISP) project using the
Purple Mountain Observatory (PMO) Delingha 13.7m telescope located at
Qinghai observing station. LDN 1225 was observed in 2015 November.
See Section 2.5.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
23 11 58 +61 39.0 LDN1225 = LDN 1225
23 13 37 +61 30.0 NGC7538 = SH 2-158
23 04.2 +63 24 CepOB3 = Ass Cep OB 3
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 105 280 Rc band polarization data
table3.dat 117 689 Photometric data of 689 stars with their
photometric uncertainties less than 0.1mag
table4.dat 75 56 Weighted mean polarization measurements
table7.dat 66 57 Total extinction Av values of 57 stars
derived using NIR extinction method
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See also:
II/183 : UBVRI Photometric Standards (Landolt 1992)
II/226 : Stellar polarization catalogs agglomeration (Heiles, 2000)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
VI/128 : Log of CGPS exposures (Taylor+, 2003-)
VII/7 : Lynds' Catalogue of Dark Nebulae (LDN) (Lynds 1962)
VII/191 : Catalogue of Southern Dark Clouds (Hartley+ 1986)
VIII/39 : Composite CO Survey of the Milky Way (Dame+ 1987)
VII/244 : Atlas and Catalog of Dark Clouds (Dobashi+, 2005)
J/ApJS/110/21 : Molecular clouds in Cepheus and Cassiopeia (Yonekura+ 1997)
J/A+A/383/631 : Catalogue of dust clouds in the Galaxy (Dutra+, 2002)
J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003)
J/MNRAS/369/1822 : Distances to nine dark globules (Maheswar+, 2006)
J/ApJ/716/893 : Polarisation at 850mu{m} in OMC-2 & OMC-3 (Poidevin+, 2010)
J/ApJ/741/21 : Polarization of stars in Taurus (Chapman+, 2011)
J/ApJ/751/138 : VRIJHK photometry of IRAS 09149-4743 region (Santos+, 2012)
J/A+A/556/A65 : LDN 1570 BV(RI)c polarisation & photom. (Eswaraiah+, 2013)
J/ApJ/764/172 : UBVRI photometry of stars toward NGC 1931 (Pandey+, 2013)
J/other/NewA/19.1 : Ages and masses of NGC1893 PMS stars (Pandey+, 2013)
J/A+A/569/L1 : Polarization hole in a starless core (Alves+, 2014)
J/ApJ/793/126 : L204 - Cloud 3 polarimetry and photometry (Cashman+, 2014)
J/A+A/567/A109 : Carina nebula optically identified YSOs (Kumar+, 2014)
J/ApJ/807/5 : R-band polarimetry data in Lupus I region (Franco+, 2015)
J/A+A/588/A104 : Molecular clouds and star formation (Gong+, 2016)
J/ApJ/828/59 : Molecular clouds in the Milky Way with CO obs. (Su+, 2016)
J/ApJ/850/195 : RCW 57A NIR polarimetry and photometry (Eswaraiah+, 2017)
J/MNRAS/467/2943 : NGC 7538 region YSOs (Sharma+, 2017)
J/ApJ/849/157 : Polarimetry obs. toward IC5146 bckg stars (Wang+, 2017)
J/A+A/618/A163 : Stokes param. of Bok globules bckg stars (Jorquera+, 2018)
http://www.radioast.nsdc.cn/mwisp.php : Milky Ways Imaging Scroll Painting
(MWISP) project home page
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- PSeq [1/280] Identifier, sequential running number
6- 7 I2 h RAh [23] Hour of Right Ascension (J2000)
9- 10 I2 min RAm [10/13] Minute of Right Ascension (J2000)
12- 17 F6.3 s RAs Second of Right Ascension (J2000)
19 A1 --- DE- [+] Sign of Declination (J2000)
20- 21 I2 deg DEd [61] Degree of Declination (J2000)
23- 24 I2 arcmin DEm [26/52] Arcminute of Declination (J2000)
26- 31 F6.3 arcsec DEs Arcsecond of Declination (J2000)
33- 35 F3.1 % Pol-Rc [0.3/8.2] Rc-band polarization
37- 39 F3.1 % e_Pol-Rc [0.1/1.1] Uncertainty in Pol-Rc
41- 43 I3 deg PA-Rc [6/132] Position angle of Rc polarization
45- 46 I2 deg e_PA-Rc [1/14] Uncertainty in PA-Rc
48- 52 F5.2 mag Jmag [7.72/14.79] 2MASS J band magnitude
54- 57 F4.2 mag e_Jmag [0.02/0.06]? Uncertainty in Jmag
59- 63 F5.2 mag Hmag [6.57/14.35] 2MASS H band magnitude
65- 68 F4.2 mag e_Hmag [0.02/0.06]? Uncertainty in Hmag
70- 74 F5.2 mag Ksmag [5.85/14.28] 2MASS Ks band magnitude
76- 79 F4.2 mag e_Ksmag [0.02/0.1]? Uncertainty in Ksmag
81- 85 I5 pc Dist [168/10070]? Gaia DR2 Distance
87- 90 I4 pc e_Dist [1/5778]? Uncertainty in Dist
92-101 A10 --- Mm Stellar Class (1)
103 A1 --- D8 [X ] Stars in 8' diameter circle in Figure 1(a)
containing the star-forming region NGC 7538
105 A1 --- IR [X ] Stars with NIR excess
--------------------------------------------------------------------------------
Note (1): Stellar Class as follows:
FG = foreground star with distance<830pc (68 occurrences);
BG = background star with 830pc<distance<2.65kpc (144 occurrences);
BG-NGC7538 = background star with distance>2.65kpc which might be part
of NGC7538 (48 occurrences);
See Section 3.3.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/689] Sequential running identifier
5- 7 I3 --- PSeq [5/228]? Table 2 polarization data identifier
9- 10 I2 h RAh [23] Hour of Right Ascension (J2000)
12- 13 I2 min RAm [10/13] 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 [61] Degree of Declination (J2000)
26- 27 I2 arcmin DEm [29/49] Arcminute of Declination (J2000)
29- 34 F6.3 arcsec DEs Arcsecond of Declination (J2000)
36- 41 F6.3 mag Vmag [11.27/19.82] HCT/HFOSC V band magnitude
43- 47 F5.3 mag e_Vmag [0/0.041] Uncertainty in Vmag
49- 53 F5.3 mag B-V [0.49/3.67] B-V color index
55- 59 F5.3 mag e_B-V [0/0.1] Uncertainty in B-V
61- 66 F6.3 mag V-R [-0.9/2.5]? V-R color index
68- 72 F5.3 mag e_V-R [0.001/0.04]? Uncertainty in V-R
74- 78 F5.3 mag V-I [0.69/4.9] V-I color index
80- 84 F5.3 mag e_V-I [0.001/0.1] Uncertainty in V-I
86- 90 F5.2 mag Jmag [9.55/15.86] 2MASS J band magnitude
92- 95 F4.2 mag e_Jmag [0.02/0.09] Uncertainty in Jmag
97-101 F5.2 mag Hmag [8.04/15.23] 2MASS H band magnitude
103-106 F4.2 mag e_Hmag [0.03/0.1] Uncertainty in Hmag
108-112 F5.2 mag Ksmag [7.47/14.85] 2MASS Ks band magnitude
114-117 F4.2 mag e_Ksmag [0.02/0.1] Uncertainty in Ksmag
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Set Field Subset (1)
4- 11 A8 --- Field Field Name
13- 14 I2 h RAh [22/23] Hour of Right Ascension (J2000) (2)
16- 17 I2 min RAm Minute of Right Ascension (J2000)
19- 24 F6.3 s RAs Second of Right Ascension (J2000)
26 A1 --- DE- [+] Sign of Declination (J2000) (2)
27- 28 I2 deg DEd [59/64] Degree of Declination (J2000) (2)
30- 31 I2 arcmin DEm Arcminute of Declination (J2000)
33- 38 F6.3 arcsec DEs Arcsecond of Declination (J2000)
40- 43 F4.2 % Pol [0.1/5.4]? Weighted mean polarization
in percent
45- 48 F4.2 % e_Pol [0.02/0.5]? Uncertainty in Pol
50- 52 I3 deg PA [27/163]? Weighted mean polarization
position angle
54- 55 I2 deg e_PA [0/34]? Uncertainty in PA
57- 58 A2 --- Filt Passband filter (R, V or r')
60- 61 I2 --- Ns [0/12] Number of Stars
63- 75 A13 --- Ref Source (3)
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Note (1): Subsets as follows:
FG = FG stars with d<830pc;
BG = BG stars (FG corrected) with 830<d<2.65kpc.
Note (2): RA and Dec (except those of the stars from Heiles (2000, II/226)
are the central coordinates of the observed fields.
Note (3): Sources for mean polarizations as follows:
AIMPOL = ARIES Imaging Polarimeter (AIMPOL; Rautela+ 2004BASI...32..159R 2004BASI...32..159R)
mounted at the Cassegrain focus of the 104-cm Sampurnanand
telescope of the Aryabhatta Research Institute of
observational sciencES (ARIES), Nainital, India;
Heiles (2000) = V-band polarization of 16 stars located within the 5x5°
field containing CepOB3 from Heiles (2000, II/226);
IMPOL = IUCAA Faint Object Spectrograph and Camera (IFOSC)
in the polarimetric mode (Sen et al 1994SPIE.2198..264S 1994SPIE.2198..264S;
Ramaprakash et al 1998A&AS..128..369R 1998A&AS..128..369R) on the 2-m telescope
of the Inter University Center for Astronomy and Astrophysics
(IUCAA), Girawali Observatory, India;
TRIPOL = Triple Range Imager and Polarimeter (TRIPOL) mounted on Lulin
One-meter Telescope (LOT) at Lulin observatory, Taiwan
(Sato et al. in prep.);
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- PSeq [5/228] Identifier, sequential running number,
as in Table 2
5- 6 I2 h RAh [23] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [10/13] 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 [61] Degree of Declination (J2000)
22- 23 I2 arcmin DEm [29/48] Arcminute of Declination (J2000)
25- 30 F6.3 arcsec DEs Arcsecond of Declination (J2000)
32- 35 F4.2 mag J-H [0.19/0.57] NIR J-H color
37- 40 F4.2 mag e_J-H [0.03/0.06] Uncertainty in J-H
42- 45 F4.2 mag H-Ks [0.06/0.22] NIR J-Ks color
47- 50 F4.2 mag e_H-Ks [0.04/0.08] Uncertainty in H-Ks
52- 54 F3.1 % Pol-Rc [0.8/4.7] Rc band polarization, percent (%)
56- 58 F3.1 % e_Pol-Rc [0.2/0.9] Uncertainty in Pol-Rc
60- 62 F3.1 mag Av [0.2/3.3] Total extinction in V-band
64- 66 F3.1 mag e_Av [0.4/0.9] Uncertainty in Av
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Sep-2020