J/A+A/556/A65 LDN 1570 BV(RI)c polarisation and photometry (Eswaraiah+, 2013)
A study of starless dark cloud LDN 1570: distance, dust properties and
magnetic field geometry.
Eswaraiah C., Maheswar G., Pandey A.K., Jose J., Ramaprakash A.N.,
Bhatt H.C.
<Astron. Astrophys. 556, A65 (2013)>
=2013A&A...556A..65E 2013A&A...556A..65E
ADC_Keywords: Molecular clouds ; Bok globules ; Interstellar medium ;
Polarization ; Photometry, UBVRI ; Photometry, infrared
Keywords: polarization - ISM: clouds - dust, extinction - ISM: magnetic fields -
techniques: polarimetric - techniques: photometric
Abstract:
We wish to map the magnetic field geometry and to study the dust
properties of the starless cloud, L1570, using multiwavelength optical
polarimetry and photometry of the stars projected on the cloud.
We made R-band imaging polarimetry of the stars projected on a cloud,
L1570, to trace the magnetic field orientation. We also made
multi-wavelength polarimetric and photometric observations to
constrain the properties of dust in L1570.
We estimated a distance of 394±70pc to the cloud using 2MASS JHKs
colours. Using the values of the Serkowskiparameters namely
σ1, {overline}ε, λmax and the position of the
stars on near infrared color-color diagram, we identified 13 stars
that could possibly have intrinsic polarization and/or rotation in
their polarization angles. One star, 2MASS J06075075+1934177, which is
a B4Ve spectral type, show the presence of diffuse interstellar bands
in the spectrum apart from showing H_α line in emission. There
is an indication for the presence of slightly bigger dust grains
towards L1570 on the basis of the dust grain size-indicators such as
λmax and RV values. The magnetic field lines are found to
be parallel to the cloud structures seen in the 250um images (also in
8um and 12um shadow images) of L1570. Based on the magnetic field
geometry, the cloud structure and the complex velocity structure, we
believe that L1570 is in the process of formation due to the
converging flow material mediated by the magnetic field lines.
Structure function analysis showed that in the L1570 cloud region the
large scale magnetic fields are stronger when compared with the
turbulent component of magnetic fields. The estimated magnetic field
strengths suggest that the L1570 cloud region is sub-critical and
hence could be strongly supported by the magnetic field lines.
Description:
Polarimetric observations of the field containing L1570 were carried
out on ten nights; namely, 23, 24, 25, 26 November 2009; 23, 24, 27,
28 December 2009 and 27, 31 December 2010 using the ARIES Imaging
Polarimeter (AIMPOL) mounted at the Cassegrain focus of the 1.04-m
Sampurnanand telescope (ST) of the Aryabhatta Research Institute of
Observational sciences (ARIES), Manora Peak, India.
The CCD optical photometric observations of the central region
(RA=06:07:33.043; DE=+19:30:52.70, 2000) of L1570 were
carried out in BVRI-bands using the 1.04-m ST on 27 November 2010.
Results based on optical broad-band (BV(RI)c) photometric and
polarimetric observations are presented. The polarization results of
various polarized standard stars (taken from Schmidt et al.
1992AJ....104.1563S 1992AJ....104.1563S) are presented along with their standard values
(Table 1). Rc-band polarization data of 127 stars along with their
2MASS data (JHKs) is presented (Table 2).
Polarization and Serkowski fit parameters for the 42 stars with V(RI)c
pass-band data is presented (Table 3). Polarization and Serkowski fit
parameters for the 15 stars with BV(RI)c pass-band data is presented
(Table 4). Photometric data of 144 stars with good signal-noise-ratio
(with BV(RI)c and 2MASS JHKs-photometric errors <0.1mag) is also
presented (Table 6).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
standard.dat 46 6 List of standard stars of table1
table1.dat 104 35 *Observed polarized standard stars from
Schmidt et al. (1992AJ....104.1563S 1992AJ....104.1563S)
table2.dat 72 127 Rc-band polarization data of 127 stars along
with their 2MASS data and positions (JHKs)
table3.dat 110 42 Polarization and Serkowski fit parameters for
the 42 stars with V(RI)c pass-band data
along with their positions
table4.dat 110 15 Polarization and Serkowski fit parameters for
the 15 stars with B, V (RI)c pass-band data
along with their positions
table6.dat 106 144 Photometric data of 144 stars with good signal/noise
ratio (with BV(RI)c and 2MASS JHK-photometric
errors 0.1 mag) along with their positions
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Note on table1.dat: obtained, using AIMPOL and IFOSC in polarimetric mode.
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Byte-by-byte Description of file: standard.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star name
11- 12 I2 h RAh Simbad Hour of Right Ascension (J2000.0)
14- 15 I2 min RAm Simbad Minute of Right Ascension (J2000.0)
17- 21 F5.2 s RAs Simbad Second of Right Ascension (J2000.0)
23 A1 --- DE- Simbad Sign of the Declination (J2000.0)
24- 25 I2 deg DEd Simbad Degree of Declination (J2000.0)
27- 28 I2 arcmin DEm Simbad Arcminute of Declination (J2000.0)
30- 33 F4.1 arcsec DEs Simbad Arcsecond of Declination (J2000.0)
35- 40 F6.3 mag Bmag Simbad B band magnitude
41- 46 F6.3 mag Vmag Simbad V band magnitude
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Inst [AI] Instrument (A: AIMPOL, I: IFOSC)
3- 11 A9 --- Name Star name
12 A1 --- n_Name [+] +: data from Schmidt et al.,
1992AJ....104.1563S 1992AJ....104.1563S
14- 23 A10 "YYYY/MM/DD" Date Observation date
26- 29 F4.2 % PB Percentage of polarization in B-band
31- 34 F4.2 % e_PB rms uncertainty on PB
36- 40 F5.1 deg PAB [0/180] Polarization angle in B-band
42- 44 F3.1 deg e_PAB rms uncertainty on PAB
46- 49 F4.2 % PV ?=9.99 Percentage of polarization in V-band
51- 54 F4.2 % e_PV ?=9.99 rms uncertainty on PV
56- 60 F5.1 deg PAV [0/180]?=999.9 Polarization angle in V-band
62- 64 F3.1 deg e_PAV ?=9.9 rms uncertainty on PAV
66- 69 F4.2 % PRc [0/180] Percentage of polarization in Rc-band
71- 74 F4.2 % e_PRc rms uncertainty on PRc
76- 80 F5.1 deg PARc Polarization angle in Rc-band
82- 84 F3.1 deg e_PARc rms uncertainty on PARc
86- 89 F4.2 % PIc ?=9.99 Percentage of polarization in Ic-band
91- 94 F4.2 % e_PIc ?=9.99 rms uncertainty on PIc
96-100 F5.1 deg PAIc ?=999.9 Polarization angle in Ic-band
102-104 F3.1 deg e_PAIc ?=9.9 rms uncertainty on PAIc
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/127] Star sequential number
4 A1 --- n_Seq [+] +: Hα emission line sources
6- 14 F9.6 deg RAdeg Right ascension (J2000)
16- 24 F9.6 deg DEdeg Declination (J2000)
26- 28 F3.1 % PRc Percentage of polarization in Rc-band
30- 32 F3.1 % e_PRc rms uncertainty on PRc
34- 36 I3 deg PARc [45/225] Polarization angle in Rc-band (G1)
38- 39 I2 deg e_PARc rms uncertainty on PARc
41- 45 F5.2 mag Jmag 2MASS J magnitude
47- 50 F4.2 mag e_Jmag rms uncertainty on Jmag
52- 56 F5.2 mag Hmag 2MASS H magnitude
58- 61 F4.2 mag e_Hmag rms uncertainty on Hmag
63- 67 F5.2 mag Ksmag 2MASS Ks magnitude
69- 72 F4.2 mag e_Ksmag rms uncertainty on Ksmag
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Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/127] Star sequential number
4 A1 --- n_Seq [+] +: Hα emission line sources
6- 14 F9.6 deg RAdeg Right ascension (J2000)
16- 24 F9.6 deg DEdeg Declination (J2000)
26- 28 F3.1 % Pmax Maximum percentage of polarization (1)
30- 32 F3.1 % e_Pmax rms uncertainty on Pmax (1)
34- 37 F4.2 um lam.max Wavelength corresponding to Pmax (1)
39- 42 F4.2 um e_lam.max rms uncertainty on lam.max (1)
44- 47 F4.1 --- sigma1 Unit weight error of the fit, σ1 (2)
49- 52 F4.1 --- eps Dispersion of the polarization angle
normalized by the average of the
polarization angle errors (ε{bar})
54- 56 F3.1 % PB ? Percentage of polarization in B-band (3)
58- 60 F3.1 % e_PB ? rms uncertainty on PB (3)
62- 64 F3.1 % PV Percentage of polarization in V-band
66- 68 F3.1 % e_PV rms uncertainty on PV
70- 72 F3.1 % PRc Percentage of polarization in Rc-band
74- 76 F3.1 % e_PRc rms uncertainty on PRc
78- 80 F3.1 % PIc Percentage of polarization in Ic-band
82- 84 F3.1 % e_PIc rms uncertainty on PIc
86- 88 I3 deg PAB [45/225]? Polarization angle in B-band (3) (G1)
90- 91 I2 deg e_PAB ? rms uncertainty on PAB (3)
93- 95 I3 deg PAV [45/225] Polarization angle in V-band (G1)
97- 98 I2 deg e_PAV rms uncertainty on PAV
100-102 I3 deg PARc [45/225] Polarization angle in Rc-band (G1)
104 I1 deg e_PARc rms uncertainty on PARc
106-108 I3 deg PAIc [45/225] Polarization angle in Ic-band (G1)
110 I1 deg e_PAIc rms uncertainty on PAIc
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Note (1): Pλ=Pmaxexp[-Kln2(λmax/λ)], where
Pλ is the percentage polarization at wavelength λ and
Pmax is the peak polarization, occurring at wavelength λmax.
Note (2): Unit weight error of the fit for each star, which quantifies the
departure of the data from the standard Serkowski law. The values of sigma1
for each star are computed using the expression
(sigma1)2= {Sum}(rλ/ε_pλ)2/(m-2), where
m is the number of colors and
rλ=Pλ-Pmax_exp[-Kln2(λmax/λ).
Note (3): For stars of table4 only.
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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- 3 I3 --- Star Star sequential number
4 A1 --- n_Star [*] Hα emission line source
6- 8 I3 --- Seq [1/127]? Star sequential number in Table 2
9 A1 --- n_Seq [+] Unreddened M-type dwarf (from (V-I)/(B-V)
colour-colour diagram)
11- 19 F9.6 deg RAdeg Right ascension (J2000)
21- 29 F9.6 deg DEdeg Declination (J2000)
31- 35 F5.2 mag Bmag B magnitude
37- 40 F4.2 mag e_Bmag rms uncertainty on Bmag
42- 46 F5.2 mag Vmag V magnitude
48- 51 F4.2 mag e_Vmag rms uncertainty on Vmag
53- 57 F5.2 mag Rcmag Rc magnitude
59- 62 F4.2 mag e_Rcmag rms uncertainty on Rmag
64- 68 F5.2 mag Icmag Ic magnitude
70- 73 F4.2 mag e_Icmag rms uncertainty on Imag
75- 79 F5.2 mag Jmag 2MASS J magnitude
81- 84 F4.2 mag e_Jmag rms uncertainty on Jmag
86- 90 F5.2 mag Hmag 2MASS H magnitude
92- 95 F4.2 mag e_Hmag rms uncertainty on Hmag
97-101 F5.2 mag Ksmag 2MASS Ks magnitude
103-106 F4.2 mag e_Ksmag rms uncertainty on Kmag
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Note (G1): 180 degree is added to the polarization angles whose values lie
between 0 degree and 45 degree. For example: 183 degree is equivalent
to 3 degree.
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Acknowledgements:
Chakali Eswaraiah, eswarbramha(at)gmail.com
(End) C. Eswaraiah [ARIES, Nainital, India], Patricia Vannier [CDS] 23-May-2013