J/ApJ/720/1045 Polarimetry toward sightlines through ChaI (Andersson+, 2010)
Observations of enhanced radiative grain alignment near HD 97300.
Andersson B.-G., Potter S.B.
<Astrophys. J., 720, 1045-1054 (2010)>
=2010ApJ...720.1045A 2010ApJ...720.1045A
ADC_Keywords: Polarization ; Photometry, UBV ; Molecular clouds ; Extinction ;
Interstellar medium
Keywords: dust, extinction - ISM: individual objects (Chamaeleon I)
Abstract:
We have obtained optical multi-band polarimetry toward sightlines
through the Chamaeleon I cloud, particularly in the vicinity of the
young B9/A0 star HD 97300. We show, in agreement with earlier studies,
that the radiation field impinging on the cloud in the projected
vicinity of the star is dominated by the flux from the star, as
evidenced by a local enhancement in the grain heating. By comparing
the differential grain heating with the differential change in the
location of the peak of the polarization curve, we show that the grain
alignment is enhanced by the increase in the radiation field. We also
find a weak, but measurable, variation in the grain alignment with the
relative angle between the radiation field anisotropy and the magnetic
field direction. Such an anisotropy in the grain alignment is
consistent with a unique prediction of modern radiative alignment
torque theory and provides direct support for radiatively driven grain
alignment.
Description:
We used the recently commissioned the HIgh speed Photo-POlarimeter
(HIPPO) on the 1.9m telescope of the South African Astronomical
Observatory (SAAO) during 2009 March 25-31 to perform multi-band
observations of the interstellar polarization of stars in the
background of the Chamaeleon I cloud. Measurements were performed
using UBVRI filters in the Kron-Cousin system. We used HD 98161 and HD
94851 as unpolarized standard stars and HD 84810, HD 298383, HD 15445,
and HD 111613 as polarized standard stars.
In addition to the newly acquired observations, we use the optical
multi-band polarimetry data from Whittet et al. (1992ApJ...386..562W 1992ApJ...386..562W)
and Covino et al. (1997A&AS..122...95C 1997A&AS..122...95C), as well as the H-band
polarimetry from McGregor et al. (1994, Cat. J/MNRAS/267/755).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 85 45 Source table, SAAO observations
table2.dat 100 45 Polarimetry results
table3.dat 90 45 Derived parameters
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See also:
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
I/297 : NOMAD Catalog (Zacharias+ 2005)
J/MNRAS/267/755 : Polarimetry in the Chamaeleon I Dark Cloud (McGregor+, 1994)
J/AJ/121/974 : JHK photometry in Cha I (Gomez+, 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Star Star name
21- 22 I2 h RAh Hour of Right Ascension (J2000)
24- 25 I2 min RAm Minute of Right Ascension (J2000)
27- 31 F5.2 s RAs Second of Right Ascension (J2000)
33 A1 --- DE- Sign of the Declination (J2000)
34- 35 I2 deg DEd Degree of Declination (J2000)
37- 38 I2 arcmin DEm Arcminute of Declination (J2000)
40- 44 F5.2 arcsec DEs Arcsecond of Declination (J2000)
46- 50 F5.2 mag Vmag Johnson V magnitude
52- 55 F4.2 mag e_Vmag Mean error on Vmag
57- 60 F4.2 mag B-V Johnson B-V color index
62- 65 F4.2 mag e_B-V Mean error on B-V
67- 85 A19 --- Notes Additional notes
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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- 19 A19 --- Star Star name (1)
21- 24 F4.2 % PU ? Polarisation in U band
26- 29 F4.2 % e_PU ? Uncertainty on PU
31- 33 I3 deg paU ? Position angle of PU (East of North)
35- 36 I2 deg e_paU ? Uncertainty on paU
38- 41 F4.2 % PB ? Polarisation in B band
43- 46 F4.2 % e_PB ? Uncertainty on PB
48- 50 I3 deg paB ? Position angle of PB (East of North)
52 I1 deg e_paB ? Uncertainty on paB
54- 57 F4.2 % PV ? Polarisation in V band
59- 62 F4.2 % e_PV ? Uncertainty on PV
64- 66 I3 deg paV ? Position angle of PV (East of North)
68 I1 deg e_paV ? Uncertainty on paV
70- 73 F4.2 % PR ? Polarisation in R band
75- 78 F4.2 % e_PR ? Uncertainty on PR
80- 82 I3 deg paR ? Position angle of PR (East of North)
84 I1 deg e_paR ? Uncertainty on paR
86- 89 F4.2 % PI ? Polarisation in I band
91- 94 F4.2 % e_PI ? Uncertainty on PI
96- 98 I3 deg paI ? Position angle of PI (East of North)
100 I1 deg e_paI ? Uncertainty on paI
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Note (1): Object 0140-0072231 is missing in this table; added by CDS.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Star Star name
21- 26 A6 --- SpT MK spectral type
28 A1 --- f_SpT [ab] Flag on SpT (2)
30- 34 F5.2 mag (B-V)0 Johnson B-V color index; corrected
36- 39 F4.2 mag E_(B-V)0 ? Positive error on (B-V)0
41- 44 F4.2 mag e_(B-V)0 ? Negative error on (B-V)0
46- 50 F5.2 mag AV ? Visual extinction
52- 55 F4.2 mag E_AV ? Positive error on AV
57- 60 F4.2 mag e_AV ? Negative error on AV
62- 65 F4.2 % Pmax ? Maximum polarization
67- 70 F4.2 % e_Pmax ? Pmax uncertainty
72- 75 F4.2 um Lmax ? Wavelength of maximum polarization
(λmax)
77- 80 F4.2 um e_Lmax ? Lmax uncertainty
82- 86 F5.1 deg PA ? Average position angle for the observed
filters (East of North)
88- 90 F3.1 deg e_PA ? PA uncertainty
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Note (2): Flag as follows:
a = Likely embedded YSO.
b = Explicit spectral classification extracted from the SIMBAD archives.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Jun-2012