J/ApJ/775/84 Polarization from stars behind IC63 nebula (Andersson+, 2013)
Evidence for H2 formation driven dust grain alignment in IC 63.
Andersson B.-G., Piirola V., De Buizer J., Clemens D.P., Uomoto A.,
Charcos-Llorens M., Geballe T.R., Lazarian A., Hoang T., Vornanen T.
<Astrophys. J., 775, 84 (2013)>
=2013ApJ...775...84A 2013ApJ...775...84A
ADC_Keywords: Polarization ; Interstellar medium ; Stars, dwarfs ; H II regions
Keywords: dust, extinction; ISM: individual: IC 63;
ISM: magnetic fields; polarization
Abstract:
In the interstellar medium (ISM), molecular hydrogen is expected to
form almost exclusively on the surfaces of dust grains. Due to that
molecule's large formation energy (-4.5eV), several dynamical effects
are likely associated with the process, including the alignment of
asymmetric dust grains with the ambient magnetic field. Such aligned
dust grains are, in turn, believed to cause the broadband
optical/infrared polarization observed in the ISM. Here, we present
the first observational evidence for grain alignment driven by H2
formation, by showing that the polarization of the light from stars
behind the reflection nebula IC 63 appears to correlate with the
intensity of H2 fluorescence. While our results strongly suggest a
role for "Purcell rockets" in grain alignment, additional observations
are needed to conclusively confirm their role. By showing a direct
connection between H2 formation and a probe of the dust
characteristics, these results also provide one of the first direct
confirmations of the grain-surface formation of H2. We compare our
observations to ab initio modeling based on Radiative Torque Alignment
(RAT) theory.
Description:
We acquired optical spectro-polarimetry toward 12 stars (Table 1) at
the Nordic Optical Telescope (NOT) on La Palma during 2008 October
6-9, using the ALFOSC instrument in linear polarimetry mode.
Additionally, we acquired five-band photo-polarimetry for five stars
with the TURPOL instrument on the same telescope in 2007 November 3-6.
Imaging polarimetry in the NIR H-band (1.6um) was conducted on the UT
nights of 2008 September 15 and 2011 December 12, using the 1.8m
Perkins Telescope operated by the Lowell Observatory outside
Flagstaff, AZ.
CCD photometry in the ugriz system was acquired using the Sloan
Digital Sky Survey (SDSS) 20 inch calibration telescope at the Apache
Point Observatory on 2006 October 27, 28, 29, and 31 and 2006 November
13 and 16.
Deep narrow-band imaging of the 2.122um 1-0 S(1) line of molecular
hydrogen (total exposure time of 4800s), together with KS broad-band
imaging (total exposure time of 1720s), were acquired using the WIRCam
instrument at the Canada-France-Hawaii Telescope (CFHT) in queue
observing mode during 2008 August 12-September 14.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 39 14 Source list, optical polarimetry
table2.dat 42 169 Polarimetry results
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
III/92 : A Library of Stellar Spectra (Jacoby+ 1984)
VII/20 : Catalogue of HII Regions (Sharpless 1959)
J/A+A/541/A52 : Polarization efficiency and dust phase (Voshchinnikov+, 2012)
J/A+A/537/A59 : Radial velocities of gamma Cas (Nemravov+, 2012)
J/MNRAS/418/2121 : CO 3-2 observations of outflows in W5 (Ginsburg+, 2011)
J/ApJ/720/1045 : Polarimetry toward sightlines through ChaI (Andersson+, 2010)
J/ApJ/665/369 : Photopolarimetry of Southern Coalsack stars (Andersson+, 2007)
J/A+A/470/161 : UBV photometry of HII regions exciting stars (Russeil+, 2007)
J/A+A/448/411 : The DRAO polarization survey (Wolleben+, 2006)
J/AJ/130/873 : Properties of BQS objects in the SDSS DR3 area (Jester+, 2005)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- --- [IC63 #]
7- 8 I2 --- Star [5/76] Background star number
(<[APD2013] IC63 #NN> in Simbad)
10- 11 I2 h RAh Hour of right ascension (J2000)
13- 14 I2 min RAm Minute of right ascension (J2000)
16- 19 F4.1 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000)
22- 23 I2 deg DEd Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 31 F4.1 arcsec DEs Arcsecond of declination (J2000)
33- 35 A3 --- Inst [AT, ] Instrument (A=ALFOSC; T=TURPOL)
37- 39 I3 s Exp [180/720]? Exposure time (1)
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Note (1): The tabulated exposure times are for the ALFOSC observations and
refer to exposure time per half-wave plate (HWP) position.
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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- 6 A6 --- --- [IC63 #]
7- 8 I2 --- Star [5/76] Star identifier
10 A1 --- f_Star [1] Synthesized photometry (1)
12 A1 --- Filt Filter identifier (UBVRI or H)
14- 18 F5.3 um lambda [0.3/1.7] Central wavelength of filter
(λc)
20- 25 F6.4 um Width [0.02/0.08]? Filter width (Δλ)
27- 30 F4.2 % Pol [0.2/9.5]? Polarization (p)
32- 35 F4.2 % e_Pol [0.05/4]? Uncertainty in Pol
37- 39 I3 deg polPA [61/140]? Position angle (θ); E of N
41- 42 I2 deg e_polPA [1/23]? Uncertainty in PA
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Note (1):
1 = The data are synthesized UBVRI filters from the Nordic Optical Telescope
(NOT) ALFOSC spectro-polarimetry.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Mar-2015