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J/ApJ/793/126      L204 - Cloud 3 polarimetry and photometry    (Cashman+, 2014)

The magnetic field of Cloud 3 in L204. Cashman L.R., Clemens D.P. <Astrophys. J., 793, 126 (2014)> =2014ApJ...793..126C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Interstellar medium ; Molecular clouds ; Polarization ; Photometry, infrared ; Extinction Keywords: dust, extinction - ISM: clouds - ISM: individual objects (L204) - ISM: magnetic fields - magnetic fields - polarization Abstract: The L204 dark cloud complex is a nearby filamentary structure in Ophiuchus North that has no signs of active star formation. Past studies show that L204 is interacting with the nearby runaway O star, ζ Oph, and hosts a magnetic field that is coherent across parsec-length scales. Near-infrared H-band (1.6 µm) linear polarization measurements were obtained for 3896 background stars across a 1°x1.5° region centered on the dense Cloud 3 in L204, using the Mimir near-infrared instrument on the 1.8 m Perkins Telescope. Analysis of these observations reveals both large-scale properties and small-scale changes in the magnetic field direction in Cloud 3. In the northern and western ζ Oph facing regions of the cloud, the magnetic field appears to be pushed up against the face of the cloud. This may indicate that the UV flux from ζ Oph has compressed the magnetic field on the western edge of L204. The plane-of-sky magnetic field strength is estimated to be ∼11-26 µG using the Chandrasekhar-Fermi method. The polarimetry data also reveal that the polarization efficiency (PE ≡ PH/AV) steadily decreases with distance from ζ Oph (-0.09%±0.03%/mag/pc). Additionally, power-law fits of PE versus AV for localized samples of probe stars show steeper negative indices with distance from ζ Oph. Both findings highlight the importance of external illumination, here from ζ Oph, in aligning dust grains to embedded magnetic fields. Description: Linear polarimetry measurements were obtained in the NIR H band (1.6 um) using the Mimir instrument (Clemens et al. 2007PASP..119.1385C) on the 1.8 m Perkins telescope outside of Flagstaff, AZ. Mimir used a 10242 Aladdin III InSb detector array, operated at 33.5 K. The instrument had a field of view (FOV) of 10'x10' and pixel scale of 0.58''. Polarimetric analysis was performed with a cold, stepping, H-band, compound half-wave plate (HWP) plus a fixed, cold wire-grid analyzer. Sky observations were planned for a grid of 54 abutting fields (a 6x9 field grid) covering a 1°x1.5° region of L204 centered on Cloud 3. They were conducted over several nights between 2010 May and 2012 May. To obtain polarimetry measurements, exposures of five second durations were obtained for 16 unique HWP position angles at six sky-dither positions, yielding a total of 96 images per field. The total on-sky integration time of the entire map (eight minutes per FOV) was 7.2 hr. Polarization flat-fields for each HWP position were taken using a lights-on/lights-off method against a uniformly illuminated flat-field screen inside the closed telescope dome. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 16 47 47.3 -12 05 16 L204 = LDN 204 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 123 7150 Polarimetry and Photometry of 7150 Stars Towards L204 - Cloud 3
See also: J/A+AS/141/175 : Dark clouds imaging polarimetry (Sen+, 2000) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 I4 --- ID [1/7150] Star index number 6- 7 I2 h RAh Hour of Right Ascension (J2000) 9- 10 I2 min RAm Minute of Right Ascension (J2000) 12- 15 F4.1 s RAs Second of Right Ascension (J2000) 17 A1 --- DE- Sign of the Declination (J2000) 18- 19 I2 deg DEd Degree of Declination (J2000) 21- 22 I2 arcmin DEm Arcminute of Declination (J2000) 24- 25 I2 arcsec DEs Arcsecond of Declination (J2000) 27- 33 F7.2 % U Stokes U Mimir measurement 35- 39 F5.2 % e_U Uncertainty in U 41- 46 F6.2 % Q Stokes Q Mimir measurement 48- 52 F5.2 % e_Q Uncertainty in Q 54- 59 F6.2 % P Degree of polarization (1) 61- 65 F5.2 % e_P Uncertainty in P 67- 69 I3 deg PA Equatorial position angle; measured East of North 71- 73 I3 deg e_PA Uncertainty in PA 75 I1 --- UFlag [1/3] Usage flag (2) 77 A1 --- l_Jmag [<] Upper limit flag on Jmag 78- 82 F5.2 mag Jmag ?=99.99 2MASS J band magnitude (3) 84- 87 F4.2 mag e_Jmag ? Uncertainty in Jmag (3) 89- 93 F5.2 mag Hmag ?=99.99 2MASS H band magnitude (3) 95- 98 F4.2 mag e_Hmag ? Uncertainty in Hmag (3) 100 A1 --- l_Ksmag [<] Upper limit flag on Ksmag 101-105 F5.2 mag Ksmag ?=99.99 2MASS KS band magnitude (3) 107-110 F4.2 mag e_Ksmag ? Uncertainty in Ksmag (3) 112 A1 --- BFlag [0/2] Background flag (4) 114-118 F5.2 mag AV ?=-9.99 The V band extinction (5) 120-123 F4.2 mag e_AV ? Uncertainty in AV
Note (1): P values have been corrected for positive bias. The correction was also propagated into the PA uncertainties. Note (2): Flag as follows: 1 = highest quality; 2 = moderate; 3 = poor. Note (3): J, H, and K values of 99.99 indicate that no matching 2MASS star was found. No values in uncertainties indicate measurements which are upper limits. Note (4): Flag as follows: 1 = foreground; 2 = background; 0 = unknown. Note (5): From NICER for BFlag=1 and 2. BFlag=0 set to AV=-9.99±0.00.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Apr-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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