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J/A+A/608/A146 Southern Hemisphere ISM FORS2 spectropolarimetry (Bagnulo+, 2017)

Large Interstellar Polarisation Survey (LIPS). I. FORS2 spectropolarimetry in the Southern Hemisphere. Bagnulo S., Cox N.L.J., Cikota A., Siebenmorgen R., Voshchinnikov N.V., Patat F., Smith K.T., Smoker J.V., Tautenberger S., Kaper L., Cami J. <Astron. Astrophys. 608, A146 (2017)> =2017A&A...608A.146B (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Polarization Keywords: polarisation - dust, extinction Abstract: Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope. Description: We make available 127 linear polarisation spectra of 101 stars, obtained with the FORS2 instrument of the ESO Very Large Telescope. These spectra cover the wavelength range 380-950nm at a spectral resolving power of about 880. We have produced a catalogue with synthetic broadband polarimetry in the BVRI filters, and we also provide the Serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table.dat 158 127 Synthetic broadband polarisation data, Serkowski curve parameters, position angle gradient and name of the tar file with the corresponding spectropolarimetric data sp/* 0 127 Individual tar file with spectropolarimetric data
Byte-by-byte Description of file: table.dat
Bytes Format Units Label Explanations
1- 13 A13 --- Name Star name 14- 23 A10 "YYYY-MM-DD" Obs.date Observation date 26- 30 A5 "h:m" Obs.time Time of observation at mid exposure (UT) 33- 37 F5.2 % P(B) ?=0 Polarisation in the B filter 39- 43 F5.1 deg theta(B) ?=0 Position angle of the polarisation in the B filter 46- 50 F5.2 % P(V) Polarisation in the V filter 52- 56 F5.1 deg theta(V) Position angle of the polarisation in the V filter 59- 63 F5.2 % P(R) Polarisation in the R filter 65- 69 F5.1 deg theta(R) Position angle of the polarisation in the R filter 72- 76 F5.2 % P(I) Polarisation in the I filter 78- 82 F5.1 deg theta(I) Position angle of the polarisation in the I filter 86- 89 F4.2 --- K ?=0 Parameter K of the Serkowski curve 91- 94 F4.2 --- e_K ?=0 Error on the parameter K of the Serkowski curve 96- 99 I4 nm Lmax ?=0 Wavelength at which polarisation is maximum 101-102 I2 nm e_Lmax ?=0 Error on wavelength at which polarisation is maximum 104-108 F5.2 % Pmax ?=0 Maximum of the polarisation 110-113 F4.2 % e_Pmax ?=0 Error on maximum of polarisation 115-119 F5.2 10-2deg/nm dT/dl Gradient of the polarisation position angle in degree/100nm 122-125 F4.2 10-2deg/nm e_dT/dl Error on gradient of the polarisation position angle in degree/100nm 129-158 A30 --- TARFILE Name of the tar file with the data in subdirectory sp (1)
Note (1): Spectra are available in form of ASCII files with names STARNAMEFILTERTYYYY-MM-DD_sxxxx.dat where YYYY-MM-DD is the date of the observations, STARNAME is the name of the star, FILTER may be either "FREE", "GG435" or "MEAN", xxxx is the bin size in nm. Files corresponding to different filters and bin size but to a same star and observing date are collected in tarballs named STARNAME_TYYYY-MM-DD.tar.gz. Each tar file contains the spectra rebinned at approximately 0.16, 0.32, 0.65, 1.29, 2.58, 5.17, 10.3, 20.7, 41.3 nm, for the three values of FILTER. FILTER refers to the instrument setting: when FREE, it means that observations were obtained with no order-separating filter. When GG435 means that this order-separating filter was inserted in the beam. MEAN is the average of the measurements obtained with and without order separating filters, as described in the paper. In most of the cases, the MEAN files will represent the best choice, while FREE or GG435 can be checked to assess whether a certain feature is likely to be real (e.g., if it is present in both observations). The rebinning depends on the user preferences. As explained in the text, it would be wrong to rebin the Stokes parameters, the rebinning must be done on the flux, this is the reason why files with different rebinning are provided. Files are organised as follows: Byte-by-byte Description of file: -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 2- 12 E11.6 nm lambda Wavelenght 17- 27 E11.6 --- Flux Flux (in ADU) 32- 42 E11.6 --- e_Flux rms uncertainty on Flux, calculated as square root of the electron counts (in ADU) 46- 57 E12.6 --- Q/I Q/I Stokes parameter 61- 72 E12.6 --- e_Q/I rms uncertainty on Q/I, due to photon noise 76- 87 E12.6 --- U/I U/I Stokes parameter 92-102 E11.6 --- e_U/I rms uncertainty on U/I 107-117 E11.6 --- Pl Fraction of linear polarisation 121-132 E12.6 deg theta Polarisation position angle 136-147 E12.6 deg e_theta rms uncertainty on theta
Acknowledgements: Stefano Bagnulo, sba(at)arm.ac.uk
(End) Stefano Bagnulo [AOP, UK], Patricia Vannier [CDS] 06-Oct-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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