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J/ApJ/665/369   Photopolarimetry of Southern Coalsack stars  (Andersson+, 2007)
Observational constraints on interstellar grain alignment.
    Andersson B.-G., Potter S.B.
   <Astrophys. J., 665, 369-389 (2007)>
   =2007ApJ...665..369A
ADC_Keywords: Interstellar medium ; Molecular clouds ; Photometry ; Polarization

Keywords: dust, extinction - ISM: individual (Southern Coalsack, Chamaeleon I,
          Musca, rho Ophiuchus, R CrA, Taurus) - polarization

Abstract:
    We present new multicolor photopolarimetry of stars behind the
    Southern Coalsack. Analyzed together with multiband polarization data
    from the literature, probing the Chamaeleon I, Musca, rho Opiuchus,
    R CrA, and Taurus clouds, we show that the wavelength of maximum
    polarization (λmax) is linearly correlated with the radiation
    environment of the grains. Using far-infrared emission data, we show
    that the large scatter seen in previous studies of λmax as a
    function of Av is primarily due to line-of-sight effects causing some
    Av measurements to not be a good tracer of the extinction (radiation
    field strength) seen by the grains being probed.

Description:
    We used the University of Cape Town Polarimeter on the 1.9m telescopes
    of the South African Astronomical Observatory (SAAO) during 2005 April
    6-8 and 13 to perform multiband observations of interstellar
    polarization of stars background to the Southern Coalsack.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table2.dat       136       15   Coalsack Polarimetry Results
table4.dat       129      141   Stars with data from archives and the literature
table5.dat        55      133   Polarization curve fits for stars from literature


Byte-by-byte Description of file: table2.dat

   Bytes Format Units   Label     Explanations

   1- 11  A11   ---     Star      Star name
  15- 18  F4.2  %       p(U)      Polarisation in U band
  21- 24  F4.2  %       e_p(U)    Mean error on p(U)
  27- 31  F5.1  deg     pa(U)     Position angle of U-band polarisation
  34- 36  F3.1  deg     e_pa(U)   Mean error on pa(U)
  40- 43  F4.2  %       p(B)      Polarisation in B band
  46- 49  F4.2  %       e_p(B)    Mean error on p(B)
  52- 56  F5.1  deg     pa(B)     Position angle of B-band polarisation
  59- 61  F3.1  deg     e_pa(B)   Mean error on pa(B)
  65- 68  F4.2  %       p(V)      Polarisation in V band
  71- 74  F4.2  %       e_p(V)    Mean error on p(V)
  77- 81  F5.1  deg     pa(V)     Position angle of V-band polarisation
  84- 86  F3.1  deg     e_pa(V)   Mean error on pa(V)
  90- 93  F4.2  %       p(R)      Polarisation in R band
  96- 99  F4.2  %       e_p(R)    Mean error on p(R)
 102-106  F5.1  deg     pa(R)     Position angle of R-band polarisation
 109-111  F3.1  deg     e_pa(R)   Mean error on pa(R)
 115-118  F4.2  %       p(I)      Polarisation in U band
 121-124  F4.2  %       e_p(I)    Mean error on p(I)
 127-131  F5.1  deg     pa(I)     Position angle of I-band polarisation
 134-136  F3.1  deg     e_pa(I)   Mean error on pa(I)


Byte-by-byte Description of file: table4.dat

   Bytes Format Units   Label     Explanations

   1- 10  A10   ---     Cloud     Cloud name (1)
  12- 22  A11   ---     Star      Star name
  24- 36  A13   ---     SpType    MK Spectral Classification (2)
  38- 43  F6.3  mag     Vmag      ? The V band magnitude
  45- 48  F4.2  mag     e_Vmag    ? Uncertainty in Vmag
  50- 55  F6.3  mag     B-V       Observed (B-V) color index
  57- 60  F4.2  mag     e_B-V     Uncertainty in B-V
  62- 66  F5.2  mag     (B-V)0    ? Intrinsic (B-V) color index
  68- 71  F4.2  mag     e_(B-V)0  ? Uncertainty in (B-V)0
  73- 78  F6.3  mag     V-K       ? Observed (V-K) color index
  80- 84  F5.3  mag     e_V-K     ? Uncertainty in V-K
  86- 90  F5.2  mag     (V-K)0    ? Intrinsic (V-K) color index
  92- 95  F4.2  mag     e_(V-K)0  ? Uncertainty in (V-K)0
  97-100  F4.2  ---     Rv        ? Ratio of total-to-selective extinction
 102-105  F4.2  ---     e_Rv      ? Uncertainty in Rv
     107  A1    ---     f_Rv      [d] Rv ignored in the analysis (3)
 109-112  F4.2  mag     Av        ? The V band extinction
 114-117  F4.2  mag     e_Av      ? Uncertainty in Av
 119-127  A9    ---     r_SpType  Reference for SpType (4)
     129  A1    ---     S?        Screened out? (5)

Note (1): Based on comparisons of Figure 1 in Arnal et al.
     (1993MNRAS.265....1A) with the Aladin tool (Bonnarel et al.,
     2000A&AS..143...33B) we have made the following target identifications
     in Musca from Arnal et al. (1993MNRAS.265....1A) (AMZ):
       AMZ16 = CD-71 836 (= [AMR93] 16)
       AMZ18 = CD-71 832 (= [AMR93] 18)
       AMZ28 = CD-70 925 (= [AMR93] 28)
       AMZ41 = CPD-69 1677 (= [AMR93] 41)
       AMZ45 = CD-69 1024 (= [AMR93] 45)
Note (2): Estimated uncertainties given in parenthesis.

Note (3): d = The derived value is unphysical and is ignored in the analysis.

Note (4): Reference for SpType as follows:
    KDH94 = Kenyon et al. (1994AJ....108..251K)
      M68 = Metreveli (1968AbaOB..38...93M)
      MSS = Houk & Cowley (1975, Cat. III/31)
      N95 = Nesterov et al. (1995, Cat. III/182)
    SSS80 = Slutskij et al. (1980SvAL....6..397S)
     SM80 = Straizys & Meistas (1980AcA....30..541S)
    SCH85 = Straizys et al. (1985Ap&SS.112..251S)
      U85 = Ungerer et al. (1985A&A...146..123U)
     VR84 = Vrba & Rydgren (1984ApJ...283..123V)
     VR85 = Vrba & Rydgren (1985AJ.....90.1490V)
     VR93 = Vrba et al. (1993AJ....105.1010V)
      W87 = Whittet et al. (1987MNRAS.224..497W)
      W01 = Whittet et al. (2001ApJ...547..872W)
        Y = Yale observatory (1997)
Note (5): Sightlines that are screened out in the Hipparcos field star
     based analysis. (see section 4.2)


Byte-by-byte Description of file: table5.dat

   Bytes Format Units   Label     Explanations

   1- 10  A10   ---     Cloud     Cloud name
  12- 22  A11   ---     Star      Star name (1)
  24- 28  F5.2  %       Pmax      Maximum polarization
  30- 33  F4.2  %       e_Pmax    Uncertainty in Pmax
  35- 39  F5.3  um      Wmax      Wavelength of maximum polarization
  41- 45  F5.3  um      e_Wmax    Uncertainty in Wmax
  47- 50  F4.2  ---     K         ? Interstellar polarization K parameter (2)
  52- 55  F4.2  ---     e_K       ? Uncertainty in K

Note (1): For HD 107875 in Musca Arnal et al. (1993MNRAS.265....1A) report
     λmax=0.641±0.009. This is only case of a significant
     discrepancy in λmax for our polarization curve fits compared
     to the literature. This sightline is excluded from the analysis.
Note (2): Serkowski's K which relates the polarisation to wavelength:
     p/pmax = exp[-K .ln2(λmax/λ)]


History:
  * 05-Sep-2009: From electronic version of the journal
  * 16-Nov-2009: added table2.
(End)                  Greg Schwarz [AAS], Patricia Vannier [CDS]    05-Sep-2009