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J/A+AS/144/195      UBVRI polarimetric observations in NGC 6611 (Orsatti+, 2000)
Dust properties in NGC 6611
     Orsatti A.M., Vega E.I., Marraco H.G.
    <Astron. Astrophys. Suppl. Ser. 144, 195 (2000)>
    =2000A&AS..144..195O
ADC_Keywords: Clusters, open ; Polarization ; Photometry, UBVRI

Keywords: dust - extinction - ISM: HII regions - ISM: magnetic fields -
          Galaxy: open clusters and associations: individual: NGC 6611

Abstract:
    An investigation on dust properties in the NW portion of NGC 6611 has
    been conducted polarimetrically to test the existence of abnormal
    extinction in that section of the open cluster in an independent way.
    As previously suggested for the η Carinae nebula by Tapia et al.
    (1988, in Conference on Dust in the Universe, Bailey M.E. and Williams
    D.A. (eds.) Cambridge University Press, Cambridge, p.19) and
    subsequently confirmed by Marraco et al. (1993), the canonical
    relation between EV-K/EB-V and λmax (the wavelength of
    maximum interstellar polarization) is not valid for stars belonging to
    dusty HII regions, as is the case for the observed portion of M 16.
    This may arise mainly from the presence of silicate grains of a
    slightly larger size than the standard ISM and also from a
    considerable increase in mean graphite grain size, according to
    previous results from Chini & Wargau (1990A&A...227..213C). About 50%
    of the observed stars in NGC 6611 present indications of intrinsic
    polarization in their measurements; a similar percentage was found in
    IC 2944 (Vega et al., 1994AJ....108.1834V), another young open cluster
    in close relation with an HII region.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
object.dat        26       39   Object positions from Simbad
table1.dat        81      195   UBVRI polarimetric observations
table1.tex       103      397   LaTeX version of table1


See also:
    J/A+AS/134/525 : NGC 6611 compiled catalog (Belikov+ 1999)
    J/A+AS/121/223 : Multiphotometry of NGC 6611 (de Winter+ 1997)


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

   Bytes Format Units   Label     Explanations

   1-  3  I3    ---     NGC6611   Star number (Walker, 1961ApJ...133..438W)
   6-  7  I2    h       RAh       Right ascension (J2000.0)
   9- 10  I2    min     RAm       Right ascension (J2000.0)
  12- 15  F4.1  s       RAs       Right ascension (J2000.0)
      17  A1    ---     DE-       Declination sign (J2000.0)
  18- 19  I2    deg     DEd       Declination (J2000.0)
  21- 22  I2    arcmin  DEm       Declination (J2000.0)
  24- 25  I2    arcsec  DEs       Declination (J2000.0)


Byte-by-byte Description of file: table1.dat

   Bytes Format Units   Label     Explanations

   1-  3  I3    ---     NGC6611   Star number (Walker, 1961ApJ...133..438W)
                                   NGC 6611 NNN in Simbad
       4  A1    ---    f_NGC6611  [*] *: star considered as being "frontside"
   6- 32  A27   ---     Name      HD, BD or H designation (1)
      34  A1    ---     Band      [UBVRI] Band (2)
  36- 40  F5.2  %       Pol       Observed percentage polarisation
  42- 45  F4.2  %       e_Pol     rms uncertainty on Pol
  47- 51  F5.1  deg     PA        Observed position angle of the electric vector
  53- 56  F4.1  deg     e_PA      rms uncertainty on PA
  58- 59  I2    ---     n         ? Number of integrations
  61- 64  F4.2  %       PolI      ? Intracluster percentage polarisation
  66- 69  F4.2  %       e_PolI    ? rms uncertainty on PolI
  71- 75  F5.1  deg     PAI       ? Intracluster position angle of the
                                     electric vector
  77- 81  F5.2  deg     e_PAI     ? rms uncertainty on PAI

Note (1): Identifications from Henry Draper, Cat. III/135,
           Bonner Durchmusterung, Cat. I/122 or
           Hoag et al., 1961PUSNO..17..343H.
Note (2): Wavelengths of the bands for which Pol and PA are measured:
          U: 0.360µm
          B: 0.440µm
          V: 0.53µm
          R: 0.690µm
          I: 0.830µm


Acknowledgements: Hugo Marraco 

(End)                                          Patricia Bauer [CDS]  04-May-2000