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J/A+A/454/295    Long-term photographic photometry of HK Lac  (Froehlich+, 2006)
The RS CVn binary HK Lacertae: long-term photometry from Sonneberg Sky-Patrol
plates.
    Froehlich H.-E., Kroll P., Strassmeier K.G.
   <Astron. Astrophys. 454, 295 (2006)>
   =2006A&A...454..295F
ADC_Keywords: Stars, late-type ; Photometry, photographic ;
              Photometry, special systems
Keywords: stars: activity - stars: individual: HK Lacertae -
          stars: late-type - stars: rotation - stars: starspots

Abstract:
    Long-term photographic photometry of the active long-period RS CVn
    binary HK Lac (HD 209813) was obtained from more than 2000 Sonneberg
    Sky-Patrol plates taken between 1956 and 1996. We achieve an internal
    accuracy of 0.07mag. The correspondence with contemporaneous
    high-precision photoelectric photometry from automatic telescopes is
    striking and successfully demonstrates the feasibility of our
    approach. Based on a Bayesian periodogram analysis, we improve
    previously published cycle periods to 13.37±0.8 and 6.7±0.1-years,
    and present evidence of an additional period of
    9.48±0.13-years. This establishes the multi-periodicity of
    dynamo action in these overactive stars as compared to the Sun. Of
    course, the 6.7-years cycle may be an overtone of the dominating
    13.4-years cycle. Our long-term photographic photometry even allowed
    the detection of the star's mean rotational period of 24.35-days.

Description:
    A photographic light-curve, from 1956 to 1996, of the RS CVn binary HK
    Lacertae is presented. For each of the 2037 data points the Julian
    Date (geocentric) and the BT magnitude (Tycho-2 photometric system) is
    given. Brightnesses are with respect to the BT brightness of HD 210731
    (BT=8.090mag).
Objects:
    --------------------------------------------
       RA   (2000)   DE      Designation(s)
    --------------------------------------------
    22 04 56.6   +47 14 04   HK Lac = HIP 109002
    --------------------------------------------

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        24     2037   Julian Date and BT magnitude


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

   Bytes Format Units   Label     Explanations

   1-  4  I4    ---     Seq       Sequence number
   7- 17  F11.3 ---     JD        Geocentric Julian Date at the middle of the
                                  exposure
  20- 24  F5.3  mag     BTmag     BT brightness in the tycho-2 system (1)

Note (1): The Tycho-2 Catalogue of the 2.5 Million Brightest Stars
            Hog et al., 2000, Cat. I/259


Acknowledgements: Hans-Erich Froehlich, hefroehlich(at)aip.de

(End)                                        Patricia Vannier [CDS]  09-Sep-2005