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J/A+A/393/225      Starspot cycles of six young solar analogues (Messina+, 2002)
Magnetic activity of six young solar analogues.
I. Starspot cycles from long-term photometry.
    Messina S., Guinan E.F.
   <Astron. Astrophys. 393, 225 (2002)>
   =2002A&A...393..225M
ADC_Keywords: Stars, late-type ; Stars, G-type ; Stars, K-type ; Magnetic fields

Keywords: stars: activity - stars: individual: BE Cet, κ1 Cet,
          π1 UMa, EK Dra, HN Peg, DX Leo - stars: late-type -
          stars: magnetic fields - stars: starspots

Abstract:
    A long-term photometric monitoring of a selected sample of solar
    analogues has been carried out since early nineties as part of
    "The Sun in tim" project, which is aimed at a multiwavelength study of
    stars with solar-like global properties, but with different ages and
    thus at different stages of their evolution. The extended time
    sequence of ground-based observations collected over more than a
    decade as part of this program has revealed the existence of starspot
    cycles. Also from these data it is possible to investigate surface
    differential rotation of the stars. In this paper we present the
    photometry collected to date and report on cycles search for a
    selected subsample of five young single G0-G5V stars with ages between
    ∼130Myr and 700Myr: EK Dra, π1 UMa, HN Peg, κ1 Cet, BE
    Cet. Also we include in this study the Pleiades-age (∼130Myr) K0V star
    DX Leo (HD 82443). All the cited stars show activity cycles whose
    period is, furthermore, the first determined from photometric data.
    They are compared to those activity cycles derived from CaII H&K
    emission fluxes and differences are discussed. All the cycle periods,
    except for EK Dra, fit well the empirical relations with global
    stellar parameters derived from larger stellar samples.

    The following results are also inferred from the present study: i) the
    fastest rotating stars tend to have longer cycles; ii) the range in
    the observed cycle lengths seems to converge with stellar age from a
    maximum dispersion around the Pleiades' age towards the solar cycle
    value at the Sun's age; iii) the overall short- and long-term
    photometric variability increases with inverse Rossby number with very
    high correlation degree, indicating that the level of magnetic
    activity at least in photosphere is still controlled by the stellar
    rotation even on the longest time scales; iiii) the increase with
    inverse Rossby number of the long-term overall photometric variability
    seems to level off at the highest rotation rate, which may be
    interpreted as due to a saturation in the level of photospheric
    magnetic activity around the activity maximum.

Description:
    The following tables contain the photometric data used to determine
    the starspot cycles and longer-term trends for a sample of six young
    solar analogues. The following data are listed: Mean epoch, first and
    last observing HJD, number of observing nights, mean magnitude
    (Vmax+Vmin)/2 and sources of photometry.
Objects:
    ----------------------------------------------------------
       RA   (2000)   DE    Designation(s)         (File)
    ----------------------------------------------------------
    00 22 51.8 -12 12 34   BE Cet = HD 1835       (table3.dat)
    03 19 21.7 +03 22 13   kap1 Cet = HD 20630    (table4.dat)
    08 39 11.7 +65 01 15   pi.1 UMa = HD 72905    (table5.dat)
    21 44 31.2 +14 46 44   HN Peg = HD 206860     (table6.dat)
    14 39 00.2 +64 17 30   EK Dra = HD 129333     (table7.dat)
    09 32 43.8 +26 59 19   DX Leo = HD 82443      (table8.dat)
    ----------------------------------------------------------

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table3.dat        51       24   BE Cet light curve
table4.dat        55       18   κ1 Cet light curve
table5.dat        54       35   π1 UMa light curve
table6.dat        51       12   HN Peg light curve
table7.dat        56       91   EK Dra light curve
table8.dat        54       53   DX Leo light curve


See also:
 J/A+AS/125/11 : 23 active stars UBV + V(RI)c photometry (Strassmeier+, 1997)
 J/A+AS/140/29 : 47 late-type stars photometric monitoring (Strassmeier+, 1999)


Byte-by-byte Description of file: table[3-8].dat

   Bytes Format Units   Label     Explanations

   1-  7  F7.2  yr      Epoch     Mean epoch of observation
   9- 18  F10.2 d       FirstJD   First observing HJD
  20- 29  F10.2 d       LastJD    Last observing HJD
  33- 34  I2    ---     Nights    Number of observing nights
  37- 41  F5.3  mag     mag       Mean magnitude (Vmax+Vmin)/2
  44- 51  A8    ---     Source    [a-l, ] Sources of photometry (1)

Note (1): Source of photometry:
      a: Stepien & Geyer, 1996A&AS..117...83S
      b: Cutispoto, 1991A&AS...89..435C
      c: Cutispoto, 1992A&AS...95..397C
      d: Cutispoto, 1995A&AS..111..507C
      e: Hipparcos, Cat. I/239
      f: Villanova photometry
      g: Gaidos et al., 2000AJ....120.1006G
      h: Frasca  et al., 2000A&A...364..179F
      i: Lockwood et al., 1997ApJ...485..789L
      j: Messina et al., 1999A&A...347..249M
      k: Strassmeier et al., 1997A&AS..125...11S, Cat. J/A+AS/125/11
      l: Strassmeier et al., 1999A&AS..140...29S, Cat. J/A+AS/140/29


Acknowledgements: Sergio Messina 

(End)                                          Patricia Bauer [CDS]  08-Aug-2002