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Alessi 95 and the short-period Cepheid SU Cassiopeiae

Authors

  • D. G. Turner,

    Corresponding author
    1. Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
      E-mail: turner@ap.smu.ca Guest Investigator, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.
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  • D. J. Majaess,

    Corresponding author
    1. Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
    2. The Abbey Ridge Observatory, Stillwater Lake, NS, Canada
      Guest Investigator, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.
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  • D. J. Lane,

    1. Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
    2. The Abbey Ridge Observatory, Stillwater Lake, NS, Canada
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  • D. D. Balam,

    1. Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V6A 3K7, Canada
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  • W. P. Gieren,

    1. Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, CL Concepción, Chile
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  • J. Storm,

    1. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
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  • D. W. Forbes,

    1. Department of Physics, Sir Wilfred Grenfell College, Memorial University, Corner Brook, NL A2H 6P9, Canada
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  • R. J. Havlen,

    Corresponding author
    1. 307 Big Horn Ridge, NE, Albuquerque, NM 87122, USA
      Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.
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  • B. Alessi

    1. Departamento de Astronomia, Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil
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E-mail: turner@ap.smu.ca

Guest Investigator, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.

Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.

ABSTRACT

The parameters for the newly discovered open cluster Alessi 95 are established on the basis of available photometric and spectroscopic data, in conjunction with new observations. Colour excesses for spectroscopically observed B- and A-type stars near SU Cas follow a reddening relation described by E(UB)/E(BV) = 0.83 + 0.02E(BV), implying a value of R=AV/E(BV) ≃ 2.8 for the associated dust. Alessi 95 has a mean reddening of E(BV)(B0) = 0.35 ± 0.02 s.e., an intrinsic distance modulus of V0MV= 8.16 ± 0.04 s.e. (±0.21 s.d.), d= 429 ± 8 pc, and an estimated age of 108.2 yr from zero-age main sequence (ZAMS) fitting of available UBV, CCD BV, NOMAD, and Two Micron All Sky Survey JHKs observations of cluster stars. SU Cas is a likely cluster member, with an inferred space reddening of E(BV) = 0.33 ± 0.02 and a luminosity of 〈MV〉=−3.15 ± 0.07 s.e., consistent with overtone pulsation (PFM= 2.75 d), as also implied by the Cepheid’s light-curve parameters, rate of period increase and Hipparcos parallaxes for cluster stars. There is excellent agreement of the distance estimates for SU Cas inferred from cluster ZAMS fitting, its pulsation parallax derived from the infrared surface brightness technique and Hipparcos parallaxes, which all agree to within a few per cent.

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