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Alessi 95 and the short-period Cepheid SU Cassiopeiae
The parameters for the newly discovered open cluster Alessi 95 areestablished on the basis of available photometric and spectroscopicdata, in conjunction with new observations. Colour excesses forspectroscopically observed B- and A-type stars near SU Cas follow areddening relation described by E(U-B)/E(B-V) = 0.83 + 0.02E(B-V),implying a value of R=AV/E(B-V) ? 2.8 for the associateddust. Alessi 95 has a mean reddening of E(B-V)(B0) = 0.35 ± 0.02s.e., an intrinsic distance modulus of V0-MV= 8.16± 0.04 s.e. (±0.21 s.d.), d= 429 ± 8 pc, and anestimated age of 108.2 yr from zero-age main sequence (ZAMS)fitting of available UBV, CCD BV, NOMAD, and Two Micron All Sky SurveyJHKs observations of cluster stars. SU Cas is a likelycluster member, with an inferred space reddening of E(B-V) = 0.33± 0.02 and a luminosity of =-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 periodincrease and Hipparcos parallaxes for cluster stars. There is excellentagreement of the distance estimates for SU Cas inferred from clusterZAMS fitting, its pulsation parallax derived from the infrared surfacebrightness technique and Hipparcos parallaxes, which all agree to withina few per cent.
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Osservazione e dati astrometrici
| Costellazione: | Cassiopea |
| Ascensione retta: | 02h30m06.75s |
| Declinazione: | +68°46'02.8" |
| Magnitudine apparente: | 9.966 |
| Moto proprio RA: | -4.5 |
| Moto proprio Dec: | -1.8 |
| B-T magnitude: | 10.449 |
| V-T magnitude: | 10.006 |
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