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TOPIC: Delta Cephei


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RE: Delta Cephei
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Delta Cephei is at minimum brightness at 23:20 UT, 10th February, 2012



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Delta Cephei is at minimum brightness at 14:30 UT, 5 February, 2012



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Maxima of the variable star Delta Cephei at 4:35 UT, 31st January, 2012.



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Maxima of the variable star Delta Cephei at 19.50 UT, 25th January, 2012.



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Maxima of the variable star Delta Cephei at 2:00 UT, 15th January, 2012.



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Title: New Evidence Supporting Cluster Membership for the Keystone Calibrator Delta Cephei
Authors: Daniel J. Majaess, David G. Turner, Wolfgang Gieren

New and existing UBVJHKs, spectroscopic, NOMAD, HST, and revised HIP observations are employed to determine properties for delta Cep and its host star cluster. The multi-faceted approach ensured that uncertainties were mitigated (~2%). The following fundamental parameters were inferred for delta Cep: E(B-V)=0.073±0.018, log(t)=7.9±0.1, and d=272±3(se)±5(sd) pc. The cluster exhibits a turnoff near B6 (M*/Ms~5), and the brightest host cluster members are the supergiants zeta Cep (K1.5Ib) and delta Cep. To within the uncertainties, the two stars share common astrometric parameters (pi, mu_ra, mu_dec, RV ~ -17 km/s) and are tied to bluer members via the evolutionary track implied by the cluster's UBVJHKs colour-colour and colour-magnitude diagrams. The cluster's existence is bolstered by the absence of an early-type sequence in colour-magnitude diagrams for comparison fields. NOMAD data provided a means to identify potential cluster members (n~30) and double the existing sample. That number could increase with forthcoming precise proper motions (DASCH) for fainter main-sequence stars associated with classical Cepheids (e.g., delta Cep), which may invariably foster efforts to strengthen the Galactic Cepheid calibration and reduce uncertainties tied to H_0.

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Maxima of the variable star Delta Cephei at 23:40 UT, 29th December, 2011.



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Maxima of the variable star Delta Cephei at 21:20 UT, 13th December, 2011.



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Maxima of the variable star Delta Cephei at 3:40 UT, 3rd December, 2011.



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Title: New Evidence for Mass Loss from delta Cephei from HI 21-cm Line Observations
Authors: L. D. Matthews (MIT Haystack), M. Marengo (Iowa State), N. R. Evans (Harvard-Smithsonian CfA), G. Bono (University of Rome)

Recently published Spitzer observations of the classical Cepheid archetype delta Cephei revealed an extended dusty nebula surrounding this star and its hot companion. The infrared emission resembles a bow shock aligned with the direction of space motion of the star, indicating that delta Cep is undergoing mass-loss through a stellar wind. Here we report HI 21-cm line observations with the VLA to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended HI nebula (~13' or 1 pc across) surrounding the position of delta Cep. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the ISM. We directly measure a mass of circumstellar hydrogen M_HI ~0.07 solar masses, although the total HI mass may be larger. The HI data imply a stellar wind with an outflow velocity V_o=35.6 ±1.2 km/s and a mass-loss rate of solar masses=(1.0 ±0.8)x10**-6 solar masses/yr. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of delta Cep, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star.

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