Astrophysical Quantities of Cepheid Variables Measured with the Navy Prototype Optical Interferometer

We present mean angular diameters for two Cepheid variables, ? UMi and ? Gem, determined with the Navy Prototype Optical Interferometer (NPOI). We present linear radii for these Cepheids and two additional Cepheids, ? Cep and ? Aql, previously observed at the NPOI. We find the limb-darkened angular diameters of ? UMi and of ? Gem to be 3.28 ? 0.02 and 1.55 ? 0.09 mas, respectively. Using trigonometric parallaxes, we find the linear radii of ? UMi, ? Gem, ? Cep, and ? Aql to be 46 ? 3, 60, 45, and 69 R?, respectively. We compare the pulsation periods and linear radii of this sample of Cepheids, which range in period from 3 to 11 days, to theoretical and empirical period-radius and period-radius-mass relations found in the literature. We find that the observed diameter of ? UMi is in excellent agreement with the predicted diameter as determined from both surface brightness techniques and theory only if ? UMi is a first-overtone pulsator.

[1]  W. Gieren,et al.  The period-radius relation for classical Cepheids from the visual surface brightness technique , 1989 .

[2]  C. D. Laney,et al.  The radii of Galactic Cepheids , 1995 .

[3]  V. Straižys,et al.  Fundamental stellar parameters derived from the evolutionary tracks , 1981 .

[4]  Gieren,et al.  A Direct Distance to the Large Magellanic Cloud Cepheid HV 12198 from the Infrared Surface Brightness Technique. , 2000, The Astrophysical journal.

[5]  Thomas G. Barnes,et al.  Stellar Angular Diameters and Visual Surface Brightness — I LATE SPECTRAL TYPES , 1976 .

[6]  A. J. Wesselink,et al.  Surface Brightnesses in the U, B, V System with Applications of $M_{\upsilon}$ and Dimensions of Stars , 1969 .

[7]  Nicholas M. Elias,et al.  Multichannel Optical Aperture Synthesis Imaging of zeta1 URSAE Majoris with the Navy Prototype Optical Interferometer , 1997 .

[8]  R. Stobie,et al.  The Masses of Cepheid Variables , 1972 .

[9]  M. Marconi,et al.  On the Theoretical Period-Radius Relation of Classical Cepheids , 1998 .

[10]  Tyler E. Nordgren,et al.  Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer , 1999 .

[11]  C. Proffitt,et al.  Blue companions of Cepheids , 1985 .

[12]  J. Fernie.  A survey of Cepheid sizes , 1984 .

[13]  Nicholas M. Elias,et al.  Direct Confirmation of Stellar Limb Darkening with the Navy Prototype Optical Interferometer , 1998 .

[14]  N. Evans,et al.  Classical Cepheid Masses: U Aquilae , 1998 .

[15]  D. Sasselov,et al.  Infrared Spectroscopy of Cepheids. II. Line Profiles from Different Atmospheric Layers , 1990 .

[16]  Carlos Jaschek,et al.  The Bright Star Catalogue , 1982 .

[17]  M. Feast,et al.  The Cepheid period-luminosity zero-point from Hipparcos trigonometrical parallaxes† , 1997 .

[18]  Thomas G. Barnes,et al.  Calibrating the Cepheid Period-Radius Relation with Galactic and Magellanic Cloud Cepheids , 1999 .

[19]  Nicholas M. Elias,et al.  Navy Prototype Optical Interferometer Observations of the Double Stars Mizar A and Matar , 1998 .