On the ephemeris of the pulsating hydrogen-deficient star V652 HER
Some new timings of maxima of the pulsating hydrogen-deficient star V652Her (BD+13 deg 3224) obtained during 1991-95 are reported. The data showthat the ephemeris for times of maxima can no longer be represented by acubic polynomial, and that a quartic term is necessary. The star couldhave brightened by up to 0.008 mag over the last decade, although thisis not firmly established (the apparent change could also be due tosmall zero-point effects, for example). The shape of the light curveappears essentially unaltered over the same time interval; any changesare less than ~0.003 mag in size. Attempts have been made to understandthe changing ephemeris in terms of changing stellar radius (R), mass (M)and pulsation constant (Q). A satisfactory match to the observations isobtained by a function including the first three derivatives of radius,R_solar, R_solar_solar and R & tdot;. The addition of a smallmass-loss term does not significantly improve the fit. With theavailable data we cannot rule out (or distinguish between) small valuesof M_solar or Q_solar, but the values derived for the radius derivativesshould stringently constrain pulsation models for V652 Her, and suggestextremely rapid evolution not yet accounted for in non-linear radialpulsation calculations.
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Observations of the pulsating hydrogen: Deficient star BD+13 deg 3224, during 1980 - 1981
Observations of BD+13 deg 3224 in the uvby and VRIc systemare presented together with over 500 V or y magnitude observations madein the period 1980 August to 1981 August. A mean light curve is derivedand the Barnes-Evans relation is used to estimate the radius from theVRIC photometry.
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Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
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On the period of the pulsating hydrogen-deficient star BD + 13 deg 3224
Recent observations of maxima of the pulsating early-typehydrogen-deficient star BD + 13 deg 3224 indicate a decrease in periodsince the discovery observations. The data are best fitted by a decreaserate of 46 x 10 to the -10 day/cycle, a value which is comparable withthe rate derived from a theoretical study of the fast evolutionary phaseof a post-giant helium star. Four-color data are averaged to give meancolors at 0.1 phase intervals around the pulsation cycle.
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Search for variability in hydrogen-poor stars. I - Preliminary results of photoelectric observations for six stars
The evolutionary status of hydrogen-poor stars is assessed.Photoelectric observations of six objects are reported as a first stepin a long-term project devoted to a search for variability of a largesample of hydrogen-poor stars. The observed stars exhibit phenomena ofmicrovariability with an amplitude of the order of 0.1m or less. Twoextreme helium stars are examined: a period in the range of0.162d-0.164d is found for BD + 10 deg 2179 with P = 0.1079962d for BD +13 deg 3324. It is noted that the mass-losing O subdwarf (sdO) BD = + 37deg 443 exhibits short-term fluctuations with a time-scale of severalminutes and long-term variations on a scale of months.
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The pulsating helium star BD + 13 deg 3224
The velocity curve of the variable helium star BD + 13 deg 3224 has beendetermined and shown to be pulsating. By combining the velocity datawith photometry, the mean radius has been deduced to be 1.6 plus orminus 0.2 solar radius, and by taking log g from neutral helium lineprofiles, the mass has been determined to be 0.9 +0.5, -0.3 solar mass.The gravity and composition are different from those of extreme heliumstars but more similar to HD 144941.
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On the optical variability of the He stars HD 160641 and BD +13 3224.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJ...196..789L&db_key=AST
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INHABITED SKY
