COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3168 Konkoly Observatory Budapest 25 March 1988 HU ISSN 0374-0676 IS nu Her REALLY A VARIABLE STAR? The bright star nu Her = HR 6707 was suspected to be a variable star by two observers independently. Searching for microvariability in bright stars, Jackisch, (1963) found an amplitude of 0.06 mag in V and a period of 29 d. It must be noted, however, that Jackisch used alpha Lyr as comparison star, which choice does not seem very adequate. Henriksson (1976) included nu Her in a list of variable that he discovered during a survey of stars located in the Cepheid instability strip. On the basis of 39 V measures he reported an amplitude of 0.05 mag but was not able to give a period. These two works led Hoffleit and Jaschek (1982) to mention the star as a probable Delta Sct variable and Kholopov et al. (1985) to classify it as a possible SRd variable. In order to confirm the variability, we undertook observations of nu Her in 1986, adding it to other F-G-K giant variables under spectroscopic and/or photometric investigation. nu Her was observed on 12 nights from May 31 to August 24, 1986 with the 50 cm reflector of Merate Observatory. HR 6775 (V=5.04, B-V=+0.52, U-B=-0.09, F7V) and HR 6814 (V=5.88, B-V=+0.01, U-B=+0.11, A3V) were used as comparison stars. On each night, 7-9 differential measurements were taken and grouped into normal points. The internal standard error of these normal points averages 0.003 mag in all colours, while the night-to- night standard deviation of magnitude differences between the comparison stars are 0.005; 0.006, 0.008 mag in V, B, U respectively. HR 6814=ADS 11149 is a close double star: its B component was suspected to vary more than 2 mag (Baize, 1962). However, if the mean difference in magnitude between the two components is really 2.5 mag (Baize, 1962), then our measures exclude variations of the B component during our survey greater than 0.1 mag. The Table shows the Delta m between HR 6775 and nu Her. Delta m's are in the sense comparison minus variable star. Taking observational errors into account, it is hard to find a variation larger than 0.01 mag in the data. If one assumes that nu Her is an SRd variable, then, we must admit that we have observed the star during a quiescent phase of its light variability. If we consider the star Table I J.D. DeltaU DeltaB DeltaV 2446582.43 + 0.592 + 0.801 + 0.654 587.41 - + 0.791 + 0.651 603.46 + 0.568 + 0.790 + 0.646 604.45 + 0.566 + 0.786 + 0.643 610.39 - + 0.796 + 0.651 616.46 - + 0.782 + 0.647 636.43 - + 0.797 + 0.652 648.43 - - + 0.646 655.44 + 0.581 + 0.807 + 0.664 662.43 + 0.586 + 0.795 + 0.651 663.46 - - + 0.657 667.39 + 0.573 + 0.809 + 0.658 to be a delta Sct variable, our results (i.e. light constancy during normal points and small peak-to-peak amplitude) are conflicting with those of Jackisch's and Henriksson's surveys. Percy, et al. (1979) found no variation larger than 0.02 mag in B and V light: this result strengthens our conclusion. Considering its spectral type and luminosity class (F2III) and the current calibrations of uvbybeta photometry, we may estimate that nu Her is located near the blue edge or more probably outside the instability strip. From these considerations it is probable, in our opinion, that nu Her is not a variable star at all. E. PORETTI L. MANTEGAZZA (*) E. ANTONELLO Osservatorio Astronomica di Brera Via E. Bianchi, 46 22055 MERATE (CO) Italy (*)and Dipartimento di Fisica Nucleare e Teorica Universita di Pavia Pavia, Italy References: Baize, P.: 1962, Journal des Observateurs, 45, 117 [BIBCODE 1962JO.....45..117B ] Henriksson, G.: 1976, Astron. Astrophys, 54, 309 [BIBCODE 1977A&A....54..309H ] Hoffleit, D., Jaschek, C.: 1982, The Bright Star Catalogue, Fourth Edition, New Haven [BIBCODE 1982bscf.book.....H ] Jackisch, G.: 1963, VSS 5, H.5 [BIBCODE 1963VeSon...5..232J ] Kholopov, P.N. et al.: 1985, General Catalogue of Variable Stars, Fourth Edition, Moscow Percy, J.R., Baskerville, I., Trevorrow, D.W.; 1979, Publ. Astron, Soc. Pacific, 91, 368 [BIBCODE 1979PASP...91..368P ]