V39: an unusual object in the field of IC 1613

The variable star V39 in the field of IC 1613 is discussed in the light of the available photometric and new spectroscopic data. It has strong emission Balmer lines, and the observed characteristics could be explained by a W Vir pulsating star with a period of 14.341 d, located at more than 115 kpc, that is in the very outer halo of our Galaxy. It should have an apparent companion, a long period (1118d) red variable, belonging to IC 1613. The main uncertainty in this interpretation is an emission feature at 668.4 nm, which we tentatively identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic

Variable stars in nearby galaxies. VI. Frequency-period distribution of Cepheids in IC 1613 and other galaxies of the Local Group

The frequency--period distribution and other properties of Cepheids in IC 1613 are discussed and compared with those of stars in our Galaxy (Milky Way), LMC, SMC, M31 and M33. Taking into account the observational limitations and related incompleteness, it is concluded that the frequency-period distribution of Cepheids in IC 1613 is similar to that of SMC; we suspect that a much larger number of stars exist in IC 1613 with a period of less than 2 d that have not yet been detected. A discussion of the deficiency of fundamental mode Cepheids with periods in the range 8 - 10 d in the Milky Way, M31 and M33 is reported. The present data are not sufficient to verify if this is produced by a real bimodal frequency--period distribution or whether depends on the lack of pulsating stars in such a period range due to pulsational stability reasons. Some arguments are presented in favor of a bimodal distribution that is a function of the average metallicity. The Milky Way, M31 and M33 have the two maxima located at the same periods, about 5 and 13 d, respectively. A comment on very long period Cepheids is also given.Comment: 6 pages; accepted for publication in Astronomy and Astrophysic

Parity Doubling and SU(2)_L x SU(2)_R Restoration in the Hadron Spectrum

We construct the most general nonlinear representation of chiral SU(2)_L x SU(2)_R broken down spontaneously to the isospin SU(2), on a pair of hadrons of same spin and isospin and opposite parity. We show that any such representation is equivalent, through a hadron field transformation, to two irreducible representations on two hadrons of opposite parity with different masses and axial couplings. This implies that chiral symmetry realized in the Nambu-Goldstone mode does not predict the existence of degenerate multiplets of hadrons of opposite parity nor any relations between their couplings or masses.Comment: 4 pages, 1 figure; v3: Note added to clarify implications for hadrons that do not couple to pions: Chiral symmetry can be realized linearly on such states, leading to parity doubling. To the extent that they are parity doubled, these hadrons must decouple from pions, a striking prediction that can be tested experimentally. This applies to the work of L. Glozman and collaborator

Search for second overtone Cepheids in the Magellanic Clouds. I. Study of three candidates in the SMC

Accurate CCD observations of three Cepheids in the SMC were made with the purpose of confirming their nature of second overtone mode Cepheids. The stars were suspected pulsating in the second overtone mode owing to the unusual light curve and short period reported by Payne-Gaposchkin & Gaposchkin (1966). The analysis of the new data shows that for two stars the previous periods are wrong, and in the three cases the new light curves are normal. According to the new observations, HV 1353 is a fundamental mode pulsator with small amplitude, and HV 1777 and HV 1779 are first overtone mode pulsators. Also the star HV 1763, whose nature was unknown, was observed in the field of HV 1777. The new data show that it is a first overtone mode Cepheid with P=2.117d.Comment: 6 pages, 8 figures. To be published in A&A Suppl.Se

Search for low instability strip variables in the young open cluster NGC 2516

In this paper we revise and complete the photometric survey of the instability strip of the southern open cluster NGC 2516 published by Antonello and Mantegazza (1986). No variable stars with amplitudes larger than $0^m.02$ were found. However by means of an accurate analysis based on a new statistical method two groups of small amplitude variables have been disentangled: one with periods $< 0^d.25$ (probably $\delta$ Scuti stars) and one with periods $>0^d.025$. The position in the HR diagram and the apparent time-scale may suggest that the stars of the second group belong to a recently discovered new class of variables, named $\gamma$ Dor variables. They certainly deserve further study. We also present a comparison between the results of the photometric survey and the available pointed ROSAT observations of this cluster.Comment: 7 pages, 2 ps figures. Accepted for P.A.S.