The Long Term Optical Variability of the BL Lac object S5 0716+714: Evidence for a Precessing Jet

We present the historic light curve of the BL Lac object S5 0716+714, spanning the time interval from 1953 to 2003, built using Asiago archive plates and our recent CCD observations, together with literature data. The source shows an evident long term variability, over which well known short term variations are superposed. In particular, in the period from 1961 to 1983 the mean brightness of S5 0716+714 remained significantly fainter than that observed after 1994. Assuming a constant variation rate of the mean magnitude we can estimate a value of about 0.11 magnitude/year. The simultaneous occurrence of decreasing ejection velocities of superluminal moving components in the jet reported by Bach et al. (2005) suggests that both phenomena are related to the change of the direction of the jet to the line of sight from about 5 to 0.7 degrees for an approximately constant bulk Lorentz factor of about 12. A simple explanation is that of a precessing relativistic jet, which should presently be close to the smallest orientation angle. One can therefore expect in the next ten years a decrease of the mean brightness of about 1 magnitude.Comment: to appear on The Astronomical Journal, 17 pages, 7 figures. Fig.2 is given as a separated jpg fil

The sperm mitochondria: clues and challenges

Sperm cells rely on different substrates to fulfil thei energy demand for different functions and diverse moments of their life. Species specific mechanism involve both energy substrate transport and their utilization: hexose transporters, a protein family of facilitative passive transporters of glucose and other hexose, have been identified in spermatozoa of different species and, within the species, their localization has been identified and, in some cases, linked to specific glycilitic enzyme presence. The catabolism of hexose sources for energy purposes has been studied in various species, and recent advances has been made in the knowledge of metabolic strategies of sperm cells. In particular, the importance of aerobic metabolism has been defined and described in horse, boar and even mouse spermatozoa; bull sperm cells demonstrate to have a good adaptability and capacity to switch between glycolysis and oxidative phosphorylation; finally, dog sperm cells have been demonstrated to have a great plasticity in energy metabolism management, being also able to activate the anabolic pathway of glycogen syntesis. In conclusion, the study of energy management and mitochondrial function in spermatozoa of different specie furnishes important base knowledge to define new media for preservation as well as newbases for reproductive biotechnologies

Optical and Radio monitoring of S5 1803+74

The optical (BVRI) and radio (8.4 GHz) light curves of S5 1803+784 on a time span of nearly 6 years are presented and discussed. The optical light curve showed an overall variation greater than 3 mag, and the largest changes occured in three strong flares. No periodicity was found in the light curve on time scales up to a year. The variability in the radio band is very different, and shows moderate oscillations around an average constant flux density rather than relevant flares, with a maximum amplitude of $\sim$30%, without a simultaneous correspondence between optical and radio luminosity. The optical spectral energy distribution was always well fitted by a power law. The spectral index shows small variations and there is indication of a positive correlation with the source luminosity. Possible explanations of the source behaviour are discussed in the framework of current models.Comment: 25 pages, 12 figure

GR 290 (Romano's Star): 2. Light history and evolutionary state

We have built the historical light curve of the luminous variable GR 290 back to 1901, from old observations of the star found in several archival plates of M 33. These old recordings together with published and new data show that for at least half a century the star was in a low luminosity state, with B ~18. After 1960, five large variability cycles of visual luminosity were recorded. The amplitude of the oscillations was seen increasing towards the 1992-1994 maximum, then decreasing during the last maxima. The recent light curve indicates that the photometric variations have been quite similar in all the bands, and that the B-V color index has been constant within +/-0.1 m despite the 1.5m change of the visual luminosity. The spectrum of GR 290 at the large maximum of 1992-94, was equivalent to late-B type, while, during 2002-2014, it has varied between WN10h-11h near the visual maxima to WN8h-9h at the luminosity minima. We have detected, during this same period, a clear anti-correlation between the visual luminosity, the strength of the HeII 4686 A emission line, the strength of the 4600-4700 A lines blend and the spectral type. From a model analysis of the spectra collected during the whole 2002-2014 period we find that the Rosseland radius R_{2/3}, changed between the minimum and maximum luminosity phases by a factor of 3, while T_eff varied between about 33,000 K and 23,000 K. The bolometric luminosity of the star was not constant, but increased by a factor of ~1.5 between minimum and maximum luminosity, in phase with the apparent luminosity variations. In the light of current evolutionary models of very massive stars, we find that GR 290 has evolved from a ~60 M_Sun progenitor star and should have an age of about 4 million years. We argue that it has left the LBV stage and is moving to a Wolf-Rayet stage of late nitrogen spectral type.Comment: Accepted on The Astronomical Journal, 10 figures. Replaced because the previous uploaded file was that without the final small corrections requested by the refere

The variable carbon star CGCS 6107

The spectroscopic and photometric variability of CGCS 6107 has been studied with four telescopes from 2015 to 2018. The star varied between R=11.4 and 14.2 mag with a time scale of 500 days. An appreciable color variation was observed, the star being bluer when brighter. H emission was present around maxima. The spectrum is that of an N type giant veiled by a variable dusty envelope