ABSTRACT
We present rotation period measurements for 107 M dwarfs in the mass range $0.15\!-\!0.70 \, \mathrm{M}_\odot$ observed within the context of the APACHE photometric survey. We measure ...rotation periods in the range 0.5–190 d, with the distribution peaking at ∼30 d. We revise the stellar masses and radii for our sample of rotators by exploiting the Gaia DR2 data. For ${\sim}20{{\ \rm per\ cent}}$ of the sample, we compare the photometric rotation periods with those derived from different spectroscopic indicators, finding good correspondence in most cases. We compare our rotation periods distribution to the one obtained by the Kepler survey in the same mass range, and to that derived by the MEarth survey for stars in the mass range $0.07\!-\!0.25 \, \mathrm{M}_\odot$. The APACHE and Kepler periods distributions are in good agreement, confirming the reliability of our results, while the APACHE distribution is consistent with the MEarth result only for the older/slow rotators, and in the overlapping mass range of the two surveys. Combining the APACHE/Kepler distribution with the MEarth distribution, we highlight that the rotation period increases with decreasing stellar mass, in agreement with previous work. Our findings also suggest that the spin-down time scale, from fast to slow rotators, changes crossing the fully convective limit at ${\approx}0.3 \, \mathrm{M}_\odot$ for M dwarfs. The catalogue of 107 rotating M dwarfs presented here is particularly timely, as the stars are prime targets for the potential identification of transiting small planets with TESS and amenable to high-precision mass determination and further atmospheric characterization measurements.
We report simultaneous observations at different energy bands in radio, optical, UV, X-rays and γ rays of the flat-spectrum radio-quasar 3C 345. We built the light curve of the source at different ...frequencies from 2008, the beginning of the Fermi all-sky survey, to 2016, using new data and public archives. In particular we obtained several optical spectra, to study the behavior of emission lines and the continuum in different activity states and to derive the black hole mass. 3C 345 showed two flaring episodes in 2009, which occurred simultaneously in γ ray, optical/UV and X-rays, and were later followed in radio. The source shows an inverse Compton dominated spectral energy distribution, which moved from higher to lower frequencies from the high to the low state. The reverberation of emission lines during one outburst event allowed us to constrain the location of production of γ rays very close to the broad-line region, and possibly in the jet-base. We report the observation of an increased accretion after the outburst, possibly induced by the decrease of magnetic field intensity with respect to the low state.
Context. The international Whole Earth Blazar Telescope (WEBT) consortium planned and carried out three days of intensive micro-variability observations of S5 0716 + 714 from February 22, 2009 to ...February 25, 2009. This object was chosen due to its bright apparent magnitude range, its high declination, and its very large duty cycle for micro-variations. Aims. We report here on the long continuous optical micro-variability light curve of 0716+714 obtained during the multi-site observing campaign during which the Blazar showed almost constant variability over a 0.5 mag range. The resulting light curve is presented here for the first time. Observations from participating observatories were corrected for instrumental differences and combined to construct the overall smoothed light curve. Methods. Thirty-six observatories in sixteen countries participated in this continuous monitoring program and twenty of them submitted data for compilation into a continuous light curve. The light curve was analyzed using several techniques including Fourier transform, Wavelet and noise analysis techniques. Those results led us to model the light curve by attributing the variations to a series of synchrotron pulses. Results. We have interpreted the observed microvariations in this extended light curve in terms of a new model consisting of individual stochastic pulses due to cells in a turbulent jet which are energized by a passing shock and cool by means of synchrotron emission. We obtained an excellent fit to the 72-hour light curve with the synchrotron pulse model.
Aims. Since the CGRO operation in 1991–2000, one of the primary unresolved questions about the blazar γ-ray emission has been its possible correlation with the low-energy (in particular optical) ...emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the γ-ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong γ-ray detection of 0716+714 by AGILE. Methods. We present the GASP-WEBT optical and radio light curves of this blazar obtained in July–November 2007, about various AGILE pointings at the source. We construct NIR-to-UV spectral energy distributions (SEDs), by assembling GASP-WEBT data together with UV data from the Swift ToO observations of late October. Results. We observe a contemporaneous optical-radio outburst, which is a rare and interesting phenomenon in blazars. The shape of the SEDs during the outburst appears peculiarly wavy because of an optical excess and a UV drop-and-rise. The optical light curve is well sampled during the AGILE pointings, showing prominent and sharp flares. A future cross-correlation analysis of the optical and AGILE data will shed light on the expected relationship between these flares and the γ-ray events.
Abstract
We present the results of a year-long photometric monitoring campaign of a sample of 23 nearby (d < 60 pc), bright (J < 12) dM stars carried out at the Astronomical Observatory of the ...Autonomous Region of the Aosta Valley, in the western Italian Alps. This programme represents a ';pilot study' for a long-term photometric transit search for planets around a large sample of nearby M dwarfs, due to start with an array of identical 40-cm class telescopes by the Spring of 2012. In this study, we set out to (i) demonstrate the sensitivity to <4 R⊕ transiting planets with periods of a few days around our programme stars, through a two-fold approach that combines a characterization of the statistical noise properties of our photometry with the determination of transit detection probabilities via simulations; and (ii) where possible, improve our knowledge of some astrophysical properties (e.g. activity, rotation) of our targets by combining spectroscopic information and our differential photometric measurements. We achieve a typical nightly root mean square (RMS) photometric precision of ∼5 mmag, with little or no dependence on the instrumentation used or on the details of the adopted methods for differential photometry. The presence of correlated (red) noise in our data degrades the precision by a factor of ∼1.3 with respect to a pure white noise regime. Based on a detailed stellar variability analysis (i) we detected no transit-like events (an expected result, given the sample size); (ii) we determined photometric rotation periods of ∼0.47 and ∼0.22 d for LHS 3445 and GJ 1167A, respectively; (iii) these values agree with the large projected rotational velocities (∼25 and ∼33 km s−1, respectively) inferred for both stars based on the analysis of archival spectra; (iv) the estimated inclinations of the stellar rotation axes for LHS 3445 and GJ 1167A are consistent with those derived using a simple spot model; and (v) short-term, low-amplitude flaring events were recorded for LHS 3445 and LHS 2686. Finally, based on simulations of transit signals of given period and amplitude injected in the actual (nightly reduced) photometric data for our sample, we derive a relationship between transit detection probability and phase coverage. We find that, using the Box-fitting Least Squares search algorithm, even when the phase coverage approaches 100 per cent, there is a limit to the detection probability of ≈90 per cent. Around programme stars with phase coverage > 50 per cent, we would have had >80 per cent chances of detecting planets with P < 1 d inducing fractional transit depths > 0.5 per cent, corresponding to minimum detectable radii in the range ∼1.0-2.2 R⊕. These findings are illustrative of our high readiness level ahead of the main survey start.
Context. BL Lacertae is the prototype of the blazar subclass named after it. Yet, it has occasionally shown a peculiar behaviour that has questioned a simple interpretation of its broad-band emission ...in terms of synchrotron plus synchrotron self-Compton (SSC) radiation. Aims. In the 2007–2008 observing season we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite in July and December 2007, and January 2008, to study its emission properties, particularly in the optical-X-ray energy range. Methods. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. Flux changes had larger amplitude at the higher radio frequencies than at longer wavelengths. Results. The X-ray spectra acquired by the EPIC instrument onboard XMM-Newton are well fitted by a power law with photon index $\Gamma \sim 2$ and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the EPIC data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is very variable, since it can change from extremely steep to extremely hard, and can be more or less curved in intermediate states. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature $ \ga$$ 20\,000 \rm \, K$ and a luminosity $ \ga$$ 6 \times 10^{44} ~\rm erg \, s^{-1}$.
The APACHE Project Sozzetti, A.; Bernagozzi, A.; Bertolini, E. ...
EPJ Web of conferences,
01/2013, Volume:
47
Journal Article
Peer reviewed
Open access
First, we summarize the four-year long efforts undertaken to build the final setup of the APACHE Project, a photometric transit search for small-size planets orbiting bright, low-mass M dwarfs. Next, ...we describe the present status of the APACHE survey, officially started In July 2012 at the site of the Astronomical Observatory of the Autonomous Region of the Aosta Valley, in the Western Italian Alps. Finally, we briefly discuss the potentially far-reaching consequences of a multi-technique characterization program of the (potentially planet-bearing) APACHE targets.
Context.The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands in the past, with the main outbursts repeating every 5–6 years. However, the predicted ...2004 outburst did not occur, and further analysis suggested a longer time scale, according to which the next event would have occurred in the 2006–2007 observing season. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. An optical outburst was observed in late 2006–early 2007, which triggered a Whole Earth Blazar Telescope (WEBT) campaign as well as target of opportunity (ToO) observations by the Swift satellite. Aims.In this paper, we present the radio-to-optical data taken by the WEBT together with the UV data acquired by the UltraViolet and Optical Telescope (UVOT) instrument onboard Swift to investigate both the outburst behaviour at different wavelengths and the nature of the extra emission component. Methods.Multifrequency light curves have been assembled with data from 27 observatories; optical and UV fluxes have been cleaned from the contamination of the southern active galactic nucleus (AGN). We have analysed spectral energy distributions at different epochs, corresponding to different brightness states; extra absorption by the foreground galaxy has been taken into account. Results.We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of ~5 mag led to the outburst peak in February 19–21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some “shutdown” mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin.
We present the results of a site characterization study carried out at the Astronomical Observatory of the Autonomous Region of the Aosta Valley (OAVdA), in the western Italian Alps, aimed at ...establishing its potential to host a photometric transit search for small-size planets around a statistically significant sample of nearby cool M dwarfs. For the purpose of the site testing campaign, we gathered photometric and seeing measurements utilizing different instruments available at the site. As in any search for new locations for astronomical observations, we gauged site-dependent observing conditions such as night-sky brightness, photometric precision, and seeing properties. Public meteorological data were also used in order to help in the determination of the actual number of useful observing nights per year. The measured zenithal -band night-sky brightness is typical of that of very good, very dark observing sites. The extinction registered at the -band is not dissimilar from that of other sites. The median seeing over the period of in situ observations is found to be approx1.7 . Given the limited duration of the observations, we did not probe any possible seeing seasonal patterns or the details of its possible dependence on other meteorological parameters, such as wind speed and direction. Moreover, our data show that the seeing at the observatory was reasonably stable during most of the nights. The fraction of fully clear nights per year amounts to 39%, while the total of useful nights increases to 57%, assuming a (conservative) cloud cover of not more than 50% of the night. Based on the analysis of photometric data collected over the period of 2009 May-August for three stellar fields centered on the transiting planet hosts WASP-3, HAT-P-7, and Gliese 436, we achieve seeing-independent best-case photometric precision IeA apptA2 3 mmag (rms) in several nights for bright stars (apptA2 11 mag). A median performance IeA approx 6 mmag during the observing period is obtained for stars with apptA2 13 mag . A by-product of the significant amount of photometric data collected in the stellar fields of WASP-3 and HAT-P-7 was the identification of a handful of new variable stars, four of which are presented and discussed here. Our results demonstrate that the OAVdA site is well poised to conduct an upcoming long-term photometric survey for transiting low-mass, small-size planets around a well-defined sample of M dwarfs in the solar neighborhood.
Small-size ground-based telescopes can effectively be used to look for transiting rocky planets around nearby low-mass M stars using the photometric transit method, as recently demonstrated for ...example by the MEarth project. Since 2008 at the Astronomical Observatory of the Autonomous Region of Aosta Valley (OAVdA), we have been preparing for the long-term photometric survey APACHE, aimed at finding transiting small-size planets around thousands of nearby early and mid-M dwarfs. APACHE (A PAthway toward the Characterization of Habitable Earths) is designed to use an array of five dedicated and Identical 40-cm Ritchey-Chretien telescopes and its observations started at the beginning of summer 2012. The main characteristics of the survey final set up and the preliminary results from the first weeks of observations will be discussed.
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