17 research outputs found

    Temporal changes of the flare activity of Proxima Cen

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    We study temporal variations of the emission lines of Halpha, Hepsilon, H and K Ca II, D1 and D2 Na I, 4026 and 5876 A He I in the HARPS spectra of Proxima Centauri across an extended time of 13.2 years, from May 27, 2004, to September 30, 2017. Aims. We analyse the common behaviour and differences in the intensities and profiles of different emission lines in flare and quiet modes of Proxima activity. Methods. We compare the pseudo-equivalent widths (pEW) and profiles of the emission lines in the HARPS high-resolution (R ~ 115,000) spectra observed at the same epochs. Results. All emission lines show variability with a timescale of at least 10 min. The strength of all lines except He I 4026 A correlate with \Halpha. During strong flares the `red asymmetry' appears in the Halpha emission line indicating the infall of hot condensed matter into the chromosphere with velocities greater than 100 km/s disturbing chromospheric layers. As a result, the strength of the Ca II lines anti-correlates with Halpha during strong flares. The He I lines at 4026 and 5876 A appear in the strong flares. The cores of D1 and D2 Na I lines are also seen in emission. During the minimum activity of Proxima Centauri, Ca II lines and Hepsilon almost disappear while the blue part of the Na I emission lines is affected by the absorption in the extending and condensing flows. Conclusions. We see different behaviour of emission lines formed in the flare regions and chromosphere. Chromosphere layers of Proxima Cen are likely heated by the flare events; these layers are cooled in the `non-flare' mode. The self-absorption structures in cores of our emission lines vary with time due to the presence of a complicated system of inward and outward matter flows in the absorbing layers.Comment: 22 pages, 12 Figures, accepted by A

    A system of three transiting super-Earths in a cool dwarf star

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    We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High resolution spectra obtained with HARPS-N/TNG showed that the star is a mid-late K dwarf. Using spectral synthesis models we infer its effective temperature, surface gravity and metallicity and subse- quently determined from evolutionary models a stellar radius of 0.58 R Sun. The planets have radii of 1.8, 2.6 and 1.9 R Earth and orbital periods of 6.34, 13.85 and 40.72 days. High resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 AU, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky - gaseous threshold, their atmospheres, internal structure, composition and interactions with host stars.Comment: Accepted for publication in MNRAS Letter

    Photometric follow-up of the 20 Myr old multi-planet host star V1298 Tau with CHEOPS and ground-based telescopes

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    Context. The 20 Myr old star V1298 Tau hosts at least four planets. Since its discovery, this system has been a target of intensive photometric and spectroscopic monitoring. To date, the characterisation of its architecture and planets' fundamental properties has been very challenging. Aims: The determination of the orbital ephemeris of the outermost planet V1298 Tau e remains an open question. Only two transits have been detected so far by Kepler/K2 and TESS, allowing for a grid of reference periods to be tested with new observations, without excluding the possibility of transit timing variations. Observing a third transit would allow for better constraints to be set on the orbital period and would also help in determining an accurate radius for V1298 Tau e because the previous transits showed different depths. Methods: We observed V1298 Tau with the CHaracterising ExOPlanet Satellite (CHEOPS) to search for a third transit of planet e within observing windows selected to test three of the shortest predicted orbital periods. We also collected ground-based observations to verify the result found with CHEOPS. We reanalysed Kepler/K2 and TESS light curves to test how the results derived from these data are affected by alternative photometric extraction and detrending methods. Results: We report the CHEOPS detection of a transit-like signal that could be attributed to V1298 Tau e. If so, that result would imply that the orbital period calculated from fitting a linear ephemeris to the three available transits is close to ~45 days. Results from the ground-based follow-up marginally support this possibility. We found that i) the transit observed by CHEOPS has a longer duration compared to that of the transits observed by Kepler/K2 and TESS; and ii) the transit observed by TESS is >30% deeper than that of Kepler/K2 and CHEOPS, and it is also deeper than the measurement previously reported in the literature, according to our reanalysis. Conclusions: If the new transit detected by CHEOPS is found to be due to V1298 Tau e, this would imply that the planet experiences TTVs of a few hours, as deduced from three transits, as well as orbital precession, which would explain the longer duration of the transit compared to the Kepler/K2 and TESS signals. Another and a priori less likely possibility is that the newly detected transit belongs to a fifth planet with a longer orbital period than that of V1298 Tau e. Planning further photometric follow-up to search for additional transits is indeed necessary to solve the conundrum, as well as to pin down the radius of V1298 Tau e

    On the 12C/13C isotopic ratio at the dawn of chemical evolution

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    The known Mega and Hyper Metal-Poor (MMP-HMP) stars with [Fe/H]<-6.0 and <-5.0, respectively, likely belong to the CEMP-no class, i.e. carbon-enhanced stars with low or absent second peak neutron capture elements. They are likely second generation stars and the few elements measurable in their atmospheres are used to infer the properties of single or very few progenitors. The high carbon abundance in the CEMP-no stars offers a unique opportunity to measure the carbon isotopic ratio, which directly monitors the presence of mixing between the He and H-burning layers either within the star or in the progenitor(s). By means of high-resolution spectra acquired with the ESPRESSO spectrograph at the VLT we aim to derive values for the 12C/13C ratio at the lowest metallicities. A spectral synthesis technique based on the SYNTHE code and on ATLAS models is used within a Markov-chain Monte Carlo methodology to derive 12C/13C in the stellar atmospheres of five of the most metal poor stars. These are the Mega Metal-Poor giant SMS J0313-6708 ([Fe/H]<-7.1), the Hyper Metal-Poor dwarf HE1327-2326 ([Fe/H]=-5.8),the Hyper Metal-Poor giant SDSS J1313-0019 ([Fe/H] = -5.0) and the Ultra Metal-Poor subgiant HE0233-0343 ([Fe/H]=-4.7). We also revise a previous value for the Mega Metal-Poor giant SMSS J1605-1443 with ([Fe/H] = -6.2). In four stars we derive an isotopic value while for HE1327-2326 we provide a lower limit. All Measurements are in the range 39<12C/13C<100 showing that the He- and H-burning layers underwent partial mixing either in the stars or, more likely, in their progenitors. This provides evidence of a primary production of 13C at the dawn of chemical evolution. [abridged]Comment: 10 pages, 6 figure, accepted A&

    VizieR Online Data Catalog: HADES RV Programme with HARPS-N at TNG. II. (Perger+, 2017)

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    Intrinsic and observational characteristics of the 78 target stars of our sample sorted by number of observations (Nobs).We show the absolute RVs and their rms and the mean uncertainties dRV of every object for TERRA (T) and YABI (Y) pipelines. V magnitudes are from SIMBAD. Their masses are the average values of targets with the same spectral type. (1 data file)

    VizieR Online Data Catalog: GJ 3998 RVs, S and Halpha indexes (Affer+, 2016)

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    In this table we report the observing log for the GJ3998 spectra and the radial velocities, S, and H╬▒ indexes. The star GJ3998 has been monitored from BJD=2456439.6 (26 May 2013) to BJD=2457307.8 (12 October 2015). We obtained a total of 136 data points spanning 869-days. The spectra were obtained at high resolution (R=115000) with the optical echelle spectrograph HARPS-N with exposure times of 15 minutes and an average signal-to-noise ratio (S/N) of 45 at 5500├ů. Of the 136 epochs, 76 were obtained within the GAPS time and 60 within the Spanish time. Observations were gathered without the simultaneous Th-Ar calibration, which is commonly used to correct for instrumental drifts during the night. The M-type stars of the HADES program were observed by the Italian team in conjunction with other GAPS targets, which used the Th-Ar simultaneous calibration, therefore we estimated the drift data between the two fibers (star and reference calibration) for each night from these observations and evaluated the interpolated drift for GJ3998 (0.7m/s). Data reduction and spectral extraction were performed using the Data Reduction Software (DRS, Lovis & Pepe, 2007A&A...468.1115L, Cat. J/A+A/468/1115). RVs were measured by means of a weighted cross-correlation function (CCF) with the M2 binary mask provided with the DRS. The RVs were also measured by matching the spectra with a high S/N template obtained by coadding the spectra of the target, as implemented in the TERRA pipeline (Anglada-Escude & Butler, 2012ApJS..200...15A, Cat. J/ApJS/200/15), which provides a better RV accuracy when applied to M dwarfs. We list the observation dates (barycentric Julian date or BJD), the signal-to-noise ratios (S/Ns), the radial velocities (RVs) from the DRS and TERRA pipelines (indicated with a T) and the H╬▒ and S indexes, calculated both by the TERRA pipeline and by an independent method described in the text. The RV errors reported are the formal ones and do not include the jitter term. The S index and H╬▒ errors are calculated as described in the text and do not take into account the photon noise. The S index and H╬▒ errors derived from the TERRA pipeline are due to photon noise through error propagation. (1 data file)