S. Leccia

A MULTISITE CAMPAIGN TO MEASURE SOLAR-LIKE OSCILLATIONS IN PROCYON. I. OBSERVATIONS, DATA REDUCTION, AND SLOW VARIATIONS

We have carried out a multisite campaign to measure oscillations in the F5 star Procyon A. We obtained high-precision velocity observations over more than three weeks with 11 telescopes, with almost continuous coverage for the central 10 days. This represents the most extensive campaign so far organized on any solar-type oscillator. We describe in detail the methods we used for processing and combining the data. These involved calculating weights for the velocity time series from the measurement uncertainties and adjusting them in order to minimize the noise level of the combined data. The time series of velocities for Procyon shows the clear signature of oscillations, with a plateau of excess power that is centered at 0.9 mHz and is broader than has been seen for other stars. The mean amplitude of the radial modes is 38:1 AE 1:3 cm s A1 (2.0 times solar), which is consistent with previous detections from the ground and by the WIRE spacecraft, and also with the upper limit set by the MOST spacecraft. The variation of the amplitude during the observing campaign allows us to estimate the mode lifetime to be 1:5 þ1:9 A0:8 days. We also find a slow variation in the radial velocity of Procyon, with good agreement between different telescopes. These variations are remarkably similar to those seen in the Sun, and we interpret them as being due to rotational modulation from active regions on the stellar surface. The variations appear to have a period of about 10 days, which presumably equals the stellar rotation period or, perhaps, half of it. The amount of power in these slow variations indicates that the fractional area of Procyon covered by active regions is slightly higher than for the Sun.

A multi-site campaign to measure solar-like oscillations in Procyon. II. Mode frequencies

We have analyzed data from a multi-site campaign to observe oscillations in the F5 star Procyon. The data consist of high-precision velocities that we obtained over more than three weeks with 11 telescopes. A new method for adjusting the data weights allows us to suppress the sidelobes in the power spectrum. Stacking the power spectrum in a so-called echelle diagram reveals two clear ridges, which we identify with even and odd values of the angular degree (l = 0 and 2, and l = 1 and 3, respectively). We interpret a strong, narrow peak at 446 μHz that lies close to the l = 1 ridge as a mode with mixed character. We show that the frequencies of the ridge centroids and their separations are useful diagnostics for asteroseismology. In particular, variations in the large separation appear to indicate a glitch in the sound-speed profile at an acoustic depth of ~1000 s. We list frequencies for 55 modes extracted from the data spanning 20 radial orders, a range comparable to the best solar data, which will provide valuable constraints for theoretical models. A preliminary comparison with published models shows that the offset between observed and calculated frequencies for the radial modes is very different for Procyon than for the Sun and other cool stars. We find the mean lifetime of the modes in Procyon to be 1.29+0.55 -0.49 days, which is significantly shorter than the 2-4 days seen in the Sun.

The star formation in the L1615/L1616 Cometary Cloud

The present work aims at performing a comprehensive census and characterization of the pre-main-sequence (PMS) population in the cometary cloud L1615/L1616, in order to assess the significance of the triggered star formation scenario and investigate the impact of massive stars on its star formation history and mass spectrum. Our study is based on UBVRCIC and JHKs photometry, as well as optical multiobject spectroscopy. We performed a physical parameterization of the young stellar population in L1615/L1616. We identified 25 new T Tauri stars mainly projected on the dense head of the cometary cloud, almost doubling the current number of known members. We studied the spatial distribution of the cloud members as a function of the age and H? emission. The star formation efficiency (SFE) in the cloud is ~7%-8%, as expected for molecular clouds in the vicinity of OB associations. The slope of the initial mass function (IMF), in the mass range -->0.1 M? ? M ? 5.5 M?, is consistent with that of other T and OB associations, providing further support of a universal IMF down to the hydrogen-burning limit, regardless of environmental conditions. The cometary appearance, as well as the high SFE, can be explained in terms of triggered star formation induced by the strong UV radiation from OB stars or supernova shock waves. The age spread and both the spatial and age distribution of the PMS objects provide strong evidence of sequential, multiple events and possibly still ongoing star formation activity in the cloud.

Gaia Data Release 1 - The Cepheid and RR Lyrae star pipeline and its application to the south ecliptic pole region

Context. The European Space Agency spacecraft Gaia is expected to observe about 10 000 Galactic Cepheids and over 100 000 Milky Way RR Lyrae stars (a large fraction of which will be new discoveries), during the five-year nominal lifetime spent scanning the whole sky to a faint limit of G = 20.7 mag, sampling their light variation on average about 70 times. Aims. We present an overview of the Specific Objects Study (SOS) pipeline developed within the Coordination Unit 7 (CU7) of the Data Processing and Analysis Consortium (DPAC), the coordination unit charged with the processing and analysis of variable sources observed by Gaia , to validate and fully characterise Cepheids and RR Lyrae stars observed by the spacecraft. The algorithms developed to classify and extract information such as the pulsation period, mode of pulsation, mean magnitude, peak-to-peak amplitude of the light variation, subclassification in type, multiplicity, secondary periodicities, and light curve Fourier decomposition parameters, as well as physical parameters such as mass, metallicity, reddening, and age (for classical Cepheids) are briefly described. Methods. The full chain of the CU7 pipeline was run on the time series photometry collected by Gaia during 28 days of ecliptic pole scanning law (EPSL) and over a year of nominal scanning law (NSL), starting from the general Variability Detection, general Characterization, proceeding through the global Classification and ending with the detailed checks and typecasting of the SOS for Cepheids and RR Lyrae stars (SOS Cep&RRL). We describe in more detail how the SOS Cep&RRL pipeline was specifically tailored to analyse Gaia ’s G -band photometric time series with a south ecliptic pole (SEP) footprint, which covers an external region of the Large Magellanic Cloud (LMC), and to produce results for confirmed RR Lyrae stars and Cepheids to be published in Gaia Data Release 1 ( Gaia DR1). Results. G -band time series photometry and characterisation by the SOS Cep&RRL pipeline (mean magnitude and pulsation characteristics) are published in Gaia DR1 for a total sample of 3194 variable stars (599 Cepheids and 2595 RR Lyrae stars), of which 386 (43 Cepheids and 343 RR Lyrae stars) are new discoveries by Gaia . All 3194 stars are distributed over an area extending 38 degrees on either side from a point offset from the centre of the LMC by about 3 degrees to the north and 4 degrees to the east. The vast majority are located within the LMC. The published sample also includes a few bright RR Lyrae stars that trace the outer halo of the Milky Way in front of the LMC.

Detection of Solar-like Oscillations in the G5 Subgiant μ Her

A clear detection of excess of power, providing a substantial evidence for solar-like oscillations in the G5 sub- giantHer, is presented. This star was observed over seven nights with the SARG echelle spectrograph operating withthe3.6m ItalianTNG Telescope,usinganiodineabsorptioncell asavelocityreference. Aclear excess of power centeredat1.2mHz, withpeakamplitudesof about0.9ms � 1 intheamplitudespectrum ispresent.Fitting theasymp- totic relation to the power spectrum, a mode identification for the l ¼ 0, 1, 2, 3 modes in the frequency range 900Y 1600 � Hz is derived.Themostlikely value for the largeseparationturns out to be56.5 � Hz, consistent with theoretical expectations. The mean amplitude per mode (l ¼ 0;1) at peak power results to be 0.63 ms � 1 , almost 3 times larger than the solar one. Subject headingg stars: individual (� Her) — stars: oscillations — techniques: radial velocities

Standard candles from the Gaia perspective

The ESA Gaia mission will bring a new era to the domain of standard candles. Progresses in this domain will be achieved thanks to unprecedented astrometric precision, whole-sky coverage and the combination of photometric, spectrophotometric and spectroscopic measurements. The fundamental outcome of the mission will be the Gaia catalogue produced by the Gaia Data Analysis and Processing Consortium (DPAC), which will contain a variable source classification and specific properties for stars of specific variability types. We review what will be produced for Cepheids, RR Lyrae, Long Period Variable stars and eclipsing binaries.

Seismology of Procyon A: Determination of mode frequencies, amplitudes, lifetimes, and granulation noise

The F5 IV-V star Procyon A (

Gaia Data Release 2: Summary of the variability processing and analysis results

\alpha\!-\!\rm CMi

The rapidly pulsating subdwarf B star PG 1325+101 - I. Oscillation modes from multisite observations

) was observed in January 2001 by means of the high-resolution spectrograph SARG operating with the TNG

Astronomy textbook images: do they really help students?

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