Photoperiodic Response of Abrostola asclepiadis (Lepidoptera: Noctuidae), a Candidate Biological Control Agent for Swallow-worts (Vincetoxicum, Apocynaceae)

A biological control program is in development for two swallow-wort species (Vincetoxicum, Apocynaceae), European vines introduced into northeastern North America. One candidate agent is the defoliator Abrostola asclepiadis (Denis and Schiffermüller) (Lepidoptera: Noctuidae). The moth reportedly has up to two generations in parts of its native range. We assessed the potential multivoltinism of Russian and French populations of the moth by rearing them under constant and changing photoperiods, ranging from 13:11 to 16:8 hour (L:D). The French population was also reared outdoors under naturally-changing day lengths at a latitude similar to northern New York State. Less than six adult moths emerged, with one exception, for any photoperiod treatment. We expect A. asclepiadis to be univoltine if it were to be released into North America, limiting its potential impact on swallow-worts. It should therefore be given a lower priority for release

The He abundance in NGC 1850 A and B: are we observing the early stage of formation of multiple populations in a stellar cluster?

We present the result of a sample of B-stars in the Large Magellanic Cloud young double stellar cluster NGC 1850 A and NGC 1850 B, observed with the integral-field spectrograph at the Very Large Telescope, the Multi Unit Spectroscopic Explorer. We compare the observed equivalent widths (EWs) of four He lines (4922 $\mathring{\mathrm A}$, 5015 $\mathring{\mathrm A}$, 6678 $\mathring{\mathrm A}$, and 7065 $\mathring{\mathrm A}$) with the ones determined from synthetic spectra computed with different He mass fraction (Y=0.25, 0.27, 0.30 and 0.35) with the code SYNSPEC, that takes into account the non-LTE effect. From this comparison, we determined the He mass fraction of the B stars, finding a not homogeneous distribution. The stars can be divided in three groups, He-weak (Y $\lt$ 0.24) and the He-normal (0.24 $\leqslant$ Y $\leqslant$ 0.26) belonging to the MS of NGC 1850 A, and the He-rich stars (0.33 $\leqslant$ Y $\leqslant$ 0.38) situated in the MS associated to NGC 1850 B. We have analyzed the stellar rotation as possible responsible of the anomalous features of the He lines in the He-rich stars. We provide a simple analysis of the differences between the observed EWs and the ones obtained from the theoretical models with different rotation velocity (V$\sin{i}$ = 0 and 250 Km/s). The resolution of the MUSE spectra do not allow to get a conclusive result, however our analysis support the He-enhanced hypothesis.Comment: Accepted for publication by MNRAS, 10 pages, 8 figure

A spectroscopic survey of the youngest field stars in the solar neighbourhood. I. The optically bright sample

We present the first results of a ground-based programme conducted on 1-4m class telescopes. Our sample consists of 1097 active and presumably young stars, all of them being optical counterparts of RASS X-ray sources in the northern hemisphere. We concentrate on the 704 optically brightest (V_Ticho<=9.5 mag) candidates. We acquired high-res spectroscopy in the Halpha/Li spectral regions for 426 of such stars without relevant literature data. We describe the sample and the observations and we start to discuss its physical properties. We used a cross-correlation technique and other tools to derive accurate radial/rotational velocities and to perform a spectral classification for both single and SB2 stars. The spectral subtraction technique was used to derive chromospheric activity levels and Li abundances. We estimated the fraction of young single stars and multiple systems in stellar soft X-ray surveys and the contamination by more evolved systems, like RS CVn's. We classified stars on the basis of Li abundance and give a glimpse of their sky distribution. The sample appears to be a mixture of young Pleiades-/Hyades- like stars plus an older Li-poor population (~1-2 Gyr). 7 stars with Li abundance compatible with the age of IC 2602 (~30 Myr) or younger were detected as well, although 2 appear to be Li-rich giants. The discovery of a large number of Li-rich giants is another outcome of this survey. The contamination of soft X-ray surveys by old systems in which the activity level is enhanced by tidal synchronisation is not negligible, especially for K-type stars. 5 stars with Li content close to the primordial abundance are probably associated with known moving groups in the solar neighbourhood. Some of them are PTTS candidates according to their positions in the HR diagram.Comment: 16 pages, 12 figures, 6 tables; 2 figures and 2 tables in electronic form only. Paper accepted by Astronomy and Astrophysic

Crossing the Gould Belt in the Orion vicinity

We present a study of the large-scale spatial distribution of 6482 RASS X-ray sources in approximately 5000 deg^2 in the direction of Orion. We examine the astrophysical properties of a sub-sample of ~100 optical counterparts, using optical spectroscopy. This sub-sample is used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions. We characterize the observed sub-sample in terms of spectral type, lithium content, radial and rotational velocities, as well as iron abundance. A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area. We find that stars associated with the Orion star-forming region do show a high lithium content. A population of late-type stars with lithium equivalent widths larger than Pleiades stars of the same spectral type (hence younger than ~70-100 Myr) is found widely spread over the studied area. Two new young stellar aggregates, namely "X-ray Clump 0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also identified. The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the direction of Orion is characterized by three distinct components, namely the clustered, the young dispersed, and the widespread field populations. The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds. The dispersed young population follows a broad lane apparently coinciding spatially with the Gould Belt, while the widespread population consists primarily of active field stars older than 100 Myr. We expect the "bi-dimensional" picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission.Comment: 17 pages, 13 figures, 4 tables. Accepted for publication in Astronomy and Astrophysics. Abstract shortene

Search for giant planets in M67 IV: survey results

We present the results of a seven-year-long radial velocity survey of a sample of 88 main-sequence and evolved stars to reveal signatures of Jupiter-mass planets in the solar-age and solar-metallicity open cluster M67. We aim at studying the frequency of giant planets in this cluster with respect to the field stars. In addition, our sample is also ideal to perform a long-term study to compare the chemical composition of stars with and without giant planets in detail. We analyzed precise radial velocity (RV) measurements obtained with five different instruments. We conducted Monte Carlo simulations to estimate the occurrence rate of giant planets in our radial velocity survey. All the planets previously announced in this RV campaign with their properties are summarized here: 3 hot Jupiters around the main-sequence stars YBP1194, YBP1514, and YBP401, and 1 giant planet around the evolved star S364. Two additional planet candidates around the stars YBP778 and S978 are also analyzed in the present work. We discuss stars that exhibit large RV variability or trends individually. For 2 additional stars, long-term trends are compatible with new binary candidates or substellar objects, which increases the total number of binary candidates detected in our campaign to 14. Based on the Doppler-detected planets discovered in this survey, we find an occurrence of giant planets of ~18.0%(+12.0/-8.0%) in the selected period-mass range. This frequency is slightly higher but consistent within the errors with the estimate for the field stars, which leads to the general conclusion that open cluster and field statistics agree. However, we find that the rate of hot Jupiters in the cluster (~5.7%(+5.5/-3.0%)) is substantially higher than in the field.Comment: Accepted by A&

MUSE observations of NGC330 in the Small Magellanic Cloud. Helium abundance of bright main sequence stars

We present observations of the most bright main sequence stars in the Small Magellanic Cloud stellar cluster NGC330 obtained with the integral field spectrograph MUSE@VLT. The use of this valuable instrument allows us to study both photometric and spectroscopic properties of stellar populations of this young star cluster. The photometric data provide us a precise color magnitude diagram, which seems to support the presence of two stellar populations of ages of $\sim$ 18 Myr and $\sim$ 30 Myr assuming a metallicity of Z = 0.002. Thanks to the spectroscopic data, we derive helium abundance of 10 main sequence stars within the effective radius Reff= 20" of NGC330, thus leading to an estimation of $\epsilon(He)$ = 10.93 $\pm$ 0.05 (1$\sigma$ ). The helium elemental abundances of stars likely belonging to the two possible stellar populations, do not show differences or dichotomy within the uncertainties. Thus, our results suggest that the two stellar populations of NGC330, if they exist, share similar original He abundances. If we consider stellar rotation velocity in our analysis, a coeval (30 Myr) stellar population, experiencing different values of rotation, cannot be excluded. In this case, the mean helium abundance rot obtained in our analysis is 11.00 $\pm$ 0.05 dex. We also verified that possible NLTE effects cannot be identified with our analysis because of the spectral resolution and they are within our derived abundance He uncertainties. Moreover, the analysis of the He abundance as a function of the distance from the cluster center of the observed stars do not show any correlation

Lithium abundance in the metal-poor open cluster NGC 2243

Lithium is a fundamental element for studying the mixing mechanisms acting in the stellar interiors, for understanding the chemical evolution of the Galaxy and the Big Bang nucleosynthesis. The study of Li in stars of open clusters (hereafter OC) allows a detailed comparison with stellar evolutionary models and permits us to trace its galactic evolution. The OC NGC 2243 is particularly interesting because of its low metallicity ([Fe/H]=$-0.54 \pm0.10$ dex). We measure the iron and lithium abundance in stars of the metal-poor OC NGC 2243. The first aim is to determine whether the Li dip extends to such low metallicities, the second is to compare the results of our Li analysis in this OC with those present in 47 Tuc, a globular cluster of similar metallicity. We performed a detailed analysis of high-resolution spectra obtained with the multi-object facility FLAMES at the ESO VLT 8.2m telescope. Lithium abundance was derived through line equivalent widths and the OSMARCS atmosphere models. We determine a Li dip center of 1.06 $M_\odot$, which is much smaller than that observed in solar metallicity and metal-rich clusters. This finding confirms and strengthens the conclusion that the mass of the stars in the Li dip strongly depends on stellar metallicity. The mean Li abundance of the cluster is $\log n{\rm (Li)}=2.70$ dex, which is substantially higher than that observed in 47 Tuc. We estimated an iron abundance of [Fe/H]=$-0.54 \pm0.10$ dex for NGC 2243, which is similar (within the errors) to previous findings. The [$\alpha$/Fe] content ranges from $0.00\pm0.14$ for Ca to $0.20\pm0.22$ for Ti, which is low when compared to thick disk stars and to Pop II stars, but compatible with thin disk objects. We found a mean radial velocity of 61.9 $\pm$ 0.8 \kms for the cluster.Comment: 16 pages, 9 figures, Accepted for publication in Astronomy and Astrophysic