A probable pre-main sequence chemically peculiar star in the open cluster Stock 16

We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Delta-a photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3-8 Myr). The probable cluster membership, the star's position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star's chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star.Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 tabl

Microbiological, biochemical and biogenic amine profiles of Terrincho cheese manufactured in several dairy farms

Terrincho is a Portuguese traditional cheese, bearing a protected denomination of origin (PDO) status, which is manufactured from raw ewes’ milk and ripened for a minimum period of 30 d. The objectives of this research effort were to characterize the microbiological and biochemical profiles of this cheese, manufactured in several dairy farms during the winter cheesemaking season (December through March), and establish tentative correlations between these profiles and formation of biogenic amines. For this goal, 29 cheeses from five batches, manufactured in as many dairy farms located throughout the PDO region, were analysed. The viable numbers of the total (mesophilic) microflora, enterococci, lactococci, lactobacilli, enterobacteria, staphylococci, pseudomonads, yeasts and moulds were determined by 30 d, following classical plate counting on specific media. Free amino acid and biogenic amine contents were determined by reverse-phase high-pressure liquid chromatography. The concentration of biogenic amines correlated well with microbial viable numbers, in both qualitative and quantitative terms; significant correlations were observed between enterococci and phenylethylamine (r ¼ 0.868, po0.0001), and between lactococci and cadaverine (r = 0.646, p <0.002) and tyramine (r = 0.868, p<0.0001). On the other hand, 220 g of Terrincho cheese would have to be consumed at a given time if the threshold of worst case risk was to be attained, which appears unrealistic for a typically single-doses meal ingredient. This study has contributed to deepen the knowledge on the microbiological and biochemical features of a unique Portuguese cheese throughout ripening, and to rationalize its safe consumption in terms of biogenic amines

Chemically peculiar stars in the Large Magellanic Cloud

The detection of magnetic chemically peculiar (CP2) stars in open clusters of extragalactic systems can give observational answers to many unsolved questions. The mean percentage of CP2 stars in the Milky Way is of the order of 5% for the spectral range from early B- to F-type, luminosity class V objects. The origin of the CP2 phenomenon seems to be closely connected to the overall metallicity and global magnetic field environment. The theoretical models are still only tested by observations in the Milky Way. It is therefore essential to provide high quality observations in rather different global environments. The young clusters NGC 2136/7 were observed in the Delta a photometric system. This intermediate band photometric system samples the depth of the 520nm flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 11nm to 23nm. The Delta a photometric system is most suitable for detecting CP2 stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. We present high precision photometric Delta a observations of 417 objects in NGC 2136/7 and its surrounding field, of which five turned out to be bona fide magnetic CP stars. In addition, we discovered two Be/Ae stars. From our investigations of NGC 1711, NGC 1866, NGC 2136/7, their surroundings, and one independent field of the LMC population, we derive an occurrence of classical chemically peculiar stars of 2.2(6)% in the LMC, which is only half the value found in the Milky Way. The mass and age distribution of the photometrically detected CP stars is not different from that of similar objects in galactic open clusters.Comment: 5 pages, 4 figures, accepted by A&

CCD photometric search for peculiar stars in open clusters. VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

We continue our survey for magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open clusters ages and metallicities can help to find a correlation of these parameters with the (non-)presence of peculiarities which has to be taken into account in stellar evolution models. The intermediate band Delta a photometric system samples the depth of the 5200A flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 110A to 230A. It is capable to detect magnetic CP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) lambda Bootis, as well as classical Be/shell stars can be successfully investigated. In addition, it allows to determine the age, reddening and distance modulus with an appropriate accuracy by fitting isochrones. From the 1677 observed members of the eight open clusters, twenty five CP2 and one Ae stars were identified. Further nineteen deviating stars are designated as questionable due to several reasons. The estimated age, reddening and distance for the programme clusters were compared with published vales of the literature and discussed in this context. The current paper shows that CP2 stars are present continuously in very young (7Myr) to intermediate age (500Myr) open clusters at distances larger than 2kpc from the Sun

The first Delta a observations of three globular clusters

Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental Distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Delta a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow band system measures the flux distribution in the region from 4900 to 5600A in order to find any peculiarities around 5200A. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Delta a photometry of 2266 stars from 109 individual frames for three globular Clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yield an excellent agreement. According to the 3 sigma detection limit of each globular cluster, about 3% of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.Comment: 8 pages, 5 figures, MNRAS, 443, 2492 (2014

CCD photometric search for peculiar stars in open clusters. V. NGC 2099, NGC 3114, NGC 6204, NGC 6705 and NGC 6756

We have investigated 1008 objects in the area of five intermediate age open clusters (NGC 2099, NGC 3114, NGC 6204, NGC 6705 and NGC 6756) via the narrow band Delta a-system. The detection limit for photometric peculiarity is very low (always less than 0.009mag) due to the high number of individual frames used (193 in total). We have detected six peculiar objects in NGC 6705 and NGC 6756 from which one in the latter is almost certainly an unreddened late type foreground star. The remaining five stars are probably cluster members and bona fide chemically peculiar objects (two are lambda Bootis type candidates). Furthermore, we have investigated NGC 3114, a cluster for which already photoelectric Delta a-measurements exist. A comparison of the CCD and photoelectric values shows very good agreement. Again, the high capability of our CCD Delta a-photometric system to sort out true peculiar objects together with additional measurements from broad or intermediate band photometry is demonstrated.Comment: 6 pages, 2 figures, accepted by A&

CCD photometric search for peculiar stars in open clusters. VI. NGC 1502, NGC 3105, Stock 16, NGC 6268, NGC 7235 and NGC 7510

In a sample of six young open clusters we investigated 1753 objects using the narrow band, three filter Delta a photometric system resulting in the detection of eleven bona-fide magnetic chemically peculiar (CP) stars and five Be or metal-weak stars. The results for the distant cluster NGC 3105 is most important because of the still unknown influence of the global metallicity gradient of the Milky Way. These findings confirm that CP stars are present in open clusters of very young ages (log t > 6.90) at galactocentric distances up to 11.4 kpc. For all programme clusters the age, reddening, and distance modulus were derived using the corresponding isochrones. Some additional variable stars within Stock 16 could be identified by comparing different photometric studies.Comment: 7 pages, 2 figures, accepted by A&

Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic beta Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign (Handler et al. 2012) and known in the literature. Using the photometric constraints on the degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for the mass (M \in [8.2,9.6] M_o) and central hydrogen abundance (X_c \in [0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and n_3=-2, and to derive an equatorial rotation velocity v_eq \in [71,75] km s^{-1}. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (alpha_ov \in [0,0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic beta Cep star theta Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.Comment: 12 pages, 6 figures and 5 tables; accepted for publication in MNRAS on 2012 August 1