Carbon-Rich Mira Variables: Radial Velocities and Distances

Optical radial velocities have been measured for 38 C-type Mira variables. These data together with others in the literature are used to study the differences between optical and CO mm observations for C-Miras and the necessary corrections to the optical velocities are derived in order to obtain the true radial velocities of the variables. The difference between absorption and emission line velocities is also examined. A particularly large difference (+30 km\s) is found in the case of the H-alpha emission line. A catalogue is given of 177 C-Miras with estimated distances and radial velocities. The distances are based on bolometric magnitudes derived in Paper I using SAAO observations or (for 60 of the stars) using non-SAAO photometry. In the latter case the necessary transformations to the SAAO system are derived. These data will be used in paper III to study the kinematics of the C-Miras.Comment: 11 pages, accepted for publication in MNRA

Photometric study of the young open cluster NGC 3293

Deep and extensive CCD photometric observations $UBV(RI)_{C}H_{\alpha}$ were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to $M_{V} \approx +4.5$, revealing that stars with $M_{V} < -2$ are evolving off the main sequence; stars with $-2 < M_{V} +2$ are placed above it. According to our analysis, the cluster distance is $d = 2750 \pm 250 pc$ ($V_{0}-M_{V} = 12.2 \pm 0.2$) and its nuclear age is $8 \pm 1 Myr$. NGC 3293 contains an important fraction of pre--main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to 2.5 \cal M_{\sun} and a mean contraction age of $10 Myr$. This last value does not differ too much from the nuclear age estimate. Actually, if we take into account the many factors that may affect the PMS star positions onto the colour--magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Besides, using the $H_{\alpha}$ data, we detected nineteen stars with signs of having $H_{\alpha}$ emission in the region of NGC 3293, giving another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope value $x = 1.2 \pm 0.2$, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.Comment: 17 pages, 13 eps figures, in press in Astronomy and Astrophysic

A maximum common substructure-based algorithm for searching and predicting drug-like compounds

Motivation: The prediction of biologically active compounds is of great importance for high-throughput screening (HTS) approaches in drug discovery and chemical genomics. Many computational methods in this area focus on measuring the structural similarities between chemical structures. However, traditional similarity measures are often too rigid or consider only global similarities between structures. The maximum common substructure (MCS) approach provides a more promising and flexible alternative for predicting bioactive compounds

Baade-Wesselink distances and the effect of metallicity in classical cepheids

The aim of this paper is to investigate the metallicity dependence of the $PL$-relation in $V$ and $K$ based on a sample of 68 Galactic Cepheids with individual Baade-Wesselink distances (some of the stars also have an HST-based parallax) and individually determined metallicities from high-resolution spectroscopy. Literature values of the $V$-band, $K$-band and radial velocity data have been collected for a sample of 68 classical cepheids that have their metallicity determined in the literature from high-resolution spectroscopy. Based on a $(V-K)$ surface-brightness relation and a projection factor derived in a previous paper, distances have been derived from a Baade-Wesselink analysis. $PL$- and $PLZ$-relations in $V$ and $K$ are derived. The effect of the adopted dependence of the projection factor on period is investigated. The change from a constant $p$-factor to one recently suggested in the literature with a mild dependence on $\log P$ results in a less steep slope by 0.1 unit, which is about the 1-sigma error bar in the slope itself. The observed slope in the $PL$-relation in $V$ in the LMC agrees with both hypotheses. In $K$ the difference between the Galactic and LMC slope is larger and would favour a mild period dependence of the $p$-factor. The dependence on metallicity in $V$ and $K$ is found to be marginal, and independent of the choice of $p$-factor on period. This result is severely limited by the small range in metallicity covered by the Galactic Cepheids.Comment: A&A accepte

The Keele-Exeter young cluster survey - I. Low-mass pre-main-sequence stars in NGC 2169

We have used RCIC CCD photometry from the Isaac Newton telescope and intermediate-resolution spectroscopy from the Gemini North telescope to identify and characterize low-mass (0.15 < M/M⊙ < 1.3) pre-main-sequence stars in the young open cluster NGC 2169. Isochrone fitting to the high- and low-mass populations yields an intrinsic distance modulus of 10.13+0.06−0.09 mag and a model-dependent age of 9 ± 2 Myr. Compared to the nearby, kinematically defined groups of a similar age, NGC 2169 has a large low-mass population which potentially offers a more precise statistical investigation of several aspects of star formation and early stellar evolution. By modelling the distribution of low-mass stars in the IC versus RC−IC diagram, we find that any age spread among cluster members has a Gaussian full width at half-maximum (FWHM) ≤ 2.5 Myr. A young age and a small age spread (<10 Myr) are supported by the lack of significant lithium depletion in the vast majority of cluster members. There is no clear evidence for accretion or warm circumstellar dust in the low-mass members of NGC 2169, bolstering the idea that strong accretion has ceased and inner discs have dispersed in almost all low-mass stars by ages of 10 Myr