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The 4D Eigenvector 1 parameter space was introduced seven years ago as an attempt at multiwavelength spectroscopic representation of quasars. It appears to be the most effective diagnostic space for unifying the diversity of broad line AGN. This progress report shows that the diagnostic power of 4DE1 is confirmed using optical spectra from the SDSS, UV spectra from HST and X-ray spectra from XMM. Our introduction of the population A-B concept continues to provide useful insights into quasar diversity. Largely radio-quiet, high accreting, low BH mass Pop. A sources (FWHM H_beta <= 4000 km/s) show strong FeII emission, a soft X-ray excess and a CIV profile blueshift. Low accreting large BH mass Pop. B quasars (FWHM H_beta > 4000 km/s) include most radio-loud AGN and show weak FeII emission and little evidence for a soft X-ray excess or a CIV blueshift.
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Let $phi_H^r(n)$ be the smallest integer such that, for all $r$-graphs $G$ on $n$ vertices, the edge set $E(G)$ can be partitioned into at most $phi_H^r(n)$ parts, of which every part either is a single edge or forms an $r$-graph isomorphic to $H$. The function $phi^2_H(n)$ has been well studied in literature, but for the case $rge 3$, the problem that determining the value of $phi_H^r(n)$ is widely open. Sousa (2010) gave an asymptotic value of $phi_H^r(n)$ when $H$ is an $r$-graph with exactly 2 edges, and determined the exact value of $phi_H^r(n)$ in some special cases. In this paper, we first give the exact value of $phi_H^r(n)$ when $H$ is an $r$-graph with exactly 2 edges, which improves Sousas result. Second we determine the exact value of $phi_H^r(n)$ when $H$ is an $r$-graph consisting of exactly $k$ independent edges.
We present a new analysis of the stellar population of the Orion Nebula Cluster (ONC) based on multi-band optical photometry and spectroscopy. We study the color-color diagrams in BVI, plus a narrow-band filter centered at 6200A, finding evidences that intrinsic color scales valid for main-sequence dwarfs are incompatible with the ONC, while a better agreement is found employing synthetic intrinsic colors obtained constraining the typical lower surface gravity of young stars. We refine these model colors even further, empirically, by comparison with a sample of ONC stars with no accretion and no extinction. We consider the stars with known spectral types from the literature, and add 65 newly classified stars from slit spectroscopy and 182 M-type from narrow-band photometry; in this way we isolate a sample of about 1000 stars with known spectral type. We introduce a new method to self-consistently derive reddening and accretion excess from the location of each star in the BVI color-color diagram. This enables us to accurately determine the extinction of the ONC members. We adopt a lower distance for the ONC than previously assumed, based on recent parallax measurements. With a careful choice also of the spectral type-temperature transformation, we produce the new H-R diagram of the ONC population, more populated than previous works. With respect to previous works, we find higher luminosity for late-type stars and a lower luminosity for early types. We determine the age distribution of the population, peaking at 2-3 Myr, a higher age than previously estimated. We study the distribution of the members in the mass-age plane, and find that taking into account selection effects due to incompleteness removes an apparent correlation between mass and age. We derive the IMF for low- and intermediate-mass members of the ONC, which turns out to be model-dependent, and shows a turn-over at ~<0.2Msun.
Spectropolarimetric observations combined with tomographic imaging techniques have revealed that all pre-main sequence (PMS) stars host multipolar magnetic fields, ranging from strong and globally axisymmetric with ~>kilo-Gauss dipole components, to complex and non-axisymmetric with weak dipole components (<~0.1 kG). Many host dominantly octupolar large-scale fields. We argue that the large-scale magnetic properties of a PMS star are related to its location in the Hertzsprung-Russell diagram. This conference paper is a synopsis of Gregory et al. (2012), updated to include the latest results from magnetic mapping studies of PMS stars.
Interstellar scintillation (ISS) has been established as the cause of the random variations seen at centimetre wavelengths in many compact radio sources on timescales of a day or less. Observations of ISS can be used to probe structure both in the ionized insterstellar medium of the Galaxy, and in the extragalactic sources themselves, down to microarcsecond scales. A few quasars have been found to show large amplitude scintillations on unusually rapid, intrahour timescales. This has been shown to be due to weak scattering in very local Galactic ``screens, within a few tens of parsec of the Sun. The short variability timescales allow detailed study of the scintillation properties in relatively short observing periods with compact interferometric arrays. The three best-studied ``intrahour variable quasars, PKS 0405-385, J1819+3845 and PKS 1257-326, have been instrumental in establishing ISS as the principal cause of intraday variability at centimetre wavelengths. Here we review the relevant results from observations of these three sources.
Weak G-band (WGB) stars are a rare class of cool luminous stars that present a strong depletion in carbon, but also lithium abundance anomalies that have been little explored in the literature since the first discovery of these peculiar objects in the early 50s. Here we focus on the Li-rich WGB stars and report on their evolutionary status. We explore different paths to propose a tentative explanation for the lithium anomaly. Using archive data, we derive the fundamental parameters of WGB (Teff, log g, log(L/Lsun)) using Hipparcos parallaxes and recent temperature scales. From the equivalent widths of Li resonance line at 6707 {AA}, we uniformly derive the lithium abundances and apply when possible NLTE corrections following the procedure described by Lind et al. (2009). We also compute dedicated stellar evolution models in the mass range 3.0 to 4.5 Msun, exploring the effects of rotation-induced and thermohaline mixing. These models are used to locate the WGB stars in the H-R diagram and to explore the origin of the abundance anomalies. The location of WGB stars in the H-R diagram shows that these are intermediate mass stars of masses ranging from 3.0 to 4.5 Msun located at the clump, which implies a degeneracy of their evolutionary status between subgiant/red giant branch and core helium burning phases. The atmospheres of a large proportion of WGB stars (more than 50%) exhibit lithium abundances A(Li) geq 1.4 dex similar to Li-rich K giants. The position of WGB stars along with the Li-rich K giants in the H-R diagram however indicates that both are well separated groups. The combined and tentatively consistent analysis of the abundance pattern for lithium, carbon and nitrogen of WGB stars seems to indicate that carbon underabundance could be decorrelated from the lithium and nitrogen overabundances.
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