Elemental Abundance Ratios in Stars of the Outer Galactic Disk. IV. A New Sample of Open Clusters

We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be 18, Be 21, Be 22, Be 32, and PWM 4. For Be 18 and PWM 4, these are the first chemical abundance measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. For this combined sample, we study the chemical abundances of open clusters as a function of distance, age, and metallicity. We confirm that the metallicity gradient in the outer disk is flatter than the gradient in the vicinity of the solar neighborhood. We also confirm that the open clusters in the outer disk are metal-poor with enhancements in the ratios [alpha/Fe] and perhaps [Eu/Fe]. All elements show negligible or small trends between [X/Fe] and distance (< 0.02 dex/kpc), but for some elements, there is a hint that the local (RGC < 13 kpc) and distant (RGC > 13 kpc) samples may have different trends with distance. There is no evidence for significant abundance trends versus age (< 0.04 dex/Gyr). We measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find that the scatter about the mean trend is comparable to the measurement uncertainties. Comparison with solar neighborhood field giants shows that the open clusters share similar abundance ratios [X/Fe] at a given metallicity. While the flattening of the metallicity gradient and enhanced [alpha/Fe] ratios in the outer disk suggest a different chemical enrichment history to the solar neighborhood, we echo the sentiments expressed by Friel et al. that definitive conclusions await homogeneous analyses of larger samples of stars in larger numbers of clusters. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.Comment: Accepted for publication in A

History of depression and survival after acute myocardial infarction

Objective: To compare survival in post-myocardial (MI) participants from the Enhancing Recovery In Coronary Heart Disease (ENRICHD) clinical trial with a first episode of major depression (MD) and those with recurrent MID, which is a risk factor for mortality after acute MI. Recent reports suggest that the level of risk may depend on whether the comorbid MD is a first or a recurrent episode. Methods: Survival was compared over a median of 29 months in 370 patients with an initial episode of MD, 550 with recurrent MD, and 408 who were free of depression. Results: After adjusting for an all-cause mortality risk score, initial Beck Depression Inventory score, and the use of selective serotonin reuptake inhibitor antidepressants, patients with a first episode of MD had poorer survival (18.4% all-cause mortality) than those with recurrent MD (11.8%) (hazard ratio (HR)=1.4; 95% Confidence Interval (CI)=1.0-2.0; p=.05). Both first depression (HR=3.1; 95% CI=1.6-6.1; p=.001) and recurrent MD (HR=2.2; 95% CI=1.1-4.4; p=.03) had significantly poorer survival than did the nondepressed patients (3.4%). A secondary analysis of deaths classified as probably due to a cardiovascular cause resulted in similar HRs, but the difference between depression groups was not significant. Conclusions: Both initial and recurrent episodes of MD predict shorter survival after acute MI, but initial MD episodes are more strongly predictive than recurrent episodes. Exploratory analyses suggest that this cannot be explained by more severe heart disease at index, poorer response to depression treatment, or a higher risk of cerebrovascular disease in patients with initial MD episodes

Elemental Abundance Ratios in Stars of the Outer Galactic Disk. I. Open Clusters

We summarize radial velocity studies of selected stars in the old, distant clusters Berkeley 20, Berkeley 21, NGC 2141, Berkeley 29, and Berkeley 31. Three members of M67 were observed similarly, and those velocities compare extremely well with prior measures. We measured the chemical compositions of all six clusters for [Fe/H] as well as abundances of alpha elements, iron-peak elements, and those synthesized in either the s-process or the r-process. For the outer disk, the abundance gradient for [Fe/H] deviates from the trend defined near the solar neighborhood. Rather than declining with increasing Galactocentric distance, [Fe/H] appears to reach a "basement" at [Fe/H]=-0.5 beyond R_GC = 10 to 12kpc. We find enhanced [O/Fe], [alpha/Fe], and [Eu/Fe] in the outer disk revealing a rapid star formation history. An intriguing, but tentative, conclusion is that the outer disk open cluster abundance ratios are consistent with the outer disk being formed via a merger event. The basement in [Fe/H] and enhanced [alpha/Fe] suggest that the outer disk formed from a reservoir of gas with a star formation history distinct from the solar neighborhood. The open clusters may have formed as a result of star formation triggered by a merger event in the outer disk. The ages of the outer disk open clusters would then be a measure of when the merger occurred. [Abridged]Comment: Accepted for publication in A

The Super Lithium-Rich Red Giant Rapid Rotator G0928+73.2600: A Case for Planet Accretion?

We present the discovery of a super lithium-rich K giant star, G0928+73.2600. This red giant (T_eff = 4885 K and log g = 2.65) is a fast rotator with a projected rotational velocity of 8.4 km/s and an unusually high lithium abundance of A(Li) = 3.30 dex. Although the lack of a measured parallax precludes knowing the exact evolutionary phase, an isochrone-derived estimate of its luminosity places the star on the Hertzsprung-Russell diagram in a location that is not consistent with either the red bump on the first ascent of the red giant branch or with the second ascent on the asymptotic giant branch, the two evolutionary stages where lithium-rich giant stars tend to cluster. Thus, even among the already unusual group of lithium-rich giant stars, G0928+73.2600 is peculiar. Using 12C/13C as a tracer for mixing---more mixing leads to lower 12C/13C---we find 12C/13C = 28, which is near the expected value for standard first dredge-up mixing. We can therefore conclude that "extra" deep mixing has not occurred. Regardless of the ambiguity of the evolutionary stage, the extremely large lithium abundance and the rotational velocity of this star are unusual, and we speculate that G0928+73.2600 has been enriched in both lithium and angular momentum from a sub-stellar companion.Comment: 5 pages, 4 figures, Accepted by ApJ Letter

Kinematic segregation of nearby disk stars from the Hipparcos database

To better understand our Galaxy, we investigate the pertinency of describing the sys tem of nearby disk stars in terms of a two-components Schwarzschild velocity distributio n.Using the proper motion and parallax information of Hipparcos database, we determine t he parameters characterizing the local stellar velocity field of a sample of 22000 disk stars. The sample we use is essentially the same as the one described by the criteria ad opted to study the LSR and the stream motion of the nearby stellar populationComment: 19 page

On the metallicity of the Milky Way thin disc and photometric abundance scales

The mean metallicity of the Milky Way thin disc in the solar neighbourhood is still a matter of debate, and has recently been subject to upward revision (Haywood, 2001). Our star sample was drawn from a set of solar neighbourhood dwarfs with photometric metallicities. In a recent study, Reid (2002) suggests that our metallicity calibration, based on Geneva photometry, is biased. We show here that the effect detected by Reid is not a consequence of our adopted metallicity scale, and we confirm that our findings are robust. On the contrary, the application to Stromgren photometry of the Schuster & Nissen metallicity scale is problematic. Systematic discrepancies of about 0.1 to 0.3 dex affect the photometric metallicity determination of metal rich stars, on the colour interval 0.22< b-y <0.59, i.e including F and G stars. For F stars, it is shown that this is a consequence of a mismatch between the standard sequence m_1(b-y) of the Hyades used by Schuster & Nissen to calibrate their metallicity scale, and the system of Olsen (1993, 1994ab). It means that although Schuster & Nissen calibration and Olsen photometry are intrinsically correct, there are mutually incompatible for metal rich, F-type stars. For G stars, the discrepancy is most probably the continuation of the same problem, albeit worthen by the lack of spectroscopic calibrating stars. A corrected calibration is proposed which renders the calibration of Schuster & Nissen applicable to the catalogues of Olsen. We also give a simpler calibration referenced to the Hyades sequence, valid over the same color and metallicity ranges.Comment: 11 pages, 11 figures, accepted in MNRA

A halo blue straggler on a highly eccentric retrograde orbit

Blue straggler, which are stars that appear to be younger than they should be, are an important population of unusual stars in both stellar clusters and the halo field of the Galaxy. Most formation scenarios evoke either stellar collisions or binary stars that transfer mass or merge. We investigate high-velocity stars in the Galactic halo and perform a spectral and kinematical analysis to shed light on their nature and origin. Here we report that SDSSJ130005.62+042201.6 (J1300+0422 for short) is an A-type star of unusually large radial velocity (504.6 $\pm$ 5 \kms). From a quantitative NLTE (and LTE) spectral analysis of medium-resolution optical spectra, the elemental composition is derived. Proper motion measurements combined with a spectroscopic distance estimate allow us to determine its present space velocity. Its kinematical properties are derived by integrating the equation of motion in the Galactic potential. We find J1300+0422 to be metal poor ([M/H]=$-1.2$) and exhibit an $\alpha$-element enrichment ($0.3-0.4$~dex) that is characteristic of the halo population, as confirmed by a kinematical analysis of its 3D space motions, which places it on a highly eccentric retrograde Galactic orbit. The mass of J1300+0422 (1.15 $\pm$ 0.10 M$_\odot$) is higher than the globular cluster turn-off masses indicating that it is a halo blue straggler star. At a Galactic rest-frame velocity of $\approx$467~\kms, the star travels faster than any known blue straggler but is still bound to the Galaxy.Comment: 6 pages, 7 figures, accepted for publication in A&

Rotational velocities of the giants in symbiotic stars: III. Evidence of fast rotation in S-type symbiotics

We have measured the projected rotational velocities (vsini) in a number of symbiotic stars and M giants using high resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass-donors in symbiotics with vsini of field giants and find that: (1) the K giants in S-type symbiotics rotate at vsini>4.5 km/s, which is 2-4 times faster than the field K giants; (2) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant: p-value < 0.001 in the spectral type bins K2III-K5III, M0III-M6III, and M2III-M5III; (3) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3-30 times larger mass loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors.Comment: MNRAS (accepted), 7 pages, 5 figure