Search

The updated H-band spectral line list (from \lambda 15,000 - 17,000\AA) adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) for the SDSS IV Data Release 16 (DR16) is presented here. The APOGEE line list is a combination of atomic and molecular lines with data from laboratory, theoretical, and astrophysical sources. Oscillator strengths and damping constants are adjusted using high signal-to-noise, high-resolution spectra of the Sun and alpha Boo (Arcturus) as "standard stars". Updates to the DR16 line list, when compared to the previous DR14 version, are the inclusion of molecular H_2O and FeH lines, as well as a much larger (by a factor of ~4) atomic line list, which includes significantly more transitions with hyperfine splitting. More recent references and line lists for the crucial molecules CO and OH were used, as well as for C_2 and SiH. In contrast to DR14, DR16 contains measurable lines from the heavy neutron-capture elements cerium (as Ce II), neodymium (as Nd II), and ytterbium (as Yb II), as well as one line from rubidium (as Rb I), that may be detectable in a small fraction of APOGEE red giants., Comment: 29 pages, 11 figures, accepted by AJ

Motivated by the desire to measure beryllium abundances in red giant stars, we have constructed a new line list for synthesizing spectra in the near-ultraviolet. Using the Sun, Arcturus, and Pollux as benchmark stars, we explore potential sources of missing continuous opacity and line absorption. Despite the inclusion of new sources of continuous opacity, fitting the ultraviolet OH lines in the solar spectrum still requires artificially inflating the continuous opacity. The red giants also require the addition of a line of unknown origin in the blue wing of the Be line at λ3131.065 A, and we find a good match can be made by adopting a Ti ii line with low excitation potential. The inclusion of this line does not affect the measurement of the solar Be abundance. Because the fits to all of the benchmark stars require tuning the properties of known spectral lines and including both an unknown source of additional continuous opacity and spectral lines of unknown origin, we argue that the absolute abundances of Be in stars should be interpreted with caution. Therefore, the question of whether the solar Be abundance is depleted may not yet be resolved, although our model favors minimal Be depletion in the Sun.

We present an analysis of high-dispersion echelle spectra of seven giant stars in the ~1-2?Gyr old open clusters NGC 1817, NGC 1883, NGC 2141, and NGC 2158. Abundances were determined relative to the bright, mildly metal-poor disk giant Arcturus. NGC 1817, NGC 1883, NGC 2141, and NGC 2158 are found to have a mean [Fe/H] = ?0.07 ? 0.04, ?0.01 ? 0.01, +0.00 ? 0.16, and ?0.03 ? 0.14 (s.d.), respectively. All four clusters show modest (~0.1 dex) enhancements of Na and Si, and scaled solar abundances of Al and Mg, while [O/Fe] ~ ?0.15 dex. [Ca/Fe] and [Ti/Fe] values are slightly subsolar in all four clusters, but this may be due to a systematic effect. Given that all four of these clusters are located at R gc > 10?kpc in the disk, and barring any systematic effects, our results imply that any abrupt transition in abundance in the Galactic disk occurs beyond R gc ~ 13?kpc.

We investigate the ability of both LTE and Non-LTE models to fit the near UV band absolute flux distribution and individual spectral line profiles of three standard stars for which high quality spectrophotometry and high resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We investigate 1) the effect of the choice of atomic line list on the ability of NLTE models to fit the near UV band flux level, 2) the amount of a hypothesized continuous thermal absorption extinction source required to allow NLTE models to fit the observations, and 3) the semi-empirical temperature structure required to fit the observations with NLTE models and standard continuous near UV extinction. We find that all models that are computed with high quality atomic line lists predict too much flux in the near UV band for Arcturus, but fit the warmer stars well. The variance among independent measurements of the solar irradiance in the near UV is sufficiently large that we cannot definitely conclude that models predict too much near UV flux, in contrast to other recent results. We surmise that the inadequacy of current atmospheric models of K giants in the near UV band is best addressed by hypothesizing that there is still missing continuous thermal extinction, and that the missing near UV extinction becomes more important with decreasing effective temperature for spectral classes later than early G, suggesting a molecular origin.

We searched for and detected stellar streams or moving groups in the solar neighbourhood, using the data provided by the 1st RAVE public data release. This analysis is based on distances to RAVE stars estimated from a color-magnitude relation that was calibrated on Hipparcos stars. Our final sample consists of 7015 stars selected to be within 500 pc of the Sun and to have distance errors better than 25%. Together with radial velocities from RAVE and proper motions from various data bases, there are estimates for all 6 phase-space coordinates of the stars in the sample. We characterize the orbits of these stars through suitable proxies for their angular momentum and eccentricity, and compare the observed distribution to the expectations from a smooth distribution. On this basis we identify at least four "phase space overdensities" of stars on very similar orbits in the Solar neighbourhood. We estimate the statistical significance of these overdensities by Monte Carlo simulations. Three of them have been identified previously: the Sirius and Hercules moving group and a stream found independently in 2006 by Arifyanto and Fuchs and Helmi et al. In addition, we have found a new stream candidate on a quite radial orbit, suggesting an origin external to the Milky Way's disk. Also, there is evidence for the Arcturus stream and the Hyades-Pleiades moving group in the sample. This analysis, using only a minute fraction of the final RAVE data set, shows the power of this experiment to probe the phase-space substructure of stars around the Sun.

The results of astrometric studies in the regions of Groombridge 34A, the Hyades, Aldebaran, Ross 47, BD+5° 1668, 81 Cancri, BD+15° 2620, Arcturus, Vega, and Ross 248 are presented. Estimates of the absolute parallax of each star are presented and a mass estimate is present for 81 Cancri. Comments include the discussion of the apparent motions of a few previously suggested planetary systems.

We evaluate observed spectroscopic activity of Arcturus (HR 5340, K2 III) from 1984 to 2007 using high-resolution spectroscopy and Ca II H+K emission. Line-depth ratios of the V I λ6251.83 A to Fe I λ6252.56 A lines and line bisectors from Fe I λ6252.56 A are used to evaluate spectroscopic activity. Chromospheric emission within H+K lines is used as a magnetic activity indicator. We observe a significant portion of what appears to be a magnetic cycle with a period of ≥14 yr. Line-depth ratios show comparable variation, but with a time lag of -->2.0 ± 0.5 yr with respect to H+K variations. This time lag is qualitatively similar to previous observations of G and K dwarfs. No corresponding variation is observed in line bisectors. H+K and line bisectors also show variability within seasons. A Fourier analysis reveals periods of 253 and 207 days during the 1984-1989 H+K seasons. Line bisectors show excess power over the range of 115-200 days from 1992 to 2007. We attribute this intraseason variability to inferred magnetic activity along active longitudes. The range of periods observed in H+K and line bisectors (115-253 days) may result from migration of active regions within longitude bands, implying differential rotation. We compare these observations with the Sun and other solar-type stars. A 1/f noise component to the Fourier spectrum of the line bisector variations is also observed.

We present an analysis of high-dispersion echelle spectra of four giant stars in the 4 Gyr open cluster NGC 7142 obtained with the KPNO 4 m telescope. Abundances were determined relative to the bright, mildly metal-poor giant Arcturus. NGC 7142 is found to have a mean [Fe/H] = +0.14 ± 0.01 (standard deviation) relative to the Sun, with an estimated uncertainty of 0.12 dex per star. Oxygen abundances, determined from the forbidden [O I] λ6300 A feature, are slightly sub-solar, while the α-elements are slightly enhanced to ~0.1 dex above solar. Na and Al are enhanced ~0.2 dex relative to scaled solar abundances. These abundance patterns are similar to those reported for other open clusters in the literature, and suggest that the Galactic disk underwent rapid chemical enrichment in early phases of its evolution. Finally, comparison of these results to those found from lower-dispersion WIYN 3.5 m HYDRA spectra of the cluster stars shows them to be comparable within the errors, verifying that detailed abundance analyses of HYDRA spectra are reliable and can be directly compared to analyses of higher-dispersion data.

We present chemical abundances for O, Na, Mg, Al, Si, Ca, Ti and Fe in eight red giants and one turnoff star in the metal rich globular cluster 47 Tuc, based on spectroscopy with the MIKE high resolution spectrograph on the Magellan 6.5-m Clay telescope. A robust line by line differential abundance analysis technique, relative to the K-giant Arcturus, was used to reduce systematic errors from atmospheric and atomic parameters. Our derived mean LTE [Fe/H] of -0.76 +- 0.01 +- 0.04 dex (random and systematic error, respectively) is more metal poor by about 0.1 dex than recent literature results. The chemical element ratios in this nearby globular cluster most closely resemble those of the Galactic bulge, although there is a non-negligible overlap with the composition of thick-disk stars. We find that the [Al/Fe] and [Na/Fe] ratios coincide with the upper boundary of the trends seen in the bulge and thick disk. There is only a small intrinsic scatter in the majority of the abundance ratios, indicating that 47 Tuc is mostly a rather chemically homogeneous system., Comment: Now with correct Figure 6; no other changes; 22 pages, 8 figures, accepted for publication in the AJ

The Chandra X-Ray Observatory has detected coronal (T 106 K) emission from the red giant γ Draconis (HD 164058: K5 III; d = 45 pc), now fully resolved from a stronger source 21'' to the SE that had confused earlier measurements by Rontgensatellit (ROSAT). The second source is coincident with the 13th magnitude visual component ADS 10923B (γ Dra B), possibly a dM star in a wide orbit around the red giant. The 0.2-2 keV luminosity of γ Dra is LX ~ 1.2 × 1027 ergs s-1 (1 σ confidence interval), assuming log(Tcor) 6.5 K, while that of the faint optical companion is 3.2 × 1027 ergs s-1, assuming the same distance. Both sources have an intermediate spectral hardness within the range displayed by coronal stars. γ Dra has LX/Lbol an order of magnitude brighter than the other red giants previously imaged by Chandra, Arcturus (α Boo: K1.5 III) and Aldebaran (α Tau: K5 III), despite having an only 2 × elevated LC iv/Lbol (T ~ 105 K).

We present an analysis of high-dispersion echelle spectra of three giant stars in the 10 Gyr open cluster Berkeley 17 obtained with the KPNO 4 m Telescope. Abundances were determined relative to the bright, somewhat metal-poor disk giant Arcturus. Be 17 is found to have a mean [Fe/H] = -0.10 ± 0.09 (rms). Oxygen abundances, determined from the forbidden [O I] lines, and the α-elements Mg, Ca, and Ti show scaled solar abundance ratios, while the Si abundance is slightly enhanced. The odd-Z elements Na and Al are significantly enhanced relative to scaled solar abundances. These abundance patterns are similar to those seen in other old open clusters and suggest that the Galactic disk was enriched to solar abundance levels at very early times.

The late-type giants and supergiants of the "hybrid chromosphere" class display signatures of cool (T 2 × 104 K) winds together with hot emission lines from species like C IV (T ~ 105 K). A survey of such stars by Reimers et al. using ROSAT reported numerous X-ray detections (T ~ 106 K), strengthening the (then heretical) idea that hot coronae and cool winds can coexist in luminous giants. However, several of the candidate sources were offset from the predicted stellar coordinates, calling into question the identifications. In an effort to secure better knowledge of the X-ray luminosities of the hybrids, the ROSAT fields from the Reimers et al. survey were reexamined, exploiting the USNO-A2.0 astrometric catalog to register the pointings to a few arcseconds accuracy. On the basis of positional mismatches, at least two of the previously reported detections of key hybrid stars—γ Dra (K5 III) and β Aqr (G0 Ib)—must be rejected. The new X-ray upper limits for these stars, combined with the remaining candidate detections (and nondetections) from the original survey, place the hybrids into the same "X-ray deficient" category as the "noncoronal" red giants like Arcturus (α Boo: K1.5 III) and Aldebaran (α Tau: K5 III). A few of the hybrid X-ray sources are exceptional, however. The archetype α TrA (K2 II-III), in particular, is securely detected in terms of positional coincidence, but its anomalous, contradictory coronal properties suggest that an unseen companion—a young hyperactive G dwarf—might dominate the X-ray emission.

We have used the High Resolution Camera (HRC-I) of the Chandra X-Ray Observatory to search for coronal (T � 10 6 K) emission from the archetype ‘‘ noncoronal ’’ red giants Arcturus (� Bootis=HD 124897, K1 III) and Aldebaran (� Tauri=HD 29139, K5 III). Our program follows up previous detections of ultraviolet coronal proxies such as C iv � 1548 (T � 1 � 10 5 K) and O vi � 1031 (T � 3 � 10 5 K). The deep (� 19 ks) HRC-I pointings obtained a tentative 3 � detection of Arcturus, with fXð0:2 2 keV Þ¼ 1:0 þ1:8 � 0:8 � 10 � 15 ergs cm � 2 s � 1 (95% confidence limits [CLs]), but failed to record Aldebaran, with an upper limit of d1:5 � 10 � 15 ergs cm � 2 s � 1 (also at 95% CL). The corresponding LX=Lbol ratios are a factor of ten thousand less than the Sun, a low-activity coronal dwarf. At the same time, Hubble Space Telescope Imaging Spectrograph far-ultraviolet spectra suggest the presence of a ‘‘ cool absorber,’’ probably near the base of the red giant chromosphere, imprinting discrete low-excitation absorptions on top of highly ionized features such as Si iv � 1393. The hot emission zones thus are at least partially buried under a large column of chromospheric material, which would severely attenuate any soft X-rays that might be emitted. The submerged hot structures presumably are magnetic because of their high temperatures and broad C iv profiles (FWHM � 130 km s � 1 ). Perhaps these structures are analogous to small-scale ephemeral bipolar regions seen ubiquitously on the Sun throughout the sunspot cycle and thought to be of direct convective origin. If small-scale magnetic fields indeed are present in the lower atmospheres of red giants such as Arcturus and Aldebaran, they might play a role in initiating the cool winds of such stars, perhaps through a mechanism similar to solar spicules. Subject headings: stars: coronae — stars: individual (Aldebaran, Arcturus) — ultraviolet: stars — X-rays: stars

We present an analysis of high-dispersion echelle spectra of four giant stars in the 8 Gyr open cluster Cr 261 obtained with the Cerro Tololo Inter-American Observatory's 4 m telescope. Abundances were determined relative to the bright, slightly metal-poor disk giant Arcturus. Cr 261 is found to have a mean [Fe/H] = -0.22 ± 0.05 (mean error). Oxygen abundances, determined from the forbidden [O I] lines, show roughly solar or slightly depleted abundance ratios. The α-elements Mg, Ca, and Ti also show scaled solar abundance ratios, with suggestions that the Si abundance is slightly enhanced. The odd-Z elements Na and Al are significantly enhanced relative to scaled solar abundances. The abundance results for Cr 261 are compared with those from high-dispersion studies of other old open clusters in the literature, which, overall, show similar behavior in all these elements. None of the abundance ratios show significant trends with overall cluster [Fe/H] or with cluster age.

We present plane-parallel and spherical LTE and NLTE atmospheric models of a variety of stellar parameters of the red giant star Arcturus (alpha Boo, HD124897, HR5340) and study their ability to fit the measured absolute flux distribution. Our NLTE models include tens of thousands of the strongest lines in NLTE, and we investigate separately the effects of treating the light metals and the Fe group elements Fe and Ti in NLTE. We find that the NLTE effects of Fe group elements on the model structure and flux distribution are much more important than the NLTE effects of all the light metals combined, and serve to substantially increases the violet and near UV flux level as a result of NLTE Fe over-ionization. Both the LTE and NLTE models predict significantly more flux in the blue and UV bands than is observed. We find that within the moderately metal-poor metallicity range, the effect of NLTE on the overall UV flux level decreases with decreasing metallicity. These results suggest that there may still be important UV opacity missing from the models. We find that models of solar metallicity giants of similar spectral type to Arcturus fit well the observed flux distributions of those stars from the red to the near UV band. This suggests that the blue and near UV flux discrepancy is metallicity dependent, increasing with decreasing metallicity.

We report detections of pure rotation lines of OH and H2O in the K1.5 III red-giant star Arcturus (alpha Bootis) using high-resolution, infrared spectra covering the regions 806-822 cm-1 (12.2-12.4 um) and 884-923 cm-1 (10.8-11.3 um). Arcturus is the hottest star yet to show water-vapor features in its disk-averaged spectrum. We argue that the water vapor lines originate from the photosphere, albeit in the outer layers. We are able to predict the observed strengths of OH and H2O lines satisfactorily after lowering the temperature structure of the very outer parts of the photosphere (log tau_500=-3.8 and beyond) compared to a flux-constant, hydrostatic, standard MARCS model photosphere. Our new model is consistently calculated including chemical equilibrium and radiative transfer from the given temperature structure. Possible reasons for a temperature decrease in the outer-most parts of the photosphere and the assumed break-down of the assumptions made in classical model-atmosphere codes are discussed., To appear in ApJ. See also http://www.astro.uu.se/~ryde/ART/

We measured phosphorus abundances in 22 FGK dwarfs and giants that span --0.55 $, Comment: 11 pages, 5 figures, Accepted to ApJ

We construct an empirical energy distribution for Arcturus from published scans, integrate it to obtain the total flux, and combine the latter with precise interferometric measurements of the limb-darkened angular diameter to derive the effective temperature. We conclude that the best value that can be derived within the framework of the associated assumptions is Teff = 4290 ± 30 K. We then select a grid of model-atmosphere energy distributions by Kurucz and extract Teff/log g/[Fe/H] by a least-squares fit to the adopted energy distribution. With the value of Teff already constrained, we could investigate values for the surface gravity and metallicity of Arcturus; our results are log g = 1.9, [Fe/H] = -0.68, and R = 23 R⊙. However, we discuss evidence that relevant grids of models may not contain sufficient opacity.

With a luminosity zero point fixed by the kinematics of old disk superclusters (HR 1614, t = 6 Gyr, [Fe/H] = +0.1 dex) and groups (Arcturus, t = 14 Gyr, [Fe/H] = -0.65 dex), the luminosities and colors of evolved old disk stars, especially red horizontal branch (RHB), early asymptotic branch [AGB(1)], thermally pulsing asymptotic giant branch [AGB(2)], and sdOB stars in old disk clusters (NGC 6791, 47 Tuc, M71, M67, Mel 66, NGC 2420, NGC 2204, and NGC 2443) are discussed. (1) The RHB stars in the old disk all have MV = +0.7 ± 0.1 (MK = -1.3 ± 0.1) mag. (2) Large-amplitude red variables (LARVs) with quasi-stable periods and light curves are old disk stars on AGB(2). (3) AGB(1) objects include CH stars and semiregular (SRa) variables. (4) The populous and overabundant cluster NGC 6791 may be the only disk cluster with sdOB stars, populating the lower portion of the bifurcated extended horizontal branch that is usual in most blue tailed and high-density halo clusters. (5) Post–red giant branch (RGB) stars in old disk clusters show a B - V (b - y) defect when compared with RGB stars, possibly because of a change in the character of the atmospheres. (6) If the bulk of the LARVs are pulsating in the fundamental mode, R Vir (P = 145 days) is possibly a first-overtone pulsator. (7) The overabundant old disk clusters are within the solar circle, with Liller 1 being at the Galactic center. (8) Several probable RHB stars at the south Galactic pole are identified. (9) The period-age relation, combined with the known spatial distribution of Galactic LARVs, leads to a relation between age and scale height of distribution that monotonically increases with age, leaving no obvious reason for a bifurcation of the population.

Several samples of nearby stars with the most accurate astrometric and photometric parameters are searched for clues to their evolutionary history. The main samples are (1) the main-sequence stars with b - y between 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) a group of high-velocity subgiants studied spectroscopically by Ryan & Lambert, and (3) high-velocity main-sequence stars in the extensive investigation by Norris, Bessel, & Pickles. The major conclusions are as follows: (1) The oldest stars (halo), t ≥ 10–12 Gyr, have V-velocities (in the direction of Galactic rotation and referred to the Sun) in the range from about -50 to -800 km s-1 and have a heavy-element abundance [Fe/H] of less than about -0.8 dex. The age range of these objects depends on our knowledge of globular cluster ages, but if age is correlated with V-velocity, the youngest may be M22 and M28 (V ~ -50 km s-1) and the oldest NGC 3201 (V ~ -500 km s-1) and assorted field stars. (2) The old disk population covers the large age range from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturus group, 47 Tuc), but the lag (V) velocity is restricted to less than about 120 km s-1 and [Fe/H] ≥ -0.8 or -0.9 dex. The [Fe/H] ~ -0.8 dex division between halo and old disk, near t ~ 10–12 Gyr, is marked by a change in the character of the CN index (Cm) and of the blanketing parameter K of the DDO photometry. (3) The young disk population, t < 2 Gyr, is confined exclusively to a well-defined area of the (U, V) velocity plane. The age separating young and old disk stars is also that separating giant evolution of the Hyades (near main-sequence luminosity) and M67 (degenerate helium cores and a large luminosity rise) kinds. The two disk populations are also separated by such indexes as the g-index of Geveva photometry. There appears to be no obvious need to invoke exogeneous influences to understand the motion and heavy-element abundance distributions of the best-observed stars near the Sun. Individual stars of special interest include the parallax star HD 55575, which may be an equal-component binary, and the high-velocity star HD 220127, with a well-determined space velocity near 1000 km s-1.

The three Mn I lines at 17325, 17339 and 17349 \AA~are among the 25 strongest lines ($\log(gf)>0.5$) in the H-band. They are all heavily broadened due to hyperfine structure and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infra-red (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines can not be described in the conventional way by the diagonal $A$ and $B$ hyperfine interaction constants. The off-diagonal hyperfine interaction not only has large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and $gf$-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, agreement between our synthetic and experimental spectra was achieved. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modelled in the relevant region, $1.73-1.74$ $\mu$m using our theoretically predicted $gf$-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and $gf$-values for all the $3d^54s({^7S})4d$ e$^{6}$D $-$ $3d^54s({^7S})4f$ w$^{6}$F hyperfine lines are available as supplementary material online, whereas only the stronger lines are presented and discussed in detail in this paper., Comment: 24 pages, 6 figures, 3 tables (more data tables will be available online when published in Astrophysical Journal Supplement Series)

We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (~ -0.1 dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements - Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H] = 0.03 +/- 0.07 dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11 +/- 0.05 dex). We also find the neutron-capture element barium to be highly enhanced - [Ba/Fe] = +0.48 +/- 0.08 - and disparate from cluster measurements of neutron-capture elements La and Zr (-0.08 +/- 0.05 and 0.08 +/- 0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments., 15 pages, 9 figures, Table 1 typo fixed

New red and violet system line lists for the CN isotopologues {sup 13}C{sup 14}N and {sup 12}C{sup 15}N have been generated. These new transition data are combined with those previously derived for {sup 12}C{sup 14}N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.

We implement a least-squares deconvolution (LSD) code to study magnetic fields on cool stars. We first apply our code to high-resolution optical echelle spectra of 53 Cam (a magnetic Ap star) and three well-studied cool stars (Arcturus, 61 Cyg A, and ? Boo A) as well as the Sun (by observing the asteroid Vesta) as tests of the code and the instrumentation. Our analysis is based on several hundred photospheric lines spanning the wavelength range 5000?? to 9000??. We then apply our LSD code to six nights of data on the Classical T Tauri Star BP Tau. A maximum longitudinal field of 370 ? 80 G is detected from the photospheric lines on BP Tau. A 1.8?kG dipole tilted at 129? with respect to the rotation axis and a 1.4?kG octupole tilted at 104? with respect to the rotation axis, both with a filling factor of 0.25, best fit our LSD Stokes V profiles. Measurements of several emission lines (He I?5876??, Ca II 8498??, and 8542??) show the presence of strong magnetic fields in the line formation regions of these lines, which are believed to be the base of the accretion footpoints. The field strength measured from these lines shows night-to-night variability consistent with rotation of the star.

Multi-wavelength centimeter continuum observations of non-dusty, non-pulsating K spectral-type red giants directly sample their chromospheres and wind acceleration zones. Such stars are feeble emitters at these wavelengths however, and previous observations have provided only a small number of modest S/N measurements slowly accumulated over three decades. We present multi-wavelength Karl G. Jansky Very Large Array thermal continuum observations of the wind acceleration zones of two dust-free red giants, Arcturus (Alpha Boo: K2 III) and Aldebaran (Alpha Tau: K5 III). Importantly, most of our observations of each star were carried out over just a few days, so that we obtained a snapshot of the different stellar atmospheric layers sampled at different wavelengths, independent of any long-term variability. We report the first detections at several wavelengths for each star including a detection at 10 cm (3.0 GHz: S band) for both stars and a 20 cm (1.5 GHz: L band) detection for Alpha Boo. This is the first time single luminosity class III red giants have been detected at these continuum wavelengths. Our long-wavelength data sample the outer layers of Alpha Boo's atmosphere where its wind velocity is approaching its terminal value and the ionization balance is becoming frozen-in. For Alpha Tau, however, our long-wavelength data are still sampling its inner atmosphere, where the wind is still accelerating probably due to its lower mass-loss rate. We compare our data with published semi-empirical models based on ultraviolet data, and the marked deviations highlight the need for new atmospheric models to be developed. Spectral indices are used to discuss the possible properties of the stellar atmospheres, and we find evidence for a rapidly cooling wind in the case of Alpha Boo. Finally, we develop a simple analytical wind model for Alpha Boo based on our new long-wavelength flux measurements.

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent Non-Local Thermodynamic Equilibrium (NLTE), and compare them to the LTE grid of Short & Hauschildt (2010) (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(tau) relation) and the SED as a finely sampled function of Teff, log g, and [A/H] among solar metallicity and mildly metal poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best fit Teff values that are ~30 to 90 K lower than those provided by LTE models, while providing greater consistency between \log g values, and, for Arcturus, Teff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best fit Teff values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant.

The value of the mode lifetime given in the first paragraph of the Discussion should be divided by 2pi and is therefore 2.0 days rather than 13 days.

Using opacity distribution functions based on a newly expanded atomic and molecular line list, we have calculated a model atmosphere for Arcturus that reproduces the observed flux distribution. Individual line parameters in the list were adjusted to match the solar spectrum in a preliminary way, in the regions 5000-5500 A, 6000-6500 A, and 7500-9000 A. The Arcturus model spectrum calculated with these adjustments reproduces well the profiles of all lines in the observed spectrum of the Griffin atlas for which the solar gf-values are well determined. The Arcturus model has an iron abundance [Fe/H]=−0.5±0.1, a temperature T eff =4300±30 K, gravity log g=1.5±0.15, and an overabundance of the light metals

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

A two-week time series of precise radial velocity measurements of Alpha Bootis (Arcturus) covering 7-8 hr per night is reported. The radial barycentric velocity of the star is found to be -5021 + or - 5 m/s. When data from the whole run are jointly analyzed, several equispaced peaks in the frequency appear in the range of a few microhertz, the highest amplitude being some 60 m/s at 4.3 microhertz. The most probable frequency spacing seems to be 50 microhertz, while the frequency cutoff is around 80 microhertz. 31 refs.

Theoretical models for chromospheric structures of late-type giant stars are computed, including the time-dependent propagation of acoustic waves. Models with short-period monochromatic shock waves as well as a spectrum of acoustic waves are discussed, and the method is applied to the stars Arcturus, Aldebaran, and Betelgeuse. Chromospheric extent, defined as the monotonic decrease with height of the time-averaged electron densities, are found to be 1.12, 1.13, and 1.22 stellar radii for the three stars, respectively; this corresponds to a time-averaged electron density of 10 to the 7th/cu cm. Predictions of the extended chromospheric obtained using a simple scaling law agree well with those obtained by the time-dependent wave models; thus, the chromospheres of all stars for which the scaling law is valid consist of the same number of pressure scale heights.