Browsing by Subject "spectroscopic analysis"
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Item The Chemical Abundances Of Stars In The Halo (CASH) Project. II. A Sample Of 14 Extremely Metal-Poor Stars(2011-11) Hollek, Julie K.; Frebel, Anna; Roederer, Ian U.; Sneden, Christopher; Shetrone, Matthew; Beers, Timothy C.; Kang, Sung-Ju; Thom, Christopher; Hollek, Julie K.; Sneden, Christopher; Shetrone, MatthewWe present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R similar to 15,000) and corresponding high-resolution (R similar to 35,000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< -3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] less than or similar to -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire similar to 500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.Item A Giant Planet In The Triple System HD 132563(2011-09) Desidera, S.; Carolo, E.; Gratton, R.; Fiorenzano, A. F. Martinez; Endl, M.; Mesa, D.; Barbieri, M.; Bonavita, M.; Cecconi, M.; Claudi, R. U.; Cosentino, R.; Marzari, F.; Scuderi, S.; Endl, M.As part of our radial velocity planet-search survey performed with SARG at TNG, we monitored the components of HD 132563 for ten years. It is a binary system formed by two rather similar solar type stars with a projected separation of 4.1 arcsec, which corresponds to 400 AU at the distance of 96 pc. The two components are moderately metal-poor ([Fe/H] = -0.19), and the age of the system is about 5 Gyr. We detected RV variations of HD 132563B with period of 1544 days and semi-amplitude of 26 m/s. From the star characteristics and line profile measurements, we infer their Keplerian origin. Therefore HD 132563B turns out to host a planet with a projected mass m sin i = 1.49 M-J at 2.6 AU with a moderately eccentric orbit (e = 0.22). The planet around HD 132563B is one of the few that are known in triple stellar systems, as we found that the primary HD 132563A is itself a spectroscopic binary with a period longer than 15 years and an eccentricity higher than 0.65. The spectroscopic component was not detected in adaptive-optics images taken with the instrument AdOpt mounted at the TNG, since it expected at a projected separation that was smaller than 0.2 arcsec at the time of our observations. A small excess in K band difference between the components with respect to the difference in V band is compatible with a companion of about 0.55 M-circle dot. A preliminary statistical analysis of when planets occur in triple systems indicate a similar frequency of planets around the isolated component in a triple system, components of wide binaries and single stars. There is no significant iron abundance difference between the components. The lack of stars in binary systems and open clusters showing strong enhancements of iron abundance, which are comparable to the typical metallicity difference between stars with and without giant planets, agrees with the idea that accretion of planetary material producing iron abundance anomalies over 0.1 dex is rare.Item A Gravitational Redshift Determination Of The Mean Mass Of White Dwarfs: DBA And DB Stars(2012-10) Falcon, Ross E.; Winget, D. E.; Montgomery, Michael H.; Williams, Kurtis A.; Falcon, Ross E.; Winget, D. E.; Montgomery, Michael H.We measure apparent velocities (nu(app)) of absorption lines for 36 white dwarfs (WDs) with helium-dominated atmospheres-16 dbAs and 20 dbs-using optical spectra taken for the European Southern Observatory SN Ia progenitor survey. We find a difference of 6.9 +/- 6.9 kms(-1) in the average apparent velocity of the H alpha lines versus that of the He I 5876 angstrom lines for our dbAs. This is a measure of the blueshift of this He line due to pressure effects. By using this as a correction, we extend the gravitational redshift method employed by Falcon et al. to use the apparent velocity of the He I 5876 angstrom line and conduct the first gravitational redshift investigation of a group of WDs without visible hydrogen lines. We use biweight estimators to find an average apparent velocity, (BI), (and hence average gravitational redshift, (BI)) for our WDs; from that we derive an average mass, < M >(BI). For the dbAs, we find (BI) = 40.8 +/- 4.7 kms(-1) and derive < M >(BI) = 0.71(-0.05)(+0.04) M-circle dot. Though different from of DAs (32.57 km s(-1)) at the 91% confidence level and suggestive of a larger dbA mean mass than that for normal DAs derived using the same method (0.647(-0.014)(+0.013) M-circle dot; Falcon et al.), we do not claim this as a stringent detection. Rather, we emphasize that the difference between (BI) of the dbAs and of normal DAs is no larger than 9.2 kms(-1), at the 95% confidence level; this corresponds to roughly 0.10 M-circle dot. For the dbs, we find (BI) = 42.9 +/- 8.49 km s(-1) after applying the blueshift correction and determine < M >(BI) = 0.74(-0.09)(+0.08) M-circle dot. The difference between (BI) of the dbs and of DAs is <= 11.5 kms(-1) (similar to 0.12 M-circle dot), at the 95% confidence level. The gravitational redshift method indicates much larger mean masses than the spectroscopic determinations of the same sample by Voss et al. Given the small sample sizes, it is possible that systematic uncertainties are skewing our results due to the potential of kinematic substructures that may not average out. We estimate this to be unlikely, but a larger sample size is necessary to rule out these systematics.Item The Hobby-Eberly Telescope Chemical Abundances Of Stars In The Halo (CASH) Project. I. The Lithium-, s-, And r-Enhanced Metal-Poor Giant HKII 17435-00532(2008-06) Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Prieto, Carlos Allende; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Sneden, Christopher; Beers, Timothy C.; Cowan, John J.; Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Prieto, Carlos Allende; Sneden, ChristopherWe present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo ( CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R similar to 15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor (Fe/H = -2.2) star has an unusually high lithium abundance [log epsilon(Li) +2.1], mild carbon (C/Fe = +0.7) and sodium (]Na/Fe] = +0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = +0.8) and r-process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current nondetection of radial velocity variations (over similar to 180 days), it is possible that HKII 17435 - 00532 is in a long-period or highly inclined binary system, similar to other stars with similar n-capture enrichment patterns.Item Improved Ni I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937(2014-04) Wood, M. P.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sneden, ChristopherAtomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.Item Improved Ti II Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937(2013-10) Wood, M. P.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sneden, ChristopherAtomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.Item Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937(2014-12) Lawler, James E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, Christopher; Cowan, John J.; Sneden, ChristopherNew emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log epsilon(V) = 3.956 +/- 0.004 (sigma = 0.037) based on 93 V I lines and log epsilon(V) = 1.89 +/- 0.03 (sigma = 0.07) based on nine Vi lines, respectively, using the Holweger-Muller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.Item Improved V II Log(gf) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937(2014-10) Wood, M. P.; Lawler, James E.; Den Hartog, E. A.; Sneden, Christopher; Cowan, John J.; Sneden, ChristopherNew experimental absolute atomic transition probabilities are reported for 203 lines of VII. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported VII transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new VII data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log epsilon(V) = 3.95 from 15 VII lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H]= -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.Item Laboratory Measurements Of White Dwarf Photospheric Spectral Lines: H Beta(2015-06) Falcon, Ross E.; Rochau, G. A.; Bailey, J. E.; Gomez, Thomas A.; Montgomery, Michael H.; Winget, D. E.; Nagayama, T.; Falcon, Ross E.; Gomez, Thomas A.; Montgomery, Michael H.; Winget, D. E.We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. Here we present time-resolved measurements of H beta and fit this line using different theoretical line profiles to diagnose electron density, n(e), and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from n(e) similar to 4 to similar to 30 x 10(16) cm(-3) throughout a 120-ns evolution of our plasma. Also, we observe n(2) to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within similar to 55 ns to become consistent with LTE. This supports our electrontemperature determination of T-e similar to 1.3 eV (similar to 15,000 K) after this time. At n(e) greater than or similar to 10(17) cm(-3), we find that computer-simulation-based line-profile calculations provide better fits (lower reduced chi(2)) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.Item Rapid Orbital Decay in the 12.75-Minute Binary White Dwarf J0651+2844(2012-10) Hermes, J. J.; Kilic, Mukremin; Brown, Warren R.; Winget, D. E.; Prieto, Carlos Allende; Gianninas, A.; Mukadam, Anjum S.; Cabrera-Lavers, Antonio; Kenyon, Scott J.; Hermes, J. J.; Winget, D. E.We report the detection of orbital decay in the 12.75-minute, detached binary white dwarf (WD) SDSS J065133.338+284423.37 (hereafter J0651). Our photometric observations over a 13 month baseline constrain the orbital period to 765.206543(55) s and indicate that the orbit is decreasing at a rate of (-9.8 +/- 2.8) x 10(-12) s s(-1) (or -0.31 +/- 0.09 ms yr(-1)). We revise the system parameters based on our new photometric and spectroscopic observations: J0651 contains two WDs with M-1 = 0.26 +/- 0.04 M-circle dot and M-2 = 0.50 +/- 0.04 M-circle dot. General relativity predicts orbital decay due to gravitational wave radiation of (-8.2 +/- 1.7) x 10(-12) s s(-1) (or -0.26 +/- 0.05 ms yr(-1)). Our observed rate of orbital decay is consistent with this expectation. J0651 is currently the second-loudest gravitational wave source known in the milli-Hertz range and the loudest non-interacting binary, which makes it an excellent verification source for future missions aimed at directly detecting gravitational waves. Our work establishes the feasibility of monitoring this system's orbital period decay at optical wavelengths.Item SDSS J074511.56+194926.5: Discovery Of A Metal-Rich And Tidally Distorted Extremely Low Mass White Dwarf(2014-02) Gianninas, A.; Hermes, J. J.; Brown, Warren R.; Dufour, Patrick; Barber, S. D.; Kilic, Mukremin; Kenyon, S. J.; Harrold, Samuel T.; Hermes, J. J.; Harrold, S. T.We present the discovery of an unusual, tidally distorted extremely low mass white dwarf (WD) with nearly solar metallicity. Radial velocity measurements confirm that this is a compact binary with an orbital period of 2.6975 hr and a velocity semi-amplitude of K = 108.7 km s(-1). Analysis of the hydrogen Balmer lines yields an effective temperature of T-eff = 8380 K and a surface gravity of log g = 6.21 that in turn indicate a mass of M = 0.16 M-circle dot and a cooling age of 4.2 Gyr. In addition, a detailed analysis of the observed metal lines yields abundances of log (Mg/H) = -3.90, log(Ca/H) = -5.80, log(Ti/ H) = -6.10, log(Cr/H) = -5.60, and log(Fe/H) = -4.50, similar to the sun. We see no evidence of a debris disk from which these metals would be accreted, though the possibility cannot entirely be ruled out. Other potential mechanisms to explain the presence of heavy elements are discussed. Finally, we expect this system to ultimately undergo unstable mass transfer and merge to form a similar to 0.3-0.6 M-circle dot WD in a few Gyr.Item Two Spotted And Magnetic Early B-Type Stars In The Young Open Cluster NGC 2264 Discovered By Most And ESPaDOnS(2014-02) Fossati, L.; Zwintz, K.; Castro, N.; Langer, N.; Lorenz, D.; Schneider, F. R. N.; Kuschnig, R.; Matthews, J. M.; Alecian, E.; Wade, G. A.; Barnes, T. G.; Thoul, A. A.; Matthews, J. MStar clusters are known as superb tools for understanding stellar evolution. In a quest for understanding the physical origin of magnetism and chemical peculiarity in about 7% of the massive main-sequence stars, we analysed two of the ten brightest members of the similar to 10 Myr old Galactic open cluster NGC 2264, the early B-dwarfs HD47887 and HD47777. We find accurate rotation periods of 1.95 and 2.64 days, respectively, from MOST photometry. We obtained ESPaDOnS spectropolarimetric observations, through which we determined stellar parameters, detailed chemical surface abundances, projected rotational velocities, and the inclination angles of the rotation axis. Because we found only small (<5 km s(-1)) radial velocity variations, most likely caused by spots, we can rule out that HD47887 and HD47777 are close binaries. Finally, using the least-squares deconvolution technique, we found that both stars possess a large-scale magnetic field with an average longitudinal field strength of about 400 G. From a simultaneous fit of the stellar parameters we determine the evolutionary masses of HD47887 and HD47777 to be 9.4(-0.7)(+0.6) M-circle dot and 7.6(-0.5)(+0.5) M-circle dot. Interestingly, HD47777 shows a remarkable helium underabundance, typical of helium-weak chemically peculiar stars, while the abundances of HD47887 are normal, which might imply that diffusion is operating in the lower mass star but not in the slightly more massive one. Furthermore, we argue that the rather slow rotation, as well as the lack of nitrogen enrichment in both stars, can be consistent with both the fossil and the binary hypothesis for the origin of the magnetic field. However, the presence of two magnetic and apparently single stars near the top of the cluster mass-function may speak in favour of the latter.