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Öğe Chemical abundances of open clusters from high-resolution infrared spectra - I. NGC 6940(Oxford Univ Press, 2019) Topcu, G. Bocek; Afsar, M.; Sneden, C.; Pilachowski, C. A.; Denissenkov, P. A.; VandenBerg, D. A.; Strickland, E.; Ozdemir, S.; Mace, G. N.; Kim, H.; Jaffe, D. T.We present near-infrared spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. High-resolution (R similar or equal to 45 000) and high-signal-to-noise ratio (S/N > 100) near-infrared H-and K-band spectra were gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7-m Smith Telescope at McDonald Observatory. We obtained abundances of H-burning (C, N, O), alpha (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni), and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH and CN features in the H band were used to obtain O and N abundances. C abundances were measured from four different features: CO molecular lines in the K band, high excitation CI lines present in both near-infrared and optical, CH and C-2 bands in the optical region. We have also determined C-12/C-13 ratios from the R-branch band heads of first overtone (2-0) and (3-1) (CO)-C-12 and (2-0) (CO)-C-13 lines near 23 440 angstrom and (3-1) (CO)-C-13 lines at about 23 730 angstrom. We have also investigated the HF feature at 23 358.3 angstrom, finding solar fluorine abundances without ruling out a slight enhancement. For some elements (such as the alpha group), IGRINS data yield more internally self-consistent abundances. We also revisited the CMD of NGC 6940 by determining the most probable cluster members using Gaia DR2. Finally, we applied Victoria isochrones and MESA models in order to refine our estimates of the evolutionary stages of our targets.Öğe Chemical abundances of open clusters from high-resolution infrared spectra - II. NGC 752(Oxford Univ Press, 2020) Topcu, G. Bocek; Afsar, M.; Sneden, C.; Pilachowski, C. A.; Denissenkov, P. A.; VandenBerg, D. A.; Sokal, K. R.We present a detailed near-infrared chemical abundance analysis of 10 red giant members of the Galactic open cluster NGC 752. High-resolution (R similar or equal to 45000) near-infrared spectral data were gathered with the Immersion Grating Infrared Spectrograph, providing simultaneous coverage of the complete H and K bands. We derived the abundances of H-burning (C, N, O), alpha (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni), and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 752 for the first time. Our analysis yields solar-metallicity and solar abundance ratios for almost all of the elements heavier than the CNO group in NGC 752. O and N abundances were measured from a number of OH and CN features in the H band, and C abundances were determined mainly from CO molecular lines in the K band. High-excitation C I lines present in both near-infrared and optical spectra were also included in the C abundance determinations. Carbon isotopic ratios were derived from the R-branch band heads of first overtone (2-0) and (3-1) (CO)-C-12 and (2-0) (CO)-C-13 lines near 23 440 angstrom and (3-1) (CO)-C-13 lines at about 23 730 angstrom. the CNO abundances and C-12/C-13 ratios are all consistent with our giants having completed 'first dredge-up' envelope mixing of CN-cyle products. We independently assessed NGC 752 stellar membership from Gaia astrometry, leading to a new colour-magnitude diagram for this cluster. Applications of Victoria isochrones and MESA models to these data yield an updated NGC 752 cluster age (1.52 Gyr) and evolutionary stage indications for the programme stars. the photometric evidence and spectroscopic light element abundances all suggest that the most, perhaps all of the programme stars are members of the helium-burning red clump in this cluster.Öğe The chemical compositions and evolutionary status of red giants in the open cluster NGC 6940(Oxford Univ Press, 2016) Topcu, G. Bocek; Afsar, M.; Sneden, C.We present the high-resolution (R a parts per thousand 60 000), high signal-to-noise ratio (S/N a parts per thousand integral 120) spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. We applied Yonsei-Yale isochrones to the colour-magnitude diagram, which suggested an age of 1.1 Gyr for the cluster with a turn-off mass of 2 M-aS (TM). Atmospheric parameters (T-eff, log g, [Fe/H], and xi(t)) were determined via equivalent widths of Fe i, Fe ii, Ti i, and Ti ii lines. Calculated mean metallicity of the cluster is aEuro[Fe/H]aEuro parts per thousand = 0.04 +/- 0.02. We derived abundances of alpha (Mg, Si, Ca), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and n-capture (Y, La, Nd, Eu) elements to be about solar. Light odd-Z elements Na and Al are slightly enhanced in MMU 108 and MMU 152 by similar to 0.34 and similar to 0.16 dex, respectively. Abundances of light elements Li, C, N, O, and C-12/C-13 ratios were derived from spectrum syntheses of the Li i resonance doublet at 6707 , [O i] line at 6300 , C-2 Swan bandheads at 5164 and 5635 , and strong (CN)-C-12,13 system lines in the 7995-8040 region. Most carbon isotopic ratios are similar to those found in other solar-metallicity giants, but MMU 152 has an unusual value of C-12/C-13 = 6. Evaluation of the LiCNO abundances and C-12/C-13 ratios along with the present theoretical models suggests that all the red giants in our sample are core-helium-burning clump stars.Öğe The chemical compositions and evolutionary status of red giants in the open cluster NGC 752(Oxford Univ Press, 2015) Topcu, G. Bocek; Afsar, M.; Schaeuble, M.; Sneden, C.We present detailed chemical compositions of 10 red giant star members of the Galactic (open) cluster NGC 752, derived from high-resolution (R approximate to 60 000), high signal-to-noise (S/N >= 140) spectra. We confirmed cluster memberships by measuring the stellar radial velocities, and by deriving model atmosphere parameters (T-eff, log g, [Fe/H] and xi(t)) from equivalent widths of Fe I, FeII, Ti I, and Ti II lines. The metallicity we obtained for NGC 752 ([Fe/H]= -0.02 +/- 0.05) is in good agreement with previous studies. We derived abundances of alpha (Mg, Si, Ca), light odd-Z (Na, A1), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), n-capture (Y, La, Nd, Eu), and p-capture (Li, C, N, O) species for each star. Furthermore, we also derived abundances of the LiCNO p-capture element group and carbon isotopic ratios, using synthetic spectrum analyses of the Li I 6707 angstrom resonance doublet, the [O I] line at 6300 angstrom, the CH G-band features near 4311 and 4325 angstrom, the C-2 bandheads at 5160 and 5631 angstrom, and (CN)-C-12,13 red system lines in the 7995-8040 angstrom region. By applying recent isochrones to NGC 752 photometry, and comparing the colour-magnitude diagram information to our Li abundances and C-12/C-13 ratios, we suggest that the 10 observed red giants can be separated into three first-ascent, six red-clump and one red horizontal branch star.Öğe Effective Temperature Estimations from Line Depth Ratios in the H- and K-band Spectra of IGRINS(Institute of Physics, 2023) Afşar, M.; Bozkurt, Z.; Topcu, G.B.; Özdemir, S.; Sneden, C.; Mace, G.N.; Jaffe, D.T.Determining accurate effective temperatures of stars buried in the dust-obscured Galactic regions is extremely difficult from photometry. Fortunately, high-resolution infrared spectroscopy is a powerful tool for determining the temperatures of stars with no dependence on interstellar extinction. It has long been known that the depth ratios of temperature-sensitive and relatively insensitive spectral lines are excellent temperature indices. In this work, we provide the first extensive line depth ratio (LDR) method application in the infrared region that encompasses both the H and K bands (1.48 ?m ? 2.48 ?m). We applied the LDR method to high-resolution (R ? 45,000) H- and K-band spectra of 110 stars obtained with the Immersion Grating Infrared Spectrograph. Our sample contained stars with 3200 < T eff (K) < 5500, 0.20 ? log g < 4.6, and ?1.5 < [M/H] < 0.5. The application of this method in the K band yielded 21 new LDR-T eff relations. We also report five new LDR-T eff relations found in the H-band region, augmenting the relations already published by other groups. The temperatures found from our calibrations provide reliable temperatures within ?70 K accuracy compared to spectral T eff values from the literature. © 2023. The Author(s). Published by the American Astronomical Society.Öğe GALACTIC CHEMICAL EVOLUTION: INSIGHTS FROM FIELD HORIZONTAL BRANCH STARS(E D P Sciences, 2015) Afsar, M.; Bozkurt, Z.; Bocek, G.; Sehitoglu, G.; Sneden, C.; Lagadec, E; Millour, FIn this study we conducted the first large-sample red horizontal branch field star survey in the Milky Way. We carried out a detailed high-resolution spectroscopic abundance analysis of the RHB candidates. We also derived C-12/C-13 isotopic ratios, important indicators of stellar evolution, by using the CN features mainly located around the 8004 angstrom.Öğe High-resolution infrared spectroscopy of the dust-obscured metal-poor open cluster Trumpler 5(Edp Sciences S A, 2025) Ozdemir, S.; Afsar, M.; Sneden, C.; VandenBerg, D. A.; Denissenkov, P. A.; Milone, A. P.; Bozkurt, Z.Context. Open clusters are important tools to investigate the chemistry of the Galactic disk. Trumpler 5 is a moderately old, dust-obscured metal-poor open cluster. In this study, high-resolution near-infrared spectroscopic data of seven giant stars from the Trumpler 5 cluster were analyzed to derive chemical abundances for 20 elements and C-12/C-13 ratios. A color-magnitude diagram (CMD) analysis of BV and Gaia photometry has also been performed for a comprehensive study of the cluster. Aims. This work uses high-resolution near-infrared spectroscopy exclusively to derive atmospheric parameters and chemical abundances in the obscured open cluster Trumpler 5. Thanks to the methodology employed, some targets are studied for the first time. Additionally, it provides a detailed CMD analysis using photometric and spectroscopic data. Methods. We gathered high-resolution spectra for seven Trumpler 5 red giants in the near-infrared H and K wavelength domains, using the Immersion Grating INfrared Spectrometer (IGRINS). Five out of seven targets have been studied for the first time here with high-resolution spectroscopy. We introduced a method to initially estimate the stellar surface gravity (log g) by using calibrated equivalent widths of the Ti II line at 15 873 & Aring; from a large sample. We performed standard spectroscopic analyses to refine the model atmospheric parameters of our targets and determined the chemical abundances primarily through spectrum synthesis. We also performed CMD analyses to extract differential reddening correction to compare cluster parameters both with and without corrections. Results. We derived stellar parameters for seven members of Trumpler 5 with our method and the results are consistent with both the literature and other methods. We also inferred elemental abundances for more than 20 species, along with the C-12/C-13 ratios. The elemental abundances are in good agreement with the literature values for similar targets. Through CMD analysis, we found the reddening value, E(B-V)similar or equal to 0.76, and estimated the age of the cluster to be approximately 2.50 Gyr.Öğe HIGH-RESOLUTION NEAR INFRARED OBSERVATIONS OF RED HORIZONTAL BRANCH STARS IN THE GALACTIC FIELD(E D P Sciences, 2015) Afsar, M.; Bozkurt, Z.; Topcu, G. Bocek; Sehitoglu, G.; Sneden, C.; Jaffe, D.; Kim, H.; Mace, G.; Lagadec, E; Millour, FWe obtained, for the first time, complete H- (from 1.5 to 1.8 mu m) and K-band (from 1.9 to 2.4 mu m) spectra of some selected Galactic field red horizontal branch stars. We measured the abundances of some important elements including P, S, K, Si and Ca. We also detected C-12/C-13 ratios from the bandheads present in both H- and K-band.Öğe IMPROVED Ni I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937(Iop Publishing Ltd, 2014) Wood, M. P.; Lawler, J. E.; Sneden, C.; Cowan, J. J.Atomic 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.Öğe M67 Blue Stragglers with High-resolution Infrared Spectroscopy(Iop Publishing Ltd, 2023) Brady, K. E.; Sneden, C.; Pilachowski, C. A.; Afsar, Melike; Mace, G. N.; Jaffe, D. T.; Gosnell, N. M.We report on the first detailed infrared chemical analysis of five binary members (S277, S997, S975, S1031, and S1195) in the open cluster M67 (NGC 2682). These stars are located outside (bluer and/or brighter than) the main-sequence turnoff region in M67. High-resolution (R & SIM; 45,000) near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope, providing full spectral coverage of the H and K bands. The abundances of C, Na, Mg, Al, Si, S, Ca, Fe, and Ni are measured using neutral atomic absorption lines. We detect v sin i & GE; 25 km s-1 in three of our program stars: S1031, S975, and S1195. We find our derived abundances to be in good agreement with turnoff star abundances, similar to published analyses of blue straggler stars in M67 from optical spectra. Detection of a carbon enhancement or depletion resulting from mass transfer is difficult due to the uncertainties in the carbon abundance and the relatively modest changes that may occur through red giant and asymptotic giant branch evolution.Öğe Red horizontal branch stars in the Galactic field: A chemical abundance survey(E D P Sciences, 2013) Afsar, M.; Sneden, C.; Fo, B. -Q.; Montalban, J; Noels, A; VanGrootel, VA large sample survey of Galactic red horizontal-branch (RHB) stars was conducted to investigate their atmospheric parameters and elemental abundances. High-resolution spectra of 76 Galactic field stars were obtained with the 2.7 m Smith Telescope at McDonald Observatory. Only the color and the parallax were considered during the selection of the field stars. Equivalent width or synthetic spectrum analyses were used in order to determine the relative abundances of the following elements: proton-capture elements C, N, O and Li, alpha-elements Ca and Si, and neutron-capture elements Eu and La. Additionally, C-12/C-13 isotopic ratios were derived by using the CN features mainly located in the 7995 - 8040 spectral region. The evaluation of effective temperatures, surface gravities and C-12/C-13 isotopic ratios together with evolutionary stages of the candidates revealed that 18 out of 76 stars in our sample are probable RHBs. Including both kinematic and evolutionary status information, we conclude that we have five thick disk and 13 thin disk RHB stars in our sample. Although RHB stars have been regarded as thick disk members of the Galaxy, the low-velocity RHBs with a solar metallicity in our sample suggests the existence of a large number of thin disk RHBs, which cannot be easily explained by standard stellar evolutionary models.Öğe Red horizontal branch stars in the Galactic field: A chemical abundance survey(E D P Sciences, 2013) Afsar, M.; Sneden, C.; Fo, B. -Q.; Montalban, J; Noels, A; VanGrootel, VA large sample survey of Galactic red horizontal-branch (RHB) stars was conducted to investigate their atmospheric parameters and elemental abundances. High-resolution spectra of 76 Galactic field stars were obtained with the 2.7 m Smith Telescope at McDonald Observatory. Only the color and the parallax were considered during the selection of the field stars. Equivalent width or synthetic spectrum analyses were used in order to determine the relative abundances of the following elements: proton-capture elements C, N, O and Li, alpha-elements Ca and Si, and neutron-capture elements Eu and La. Additionally, C-12/C-13 isotopic ratios were derived by using the CN features mainly located in the 7995 - 8040 spectral region. The evaluation of effective temperatures, surface gravities and C-12/C-13 isotopic ratios together with evolutionary stages of the candidates revealed that 18 out of 76 stars in our sample are probable RHBs. Including both kinematic and evolutionary status information, we conclude that we have five thick disk and 13 thin disk RHB stars in our sample. Although RHB stars have been regarded as thick disk members of the Galaxy, the low-velocity RHBs with a solar metallicity in our sample suggests the existence of a large number of thin disk RHBs, which cannot be easily explained by standard stellar evolutionary models.
