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High Resolution Near-IR Spectra of NGC 6624 and NGC 6569

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High Resolution Near-IR Spectra of NGC 6624 and NGC 6569 Mon. Not. R. Astron. Soc. 000, 1{7 (2010) Printed 31 July 2021 (MN LATEX style file v2.2) High resolution near IR spectra of NGC 6624 and NGC 6569? E. Valenti1y, L. Origlia2 & R. M. Rich3 1European Southern Observatory, Karl Schwarzschild-Straße 2, D-85748 Garching bei M¨unchen,Germany. 2INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy 3Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, CA 90095 - 1562, US ABSTRACT We present the first abundances analysis based on high-resolution infrared (IR) echelle spectra of NGC 6569 and NGC 6624, two moderately reddened globular clusters lo- cated in the outer bulge of the Galaxy. We find [Fe/H]=-0.79±0.02 dex and [Fe/H]=-0.69±0.02 dex for NGC 6569 and NGC 6624, respectively and an average α-elements enhancement of ≈+0.43±0.02 dex and +0.39±0.02 dex, consistent with previous measurements on other metal-rich Bulge −1 clusters. We measure accurate radial velocities of < vr >= −47 ± 4 km s and −1 −1 −1 < vr >= +51 ± 3 km s and velocity dispersions of ≈ 8 km s and ≈ 6 km s for NGC 6569 and NGC 6624, respectively. 12 13 Finally, we find very low C= C isotopics ratio (67 in NGC 6624 and ≈5 in NGC 6569), confirming the presence extra-mixing mechanisms during the red giant branch evolution phase. Key words: Galaxy: bulge, globular clusters: individual (NGC 6569 and NGC 6624) { stars: abundances, late-type { techniques: spectroscopic . 1 INTRODUCTION in constraining the history of Bulge formation and chemical enrichment (McWilliam 1997). The new generation of high-resolution IR spectrographs We have used this method to derive abundances for ten showed its tremendous potential to study both distant and globular clusters in the inner and outer Bulge regions: the obscured stellar populations. Particularly in the case of resulting abundances for NGC6553 and Liller 1 are given in heavily reddened regions such as the Galactic bulge and Origlia, Rich & Castro (2002), for Terzan 4 and Terzan 5 center, IR spectroscopy offers the best, and sometimes a in Origlia & Rich (2004), for NGC 6342 and NGC 6528 in unique, approach to measuring the composition of the old Origlia, Valenti & Rich (2005), for NGC 6539 and UKS 1 in stellar populations. arXiv:1103.0233v1 [astro-ph.SR] 1 Mar 2011 Origlia et al. (2005), and for NGC 6440 and NGC 6441 in In the last few years, we have started a high-resolution Origlia, Valenti & Rich (2008). We also measured detailed spectroscopic survey of the Galactic bulge in the near-IR abundances of Bulge M giants in the Baade's window (Rich by using NIRSPEC, a high-throughput IR echelle spectro- & Origlia 2004) and in three inner fields at (l; b) = (0◦; −1◦) graph at the Keck Observatory (McLean 1998). H-band (1:5- (Rich, Origlia & Valenti 2007), (l; b) = (0◦; −1:75◦), (l; b) = −1:8µm) spectra of bright giants in the Bulge globular clus- (1◦; −2:65◦) (Rich, Origlia & Valenti 2011). We found α- ters and field population are ideal for detailed abundance enhancement at a level of a factor between 2 and 3 over the analysis of Fe, C, O and other α-elements, using the ap- whole range of metallicity spanned by the Bulge clusters in proach of synthesizing the entire spectrum. The abundance our survey, from [Fe/H]≈ −1:6 (cf. Terzan 4) up to [Fe/H]≈ distributions in the cluster and field populations are crucial −0:2 (cf. Terzan 5). Here we present the high resolution IR spectra and abundance analysis of bright giants in NGC 6569 and NGC 6624, two globular clusters of the outer Bulge, located ? Data presented herein were obtained at the W. M. Keck Ob- at (l; b) = (0:48; −6:68) and (l; b) = (2:79; −7:91), respec- servatory, which is operated as a scientific partnership among the tively (Harris 1996). California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The NGC 6569 is a rather compact cluster located in the Observatory was made possible by the generous support of the Sagittarius region. Zinn (1985) from integrated photometry W. M. Keck Foundation. obtained [Fe/H]= −0:86 and E(B-V)= 0:55, while from inte- y E-mail: [email protected] (EV) grated DDO photometry, Bica & Pastoriza (1983) estimated c 2010 RAS 2 E. Valenti, L. Origlia & R. M. Rich Figure 1. H-band image of the core region (left panel) and the K, J-K colour-magnitude diagram (right panel) of NGC 6569 (Valenti, Ferraro & Origlia 2005). The stars spectroscopically observed are numbered (cf. Table 1). [Fe/H]= −0:76 and E(B-V)= 0:59. The optical photometric Table 1. Coordinates and photometric parameters for the giants studies by Ortolani, Bica & Barbuy (2001) and Piotto et al. observed in NGC 6569 and NGC 6624. (2002) suggested a metallicity consistent with that of 47 Tuc. The only IR photometric study is that by Valenti, Ferraro & Origlia (2005) who found [Fe/H]= −0:85 and E(B-V)= 0:49. a a No high spectral resolution measurements of this cluster ex- Star R.A. Decl. (J-K)0 Mbol ist so far. In the last few years, NGC 6624 has been subject of several studies aimed at investigating its population of "ex- NGC 6569-s1 18:13:39.015 -31:49:18.88 0.91 -3.06 NGC 6569-s2 18:13:39.392 -31:49:21.00 1.01 -3.85 otic" objects, such as X-ray binaries (see Zdziarski et al. NGC 6569-s3 18:13:38.276 -31:49:41.29 0.88 -2.83 2007, and reference therein) and millisecond pulsars (see NGC 6569-s4 18:13:38.165 -31:50:02.95 0.91 -2.79 Ransom et al. 2005). Deep optical HST photometry, down NGC 6569-s5 18:13:38.179 -31:49:35.40 0.93 -2.94 to the main sequence turnoff region, have been presented by NGC 6569-s6 18:13:38.647 -31:49:39.28 0.91 -2.91 Heasley et al. (2000); Piotto et al. (2002) finding the clus- ter to be coeval to 47 Tuc. Its similarity to 47 Tuc is also NGC 6624-s1 18:23:40.129 -30:21:53.72 1.04 -3.76 based on the metallicity, in fact Heasley et al. (2000) found NGC 6624-s2 18:23:40.100 -30:21:47.57 1.04 -3.41 [Fe/H]= −0:63 based on observations of the Ca II IR triplet NGC 6624-s3 18:23:41.646 -30:21:41.19 1.01 -3.05 lines in giant stars of NGC 6624. More recently, Valenti, NGC 6624-s4 18:23:40.635 -30:21:44.83 1.01 -3.12 Ferraro & Origlia (2004a,b) presented a detailed analysis of NGC 6624-s5 18:23:42.136 -30:21:26.29 1.08 -3.85 the cluster Red Giant Branch properties based on high reso- (a) NGC 6569: J, K colours, E(B-V)=0.49, and (m-M)0=15.40 lution IR photometry, finding E(B-V)=0.28, (m-M)0=14.63 from Valenti, Ferraro & Origlia (2005) and a metallicity like 47 Tuc. However, also in the case of NGC 6624: J, K colours, E(B-V)=0.28, and (m-M)0=14.63 NGC 6624, no high resolution spectroscopic measurements from Valenti, Ferraro & Origlia (2004a) have been published so far. A description of the observations and abundance analy- sis follows in x 2, while in x 3 and x 4 we present and discusses of the Keck II telescope. NGC 6569 was observed on May our results. 2006, while NGC 6624 on April 2004, May 2005 and May 2006. The high resolution echelle mode, with a slit width of 0:4300 (3 pixels) and a length of 12 − 2400 and the standard NIRSPEC-5 setting, which covers most of the 1:5−1:8µm H- 2 OBSERVATIONS AND ABUNDANCE band, have been selected. Typical exposure times (on source) ANALYSIS are ≈8 min. A total of 6 and 5 giants have been observed in Near-IR, high resolution echelle spectra of bright giants NGC 6569 and NGC 6624, respectively. Figures 1, 2 show in the core of the Bulge globular clusters NGC 6569 and the IR image and the colour-magnitude diagram (CMD) NGC 6624 have been acquired with the IR spectrograph (Valenti, Ferraro & Origlia 2005, 2004a) of the core region of NIRSPEC (McLean 1998) mounted at the Nasmyth focus NGC 6569 and NGC 6624, respectively. The position in the c 2010 RAS, MNRAS 000, 1{7 HR-IR spectra of NGC6624 & NGC6569 3 near-IR CMD of the giant stars spectroscopically observed is mentioned above (see Origlia & Rich 2004). If the stellar pa- also shown. Table 1 lists the absolute coordinates, intrinsic rameters are varied simultaneously, appreciable variations in J, K colours and bolometric magnitudes of the giant stars the spectrum can be measured for smaller (by a factor of 2-3) in our sample. variations of the single quantities, depending on the range The two raw dimensional spectra were processed using of temperature and metallicity of the observed stars. The the REDSPEC IDL-based package written at the UCLA IR adopted variation for the stellar parameters are somewhat Laboratory. Each order has been sky subtracted by using conservative and have been empirically estimated compar- the pairs of spectra taken with the object nodded along the ing observed spectra with synthetic ones covering a fine grid slit, and subsequently flat-field corrected.
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