Charli M. Sakari

Spectrum Syntheses of High Resolution Integrated Light Spectra of Galactic Globular Clusters

Spectrum syntheses for three elements (Mg, Na, and Eu) in high-resolution integrated light spectra of the Galactic globular clusters 47 Tuc, M3, M13, NGC 7006, and M15 are presented, along with calibration syntheses of the Solar and Arcturus spectra. Iron abundances in the target clusters are also derived from integrated light equivalent width analyses. Line profiles in the spectra of these five globular clusters are well fit after careful consideration of the atomic and molecular spectral features, providing levels of precision that are better than equivalent width analyses of the same integrated light spectra, and that are comparable to the precision in individual stellar analyses. The integrated light abundances from the 5528 and 5711 A Mg I lines, the 6154 and 6160 A Na I lines, and the 6645 A Eu II line fall within the observed ranges from individual stars; however, these integrated light abundances do not always agree with the average literature abundances. Tests with the second parameter clusters M3, M13, and NGC 7006 show that assuming an incorrect horizontal branch morphology is likely to have only a small (< 0.06 dex) effect on these Mg, Na, and Eu abundances. These tests therefore show that integrated light spectrum syntheses can be applied to unresolved globular clusters over a wide range of metallicities and horizontal branch morphologies. Such high precision in integrated light spectrum syntheses is valuable for interpreting the chemical abundances of globular cluster systems around other galaxies.

Detailed Chemical Abundances of Four Stars in the Unusual Globular Cluster Palomar 1

Detailed chemical abundances for twenty one elements are presented for four red giants in the anomalous outer halo globular cluster Palomar 1 (RGC = 17.2 kpc, Z = 3.6 kpc) using high-resolution (R = 36000) spectra from the High Dispersion Spectrograph (HDS) on the Subaru Telescope. Pal 1 has long been considered unusual because of its low surface brightness, sparse red giant branch, young age, and its possible association with two extragalactic streams of stars—this paper shows that its chemistry further confirms its unusual nature. The mean metallicity of the four stars, [Fe/H] = 0.60±0.01, is high for a globular cluster so far from the Galactic center, but is low for a typical open cluster. The [α/Fe] ratios, though in agreement with the Galactic stars within the 1σ errors, agree best with the lower values in dwarf galaxies. No signs of the Na/O anticorrelation are detected in Pal 1, though Na appears to be marginally high in all four stars. Pal 1’s neutron capture elements are also unusual: its high [Ba/Y] ratio agrees best with dwarf galaxies, implying an excess of second-peak over first-peak s-process elements, while its [Eu/α] and [Ba/Eu] ratios show that Pal 1’s contributions from the rprocess must have differed in some way from normal Galactic stars. Therefore, Pal 1 is chemically unusual, as well in its other properties. Pal 1 shares some of its unusual abundance characteristics with the young clusters associated with the Sagittarius dwarf galaxy remnant and the intermediateage LMC clusters, and could be chemically associated with the Canis Majoris overdensity; however it does not seem to be similar to the Monoceros/Galactic Anticenter Stellar Stream. Subject headings: galaxies: dwarf — globular clusters: general — globular clusters: individual(Pal 1)

Integrated light chemical tagging analyses of seven M31 outer halo globular clusters from the Pan-Andromeda Archaeological Survey

Detailed chemical abundances are presented for seven M31 outer halo globular clusters (with projected distances from M31 greater than 30 kpc), as derived from high resolution integrated light spectra taken with the Hobby Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS)—this paper presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal-poor ([Fe/H] < 1.5), �-enhanced (though they are possibly less �-enhanced than Milky Way stars at the 1� level), and show signs of star-to-star Na and Mg variations. The other three globular clusters (H10, H23, and PA17) are more metal rich, with metallicities ranging from [Fe/H] = 1.4 to 0.9. While H23 is chemically similar to Milky Way field stars, Milky Way globular clusters, and other M31 clusters, H10 and PA17 have moderately low [Ca/Fe], compared to Milky Way field stars and clusters. Addi tionally, PA17’s high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud (LMC). None of the clusters studied here can be conclusively linked to any of the identified streams fr om PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW Cloud, and PA53 and PA56 may be associated with the Eastern Cloud.

Chemical abundances in the globular clusters NGC 5024 and NGC 5466 from optical and infrared spectroscopy

Detailed chemical abundances for ve stars in two Galactic globular clusters, NGC 5466 and NGC 5024, are presented from high resolution optical (from the HobbyEberley Telescope) and infrared spectra (from the SDSS-III APOGEE survey). We nd [Fe/H] = -1.97 0.13 dex for NGC 5466, and [Fe/H] = -2.06 0.13 dex for NGC 5024, and the typical abundance pattern for globular clusters for the remaining elements, e.g., both show evidence for mixing in their light element abundance ratios (C, N), and AGB contributions in their heavy element abundances (Y, Ba, and Eu). These clusters were selected to examine chemical trends that may correlate them with the Sgr dwarf galaxy remnant, but at these low metallicities no obvious dierences from the Galactic abundance pattern are found. Regardless, we compare our results from the optical and infrared analyses to nd that oxygen and silicon abundances determined from the infrared spectral lines are in better agreement with the other alpha-element ratios and with smaller random errors.

A Peculiar Faint Satellite in the Remote Outer Halo of M31

We present Hubble Space Telescope imaging of a newly discovered faint stellar system, PAndAS-48, in the outskirts of the M31 halo. Our photometry reveals this object to be comprised of an ancient and very metal-poor stellar population with age 10?Gyr and [Fe/H]? ?2.3. Our inferred distance modulus (m ? M)0 = 24.57 ? 0.11 confirms that PAndAS-48 is most likely a remote M31 satellite with a three-dimensional galactocentric radius of ?kpc. We observe an apparent spread in color on the upper red giant branch that is larger than the photometric uncertainties should allow, and briefly explore the implications of this. Structurally, PAndAS-48 is diffuse, faint, and moderately flattened, with a half-light radius ?pc, integrated luminosity MV = ?4.8 ? 0.5, and ellipticity . On the size-luminosity plane it falls between the extended globular clusters seen in several nearby galaxies and the recently discovered faint dwarf satellites of the Milky Way; however, its characteristics do not allow us to unambiguously classify it as either type of system. If PAndAS-48 is a globular cluster then it is among the most elliptical, isolated, and metal-poor of any seen in the Local Group, extended or otherwise. Conversely, while its properties are generally consistent with those observed for the faint Milky Way dwarfs, it would be a factor of ~2-3 smaller in spatial extent than any known counterpart of comparable luminosity.

Probing the behaviour of the X-ray binary Cygnus X-3 with very long baseline radio interferometry

In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cygnus X-3 (Cyg X-3), we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival Very Long Baseline Array data at 5 or 15 GHz and new electronic European Very Long Baseline Interferometry Network data at 5 GHz. We also present 5-GHz Multi-Element Radio Linked Interferometer Network observations of an outburst of Cyg X-3. In the X-ray regime, we use quasi-simultaneous with radio, monitoring and pointed Rossi X-ray Timing Explorer observations. We find that when the radio emission from both jet and core is globally considered, the behaviour of Cyg X-3 at mas scales is consistent with that described at arcsec-scales. However, when the radio emission is disentangled in a core component and a jet component, the situation changes. It becomes clear that in active states the radio emission from the jet is dominating that from the core. This shows that in these states the overall radio flux cannot be used as a direct tracer of the accretion state.

Optimal integrated abundances for chemical tagging of extragalactic globular clusters

High resolution integrated light (IL) spectroscopy provides detailed abundances of distant globular clusters whose stars cannot be resolved. Abundance comparisons with other systems (e.g. for chemical tagging) require understanding the systematic offsets that can occur between clusters, such as those due to uncertainties in the underlying stellar population. This paper analyses high resolution IL spectra of the Galactic globular clusters 47 Tuc, M3, M13, NGC 7006, and M15 to (1) quantify potential systematic uncertainties in Fe, Ca, Ti, Ni, Ba, and Eu and (2) identify the most stable abundance ratios that will be useful in future analyses of unresolved targets. When stellar populations are well-modelled, uncertainties are ~0.1-0.2 dex based on sensitivities to the atmospheric parameters alone; in the worst case scenarios, uncertainties can rise to 0.2-0.4 dex. The [Ca I/Fe I] ratio is identified as the optimal integrated [alpha/Fe] indicator (with offsets <0.1 dex), while [Ni I/Fe I] is also extremely stable to within <0.1 dex. The [Ba II/Eu II] ratios are also stable when the underlying populations are well modelled and may also be useful for chemical tagging.

INFRARED HIGH-RESOLUTION INTEGRATED LIGHT SPECTRAL ANALYSES OF M31 GLOBULAR CLUSTERS FROM APOGEE

Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution (R = 22,500) H-band integrated light (IL) spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared (IR) spectra offer lines from new elements, lines of different strengths, and lines at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical, demonstrating the validity and value of IR IL analyses. The CNO abundances are consistent with typical tip of the red giant branch stellar abundances but are systematically offset from optical Lick index abundances. With a few exceptions, the other abundances agree between the optical and the IR within the 1σ uncertainties. The first integrated K abundances are also presented and demonstrate that K tracks the α elements. The combination of IR and optical abundances allows better determinations of GC properties and enables probes of the multiple populations in extragalactic GCs. In particular, the integrated effects of the Na/O anticorrelation can be directly examined for the first time.

The integrated calcium II triplet as a metallicity indicator: comparisons with high-resolution [Fe/H] in M31 globular clusters

Medium resolution (R=4,000 to 9,000) spectra of the near infrared Ca II lines (at 8498, 8542, and 8662 A) in M31 globular cluster integrated light spectra are presented. In individual stars the Ca II triplet (CaT) traces stellar metallicity; this paper compares integrated CaT strengths to well determined, high precision [Fe/H] values from high resolution integrated light spectra. The target globular clusters cover a wide range in metallicity (from [Fe/H] = -2.1 to -0.2). While most are older than 10 Gyr, some may be of intermediate age (2-6 Gyr). A handful (3-6) have detailed abundances (e.g. low [Ca/Fe]) that indicate they may have been accreted from dwarf galaxies. Using various measurements and definitions of CaT strength, it is confirmed that for GCs with [Fe/H] < -0.4 and older than 2 Gyr the integrated CaT traces cluster [Fe/H] to within about 0.2 dex, independent of age. CaT lines in metal rich GCs are very sensitive to nearby atomic lines (and TiO molecular lines in the most metal rich GCs), largely due to line blanketing in continuum regions. The [Ca/Fe] ratio has a mild effect on the integrated CaT strength in metal poor GCs. The integrated CaT can therefore be safely used to determine rough metallicities for distant, unresolved clusters, provided that attention is paid to the limits of the measurement techniques.

RAVE J203843.2–002333: The First Highly R-process-enhanced Star Identified in the RAVE Survey

We report the discovery of RAVE J203843.2-002333, a bright (V = 12.73), very metal-poor ([Fe/H] = -2.91), r-process-enhanced ([Eu/Fe] = +1.64 and [Ba/Eu] = -0.81) star selected from the RAVE survey. This star was identified as a metal-poor candidate based on its medium-resolution (R ~ 1,600) spectrum obtained with the KPNO/Mayall Telescope, and followed-up with high-resolution (R ~ 66,000) spectroscopy with the Magellan/Clay Telescope, allowing for the determination of elemental abundances for 24 neutron-capture elements, including thorium and uranium. RAVE J2038-0023 is only the fourth metal-poor star with a clearly measured U abundance. The derived chemical-abundance pattern exhibits good agreement with those of other known highly r-process-enhanced stars, and evidence in hand suggests that it is not an actinide-boost star. Age estimates were calculated using Th/X and U/X abundance ratios, yielding a mean age of 13.0 +/- 1.1 Gyr.