480 research outputs found

    An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13

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    At a Galactocentric distance of 27 kpc, Pal 13 is an old globular cluster (GC) in the outer halo. We present a chemical abundance analysis of this remote system from high-resolution spectra obtained with Keck/HIRES. Owing to the low signal-to-noise ratio of the data, our analysis is based on a coaddition of the spectra of 18 member stars. We are able to determine integrated abundance ratios for 16 species of 14 elements, of Ī±\alpha-elements (Mg,Si,Ca,Ti), Fe-peak (Sc,Mn,Cr,Ni,Cu,and Zn), and n-capture elements (Y,Ba). While the mean Na abundance is found to be slightly enhanced and halo-like, our method does not allow us to probe an abundance spread that would be expected in this light element if multiple populations are present in Pal 13. We find a metal-poor mean metallicity of āˆ’1.91Ā±0.05-1.91\pm0.05 (statistical) Ā±\pm 0.22 (systematic), confirming that Pal 13 is a typical metal-poor representative of the outer halo. While there are some differences between individual Ī±\alpha-elements, such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the mean [Ī±\alpha/Fe] of 0.34Ā±\pm0.06 is consistent with the marginally lower Ī±\alpha component of the halo field and GC stars. We discuss our results in the context of other objects in the outer halo and consider which of these objects were likely accreted. We also discuss the properties of their progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of its GCs, this is not supported by its kinematic properties. Moreover, its chemodynamical similarity with NGC 5466, a progeny of the Sequoia accretion event, might indicate a common origin in this progenitor. However, the ambiguities in the full abundance space of this comparison emphasize the difficulties in unequivocally labeling a single GC as an accreted object, let alone assigning it to a single progenitor. (Abridged)Comment: 10 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

    Relation entre l'accĆØs Ć  des services pour des problĆØmes de santĆ© mentale et le partage de matĆ©riel dā€™injection chez des utilisateurs de drogue par injection Ć  MontrĆ©al

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    Objectif : Cette eĢtude voulait examiner l'association entre l'acceĢ€s aĢ€ des services pour des probleĢ€mes de santeĢ mentale et le partage reĢceptif de mateĢriel dā€™injection dans une cohorte d'utilisateurs de drogue par injection (UDIs) aĢ€ MontreĢal. De plus, elle eĢtudiait le possible effet modificateur de la deĢtresse psychologique (DP). MeĢthodologie : Les participants de la cohorte HEPCO vus entre 2011 et 2015 (n = 358) ont compleĢteĢ des questionnaires aux 3 mois. Le partage reĢceptif de mateĢriel dā€™injection eĢtait deĢfini comme eĢtant sā€™eĢ‚tre injecteĢ avec une seringue ou tout autre mateĢriel dā€™injection deĢjaĢ€ utiliseĢ par quelquā€™un dā€™autre dans les 3 derniers mois. Lā€™acceĢ€s aĢ€ des services pour des probleĢ€mes mentaux eĢtait deĢfini comme ayant visiteĢ au moins un professionnel de la santeĢ pour des probleĢ€mes mentaux dans les 3 derniers mois. La DP eĢtait mesureĢe par le Kessler Psychological Distress Scale. ReĢsultats : En analyses multivarieĢes, une association significative a eĢteĢ trouveĢe entre le partage reĢceptif de mateĢriel dā€™injection et lā€™acceĢ€s aux services pour des probleĢ€mes de santeĢ mentale. Lā€™aĢ‚ge et le sexe masculin sont associeĢs aĢ€ de plus faibles probabiliteĢs de partage, tandis que lā€™utilisation dā€™opioiĢˆdes et avoir partageĢ dans les 3 mois preĢceĢdant lā€™entrevue dā€™entreĢe sont associeĢs avec de plus grandes chances de partager. Aucune eĢvidence que la DP ne vient modifier cette association nā€™a eĢteĢ trouveĢe. Conclusion : Dans cet eĢchantillon, une association protectrice existe entre lā€™acceĢ€s aĢ€ des services pour des probleĢ€mes de santeĢ mentale et le partage reĢceptif, peu importe le degreĢ de deĢtresse psychologique.Objective: The main objective of the present study was to assess the association between access to services for mental health problem and receptive sharing of injection material among people who inject drugs (PWID) in MontrĆ©al. Moreover, it wanted to examine the potential modifying effect by the level of psychological distress (PD). Method: At 3-month intervals, between March 2011 and December 2015, participants (n = 358) answered an interviewer-administered questionnaire eliciting information on sociodemographic characteristics, substance use and related behaviours, utilization of services, and mental health indicators. Receptive sharing was defined as having injected with previously used injection material. Access to services for mental health problems was defined as at least one visit to various professionals for mental health problems. PD was measured by the Kessler Psychological Distress Scale (K10). General estimating equation (GEE) analyses were performed. Results: In multivariate analyses, a significant association was found between receptive sharing of injection material and access to services for mental health problems. Age (per 5 years increased) and male gender are associated with a lower likelihood of receptive sharing, while opioids consumption and receptive sharing in the past 3 months at baseline are associated with a higher likelihood of receptive sharing. No evidence of effect modification by psychological distress was found. Conclusion: Among PWID, access to services for mental health problems was associated with a lower likelihood of receptive sharing, regardless of the level of psychological distress

    Complex microwave conductivity of Pr1.85_{1.85}Ce0.15_{0.15}CuO4āˆ’Ī“_{4-\delta} thin films using a cavity perturbation method

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    We report a study of the microwave conductivity of electron-doped Pr1.85_{1.85}Ce0.15_{0.15}CuO4āˆ’Ī“_{4-\delta} superconducting thin films using a cavity perturbation technique. The relative frequency shifts obtained for the samples placed at a maximum electric field location in the cavity are treated using the high conductivity limit presented recently by Peligrad et\textit{et} al.\textit{al.} Using two resonance modes, TE102_{102} (16.5 GHz) and TE101_{101} (13 GHz) of the same cavity, only one adjustable parameter Ī“\Gamma is needed to link the frequency shifts of an empty cavity to the ones of a cavity loaded with a perfect conductor. Moreover, by studying different sample configurations, we can relate the substrate effects on the frequency shifts to a scaling factor. These procedures allow us to extract the temperature dependence of the complex penetration depth and the complex microwave conductivity of two films with different quality. Our data confirm that all the physical properties of the superconducting state are consistent with an order parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of these properties on the quality of the films

    The ACS Fornax Cluster Survey. III. Globular Cluster Specific Frequencies of Early-Type Galaxies

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    The globular cluster (GC) specific frequency (SNS_N), defined as the number of GCs per unit galactic luminosity, represents the efficiency of GC formation (and survival) compared to field stars. Despite the naive expectation that star cluster formation should scale directly with star formation, this efficiency varies widely across galaxies. To explore this variation we measure the z-band GC specific frequency (SN,zS_{N,z}) for 43 early-type galaxies (ETGs) from the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) Fornax Cluster Survey. Combined with the homogenous measurements of SN,zS_{N,z} in 100 ETGs from the HST/ACS Virgo Cluster Survey from Peng et al. (2008), we investigate the dependence of SN,zS_{N,z} on mass and environment over a range of galaxy properties. We find that SN,zS_{N,z} behaves similarly in the two galaxy clusters, despite the clusters' order-of-magnitude difference in mass density. The SN,zS_{N,z} is low in intermediate-mass ETGs (āˆ’20<Mz<āˆ’23-20<M_z<-23), and increases with galaxy luminosity. It is elevated at low masses, on average, but with a large scatter driven by galaxies in dense environments. The densest environments with the strongest tidal forces appear to strip the GC systems of low-mass galaxies. However, in low-mass galaxies that are not in strong tidal fields, denser environments correlate with enhanced GC formation efficiencies. Normalizing by inferred halo masses, the GC mass fraction, Ī·=(3.36Ā±0.2)Ɨ10āˆ’5\eta=(3.36\pm0.2)\times10^{-5}, is constant for ETGs with stellar masses Mā‹†ā‰²3Ɨ1010MāŠ™\mathcal{M}_\star \lesssim 3\times10^{10}M_\odot, in agreement with previous studies. The lack of correlation between the fraction of GCs and the nuclear light implies only a weak link between the infall of GCs and the formation of nuclei.Comment: 16 pages, 7 figures, 6 tables; accepted by Ap

    Galaxies at the extremes: Ultra-diffuse galaxies in the Virgo Cluster

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    We report the discovery of three large (R29 >~ 1 arcminute) extremely low surface brightness (mu_(V,0) ~ 27.0) galaxies identified using our deep, wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope. Complementary data from the Next Generation Virgo Cluster Survey do not resolve red giant branch stars in these objects down to i=24, yielding a lower distance limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii 3-10 kpc and luminosities L_V=2-9x10^7 Lsun. These galaxies are comparable in size but lower in surface brightness than the large ultradiffuse LSB galaxies recently identified in the Coma cluster, and are located well within Virgo's virial radius; two are projected directly on the cluster core. One object appears to be a nucleated LSB in the process of being tidally stripped to form a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal disruption, despite the fact that such objects should be most vulnerable to tidal destruction in the cluster environment. The relative proximity of Virgo makes these objects amenable to detailed studies of their structural properties and stellar populations. They thus provide an important new window onto the connection between cluster environment and galaxy evolution at the extremes.Comment: 7 pages, 4 figures, to appear in ApJ Letters. Updated with minor revisions to match accepted versio

    Galaxies at the extremes: Ultra-diffuse galaxies in the Virgo Cluster

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    We report the discovery of three large (R29 >~ 1 arcminute) extremely low surface brightness (mu_(V,0) ~ 27.0) galaxies identified using our deep, wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope. Complementary data from the Next Generation Virgo Cluster Survey do not resolve red giant branch stars in these objects down to i=24, yielding a lower distance limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii 3-10 kpc and luminosities L_V=2-9x10^7 Lsun. These galaxies are comparable in size but lower in surface brightness than the large ultradiffuse LSB galaxies recently identified in the Coma cluster, and are located well within Virgo's virial radius; two are projected directly on the cluster core. One object appears to be a nucleated LSB in the process of being tidally stripped to form a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal disruption, despite the fact that such objects should be most vulnerable to tidal destruction in the cluster environment. The relative proximity of Virgo makes these objects amenable to detailed studies of their structural properties and stellar populations. They thus provide an important new window onto the connection between cluster environment and galaxy evolution at the extremes.Comment: 7 pages, 4 figures, to appear in ApJ Letters. Updated with minor revisions to match accepted versio

    The ACS Virgo Cluster Survey. XVII. The Spatial Alignment of Globular Cluster Systems With Early-Type Host Galaxies

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    We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (epsilon > 0.2) and intermediate to high luminosities (M_z<-19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and where the present day major axis is an indicator of the preferred merging axis.Comment: 8 pages, 7 figures, accepted for publication in The Astrophysical Journa

    Sensory afferents use different coding strategies for heat and cold

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    Primary afferents transduce environmental stimuli into electrical activity that is transmitted centrally to be decoded into corresponding sensations. However, it remains unknown how afferent populations encode different somatosensory inputs. To address this, we performed two-photon Ca2+ imaging from thousands of dorsal root ganglion (DRG) neurons in anesthetized mice while applying mechanical and thermal stimuli to hind paws. We found that approximately half of all neurons are polymodal and that heat and cold are encoded very differently. As temperature increases, more heating-sensitive neurons are activated, and most individual neurons respond more strongly, consistent with graded coding at population and single-neuron levels, respectively. In contrast, most cooling-sensitive neurons respond in an ungraded fashion, inconsistent with graded coding and suggesting combinatorial coding, based on which neurons are co-activated. Although individual neurons may respond to multiple stimuli, our results show that different stimuli activate distinct combinations of diversely tuned neurons, enabling rich population-level coding
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