Mayall II = G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy ?

(Abridged version) Mayall II = G1 is one of the brightest globular clusters belonging to M31, the Andromeda galaxy. Our observations with HST/WFPC2 provide data for the (I vs. V-I) and (V vs. V-I) color-magnitude diagrams. From model fitting, we determine a rather high mean metallicity of [Fe/H] = --0.95 +- 0.09, somewhat similar to 47 Tucanae. We find a larger spread in V-I than can be explained by the measurement errors, and we attribute this to an intrinsic metallicity dispersion amongst the stars of G1. So far, only omega Centauri, the giant Galactic globular cluster, has been known to exhibit such an intrinsic metallicity dispersion. Three estimates of the total mass of this globular cluster can be obtained: King mass = 15 x 10^6 with M/Lv ~ 7.5, Virial mass = 7.3 x 10^6 with M/Lv ~ 3.6, and King-Michie mass range from 14 to 17 x 10^6. Although uncertain, all of these mass estimates make G1 more than twice as massive as omega Centauri. Such large masses relate to the metallicity spread whose origin is still unknown (either self-enrichment, an inhomogeneous proto-cluster cloud, or remaining core of a dwarf galaxy). When considering the positions of G1 in the different diagrams defined by Kormendy (1985), G1 always appears on the sequence defined by globular clusters, and definitely away from the other sequences defined by elliptical galaxies, bulges, and dwarf spheroidal galaxies. The same is true for omega Centauri and for the nucleus of the dwarf elliptical NGC 205. This does not prove that all (massive) globular clusters are the remnant cores of nucleated dwarf galaxies.Comment: 24 pages, 5 figures, accepted for publication in AJ (August 2001

GAMBARAN KELUHAN PENYAKIT DEKOMPRESI PADA PENYELAM TRADISIONAL DI KAMPUNG SIMUENG KABUPATEN KEPULAUAN SANGIHE TAHUN 2017

Pada dasarnya nelayan penyelam tradisional yang sering disebut dengan nelayan kompresor yaitu penyelam yang menggunakan peralatan sangat terbatas. Potensi bahaya dapat dilihat juga dari perilaku nelayan yang bekerja tanpa memperhatikan aspek keselamatan (safety diving), keluhan yang sering terjadi antara lain rasa kesemutan pada daerah persendihan, gatal, keluar darah dari hidung bahkan dapat terjadi kelumpuhan (Navisah,2016). Metode yang digunakan dalam Penelitian ini ialah deskriptif dengan pendekatan survey pada 40 orang penyelam tradisional yang juga berprofesi sebagai nelayan di Kampung Simueng, Kabupaten Kepulauan Sangihe yang dilaksanakan selang bulan Mei 2017. Hasil penelitian menunjukan bahwa gejala ringan 35 % dan berat 27 % . Gejala ringan dialami berupa nyeri sendi, gatal– gatal, timbul bercak darah pada kulit dan kesemutan, adapun selain itu gejala berat yang dialami responden berupah pecah pembuluh darah, lumpuh, dan tuli. Kesimpulan dalam penelitian yakni sebagian responden mengalami gangguan akibat penyelaman, hal tersebut diakibatkan karena penyelam tidak mengikuti aturan serta standar penyelaman yang baik dan menurut para nelayan mereka belum pernah mendapatkan materi/penyuluhan tentang standar penyelaman oleh karena itu pelulis menyarankan kepada Pemerintah Daerah untuk menyelenggarakan pelatihan standar penyelaman kepada para Nelayan tersebut

Palomar 13: An Unusual Stellar System in the Galactic Halo

We have measured Keck/HIRES radial velocities for 30 candidate red giants in the direction of Palomar 13: an object traditionally cataloged as a compact, low-luminosity globular cluster. From a sample of 21 confirmed members, we find a systemic velocity of 24.1 km/s and a projected, intrinsic velocity dispersion of 2.2 km/s. Although small, this dispersion is several times larger than that expected for a globular cluster of this luminosity and central concentration. Taken at face value, this dispersion implies a mass-to-light ratio of ~ 40 (in solar units) based on the best-fit King-Michie model. The surface density profile of Palomar 13 also appears to be anomalous among Galactic globular clusters -- depending upon the details of background subtraction and model-fitting, Palomar 13 either contains a substantial population of "extra-tidal" stars, or it is far more spatially extended than previously suspected. The full surface density profile is equally well-fit by a King-Michie model having a high concentration and large tidal radius, or by a NFW model. We examine -- and tentatively reject -- a number of possible explanations for the observed characteristics of Palomar 13 (e.g., velocity "jitter" among the red giants, spectroscopic binary stars, non-standard mass functions, modified Newtonian dynamics), and conclude that the two most plausible scenarios are either catastrophic heating during a recent perigalacticon passage, or the presence of a massive dark halo. Thus, the available evidence suggests that Palomar 13 is either a globular cluster which is now in the process of dissolving into the Galactic halo, or a faint, dark-matter-dominated stellar system (ABRIDGED).Comment: 31 pages, 13 postscript figures and 1 color gif image. Also available at http://www.physics.rutgers.edu/ast/ast-rap.html. Accepted for publication in the Astrophysical Journa

The redshift of the gravitationally lensed radio source PKS1830-211

We report on the spectroscopic identification and the long awaited redshift measurement of the heavily obscured, gravitationally lensed radio source PKS 1830-211, which was first observed as a radio Einstein ring. The NE component of the doubly imaged core is identified, in our infrared spectrum covering the wavelength range 1.5-2.5 microns, as an impressively reddened quasar at z=2.507. Our redshift measurement, together with the recently measured time delay (Lovell et al.), means that we are a step closer to determining the Hubble constant from this lens. Converting the time delay into the Hubble constant by using existing models leads to high values for the Hubble constant. Since the lensing galaxy lies very close to the center of the lensed ring, improving the error bars on the Hubble constant will require not only a more precise time delay measurement, but also very precise astrometry of the whole system.Comment: 11 pages, 2 figures, Accepted ApJ

Surface Brightness Profiles of Galactic Globular Clusters from Hubble Space Telescope Images

Hubble Space Telescope allows us to study the central surface brightness profiles for globular clusters at unprecedented detail. We have mined the HST archives to obtain 38 WFPC2 images of galactic globular clusters with adequate exposure times and filters, which we use to measure their central structure. We outline a reliable method to obtain surface brightness profiles from integrated light that we test on an extensive set of simulated images. Most clusters have central surface brightness about 0.5 mag brighter than previous measurements made from ground-based data, with the largest differences around 2 magnitudes. Including the uncertainties in the slope estimates, the surface brightness slope distribution is consistent with half of the sample having flat cores and the remaining half showing a gradual decline from 0 to -0.8 (dlog(Sigma)/dlogr). We deproject the surface brightness profiles in a non-parametric way to obtain luminosity density profiles. The distribution of luminosity density logarithmic slopes show similar features with half of the sample between -0.4 and -1.8. These results are in contrast to our theoretical bias that the central regions of globular clusters are either isothermal (i.e. flat central profiles) or very steep (i.e. luminosity density slope ~-1.6) for core-collapse clusters. With only 50% of our sample having central profiles consistent with isothermal cores, King models appear to poorly represent most globular clusters in their cores.Comment: 23 pages, 14 figures, AJ accepte

Chandra Study of a Complete Sample of Millisecond Pulsars in 47Tuc and NGC6397

We report Chandra observations of the complete sample of millisecond pulsars (MSPs) with precise radio positions in the globular clusters 47Tuc (NGC104) and NGC6397. The 47Tuc MSPs are predominantly soft sources suggestive of thermal emission from small (r_x < 0.6km) polar caps on the neutron star rather than magnetospheric emission and are a relatively homogeneous sample, with most x-ray luminosities in a surprisingly narrow range (Lx ~1-4 X 10^30 erg/s). We use previously derived intrinsic Pdot values and find a new relation between Lx and spindown luminosity, Edot: Lx ~ Edot^beta, with beta ~0.5 vs. ~1.0 for both pulsars and MSPs in the field. This Lx-Edot relation and also the Lx/Edot vs. spindown age are each similar to that found by Harding & Muslimov (2002) for thermal emission from polar cap heating although the cluster MSPs are relatively longer-lived (in thermal x-rays) than either the models or field MSPs. We suggest the cluster MSPs may have altered surface magnetic field topology (e.g.multipole) or their neutron stars are more massive from repeated accretion episodes due to encounters and repeated exchange interactions. MSP binary companions on or just off the main sequence are likely to have been re-exchanged and might show anomalous Pdot and Edot values due to relaxation of misaligned core-crust spins. The radial distribution of 40 soft Chandra sources in 47Tuc is consistent with a 1.4Msun component. The implied total MSP population in 47Tuc with Lx >10^30 erg/s is ~35-90, and can constrain the relative beaming in radio vs. soft x-rays. NGC6397 is relatively deficient in MSPs; its single detected example may have been re-exchanged out of the cluster core. (abridged)Comment: 16 pages, 11 figures, 5 tables. Accepted for Ap

The low-mass Initial Mass Function in the 30 Doradus starburst cluster

We present deep Hubble Space Telescope (HST) NICMOS 2 F160W band observations of the central 56*57" (14pc*14.25pc) region around R136 in the starburst cluster 30 Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to derive the stellar Initial Mass Function (IMF) down to ~1 Msun in order to test whether the IMF in a massive metal-poor cluster is similar to that observed in nearby young clusters and the field in our Galaxy. We estimate the mean age of the cluster to be 3 Myr by combining our F160W photometry with previously obtained HST WFPC2 optical F555W and F814W band photometry and comparing the stellar locus in the color-magnitude diagram with main sequence and pre-main sequence isochrones. The color-magnitude diagrams show the presence of differential extinction and possibly an age spread of a few megayears. We convert the magnitudes into masses adopting both a single mean age of 3 Myr isochrone and a constant star formation history from 2 to 4 Myr. We derive the IMF after correcting for incompleteness due to crowding. The faintest stars detected have a mass of 0.5 Msun and the data are more than 50% complete outside a radius of 5 pc down to a mass limit of 1.1 Msun for 3 Myr old objects. We find an IMF of dN/dlog(M) M^(-1.20+-0.2) over the mass range 1.1--20 Msun only slightly shallower than a Salpeter IMF. In particular, we find no strong evidence for a flattening of the IMF down to 1.1 Msun at a distance of 5 pc from the center, in contrast to a flattening at 2 Msun at a radius of 2 pc, reported in a previous optical HST study. We examine several possible reasons for the different results. If the IMF determined here applies to the whole cluster, the cluster would be massive enough to remain bound and evolve into a relatively low-mass globular cluster.Comment: Accepted in ApJ. Abstract abridge

An Error Analysis of the Geometric Baade-Wesselink Method

We derive an analytic solution for the minimization problem in the geometric Baade-Wesselink method. This solution allows deriving the distance and mean radius of a pulsating star by fitting its velocity curve and angular diameter measured interferometrically. The method also provide analytic solutions for the confidence levels of the best fit parameters, and accurate error estimates for the Baade-Wesselink solution. Special care is taken in the analysis of the various error sources in the final solution, among which the uncertainties due to the projection factor, the limb darkening and the velocity curve. We also discuss the importance of the phase shift between the stellar lightcurve and the velocity curve as a potential error source in the geometric Baade-Wesselink method. We finally discuss the case of the Classical Cepheid zeta Gem, applying our method to the measurements derived with the Palomar Testbed Interferometer. We show how a careful treatment of the measurement errors can be potentially used to discriminate between different models of limb darkening using interferometric techniques.Comment: 24 pages, to be published on the Astrophysical Journal, vol. 603 March 200

Simultaneous Estimation of Time Delays and Quasar Structure

We expand our Bayesian Monte Carlo method for analyzing the light curves of gravitationally lensed quasars to simultaneously estimate time delays and quasar structure including their mutual uncertainties. We apply the method to HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and intrinsic variability on comparable time scales. For HE1104-1805 the resulting time delay of (Delta t_AB) = t_A - t_B = 162.2 -5.9/+6.3 days and accretion disk size estimate of log(r_s/cm) = 15.7 -0.5/+0.4 at 0.2 micron in the rest frame are consistent with earlier estimates but suggest that existing methods for estimating time delays in the presence of microlensing underestimate the uncertainties. We are unable to measure a time delay for QJ0158-4325, but the accretion disk size is log(r_s/cm) = 14.9 +/- 0.3 at 0.3 micron in the rest frame.Comment: 21 pages, 6 figures, submitted to Ap