Browsing by Subject "photometry"

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The ACS Survey Of Galactic Globular Clusters. VIII. Effects Of Environment On Globular Cluster Global Mass Functions
(2010-02) Paust, Nathaniel EQ; Reid, I. Neill; Piotto, Giampaolo; Aparicio, Antonio; Anderson, Jay; Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Hempel, Maren; Majewski, Steven; Marin-Franch, A.; Milone, Antonio; Rosenberg, Alfred; Siegel, Michael; Siegel, Michael
We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, approximate to 0.8 M(circle dot), to 0.2-0.3 M(circle dot) on the lower main sequence. The slopes of those power-law fits, alpha, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form of the present-day mass function. We do not confirm previous suggestions of correlations between alpha and either metallicity or Galactic location. However, we do find a strong statistical correlation with the related parameters central surface brightness, mu(V), and inferred central density, rho(0). The correlation is such that clusters with denser cores (stronger binding energy) tend to have steeper mass functions (a higher proportion of low-mass stars), suggesting that dynamical evolution due to external interactions may have played a key role in determining alpha. Thus, the present-day mass function may owe more to nurture than to nature. Detailed modeling of external dynamical effects is therefore a requisite for determining the initial mass function for Galactic globular clusters.
Angular Momenta, Dynamical Masses, And Mergers Of Brightest Cluster Galaxies
(2013-12) Tran, Kim-Vy; Brough, Sarah; Gebhardt, Karl; von der Linden, Anja; Couch, Warrick J.; Sharp, Rob; Gebhardt, Karl
Using the VIMOS integral field unit (IFU) spectrograph on the Very Large Telescope, we have spatially mapped the kinematic properties of 10 nearby brightest cluster galaxies (BCGs) and 4 BCG companion galaxies located within a redshift of z = 0.1. In the hierarchical formation model, these massive galaxies (10(10.5) M-circle dot < M-dyn < 10(11.9) M-circle dot) are expected to undergo more mergers than lower mass galaxies, and simulations show that dry minor mergers can remove angular momentum. We test whether BCGs have low angular momenta by using the lambda(Re) parameter developed by the SAURON and ATLAS(3D) teams and combine our kinematics with Sloan Digital Sky Survey photometry to analyze the BCGs' merger status. We find that 30% (3/10) of the BCGs and 100% of the companion galaxies (4/4) are fast rotators as defined by the ATLAS(3D) criteria. Our fastest rotating BCG has a lambda(Re) = 0.35 +/- 0.05. We increase the number of BCGs analyzed from 1 in the combined SAURON and ATLAS(3D) surveys to 11 BCGs total and find that above M-dyn similar to 11.5 M-circle dot, virtually all galaxies, regardless of environment, are slow rotators. To search for signs of recent merging, we analyze the photometry of each system and use the G - M-20 selection criteria to identify mergers. We find that 40% +/- 20% of our BCGs are currently undergoing or have recently undergone a merger (within 0.2 Gyr). Surprisingly, we find no correlation between galaxies with high angular momentum and morphological signatures of merging.
Beyond The Brim Of The Hat: Kinematics Of Globular Clusters Out To Large Radii In The Sombrero Galaxy
(2014-06) Dowell, Jessica L.; Rhode, Katherine L.; Bridges, Terry J.; Zepf, Stephen E.; Gebhardt, Karl; Freeman, Ken C.; de Boer, Elizabeth Wylie; Gebhardt, Karl
We have obtained radial velocity measurements for 51 new globular clusters around the Sombrero galaxy. These measurements were obtained using spectroscopic observations from the AAOmega spectrograph on the Anglo-Australian Telescope and the Hydra spectrograph at WIYN. Combining our own past measurements and velocity measurements obtained from the literature, we have constructed a large database of radial velocities that contains a total of 360 confirmed globular clusters. Previous studies' analyses of the kinematics and mass profile of the Sombrero globular cluster system have been constrained to the inner similar to 9' (similar to 24 kpc or similar to 5R(e)), but our new measurements have increased the radial coverage of the data, allowing us to determine the kinematic properties of M104 out to similar to 15' (similar to 41 kpc or similar to 9R(e)). We use our set of radial velocities to study the GC system kinematics and to determine the mass profile and V-band mass-to-light profile of the galaxy. We find that M/L-V increases from 4.5 at the center to a value of 20.9 at 41 kpc (similar to 9R(e) or 15'), which implies that the dark matter halo extends to the edge of our available data set. We compare our mass profile at 20 kpc (similar to 4R(e) or similar to 7.'4) to the mass computed from X-ray data and find good agreement. We also use our data to look for rotation in the globular cluster system as a whole, as well as in the red and blue subpopulations. We find no evidence for significant rotation in any of these samples.
The Cluster Of Blue Stars Surrounding The M31 Nuclear Black Hole
(2012-02) Lauer, Tod R.; Bender, Ralf; Kormendy, John; Rosenfield, Philip; Green, Richard F.; Kormendy, John
We obtained U330- and B-band images of the M31 nucleus using the High Resolution Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The spatial resolution in the U-330 band, 0.'' 03 FWHM, or 0.1 pc at M31, is sufficient to resolve the outskirts of the compact cluster (P3) of UV-bright stars surrounding the M31 black hole. The center of the cluster is marked by an extended source that is both brighter and redder than the other point sources within P3; it is likely to be a blend of several bright stars. We hypothesize that it marks the location of the M31 black hole. Both stellar photometry and a surface brightness fluctuation analysis show that the P3 stellar population is consistent with early-type main-sequence stars formed in a similar to 100-200 Myr old starburst population. Evolutionary tracks of post early asymptotic giant branch (PEAGB) stars, associated with late-stage evolution of an old population, also traverse the U and U - B domain occupied by the P3 stars; but we argue that only a few stars could be accounted for that way. PEAGB evolution is very rapid, and there is no progenitor population of red giants associated with P3. The result that P3 comprises young stars is consistent with inferences from earlier HST observations of the integrated light of the cluster. Like the Milky Way, M31 harbors a black hole closely surrounded by apparently young stars.
Color Variability Of HBC 722 In The Post-Outburst Phases
(2015) Baek, Giseon; Pak, Soojong; Green, Joel D.; Meschiari, Stefano; Lee, Jeong-Eun; Jeon, Yiseul; Choi, Changsu; Im, Myungshin; Sung, Hyun-Il; Park, Won-Kee; Green, Joel D.; Meschiari, Stefano
We carried out photometric observations for HBC 722 in the Sloan Digital Sky Survey r, i, and z bands from 2011 April to 2013 May with the Camera for QUasars in EArly uNiverse attached to the 2.1 m Otto Struve telescope at McDonald Observatory. The post-outburst phenomena were classified into five phases according to not only brightness but also color variations, which might be caused by physical changes in the emitting regions of optical and near-infrared bands. A series of spectral energy distributions (SEDs) is presented to support color variations and track the time evolution of the SED in optical/near-infrared bands after the outburst. Given two years of data, possible periodicities of r, i, and z bands were checked. We found three families of signals around similar to 6, similar to 10, and similar to 1 days in three bands, which is broadly consistent with Green et al. We also examined short-term variability (intra-day and day scales) to search for evidences of flickering by using the micro-variability method. We found clear signs of day scale variability and weak indications of intra-day scale fluctuations, which implies that the flickering event occurs in HBC 722 after outburst.
A Critical Assessment Of Photometric Redshift Methods: A CANDELS Investigation
(2013-10) Dahlen, Tomas; Mobasher, Bahram; Faber, Sandra M.; Ferguson, Henry C.; Barro, Guillermo; Finkelstein, Steven L.; Finlator, Kristian; Fontana, Adriano; Gruetzbauch, Ruth; Johnson, Seth; Pforr, Janine; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn; Acquaviva, Viviana; Dickinson, Mark E.; Guo, Yicheng; Huang, Jiasheng; Huang, Kuang-Han; Newman, Jeffrey A.; Bell, Eric F.; Conselice, Christopher J.; Galametz, Audrey; Gawiser, Eric; Giavalisco, Mauro; Grogin, Norman A.; Hathi, Nimish; Kocevski, Dale; Koekemoer, Anton M.; Koo, David C.; Lee, Kyoung-Soo; McGrath, Elizabeth J.; Papovich, Casey; Peth, Michael; Ryan, Russell; Somerville, Rachel; Weiner, Benjamin; Wilson, Grant; Finkelstein, Steven L.
We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from 11 participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs), and priors, are used to examine the properties of photometric redshifts applied to deep fields with broadband multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find that codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting, or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter; the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates.
Discovery Of A Low-Mass Companion To The Solar-Type Star Tyc 2534-698-1
(2009-02) Kane, Steven R.; Mahadevan, Suvrath; Cochran, William D.; Street, Rachel A.; Sivarani, Thirupathi; Henry, Gregory W.; Williamson, Michael H.; Cochran, William D.
Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M(circle dot) and an orbital period of similar to 103 days for the companion. Photometry outside of the transit window shows the star to be stable to within similar to 6 millimags. The semimajor axis of the orbit places the companion in the "brown dwarf desert" and we discuss potential follow-up observations that could constrain the mass of the companion.
The Discovery Of Hd 37605C And A Dispositive Null Detection Of Transits Of Hd 37605B
(2012-12) Wang, Sharon Xuesong; Wright, Jason T.; Cochran, William; Kane, Steven R.; Henry, Gregory W.; Payne, Matthew J.; Endl, Michael; MacQueen, Phillip J.; Valenti, Jeff A.; Antoci, Victoria; Dragomir, Diana; Matthews, Jaymie M.; Howard, Andrew W.; Marcy, Geoffrey W.; Isaacson, Howard; Ford, Eric B.; Mahadevan, Suvrath; von Braun, Kaspar; Cochran, William; Endl, Michael; MacQueen, Phillip
We report the radial velocity discovery of a second planetary mass companion to the K0 V star HD 37605, which was already known to host an eccentric, P similar to 55 days Jovian planet, HD 37605b. This second planet, HD 37605c, has a period of similar to 7.5 years with a low eccentricity and an M sin i of similar to 3.4 M-Jup. Our discovery was made with the nearly 8 years of radial velocity follow-up at the Hobby-Eberly Telescope and Keck Observatory, including observations made as part of the Transit Ephemeris Refinement and Monitoring Survey effort to provide precise ephemerides to long-period planets for transit follow-up. With a total of 137 radial velocity observations covering almost 8 years, we provide a good orbital solution of the HD 37605 system, and a precise transit ephemeris for HD 37605b. Our dynamic analysis reveals very minimal planet-planet interaction and an insignificant transit time variation. Using the predicted ephemeris, we performed a transit search for HD 37605b with the photometric data taken by the T12 0.8 m Automatic Photoelectric Telescope (APT) and the MOST satellite. Though the APT photometry did not capture the transit window, it characterized the stellar activity of HD 37605, which is consistent of it being an old, inactive star, with a tentative rotation period of 57.67 days. The MOST photometry enabled us to report a dispositive null detection of a non-grazing transit for this planet. Within the predicted transit window, we exclude an edge-on predicted depth of 1.9% at the >> 10 sigma level, and exclude any transit with an impact parameter b > 0.951 at greater than 5 sigma. We present the BOOTTRAN package for calculating Keplerian orbital parameter uncertainties via bootstrapping. We made a comparison and found consistency between our orbital fit parameters calculated by the RVLIN package and error bars by BOOTTRAN with those produced by a Bayesian analysis using MCMC.
The Discovery Of Stellar Oscillations In The K Giant Iota Draconis
(2008-11) Zechmeister, M.; Reffert, S.; Hatzes, A. P.; Endl, M.; Quirrenbach, A.; Endl, M.
iota Dra (HIP 75458) is a well-known example of a K giant hosting a substellar companion. We present radial velocity measurements of this star from observations taken with three different instruments spanning nearly 8 years. They show more clearly that the RV period is long-lived and coherent thus supporting the companion hypothesis. The longer time baseline now allows for a more accurate determination of the orbit with a revised period of P = 511 d and an additional small linear trend, indicative of another companion in a wide orbit. Moreover we show that the star exhibits low amplitude, solar-like oscillations with frequencies around 3-4 d(-1) (34.7-46.3 mu Hz).
A Dynamical N-Body Model For The Central Region Of Omega Centauri
(2012-02) Jalali, B.; Baumgardt, H.; Kissler-Patig, M.; Gebhardt, K.; Noyola, E.; Lutzgendorf, N.; de Zeeuw, P. T.; Gebhardt, K.
Context. Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of SMBHs from seed intermediate-mass black holes (IMBHs, 10(2) to 10(5)M(circle dot)) formed in star clusters. In this context, and also with respect to the low mass end of the M-center dot - sigma relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Among Galactic star clusters, the massive cluster omega Centauri is a special target due to its central high velocity dispersion and also its multiple stellar populations. Aims. We study the central structure and dynamics of the star cluster omega Centauri to examine whether an IMBH is necessary to explain the observed velocity dispersion and surface brightness profiles. Methods. We perform direct N-body simulations on GPU and GRAPE special purpose computers to follow the dynamical evolution of omega Centauri. The simulations are compared to the most recent data-sets in order to explain the present-day conditions of the cluster and to constrain the initial conditions leading to the observed profiles. Results. We find that starting from isotropic spherical multi-mass King models and within our canonical assumptions, a model with a central IMBH mass of 2% of the cluster stellar mass, i.e. a 5. x 104 M-circle dot IMBH, provides a satisfactory fit to both the observed shallow cusp in surface brightness and the continuous rise towards the center of the radial velocity dispersion profile. In our isotropic spherical models, the predicted proper motion dispersion for the best-fit model is the same as the radial velocity dispersion one. Conclusions. We conclude that with the presence of a central IMBH in our models, we reproduce consistently the rise in the radial velocity dispersion. Furthermore, we always end up with a shallow cusp in the projected surface brightness of our model clusters containing an IMBH. In addition, we find that the M/L ratio seems to be constant in the central region, and starts to rise slightly from the core radius outwards for all models independent of the presence of a black hole. Considering our initial parameter space, it is not possible to explain the observations without a central IMBH for omega Centauri. To further strengthen the presence of an IMBH as a unique explanation of the observed light and kinematics more detailed analysis such as investigating the contribution of primordial binaries and different anisotropy profiles should be studied.
EPOXI: Comet 103P/Hartley 2 Observations from a Worldwide Campaign
(2011-06) Meech, K. J.; A'Hearn, M. F.; Adams, J. A.; Bacci, P.; Bai, J.; Barrera, L.; Battelino, M.; Bauer, J. M.; Becklin, E.; Bhatt, B.; Biver, N.; Bockelee-Morvan, D.; Bodewits, D.; Bohnhardt, H.; Boissier, J.; Bonev, B. P.; Borghini, W.; Brucato, J. R.; Bryssinck, E.; Buie, M. W.; Canovas, H.; Castellano, D.; Charnley, S. B.; Chen, W. P.; Chiang, P.; Choi, Y. J.; Christian, D. J.; Chuang, Y. L.; Cochran, Anita L.; Colom, P.; Combi, M. R.; Coulson, I. M.; Crovisier, J.; Dello Russo, N.; Dennerl, K.; DeWahl, K.; DiSanti, M. A.; Facchini, M.; Farnham, T. L.; Fernandez, Y.; Floren, H. G.; Frisk, U.; Fujiyoshi, T.; Furusho, R.; Fuse, T.; Galli, G.; Garcia-Hernandez, D. A.; Gersch, A.; Getu, Z.; Gibb, E. L.; Gillon, M.; Guido, E.; Guillermo, R. A.; Hadamcik, E.; Hainaut, O.; Hammel, H. B.; Harker, D. E.; Harmon, J. K.; Harris, W. M.; Hartogh, P.; Hashimoto, M.; Hausler, B.; Herter, T.; Hjalmarson, A.; Holland, S. T.; Honda, M.; Hosseini, S.; Howell, E. S.; Howes, N.; Hsieh, H. H.; Hsiao, H. Y.; Hutsemekers, D.; Immler, S. M.; Jackson, W. M.; Jeffers, S. V.; Jehin, E.; Jones, T. J.; Ovelar, M. D.; Kaluna, H. M.; Karlsson, T.; Kawakita, H.; Keane, J. V.; Keller, L. D.; Kelley, M. S.; Kinoshita, D.; Kiselev, N. N.; Kleyna, J.; Knight, M. M.; Kobayashi, H.; Kobulnicky, H. A.; Kolokolova, L.; Kreiny, M.; Kuan, Y. J.; Kuppers, M.; Lacruz, J. M.; Landsman, W. B.; Lara, L. M.; Lecacheux, A.; Levasseur-Regourd, A. C.; Li, B.; Licandro, J.; Ligustri, R.; Lin, Z. Y.; Lippi, M.; Lis, D. C.; Lisse, C. M.; Lovell, A. J.; Lowry, S. C.; Lu, H.; Lundin, S.; Magee-Sauer, K.; Magain, P.; Manfroid, J.; Epifani, E. M.; McKay, A.; Melita, M. D.; Mikuz, H.; Milam, S. N.; Milani, G.; Min, M.; Moreno, R.; Mueller, B. E. A.; Mumma, M. J.; Nicolini, M.; Nolan, M. C.; Nordh, H. L.; Nowajewski, P. B.; Team, O.; Ootsubo, T.; Paganini, L.; Perrella, C.; Pittichova, J.; Prosperi, E.; Radeva, Y. L.; Reach, W. T.; Remijan, A. J.; Rengel, M.; Riesen, T. E.; Rodenhuis, M.; Rodriguez, D. P.; Russell, R. W.; Sahu, D. K.; Samarasinha, N. H.; Caso, A. S.; Sandqvist, A.; Sarid, G.; Sato, M.; Schleicher, D. G.; Schwieterman, E. W.; Sen, A. K.; Shenoy, D.; Shi, J. C.; Shinnaka, Y.; Skvarc, J.; Snodgrass, C.; Sitko, M. L.; Sonnett, S.; Sosseini, S.; Sostero, G.; Sugita, S.; Swinyard, B. M.; Szutowicz, S.; Takato, N.; Tanga, P.; Taylor, P. A.; Tozzi, G. P.; Trabatti, R.; Trigo-Rodriguez, J. M.; Tubiana, C.; de Val-Borro, M.; Vacca, W.; Vandenbussche, B.; Vaubaillion, J.; Velichko, F. P.; Velichko, S. F.; Vervack, R. J.; Vidal-Nunez, M. J.; Villanueva, G. L.; Vinante, C.; Vincent, J. B.; Wang, M.; Wasserman, L. H.; Watanabe, J.; Weaver, H. A.; Weissman, P. R.; Wolk, S.; Wooden, D. H.; Woodward, C. E.; Yamaguchi, M.; Yamashita, T.; Yanamandra-Fischer, P. A.; Yang, B.; Yao, J. S.; Yeomans, D. K.; Zenn, T.; Zhao, H.; Ziffer, J. E.; Cochran, Anita L.
Earth- and space-based observations provide synergistic inFormation for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was similar to 16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production.
The Fast Declining Type Ia Supernova 2003Gs, And Evidence For A Significant Dispersion In Near-Infrared Absolute Magnitudes Of Fast Decliners At Maximum Light
(2009-12) Krisciunas, Kevin; Marion, G. H.; Suntzeff, Nicholas B.; Blanc, Guillaume; Bufano, Filomena; Candia, Pablo; Cartier, Regis; Elias-Rosa, Nancy; Espinoza, Juan; Gonzalez, David; Gonzalez, Luis; Gonzalez, Serio; Gooding, Samuel D.; Hamuy, Mario; Knox, Ethan A.; Milne, Peter A.; Morrell, Nidia; Phillips, Mark M.; Stritzinger, Maximillian; Thomas-Osip, Joanna; Marion, G. H.
We obtained optical photometry of SN 2003gs on 49 nights, from 2 to 494 days after T(B(max)). We also obtained near-IR photometry on 21 nights. SN 2003gs was the first fast declining Type Ia SN that has been well observed since SN 1999by. While it was subluminous in optical bands compared to more slowly declining Type Ia SNe, it was not subluminous at maximum light in the near-IR bands. There appears to be a bimodal distribution in the near-IR absolute magnitudes of Type Ia SNe at maximum light. Those that peak in the near-IR after T(B(max)) are subluminous in the all bands. Those that peak in the near-IR prior to T(B(max)), such as SN 2003gs, have effectively the same near-IR absolute magnitudes at maximum light regardless of the decline rate Delta m(15)(B). Near-IR spectral evidence suggests that opacities in the outer layers of SN 2003gs are reduced much earlier than for normal Type Ia SNe. That may allow gamma rays that power the luminosity to escape more rapidly and accelerate the decline rate. This conclusion is consistent with the photometric behavior of SN 2003gs in the IR, which indicates a faster than normal decline from approximately normal peak brightness.
The First Two Transient Supersoft X-Ray Sources In M 31 Globular Clusters And The Connection To Classical Novae
(2009-06) Henze, M.; Pietsch, W.; Haberl, F.; Sala, G.; Quimby, R.; Hernanz, M.; Della Valle, M.; Milne, P.; Williams, G. G.; Burwitz, V.; Greiner, J.; Stiele, H.; Hartmann, D. H.; Kong, A. K. H.; Hornoch, K.; Quimby, R.
Context. Classical novae (CNe) have been found to represent the major class of supersoft X-ray sources (SSSs) in our neighbour galaxy M 31. Aims. We determine the properties and evolution of the two first SSSs ever discovered in the M 31 globular cluster (GC) system. Methods. We have used XMM-Newton, Chandra and Swift observations of the centre region of M 31 to discover both SSSs and to determine their X-ray light curves and spectra. We performed detailed analysis of XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and NLTE white dwarf (WD) atmosphere models. For the SSS in Bol 194 (SS2) we used optical monitoring data to search for an optical counterpart. Results. Both GC X-ray sources were classified as SSS. We identify SS1 with the CN M31N 2007-06b recently discovered in the M 31 GC Bol 111. For SS2 we did not find evidence for a recent nova outburst and can only provide useful constraints on the time of the outburst of a hypothetical nova. Conclusions. The only known CN in a M 31 GC can be identified with the first SSS found in a M 31 GC. We discuss the impact of our observations on the nova rate for the M 31 GC system.
A Four-Planet System Orbiting The K0V Star HD 141399
(2014-06) Vogt, Steven S.; Butler, R. Paul; Rivera, Eugenio J.; Kibrick, Robert; Burt, Jennifer; Hanson, Russell; Meschiari, Stefano; Henry, Gregory W.; Laughlin, Gregory; Meschiari, Stefano
We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 yr suggest the presence of four planets with orbital periods of 94.35, 202.08, 1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69M(J), respectively. The orbital eccentricities of the three inner planets are small, and the phase curves are well sampled. The inner two planets lie just outside the 2:1 resonance, suggesting that the system may have experienced dissipative evolution during the protoplanetary disk phase. The fourth companion is a Jupiter-like planet with a Jupiter-like orbital period. Its orbital eccentricity is consistent with zero, but more data will be required for an accurate eccentricity determination.
Galactic Globular and Open Clusters in the Sloan DIGITal Sky Survey. I. Crowded-Field Photometry and Cluster Fiducial Sequences in Ugriz
(2008-12) An, Deokkeun; Johnson, Jennifer A.; Clem, James L.; Yanny, Brian; Rockosi, Constance M.; Morrison, Heather L.; Harding, Paul; Gunn, James E.; Prieto, Carlos Allende; Beers, Timothy C.; Cudworth, Kyle M.; Ivans, Inese I.; Ivezic, Zeljko; Lee, Young Sun; Lupton, Robert H.; Bizyaev, Dmitry; Brewington, Howard; Malanushenko, Elena; Malanushenko, Viktor; Oravetz, Dan; Pan, Kaike; Simmons, Audrey; Snedden, Stephanie; Watters, Shannon; York, Donald G.; Prieto, Carlos Allend
We present photometry for globular and open cluster stars observed with the Sloan Digital Sky Survey (SDSS). In order to exploit the over 100 million stellar objects with r < 22:5 mag observed by SDSS, we need to understand the characteristics of stars in the SDSS ugriz filters. While star clusters provide important calibration samples for stellar colors, the regions close to globular clusters, where the fraction of field stars is smallest, are too crowded for the standard SDSS photometric pipeline to process. To complement the SDSS imaging survey, we reduce the SDSS imaging data for crowded cluster fields using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17 globular clusters and three open clusters in a SDSS value-added catalog. Our photometry and cluster fiducial sequences are on the native SDSS 2.5 m ugriz photometric system, and the fiducial sequences can be directly applied to the SDSS photometry without relying on any transFormations. Model photometry for red giant branch and main-sequence stars obtained by Girardi et al. cannot be matched simultaneously to fiducial sequences; their colors differ by similar to 0.02-0.05 mag. Good agreement (similar to 0.02 mag in colors) is found with Clem et al. empirical fiducial sequences in u'g'r'i'z' when using the transFormation equations in Tucker et al.
The Hubble Space Telescope Advanced Camera for Surveys Coma Cluster Survey. I. Survey Objectives and Design
(2008-06) Carter, David; Goudfrooij, Paul; Mobasher, Bahram; Ferguson, Henry C.; Puzia, Thomas H.; Aguerri, Alfonso L.; Balcells, Marc; Batcheldor, Dan; Bridges, Terry J.; Davies, Jonathan I.; Erwin, Peter; Graham, Alister W.; Guzman, Rafael; Hammer, Derek; Hornschemeier, Ann; Hoyos, Carlos; Hudson, Michael J.; Huxor, Avon; Jogee, Shardha; Komiyama, Yutaka; Lotz, Jennifer; Lucey, John R.; Marzke, Ronald O.; Merritt, David; Miller, Bryan W.; Miller, Neal A.; Mouhcine, Mustapha; Okamura, Sadanori; Peletier, Reynier F.; Phillipps, Steven; Poggianti, Bianca M.; Sharples, Ray M.; Smith, Russell J.; Trentham, Neil; Tully, R. Brent; Valentijn, Edwin; Kleijn, Gijs Verdoes; Jogee, Shardha
We describe the HST ACS Coma Cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma Cluster (Abell 1656). The survey was designed to cover an area of 740 arcmin(2) in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of 2007 January 27 leaves the survey 28% complete, with 21 ACS pointings (230 arcmin(2)) complete, and partial data for a further four pointings (44 arcmin(2)). The predicted survey depth for 10 sigma detections for optimal photometry of point sources is g' = 27.6 in the F475W filter and I-C = 26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g' = 27.55 and I-C = 26.65. For extended sources, the predicted 10 sigma limits for a 1 arcsec(2) region are g' = 25.8 mag arcsec(-2) and I-C = 25.0 mag arcsec(-2). We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultracompact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well-known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies.
Hubble Space Telescope Spectroscopy Of Brown Dwarfs Discovered With The Wide-Field Infrared Survey Explorer
(2015-05) Schneider, Adam C.; Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Mace, Gregory N.; Wright, Edward L.; Eisenhardt, Peter R.; Skrutskie, M. F.; Griffith, Roger L.; Marsh, Kenneth A.; Mace, Gregory N.
We present a sample of brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE) for which we have obtained Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-infrared grism spectroscopy. The sample (22 in total) was observed with the G141 grism covering 1.10-1.70 mu m, while 15 were also observed with the G102 grism, which covers 0.90-1.10 mu m. The additional wavelength coverage provided by the G102 grism allows us to (1) search for spectroscopic features predicted to emerge at low effective temperatures (e.g., ammonia bands) and (2) construct a smooth spectral sequence across the T/Y boundary. We find no evidence of absorption due to ammonia in the G102 spectra. Six of these brown dwarfs are new discoveries, three of which are found to have spectral types of T8 or T9. The remaining three, WISE J082507.35+280548.5 (Y0.5), WISE J120604.38+840110.6 (Y0), and WISE J235402.77+024015.0 (Y1), are the 19th, 20th, and 21st spectroscopically confirmed Y dwarfs to date. We also present HST grism spectroscopy and reevaluate the spectral types of five brown dwarfs for which spectral types have been determined previously using other instruments.
A Hubble Space Telescope Transit Light Curve For GJ 436B
(2008-08) Bean, J. L.; Benedict, G. F.; Charbonneau, D.; Homeier, D.; Taylor, D. C.; McArthur, B.; Seifahrt, A.; Dreizler, S.; Reiners, A.; Benedict, G. F.
We present time series photometry for six partial transits of GJ 436b obtained with the Fine Guidance Sensor instrument on the Hubble Space Telescope (HST). Our analysis of these data yields independent estimates of the host star's radius R-* = 0.505(-0.029) (+0.020) R-circle dot, and the planet's orbital period P = 2.643882(-0.000058)(+0.000060) d, orbital inclination i = 85.80 degrees(-0.25 degrees),(+ 0.21 degrees), mean central transit time T-c = 2 454 455.279241(-0.00025)(+0.00026) HJD, and radius Rp = 4.90(-0.33)(+ 0.45) R-circle plus. The radius we determine for the planet is larger than the previous findings from analyses of an infrared light curve obtained with the Spitzer Space Telescope. Although this discrepancy has a 92% formal significance (1.7s), it might be indicative of systematic errors that still influence the analyses of even the highest-precision transit light curves. Comparisons of all the measured radii to theoretical models suggest that GJ 436b has a H/ He envelope of similar to 10% by mass. We point out the similarities in structure between this planet and Uranus and Neptune and discuss possible parallels between these planets' formation environments and dynamical evolution. We also find that the transit times for GJ 436b are constant to within 10s over the 11 planetary orbits that the HST data span. However, the ensemble of published values exhibits a long-term drift and our mean transit time is 128 s later than that expected from the Spitzer ephemeris. The sparseness of the currently available data hinders distinguishing between an error in the orbital period or perturbations arising from an additional object in the system as the cause of the apparent trend. Assuming the drift is due to an error in the orbital period we obtain an improved estimate for it of P = 2.643904 +/- 0.000005 d. This value and our measured transit times will serve as important benchmarks in future studies of the GJ 436 system.
Identification Of Faint Chandra X-Ray Sources In The Core-Collapsed Globular Cluster NGC 6397: Evidence For A Bimodal Cataclysmic Variable Population
(2010-10) Cohn, Haldan N.; Lugger, Phyllis M.; Couch, Sean M.; Anderson, Jay; Cool, Adrienne M.; van den Berg, Maureen; Bogdanov, Slavko; Heinke, Craig O.; Grindlay, Jonathan E.; Couch, Sean M.
We have searched for optical identifications for 79 Chandra X-ray sources that lie within the half-mass radius of the nearby, core-collapsed globular cluster NGC 6397, using deep Hubble Space Telescope Advanced Camera for Surveys Wide Field Channel imaging in H alpha, R, and B. Photometry of these images allows us to classify candidate counterparts based on color-magnitude diagram location. In addition to recovering nine previously detected cataclysmic variables (CVs), we have identified six additional faint CV candidates, a total of 42 active binaries (ABs), two millisecond pulsars, one candidate active galactic nucleus, and one candidate interacting galaxy pair. Of the 79 sources, 69 have a plausible optical counterpart. The 15 likely and possible CVs in NGC 6397 mostly fall into two groups: a brighter group of six for which the optical emission is dominated by contributions from the secondary and accretion disk and a fainter group of seven for which the white dwarf dominates the optical emission. There are two possible transitional objects that lie between these groups. The faintest CVs likely lie near the minimum of the CV period distribution, where an accumulation is expected. The spatial distribution of the brighter CVs is much more centrally concentrated than those of the fainter CVs and the ABs. This may represent the result of an evolutionary process in which CVs are produced by dynamical interactions, such as exchange reactions, near the cluster center and are scattered to larger orbital radii, over their lifetimes, as they age and become fainter.
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades
(2009-05) Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; van Dyk, David; Jeffery, Elizabeth; Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; Jeffery, Elizabeth
We have extended our Bayesian modeling of stellar clusters-which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres-to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 +/- 45 Myr, consistent with the best prior analysis of the cluster main-sequence turnoff (MSTO) age by Perryman et al. Since the faintest WDs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's WD age. Our result demonstrates the power of the bright WD technique for deriving ages and further demonstrates complete age consistency between WD cooling and MSTO ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr.