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Yale University
Department of Astronomy
1. FOREWORD
• Pierre Demarque ͑emeritus͒ — Theoretical Solar and The Department of Astronomy at Yale University is one of the oldest astronomy programs in the country, and has • Jeffrey Kenney — Observational Extragalactic As- granted Ph.D.s since the nineteenth century. Yale has tradi- tion strengths in stellar physics, stellar populations and as- • Richard Larson ͑Dir. Undergraduate Studies͒ — Theo- trometry, and newly invigorated programs in high-energy as- retical Galactic and Extragalactic Astronomy trophysics and extragalactic astronomy and cosmology. The • Priyamvada Natarajan — Theoretical Extragalactic As- department is housed on the second floor of the Gibbs Labo- ratory in New Haven, Connecticut, and owns telescopes at • Peter Parker* — Nuclear Physics, Laboratory Stellar Kitt Peak in Arizona and Cerro Tololo in Chile. The Yale Southern Observatory operates telescopes in Argentina, and • Sabatino Sofia — Observational and Theoretical Solar Yale is part of consortium that operate telescopes in Venezu- ela and on Mt. Palomar in California. Yale also has a joint • Jeffrey Snyder* — Astronomical Instrumentation, Ob- program with the University of Chile, through which re- searchers have access to the Chilean share of the many tele- • Andrew Szymkowiak* — Astronomical Instrumenta- scope facilities located in that country. Further information tion, Observational High Energy Astrophysics on all departmental activities can be found at http://www.astro.yale.edu.
• Meg Urry* — Observational High Energy Astrophysics Yale offers undergraduate and graduate degrees in As- tronomy. We typically enroll 3-4 new graduate students • William van Altena — Astrometry, Observational Ga- studying for the PhD each year. Undergraduate majors have numbered between 2 and 7 per year in recent years. Remark- • Pieter van Dokkum — Observational Extragalactic As- ably, 18 out of the last 24 undergraduate majors have been women. The relatively small size of the undergraduate major • Robert Zinn — Observational Galactic Astronomy and and the graduate program allow an unusual level of personal An event of particular importance over the past two years has been the founding of the Yale Center for Astronomy and 2.2 Post-Docs and Research Staff 2003-4
Astrophysics ͑YCAA͒. This Center, directed by Prof. Meg Michelle Buxton, Eleni Chatzichristou*, Dana Dinescu, Urry, is designed to bring together efforts in astrophysics Gordon Drukier, Eric Gawiser, Terry Girard, Dorrit Hoffleit, underway in the Departments of Astronomy, Physics and Vladimir Korchagin, Linghuai Li, Nicholas Morgan*, Sean Applied Physics at Yale. As part of the development of the O’Brien, Katherine Rhode, Kenneth Rines*, Frank Robin- YCAA, the Yale Department of Physics has initiated a major increase in its astrophysics group, including new faculty and post-doctoral positions. While this report is primarily fo-cussed on the Department of Astronomy, it should be noted 2.3 Graduate Students 2003-2004
that considerable effort, particularly in astronomical instru-mentation and cosmology, is being conducted at the YCAA Pedro Capelo, Bethany Cobb, Juan Cortes*, Hugh Crowl, outside the purview of the Astronomy Department proper.
Sonia Duffau*, Andres Escala*, Leonor Huerta*, Dipankar Many department members, including graduate students, are Maitra, Eric Murphy, Kwang-Ho Park, Ryan Quadri, Brooke Simmons, Ezequiel Triester*, Jeffrey van Duyne, KatherineVieira, Jong-Hak Woo, Bing Zhao 2. PERSONNEL
͑* ϭ Yale/Chile joint graduate program͒ 2.1 Yale Faculty
3. FACILITIES
• Charles Bailyn ͑Chair͒ — Observational High Energy 3.1 WIYN Telescope
Yale owns 1/6 of the 3.5m WIYN telescope, located at • Charles Baltay* — Observational Extragalactic As- Kitt Peak Observatory in Arizona. This modern alt-azimuth telescope has exceptionally fine image quality, with a median • Sarbani Basu ͑Dir. Graduate Studies͒ — Theoretical delivered image quality of 0.7Љ. Current instrumentation in- cludes the ‘‘mini-mosaic’’ imager, which covers a 10Ј field, • Paolo Coppi — Theoretical High Energy Astrophysics the Hydra Multi-Object Spectrograph, and the sparsepak and densepak fiber arrays. Yale researchers also use the Roches- ter Institute of Technology speckle interferometer at WIYN.
including Yale, Caltech, and JPL. In driftscan mode, this Arrangements have also been made to borrow IR imagers.
camera can obtain four-color data down to 19th magnitude Current instrumentation plans include development of a high over Ͼ 300 square degrees in a single night.
throughput spectrograph at Yale, and a One Degree Imageras a WIYN consortium project. Much of Yale’s observing 3.6 Computing
time at WIYN is devoted to graduate student research.
In addition to an extensive network of linux workstations, the department is a major player in a university-wide high- 3.2 Joint Program with the University of Chile
performance computing cluster now under construction. Fur- Yale and the University of Chile have established a Joint ther details can be obtained from Prof. Paolo Coppi.
Program in education and research in Astronomy. The re-search program provides for the creation of joint projects 4. SCIENTIFIC ACCOMPLISHMENTS
involving researchers from both institutions. Through these 4.1 Astrometry
joint projects Yale researchers have access to the wide rangeof astronomical instrumention in Chile, including the Euro- van Altena continued speckle interferometry at the WIYN pean VLT, and telescopes at CTIO, Las Campanas and La telescope in collaboration with E. Horch ͑U. Mass Dart- Silla. Current joint projects include the MUSYC Deep Sur- mouth͒ and Z. Ninkov ͑Rochester Institute of Technology͒.
veys project, the Local Group group, and a smaller project Yale Graduate student R. Meyer received his Ph.D. for a dissertation on binary star photometry, based on speckle in-terferometry. The observations at WIYN during the lastyears are a part of our long-term effort to provide high- 3.3 SMARTS
precision relative astrometry of binary stars. Relative astrom- Yale has a 14% share in the SMARTS consortium, which etry has now been published for nearly 800 speckle observa- operates four small telescopes, including the Yale 1m tele- tions at WIYN. A second major speckle program involves scope, at Cerro Tololo Interamerican Observatory in Chile.
observing Hipparcos double star discoveries since the publi- Yale faculty member Charles Bailyn serves as principal sci- cation of the Hipparcos Catalogue ͑ESA, 1997͒. Of the tar- entist of the SMARTS consortium. In 2004, it is expected gets observed, a substantial fraction of the Hipparcos stars that the SMARTS instrumentation configuration will include observed have exhibited large changes in separation and/or the CTIO 0.9m ϩ 2K CCD; the Yale 1.0m ϩ 4K CCD; the position angle since the Hipparcos observation ͑1991.25͒. To 1.3m ͑2MASS͒ telescope ϩ ANDICAM dual channel date 23 Hipparcos doubles with probable or definitive orbital optical/IR imager; and the CTIO 1.5m ϩ RC spectrograph motion have been discovered. An NSF award has just been made to Horch, van Altena and Ninkov ͑RIT͒ to use theexisting WIYN speckle archive in addition to new observa-tions and other information in the literature to investigate the 3.4 Yale Southern Observatory
statistics of binaries in the nearby region of the galaxy.
The Yale Southern Observatory operates the 51-cm Recent advances in understanding the nature of ␻ Cen- double astrograph at Cesco Observatory in El Leoncito, Ar- tauri - the most massive Milky Way globular cluster - have gentina. CCD observations have now begun with this facil- now placed on a firmer ground its accretion origin as op- ity, which is primarily used by the Yale astrometry group, posed to formation within the Milky Way. Unlike the major- directed by Prof. van Altena. Major improvements in hard- ity of the Milky Way globular clusters, ␻ Cen is a complex ware and software have greatly increased the efficiency of chemical system with an extended star formation history.
Korchagin and Dinescu, in collaboration with T. Tsuchyia of One of the original instruments of the YSO, the the Astronomishes Rechen-Institut, have explored an accre- Schlesinger 26-inch refractor was destroyed by a firestorm tion origin for omega Cen by N-body modeling of the orbital on January 18, 2003, along with the other telescopes on decay and disruption of a Milky-Way dwarf satellite. A Mount Stromlo, the workshop, library and many of the resi- range of models with two different density profiles for the dences. This event was a sad ending to a telescope that satellite, ͑King and Hernquist͒, were used in the analysis. It played a major role in defining our knowledge of the dis- was found that a capture scenario can produce an ␻ Cen-like tances, motions and masses of the brighter stars during the object, exhibiting the current low-energy orbit of the cluster.
middle of the 20th century. van Altena and Hoffleit ͑2003͒ The best model is a nucleated dwarf galaxy with a Hernquist have summarized the history of Schlesinger’s telescope.
density profile that has an initial mass of 8 ϫ 109 M ᭪ , anda half-mass radius of 1.4 kpc.
The Southern Proper Motion ͑SPM͒ Program continued, 3.5 QUEST
on several fronts, under the supervision of van Altena with The QUEST group, under the direction of Prof. Charles significant effort from Girard and Dinescu, as well as Carlos Baltay, has built two large astronomical imagers over the Lo´pez of the Universidad de San Juan, Argentina and Paulo past few years. The first is operating on the 1m Schmidt Holvorcem of the Universidade Estadual de Campinas, Bra- telescope at the Venezuelan national observatory at Llano zil. CCD observations have begun using the 51-cm double del Hato. The second is now in operation at the 1.5m astrograph at Cesco Observatory in El Leoncito, Argentina.
Schmidt telescope at Mt. Palomar, as part of a consortium These will eventually fill in the approximately two thirds of the SPM survey region for which second-epoch photographic Ph.D. thesis of A. Katherina Vivas. 380 sq. deg. of the sky observations do not exist. A new version of the SPM Catalog were surveyed for these stars in a band 2.3° wide in decli- has also been released this year, one which is based solely on nation, centered at dec.ϭϪ1°, and covering ϳ11 hours in photographic material, as in previous versions. However, this right ascension. The bright ͑due to CCD saturation͒ and the version, the SPM3 Catalog, is near-complete to Vϭ17.5, and faint limits of the survey are V ϳ13.5 and ϳ19.7 respec- contains absolute proper motions, positions, and B and V tively, which correspond to distances of ϳ4 and ϳ60 kpc photographic photometry for 10.7 million objects in the from the Sun. A total of 498 RR Lyrae variables were dis- covered in the survey, 86% of which are new. This survey has identified several substructures in the galactic halo that Based on SPM plate material, absolute proper motions of may have been produced by the tidal disruptions of satellite 4 globular clusters ͑NGC 6266, NGC 6304, NGC 6316, and galaxies or globular clusters. The most prominent feature is a NGC 6723͒, located in the bulge region, have been deter- clump of about 80 RR Lyrae variables at roughly 50 kpc mined with uncertainties ranging between 0.3 and 0.6 mas/ from the Sun. This feature, which is about 30 kpc long, is yr. The absolute proper motions are on the Hipparcos sys- part of the northern tidal stream from the Sagittarius dSph tem, and, in combination with distances and radial velocities galaxy, which had been detected previously in other types of already published, yield space velocities. Interestingly, only surveys. Other features have also been identified.
NGC 6723 of the two metal-poor clusters has kinematics A large program to measure the radial velocities and the consistent with halo membership, while that of NGC 6266 metallicities of the the RR Lyrae variables in the most con- indicates membership to a rotationally supported system of spicuous features revealed by the QUEST survey was begun the thick-disk type. The kinematics of the two metal-rich as part of the Yale-U. de Chile project on the Local Group.
clusters are consistent with their metallicity-based bulge Observations have been obtained with the 8m VLT, the 1.5m membership, however NGC 6304 seems to have significant ESO, the 3.5m WIYN, and 1.5m CTIO ͑SMARTS͒ tele- rotation, more closely resembling the thick disk, rather than scopes. The VLT observations have shown that the radial velocities of the RR Lyrae variables in the 50 kpc clump ͑see Girard, Korchagin, and van Altena submitted 88 minor- above͒ are in good agreement with the predictions of models planet position measurements to the Minor Planet Center, of the tidal streams from the Sgr dSph. The WIYN observa- based on observations with the YALO 1-m telescope at tions were obtained at the infra-red Ca II triplet during the CTIO. This is part of a NASA-funded program at Yale to same observing runs as some of the observations of the make Southern-sky observations of Near Earth Objects. This Draco and Ursa Minor dSph galaxies. Graduate student So- program is continuing, using the SMARTS 1.3-m telescope nia Duffau, Zinn, and Vivas have developed a technique to measure the metallicities of the stars using the Ca II lines,which are blended with Paschen series hydrogen lines, and 4.2 Stellar Populations and Galactic Astronomy
unblended Paschen lines as a temperature index.
The research of Robert Zinn concentrated in two areas: Winnick completed her PhD thesis under the direction of the stellar populations of the satellite galaxies of the Milky Zinn, and continued to work at Yale as a SMARTS post-doc.
Way and the detection of substructure in the Milky Way’s Using the 3.5m WIYN telescope and the Hydra multiobject halo. The major goals were to document the star formation spectrograph, she measured the metallicities of numerous and chemical enrichment histories of dwarf galaxies and to stars in three nearby dwarf spheroidal galaxies. The large determine whether the galactic halo contains stellar streams samples of stars in each of Draco, Ursa Minor and Sculptor from disrupted satellite galaxies. As part of the Yale-U. de allow a more detailed study of the metallicity distributions.
Chile joint project on the Local Group galaxies, both spec- Despite similar abundance spreads, each galaxy exhibits a troscopic and photometric observations of the Fornax dwarf different distribution. The differences suggest that star for- spheroidal ͑dSph͒ galaxy were obtained with 8m VLT.
mation and chemical enrichment processes proceeded some- Color-magnitude diagrams that extend ϳ2 magnitudes be- low the main-sequence turnoff of the oldest stars were con- Also as part of the Calan-Yale Local Group Key Project, structed for three fields in Fornax. The spectroscopic obser- Demarque has published three papers on LMC cluster vations of 117 red giants at the infra-red Ca II triplet reveal a CMD’s, based on VLT photometry. The first paper ͑Gallart surprisingly large variation in Ca II line strength. The colors et al. 2002͒ presents the observations. For comparison, two of the red giants of the highest metallicities are much bluer independent analyses, one using the Yale models ͑Woo, J.H.
than the colors of very old red giants of the same metallicity, et al. 2002͒, the other using the Padua models ͑Bertelli et al. such as the ones in galactic globular clusters. This indicates 2002͒, Papers 2 and 3 respectively, were made.
that the metal-rich Fornax stars are considerably younger. An Drukier, Bailyn, van Altena, and Girard finished their age-metallicity relation was constructed from the combina- study of the proper motions in the center of the globular tion of the spectroscopy of the red giants and the deep color- cluster NGC 6752. The resulting central velocity dispersion magnitude diagrams. It suggests that the metallicity of For- for this unusual cluster is about 12 km sϪ1, indicating a nax climbed quickly to ͓Fe/H͔ϳϪ1 when Fornax formed higher-than-expected central mass-to-light ratio. In connec- and then rose more slowly over the past ϳ10 Gyrs.
tion with this Drukier and Bailyn have estimated the number Zinn also participated in the QUEST survey in Venezuela, of high-velocity stars to be expected in the central part of searching for RR Lyrae variables. This effort constituted the globular cluster hosting a massive black hole. They have begun reduction of HST data with the aim of testing this understand the details of the structure and dynamics of the solar interior. The second is to determine internal variability Graduate student B. Zhao continued his Ph.D. thesis re- mechanisms that change the structure and the global param- search with Bailyn on binary stars in globular clusters. By eters of the Sun ͑mainly luminosity͒ and may have signifi- analyzing HSF images of the cores of clusters, Zhao has cant consequences for climate change and other terrestrial demonstrated interesting differences in the binary popula- phenomena. To accomplish these tasks, we use primarily tions of M3 and M13, a so-called ‘‘second parameter’’ pair theoretical tools, which we complement with the helioseis- of clusters, similar in most respects, but quite different in mic analysis and interpretation of data available from space- horizontal branch morphology. The techniques thus devel- based and from ground-based observatories. For the case of oped are now being extended to 47 Tucanae.
one specific global parameter, the solar diameter, which our Korchagin, Girard, Dinescu and van Altena in collabora- studies suggest to be critical, but for which at the present tion with T. Borkova from the Institute of Physics, Rostov time no adequate national or international observational pro- University, Russia, re-estimated the surface density of the gram exists, we have established our own program to fill in Galactic disk in the solar neighborhood within Ϯ 0.4 kpc of this lacuna. This is a balloon-based observational program, the Sun using parallaxes and proper motions of a kinemati- called the Solar Disk Sextant ͑SDS͒ that we have been pur- cally and spatially unbiased sample of 1476 old bright red suing in collaboration with the NASA/Goddard Space Flight giant stars from the Hipparcos catalog which have measured Center for the last 20 years, and more recently, in collabora- radial velocities. The vertical distribution of the sample to- tion with colleagues at the University of Rome at Tor Ver- gether with its accurately measured velocity dispersion com- gata. Since one of main uncertainties in solar and stellar bine to yield a determination of the surface density of gravi- models is that which results from the incomplete treatment of tating matter in the Galactic disk as a function of the Galactic coordinate z. The surface density of the disk increases from dimensional simulations of convection to study the proper- 10.5 Ϯ 0.5 M ᭪ / pc2 within Ϯ 50 pc to 42 Ϯ 6 M ᭪ / pc2 ties of convective transport in the Sun and other stars at within Ϯ 350 pc. The estimated volume density of the Ga- lactic disk within Ϯ 50 pc is about 0.1 M ᭪ / pc3 which is Helioseismology: We have been studying the structure close to the volume density estimates of the observed bary- and dynamics of the Sun using data from both the Global onic matter in the solar neighborhood.
Oscillation Network Group ͑GONG͒ project and the Michel- Korchagin in collaboration with N. Orlova ͑Institute of son Doppler Imager ͑MDI͒ on board SOHO. We find that Physics, Rostov University, Russia͒, S.M. Miyama and N.
although solar frequencies change with solar activity, there is Kikuchi ͑National Astronomical Observatory, Tokyo, Japan͒ no observable change in the structure of the inner layers of and A. Moiseev ͑Special Astrophysical Observatory, Russia͒ the Sun, the evidence points to changes only in the outer have tested the applicability of the global modal approach in 3-4% i.e., in the near-surface layers. Solar dynamics however the density wave theory of spiral structure for a sample of shows considerable change — solar zonal flows from the spiral galaxies with measured axisymmetric background mid-latitude regions converge towards the equator as solar properties. Using the observed radial distributions for the activity increases, while the high latitude flows moved to- stellar velocity dispersions and the rotation velocities, they wards the poles. The meridional flows changed too — the have constructed equilibrium models for the galactic disks in maximum flow velocity decreased with increase in solar ac- each galaxy and implemented two kinds of stability analyses tivity. We have paid particular attention to studying the base - the linear global analysis and 2D-nonlinear simulations. In of the convection zone, where the solar dynamo is believed general, the global modal approach is able to reproduce the to be located. We find that there is no significant temporal observed properties of the spiral arms in the galactic disks.
variation in the depth of the convection zone. This implies The growth of spirals in the galactic disks can be physically that any variation in the magnetic field at base of the con- understood in terms of amplification by over-reflection at the vection zone has to be small. We do not see any significant corotation resonance. The results support the global modal temporal variations in the dynamics of this region ͑the ‘ta- approach as a theoretical explanation of spiral structure in Using local helioseismic techniques we have investigated Girard, Korchagin, and van Altena submitted 88 minor- the differences in the acoustic properties of solar active re- planet position measurements to the Minor Planet Center, gions. Frequencies of acoustic oscillations are higher in ac- based on observations with the YALO 1-m telescope at tive regions when compared to those in the quieter regions of CTIO. This is part of a NASA-funded program at Yale to the Sun. On inverting the frequency differences between ac- make Southern-sky observations of Near Earth Objects. This tive and quiet region, we find that active regions have lower program is continuing, using the SMARTS 1.3-m telescope sound-speeds ͑and hence temperature͒ than quiet regions im- mediately below the surface, but the sound-speed ͑and tem-perature͒ rises sharply in the active regions at depths below 4.3 Solar Physics
5-7 Mm. We have also studied the evolution of active re- Investigations into solar physics are conducted at Yale by gions that produce flares. We find that in most cases, during faculty members Sofia, Demarque and Basu, and research the period of high flare activity, power in acoustic modes is staff Li and Robinson. Two principal objectives guide the larger compared to that in a non-flaring region active region solar research in our department. One, is to determine and Solar Variability Models: The main purpose of monitor- the solar granules. Extending our ideas to the evolved Sun at ing the solar-cycle related changes in the Sun is ultimately to 11.3 and 11.6 billion years, we find that the horizontal size of try and understand what causes the changes. To this effect the granules are larger. By extrapolating our result to a su- we have been constructing solar models that include mag- pergiant such as Betelgeuse, we tentatively estimate about netic fields as a part of the structure equations. We therefore, 600 granules would occupy the surface of a supergiant such do not treat the effects of magnetic fields as a perturbation on as Betelgeuse. This is in rough agreement with the spectral the structure of a non-magnetic star. We have looked at the observations by ͑D.F. Gray 2000, ApJ, 532, 487͒.
effect of placing magnetic fields of various strengths at dif-ferent depths inside the Sun, and compared the results withobservations related to the irradiance, effective temperature 4.4 Stellar Physics
and frequency changes in the Sun as a function of activity.
Basu and Sofia have been a program of theoretical re- Given that most evidence points to changes taking place in search into asteroseismology. This work has been made very the outer layers of the Sun, we have paid particular attention relevant by the recent success in observing stellar oscilla- to convection and turbulence. Our best models include prop- tions from the ground and by the launch of space missions.
erties of convection and turbulence as obtained from 3-D We have been concentrating on trying to determine what we simulations of convection in the outer layers of the Sun. We can learn about stellar parameters using low-degree oscilla- find that a variable magnetic field is not enough to reproduce tion modes. We find that we can do reasonable inversions to the observable solar cycle related changes in the Sun. While find the sound-speed profile of stellar cores. We also find that the irradiance and effective temperature variations can be it is possible to determine the envelope helium abundance of reproduced by many magnetic-field configurations, the low-mass stars using low degree modes. For frequency errors changes in the oscillation frequencies are not easy to repro- of 1 part in 104, we expect errors ␴Y in the estimated helium duce. A variable magnetic field at the base of the convection abundance to range from 0.03 for 0.8M᭪ stars to 0.01 for zone that can reproduce the observed irradiance and tempera- 1.2M᭪ stars. The task is more complicated in evolved stars, ture changes produces observable changes in the position of such as subgiants, but is still feasible if the relative errors in the base. Such changes are not seen in the Sun. Additionally, the frequencies are less than 10Ϫ4.
the frequency changes are not reproduced. The shape of the Demarque’s work on the Yale-Yonsei (Y 2) isochrones frequency changes as a function of frequency requires a shal- has continued, following up on Paper 1 which contains iso- low magnetic field. However, this does not reproduce the chrones and luminosity functions for the scaled solar abun- sign of the changes. Observations show that solar frequen- dances ͑Yi, Demarque, Kim, Lee, Ree, Lejeune & Barnes cies increase with increase in activity, while in the models an 2001, ApJS 136, 417, 2001͒. Paper 2 ͑Kim et al. 2002͒, increase in the magnetic field led to decrease in frequencies.
which contains isochrones for mixtures in which ␣-enhanced We find that a crucial role is played by turbulence in the elements have twice and four times the solar abundance͒, and sub-surface layers. To reproduce the sign of the frequency Paper 3 ͑Yi et al. 2003͒, which contains evolutionary tracks, change, we need to introduce a negative feedback between have recently been published. Paper 4, which deals with the turbulence and magnetic fields. A negative feedback is not treatment of convective core overshoot in the isochrones, is surprising since magnetic fields are known to inhibit turbu- being prepared for submission. Work is proceeding on ex- lence. We are currently in the process of developing codes to tending the isochrone tables to different helium abundances construct two dimensional solar models that will enable us to and on updating the equation of state at the low mass end.
test more realistic magnetic field configurations.
The isochrone tables, together with interpolation pro- The SDS Program: During this past year we have been developing sophisticated techniques to analyze data obtained http://www.astro.yale.edu/demarque/yyiso.html. A web in- during all the past flights of the SDS for which the instru- terface for the CMD synthesis code based on the Y 2 iso- ment had acquired the final stable configuration. Those chrones, written by graduate student J.H. Woo, is under con- flights occurred in 1992, 1994, 1995, 1996, and 2001. We struction with the help of graduate student Eric J. Murphy.
find that the solar diameter during the descending phase of Christian W. Straka, a visiting postdoctoral fellow from the activity cycle was increasing. Although the phase of the Heidelberg, is investigating the signature of convective core increase agrees with the result from the analysis of the overshoot on the seismic properties of stars near the main f-mode oscillations, the magnitude is substantially larger. Al- sequence. He is focussing on Procyon, a star on the first though both experiments measure the radius changes at dif- target list of the asteroseismic space mission MOST. Straka ferent solar layers, it will be interesting to understand those has implemented the Kuhfuss ͑1986, A&A, 160, 116͒ theory of core overshoot in the Yale stellar evolution code and com- Convection Simulations: In the case of the Sun we find pared the predictions with other simpler core overshoot pre- that the mixing length theory breaks down within about 1000 Km of the solar surface. By putting the turbulent pressure Also, in anticipation of the MOST observations, evolu- and kinetic energy from the 3D model back into the 1D tionary interior models have been constructed by graduate stellar evolution code, we find that the re-computed adiabatic students Eric J. Murphy ͑51 Pegasi͒ and Bethany Cobb (␶ p-mode frequencies were a better match to the observed val- Ceti͒, and their pulsation properties have been calculated.
ues. We also find that the auto-correlation length of the ver- Demarque is currently implementing in these models the ef- tical velocity provides a well defined vertical length scale for fects of turbulence on the pulsation frequencies, starting from the 3D simulations of Robinson et al. ͑2003͒, and using optical lightcurves were strongly correlated, with the optical the formalism of Li et al. ͑2002͒.
delayed by Ϸ25 seconds from the X-rays, strongly implying Sean O’Brien continued his work on variable and binary stars, including time-series spectroscopy obtained with the D. Maitra has begun PhD thesis work under Bailyn’s di- Hubble Space Telescope and Keck, and time-series photom- rection, focussing on state changes in X-ray binaries. A pa- etry obtained with the Whole Earth Telescope collaboration.
per has been submitted studying in detail the 2001 outburst He was also awarded HST time to measure the parallax dis- of Aql X-1, demonstrating clearly that the sequence of X-ray tance to a neutrino-luminous white dwarf. The ultimate goal states is somewhat different during the rise as compared to of this work is to test lepton theory in dense plasma by using information from pulsation to determine the neutrino lumi- Post-doc Buxton and Bailyn, along with undergraduate L.
nosity of hot white dwarf stars. O’Brien is also studying the Jeanty, are investigating whether the MACHO database can results of LMC microlensing events reported by the MA- reveal X-ray binaries in quiescence. A series of criteria have CHO collaboration, to determine whether the events are best been developed to identify potential quiescent X-ray bina- explained by a hypothetical population of white dwarfs in the ries, and promising candidates will be followed up spectro- galactic halo or low mass stars within the LMC itself. Yale scopically with the WIYN and other telescopes in the future.
undergraduate student Meredith Hughes is assisting with this Bailyn and van Dokkum have established a collaboration with J. Bloom ͑CfA͒ to use the SMARTS telescopes to study Coppi, Larson and former student Volker Bromm contin- the optical/IR afterglows of gamma-ray bursts. The ability to ued their collaboration on understanding primordial star for- carry out target of opportunity observations in the optical and mation. Using an adaptive refinement method developed inhis thesis, Bromm carried out a new high resolution simula- IR simultaneously from an excellent southern hemisphere tion of accretion onto a primordial protostar which adds site makes SMARTS potentially an excellent facility for this more support to the hypothesis that the very first stars were purpose. The first fruits of this effort were a study of GRB massive. Bromm received the 2002 Trumpler ͑Astronomical 030329, which demonstrated that the absorption from the Society of the Pacific͒ prize for his work on primordial star Coppi obtained Chandra time to follow up four of the most powerful, narrow-lined H␣ emitting objects found inthe QUEST objective prism survey of 700 square degrees of 4.5 High Energy Astrophysics
equatorial sky down to Rϭ19. All objects were detected, butproved to be extremely faint with soft spectra. This result Observational and theoretical research into High Energy indicates very obscured AGN activity or unusually powerful Astrophyiscs is carried out at Yale both in the Department of star formation activity. In either case, these objects are part Astronomy, and at the YCAA. Here we describe the research of a new class of X-ray emitting objects whose H␣/X-ray carried out in the department. We note that a very significant emission characteristics lie very far from the correlation be- effort in Active Galactic Nuclei is being conducted by Meg tween H␣ luminosity and X-ray emission established by Urry and her associates in the YCAA, and there is close collaboration between the YCAA and astronomy department Together with post-doc Henric Krawczynski, Coppi ob- tained 700 kilosec of target-of-opportunity ͑TOO͒ time on Bailyn continued research into black hole candidates and the RXTE X-ray satellite for simultaneous X-ray/TeV obser- other X-ray binaries. Much of this research centers on vations of TeV blazars. All TOO’s were triggered and suc- SMARTS data from the optical and infrared ͑OIR͒ counter- cessfully carried. The most intriguing result was the discov- parts of these sources. Daily OIR observations are being ob- ery of an ‘‘orphan’’ gamma-ray flare that had no counterpart tained from over a dozen soft X-ray transients, many of at X-ray energies, contrary to the predictions of the standard which are dynamically confirmed black hole candidates. Re-cent highlights of this work include the following.
synchrotron-self Compton ͑SSC͒ models. Together with 1͒ The discovery of an IR reflare coincident with radio Krawczynski and Felix Aharonian ͑MPIK, Heidelberg͒, emission in the 2002 outburst of black hole candidate Coppi also carried out a detailed SSC modeling analysis of 4U1543-47. No X-ray emission was observed at the time, X-ray/TeV data from the 1997 outburst of Mkn 501. The suggesting that this radiation may be synchrotron emission results strongly suggest that a non-variable, soft X-ray com- associated with the formation of a radio jet.
ponent needs to be considered in future TeV blazar modeling 2͒ The 4-year lightcurve of neutron star transient Aql X-1, and also raise significant questions about the overall SSC which has revealed the presence of short ‘‘mini-outbursts,’’ model because of the extreme model parameters found.
which may be interpreted as instability events that start on Graduate student Maccarone completed and published his the inside of the accretion disk and propagate outwards, in thesis with Coppi on spectral and timing constraints on mod- contrast to the traditional ‘‘outside-in’’ instabilities that trig- els for galactic black hole binary sources. Maccarone’s dis- covery of a hysteresis effect in the outburst of both neutron 3͒ Intensive study of the 2003 outburst of the black hole star and black hole system drew considerable attention. The binary V4641 Sgr, which included simultaneous X-ray ob- results suggest that a common mechanism is responsible for servations with RXTE and optical observations obtained by the state transitions in both systems, and that source lumi- A. Chen at the Lu Lin observatory in Taiwan. The X-ray and nosity, i.e., accretion rate, is not the only quantity respon- sible for determining which X-ray emission state a black Natarajan is conducting a wide range of research into the- oretical extragalactic astronomy and cosmology, including Coppi, Larson and graduate student Andres Escala initi- ated a collaboration to study the impact of gas on the merger 1͒ Gravitational Lensing: combining strong and weak of massive black holes using the GADGET smooth particle lensing analysis techniques; use of lensing as a probe to hydrodynamics ͑SPH͒ code. Simulations of galaxy mergers study galaxy evolution in clusters via local weak shear ef- that do not include gas show that while the central black fects; weak lensing by large-scale structure; using lensing as holes of the merging galaxies often move rapidly to the cen- a probe of the shapes of dark matter halos; and understand- ter of the merged system, the black holes can ‘‘hang up’’ and ing intrinsic correlations in the shapes of galaxies.
form a long-lived binary. Preliminary results from this study 2͒ Clusters of Galaxies: using lensing, X-ray and were presented at a press release at the May 2003 AAS meet- Sunyaev-Zeldovich data in conjunction to study the dynam- ing and indicate that the presence of gas can have a very ics of galaxies in clusters; velocity anisotropy of galaxy or- important effect, allowing the coalescence of the black hole bits; characterizing cluster growth and evolution in phase binary to proceed rapidly. This has important implications space and physics of the relaxation process.
for supermassive black hole formation scenarios, and the 3͒ Accretion physics: issues of the alignment of the spin gravitational wave signal rate expected for the LISA space of disks and the central black holes; the evolution of warped accretion disks; Lense-Thirring precession; the Blandford-Znajek mechanism, and the accretion history of supermas- 4.6 Extragalactic Astronomy and Cosmology
4͒ Issues in galaxy formation and the fueling of quasars: Very substantial work in this area is conducted in the the connection between high redshift galaxies, active galactic YCAA. Meg Urry is a major player in the GOODS survey, nuclei and their central black holes; the black hole mass which is the focus of PhD thesis work by Astronomy Depart- function; role of quasars and their outflows in galaxy forma- ment graduate students B. Simmons, J. van Duyne and J.-H.
tion; kinematic Sunyaev-Zeldovich effect from quasars; the Woo. The QUEST group also works out of the YCAA. Be- physics of feedback processes in galaxy formation; stellar low we describe in more detail research being conducted contributors to the X-ray background and the evolution of primarily in the Department of Astronomy.
A major effort involving many members of the depart- 5͒ Binary Black Holes: the merger and evolution of su- ment, including faculty members Coppi and van Dokkum, permassive black hole binaries in gas-rich galaxy cores; the and post-docs Castander and Gawiser, and graduate students electro-magnetic and gravitational wave signatures from Quadri and Triester, has been the Yale-Calan Deep Survey these systems; the implications for structure formation at collaboration, now called MUSYC. This is the largest of the joint projects between Yale and Chile, and has obtained sig- Kenney continued to work on dynamics and star forma- nificant amounts of telescope time to carry out its square tion of the inner regions of galaxies, and on the effects of degree, ‘‘Phase II’’ multi-band imaging ͑U,B,V,R,I,Z,J,K͒ environment on the evolution of galaxies. Much of this work and spectroscopy survey. The ‘‘Phase I’’ version of the Yale- focussed on obtaining a detailed understanding of particular Calan survey, now completed, followed up faint Chandra galaxies in the Virgo cluster. Observations with the WIYN X-ray sources in the optical and near infrared. The survey telescope, and with the Owen’s Valley millimeter wave in- discovered one of the first X-ray selected, optically faint terferometer are of particular importance. Graduate students AGN at high redshift ͑zϭ4.2͒. Recently, the survey has dis- Crowl and Murphy are beginning thesis work in this area, covered another at redshift zϭ4.6. A detailed description of this project can be found at http://www.astro.yale.edu/ Rhode completed her PhD thesis under the direction of dept/research/calan/deepsurvey.html.
van Dokkum’s research focuses on observational studies Bailyn and former faculty member Zepf ͑now at Michigan of the formation and evolution of galaxies, using the Hubble St͒ and continued work at the department as an NSF fellow Space Telescope and a large range of ground based facilities.
jointly at Yale and at Wesleyan University. Her thesis work Current projects include studies of a newly discovered popu- was a survey of globular clusters in elliptical and spiral gal- lation of red galaxies at very high redshift. He is co-PI of the axies outside the Local Group. The survey combines images MUSYC survey, a joint project of the Universidad de Chile from the WIYN and Mayall telescopes at KPNO with archi- and Yale, which encompasses a broad range of projects uti- val HST data to study the global properties of the galaxies’ lizing the excellent telescopes in Chile.
globular cluster systems. With advisors Stephen Zepf ͑Mich.
Post-doc Gawiser’s work also focussed on the MUSYC State͒ and Charles Bailyn, Rhode quantified the total num- survey, with a particular emphasis on optical spectroscopic bers, spatial and color distributions of globular clusters in followup. By studying quasars, Lyman break galaxies, Ly- each galaxy, in order to test models of galaxy formation.
man ␣ emitters, and damped Lyman ␣ absorbers, all of Futre efforts will focus on spectroscopy to study the kine- which represent families of protogalaxies selected in differ- matics of globular clusters in massive galaxies, and also in- ent ways, he hopes to determine the extent to which these vestigate the connection between low-mass X-ray binaries different types of protogalaxies overlap and cluster with each and globular clusters using optical images and data from the PUBLICATIONS
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