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ASNY Fall 2009 Meeting
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We will review briefly the evidence for lunar surface hydration including interesting, older data which have been largely overlooked. We present a theory which successfully predicted the strength and latitude distribution of the recently reported 3-micron hydration signal. This is based on the assumption that water vapor has leaked from the lunar interior. We present independent evidence that such processes have occurred on significant scales.
This talk in intended to provide a few suggestions as a catalyst for the ASNY consortium in planning a telescope of significant aperture at reasonable cost. The performance of the 6.5-m MMT and the Magellan telescopes will be reviewed. Work in progress at the Steward Observatory Mirror Lab will be discussed. Site selection and ease of access are equally important considerations. Instruments that explore unusual parts of the spectrum may yield surprising results and discoveries even if the instruments are not on the world's largest telescope.
Planetary nebulae (PN) are the last stages of evolution of
intermediate mass (1-8 Msolar) stars. Their shapes are thought to
result from interactions between the present-day, fast (emerging white
dwarf) and previously ejected, slow (red giant) stellar winds. Such
interactions can superheat wind material via shocks, generating X-rays
in the process. We observed the X-ray bright, young PN, BD +30°3639 in
2006 for 300 ks using the Chandra X-ray Observatory's Low Energy
Transmission Gratings in combination with its Advanced CCD Imaging
Spectrometer (LETG/ACIS). We present the results of the first X-ray
gratings spectroscopy observations of a planetary nebula (PN) - the
X-ray-bright, young BD +30°3639. The LETG/ACIS results indicate that
the X-ray source originates essentially from the present-day stellar
wind (Ne/O and C/O are greatly enhanced over solar, while Fe/O is sub
solar) and suggest the presence of a range of plasma temperatures from
Tx ~ 1.7 MK to 2.9 MK and an intervening absorbing column NH ~ 2.4 ×
1021 cm–2. The range of temperatures implied by the plasma model
fitting offers the first direct indication of the presence of a
temperature gradient within the wind-collision-generated "hot bubble"
of a planetary nebula.
To determine whether there is evidence for
X-ray proper motions within this PN, we obtained a second-epoch direct
image of BD +30°3639 in 2009 for 80 ks using the Chandra/ACIS-S3. We
compared this image with the direct image obtained in 2000 and the 0th
order image obtained in 2006, and present our preliminary
results. Additionally, ongoing work on volumetric 3D modeling of the
PN, providing insight into the detailed structure of the X-ray
emitting "hot bubble" within BD +30°3639, will be introduced. The
results should provide much-needed constraints on models of PN
shaping.
The new, precise age for the Universe from WMAP and the work on star formation rates at high redshift tantalizes us with the possibility of working out the detailed timeline for the formation and assembly of galaxies, particularly our own Milky Way. I discuss my group's efforts to improve stellar chronometers in our Galaxy by comparing white dwarf cooling ages to main sequence turn-off ages in star clusters using a new Bayesian statistical approach. I will present some current problems in stellar evolution as well as some optimism. In particular, we find good agreement between the two stellar chonometers from 0.1 to 4 Gyr and possibly to 6 Gyr. Beyond 6 Gyr the jury is still out, and new data are required.
Recurrent novae are subset of the cataclysmic variable class of objects. They consist of a white dwarf and an evolved secondary star that is transferring material onto the white dwarf. Novae are thermonuclear detonations that take place on the surface of the white dwarf, a consequence of the matter that is being accreted on the stars surface. The release of nuclear binding energy causes a brief 8-12 magnitude increase in brightness. A recurrent nova is simply a class of white dwarfs that have been observed to have multiple outbursts. Novae are studied in order to gain a better understanding of the processes behind mass accretion, thermonuclear outbursts, dust formation, and the evolution of binary systems. It has been proposed that recurrent novae are progenitors of type Ia supernovae. This type of supernova is very important in cosmology for determining intergalactic distances. YY Dor is a recurrent nova located in the Large Magellanic Cloud, a nearby galaxy at a distance of approximately 60kpc. It was seen in outburst in 1937. Its second recorded outburst occurred in October 2004. We will report on a photometric and spectroscopic analysis of latest outburst as observed with the SMARTS telescopes on Cerro Tololo, Chile. We will report the decay times t_2 and t_3, which determine the speed class of the nova, and quantify the overall rate of decay. We will attempt to constrain the nature of the post-outburst system from its present brightness. We will discuss how the accretion disk appears to survive the outburst by comparing observations to disk models. We will also use this model to determine the mass and radius of the white dwarf.
Non-redundant masking (NRM) is a high contrast high resolution technique that is relevant for future space missions dedicated to either general astrophysics or extrasolar planetary astronomy. NRM mitigates not only atmospheric but instrument-induced speckle noise as well. The recently added mask in the Fine Guidance Sensor Tunable Filter Imager (FGS-TFI) on the James Webb Space Telescope (JWST) will open up a search space between 50 and 400 mas at wavelengths longer than 3.8um. Contrast of 1e4 will be achievable in a 10 ks exposure of an M=7 star, with routine observing, target acquisition, and data calibration methods. NRM places protoplanets in Taurus as well as Jovians younger than 300Myr and more massive than 2 Jupiter masses orbiting solar type stars within JWST's reach. Stars as bright as M=3 will also be observable, thus meshing well with next-generation ground-based extreme adaptive optics coronagraphs. This parameter space is inaccessible to both JWST coronagraphs and future 30-m class ground-based telescopes, especially in the mid-IR. We show that NRM used on future space telescopes can deliver unsurpassed image contrast in key niches, while reducing mission risk associated with active primary mirrors.
Asteroids have a complex thermal history, the cause of which has been a mystery for nearly half a century. Asteroids in the inner Main Belt near 2AU contain igneous minerals which require heating in the past to temperatures exceeding 1000K. Further out at 3AU, the presence of hydrated silicates indicates heating up to 300-500K. Two mechanisms called "induction heating" and "radioactive heating" have been invoked to explain these temperatures but neither is entirely satisfactory for reasons we discuss. As an alternative we propose a new "magnetic heating" mechanism with some interesting and potentially controversial implications.
We present Spitzer MIPS 24um observations of 16 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24um survey of clusters at intermediate redshift. The depth of our imaging corresponds to 8 x 1010 times the luminosity of the Sun, just below that of luminous infrared galaxies. The clusters contain a lower fraction of IR-emitting galaxies than the coeval field. However, the distribution of IR luminosities is identical for the cluster and field galaxies. The fraction of IR galaxies decreases significantly over the 2.4 Gyr interval spanned by our sample, and the rate of decline is the same for the cluster and field populations. The majority of IR cluster galaxies are normal spiral galaxies, similar to results found in the field. Approximately 80% of the IR galaxies live in the blue cloud and the remaining 20% lie on the red sequence. The majority of IR galaxies have optical spectra that show [OII] emission, but the star-formation rates derived from this optical emission line severely underestimate the total amount of ongoing star formation even after the optical emission is corrected for dust extinction.
Novae are thermonuclear detonations of hydrogen-rich material accreted onto the surface of a white dwarf, generally via either Roche-lobe overflow in a close binary or wind accretion from a giant in a wider system. There are of order two dozen galactic novae detected every year. They display a bewildering diversity of photometric and spectral characteristics. Despite the multitude of data, the nova mechanism is still poorly understood. We do not know how uniform the nova outburst is, or whether there are multiple physical mechanisms involved. Novae are important for understanding galactic evolution. Because of their larger numbers, they eject about as much matter (generally of low atomic weight) into the ISM as do supernovae. They are important for cosmology, because some recurrent novae may be the progenitors of type Ia supernovae. They are a laboratory wherein we can study the formation and destruction of dust grains. And the nuclear reactions predicted to occur in the nova outburst occur under conditions that can be reproduced in the laboratory. Since 2003 we have been using the SMARTS facilities to follow selected southern novae both spectroscopically and photometrically. At present we have data on 39 novae. To facilitate the ingestion of the data, we have constructed an on-line atlas showing the photometric and spectral evolution of these novae. I shall give an overview of the atlas and its contents, with illustrations of some of the more interesting novae.
Dust grains within interstellar molecular clouds are likely
to be charged. If the grains are small enough, they can
become coupled ("loaded") to the magnetic field that threads
a cloud, and thereby affect the propagation of magnetohydrodynamic
waves inside a partially-ionized star-forming cloud or dense
cloud core. Because they have a much greater mass than ions or
electrons, charged dust grains can significantly alter the signal
speed of MHD waves in a cloud or core. We present an analysis of
hydromagnetic wave propagation in a dusty plasma containing grains
having a continuous distribution in size. The conditions for
coupling of the grains and the addition of their inertia to the
magnetic field are described, and we present results that show the
degree to which dust loading can affect MHD wave speeds and
damping in model molecular clouds and cores.
We also show that a finite, discrete-bin approximation can
reasonably reproduce the physical results for a continuous grain
distribution model. This approximate finite-distribution
grain model may be particularly helpful in modeling nonlinear MHD
flows in clouds, such as the formation of J- or C-type shock waves,
since the type of shock that can form is crucially dependent
on the existence and properties of hydromagnetic precursors that
can be established in the dusty multicomponent plasma within a cloud.
The r-process is an important process in nucleosynthesis in which nuclei will undergo rapid neutron captures. Models of the r-process require nuclear data such as neutron capture rates for thousands of individual nuclei, many of which lie far from stability. Among the potential sites for the r-process, and the one that we investigate, is the shocked neutrino-driven wind in core-collapse supernovae. Here we examine the importance of the neutron capture rates of specific, individual nuclei in the second r-process abundance peak occurring at A ~ 130 for a range of parameterized neutrino-driven wind trajectories. Of specific interest are the nuclei whose capture rates affect the abundances of nuclei outside of the A ~ 130 peak. We found that increasing the neutron capture rate for a number of nuclei including 135In, 132Sn, 133Sb, 137Sb, and 136Te can produce changes in the resulting abundance pattern of up to 13%.
The Haystack VSRTs (Very Small Radio Telescopes) provide an
inexpensive (less than $500) and reliable interferometer with which
introductory in-class labs exploring the basics of radio astronomy and
aperture synthesis can be conducted. (See
this page). We will
demonstrate the ease with which the VSRT interferometer can be used,
and discuss the development of a set of four labs suitable for a
college-level radio astronomy class:
1. measuring the VSRT beam width;
2. detecting the fringe pattern of a moving source;
3. measuring the interferometer response to a single resolved source as
a function of baseline distance; and
4. measuring the interferometer response to a pair of sources at assorted
separations as a function of the baseline distance.
We hope, in the future, to develop two additional labs which involve using Python to transform the interferometric data to an image and inferring the morphology of an "unknown" radio source.
The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 8 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The Union College team is analyzing the galaxy group NGC 5846 and its environs. Preliminary analysis of ALFALFA data in the region surrounding the group (14h48m < RA < 15h20m, 0d < DEC < 4d) shows that ~10% of the group members are detected in HI, consistent with the high early-type fraction of this group.
The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 8 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The Siena College team is analyzing a 4 degree by 4 degree region around the galaxy group MKW 10, a compact group that lies at an average recession velocity of 6,150 km/s. We calculate HI mass using the ALFALFA data, and stellar mass using photometry from the Sloan Digital Sky Survey. Of the 24 group galaxies that lie within a projected distance of 1 Mpc, 15 are detected in HI with HI masses above 7E8 solar masses. We present preliminary results comparing the HI content of the group members with the HI content of surrounding field galaxies.
We use data from the Sloan Digital Sky Survey Data Release 7, and maximum likelihood methods, to accurately determine positions of the Sagittarius Dwarf Tidal stream. The Sagittarius Dwarf Stream dominates a significant portion of the Milky Way Halo, complicating other searches for galactic halo structure. Mapping this stream will make further investigations of the galactic halo more accurate, and provide information on overall halo star distribution. The data sets contain upwards of several hundred thousand stars each, providing a computationally expensive problem. We solve this problem through the MilkyWay@Home BOINC (Berkeley Open Infrastructure for Network Computing) volunteer computing network. MilkyWay@home currently has over 25,000 active volunteer hosts in 128 countries, and has the computing power equivalent to 520 teraFLOPS (floating point operations per second).
In Willett, et al. (2009), we fit an orbit to the narrow 63-degree stellar stream of Grillmair and Dionatos (GD-1). We showed the stream to be in a fast (~280 km/s) retrograde orbit that was independent of the parameters of the static Galactic dark matter halo. We will review these findings, as well as present new results of an effort to simultaneously fit orbits to GD-1 and the newly discovered Cetus Polar Stream (Newberg, Yanny, and Willett, 2009). We hope that by sampling streams in two different locations of the galactic halo, we can constrain its flattening and scale length.
Last modified: October 22, 2009
