J. N. Heasley

The XO Project: Searching for Transiting Extrasolar Planet Candidates

The XO project’s first objective is to find hot Jupiters transiting bright stars, i.e. V < 12, by precision differential photometry. Two XO cameras have been operating since September 2003 on the 10,000-foot Haleakala summit on Maui. Each XO camera consists of a 200-mm f/1.8 lens coupled to a 1024x1024 pixel, thinned CCD operated by drift scanning. In its first year of routine operation, XO has observed 6.6% of the sky, within six 7 ◦ -wide strips scanned from 0 ◦ to +63 ◦ of declination and centered at RA=0, 4, 8, 12, 16, and 20 hours. Autonomously operating, XO records 1 billion pixels per clear night, calibrates them photometrically and astrometrically, performs aperture photometry, archives the pixel data and transmits the photometric data to STScI for further analysis. From the first year of operation, the resulting database consists of photometry of �100,000 stars at more than 1000 epochs per star with differential photometric precision better than 1% per epoch. Analysis of the light curves of those stars produces transiting-planet candidates requiring detailed follow up, described elsewhere, culminating in spectroscopy to measure radial-velocity variation in order to differentiate genuine planets from the more numerous impostors, primarily eclipsing binary and multiple stars.

The Pan-STARRS Moving Object Processing System

ABSTRACT.We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes. MOPS achieves >99.5%>99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a nonphysical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope despite differences in expected false detection rates, fill-factor loss, and relatively sparse observing cadence compared to a hypothetical Pan-STARRS4 telescope and survey. MOPS remains highly efficient at detecting objects but drops to 80% efficiency at producing orbits. This loss is primarily due to configurable MOPS processing limits that a...

GrayWulf: Scalable Clustered Architecture for Data Intensive Computing

Data intensive computing presents a significant challenge for traditional supercomputing architectures that maximize FLOPS since CPU speed has surpassed IO capabilities of HPC systems and BeoWulf clusters. We present the architecture for a three tier commodity component cluster designed for a range of data intensive computations operating on petascale data sets named GrayWulf. The design goal is a balanced system in terms of IO performance and memory size, according to Amdahls Laws. The hardware currently installed at JHU exceeds one petabyte of storage and has 0.5 bytes/sec of I/O and 1 byte of memory for each CPU cycle. The GrayWulf provides almost an order of magnitude better balance than existing systems. The paper covers its architecture and reference applications. The software design is presented in a companion paper.

Hubble Space Telescope Photometry of the Metal-rich Globular Clusters NGHC 6624 and NGC 6637

We have observed the metal-rich globular clusters NGC 6624 and NGC 6637 (M69) using the planetary camera of the WFPC2 on the Hubble Space Telescope (HST). Observations of the Ca II triplet lines in giant stars in these clusters show that NGC 6624 and NGC 6637 have metallicities on the Zinn and West scale of [Fe/H] = -0.63 ? 0.09 and -0.65 ? 0.09, only slightly more metal rich than 47 Tuc [Fe/H] = -0.71 ? 0.07. For clusters of identical (or nearly so) metallicity, one can make a direct comparison of the color-magnitude diagrams to derive the relative ages of the clusters. From the color-magnitude diagrams derived from the HST photometry, we find that NGC 6624 and NGC 6637 differ in age by less than 0.5 Gyr. Their color-magnitude diagrams are also compared with those of 47 Tuc and NGC 6352, and while these latter diagrams are of somewhat lower quality, they are consistent with all of these clusters having the same ages. Adopting an apparent distance modulus of 13.40 and reddening E(B-V) = 0.04 for 47 Tuc, the new Yale isochrones yield an age for the clusters of 14 Gyr. The positions of NGC 6624 and NGC 6637 in the Galaxy suggest that they belong to the bulge population of globular clusters. The only other bulge clusters that have been dated so far are the more metal rich clusters NGC 6528 and NGC 6553, which also appear to be very old. Consequently, the age-metallicity relation of the bulge may be very steep. The close similarity of the ages and metallicities of NGC 6624 and NGC 6637 to the thick-disk globular clusters 47 Tuc and NGC 6352 indicates that the age-metallicity relations of these populations intersect. We briefly discuss the possibility that these populations had a common origin.

Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1 optical observations of the low-mass stellar content

The Hyades cluster is an ideal target to study the dynamical evolution of a star cluster over the entire mass range due to its intermediate age and proximity to the Sun. We wanted to extend the Hyades mass function towards lower masses down to 0.1 Msol and to use the full three-dimensional spatial information to characterize the dynamical evolution of the cluster. We performed a kinematic and photometric selection using the PPMXL and Pan-STARRS1 sky surveys, to search for cluster members up to 30 pc from the cluster centre. We determined our detection efficiency and field star contamination rate to derive the cluster luminosity and mass functions down to masses of 0.1 Msol. The thorough astrometric and photometric constraints minimized the contamination. A minimum spanning tree algorithm was used to quantify the mass segregation. We discovered 43 new Hyades member candidates with velocity perpendicular to the Hyades motion up to 2 km/s. They have mass estimates between 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the number of Hyades candidates with masses smaller than 0.15 Msol. We provide an additional list of 11 possible candidates with velocity perpendicular to the Hyades motion up to 4 km/s. The cluster is significantly mass segregated. The extension of the mass function towards lower masses provided an even clearer signature than estimated in the past. We also identified as likely Hyades member an L0 dwarf previously assumed to be a field dwarf. Finally we question the membership of a number of previously published candidates, including a L2.5-type dwarf.

THE PROSPECTS FOR ASTEROSEISMOLOGY FROM GROUND-BASED SITES

We reexamine the possibility of detecting p-mode oscillations in Sun-like stars with ground-based telescopes. Previous attempts to make such observations with photometric techniques have been limited to subgiant stars in M67 and have illustrated the great difficulties involved in performing ground-based asteroseismology. Substantial gains in observing efficiency can be realized from new diagnostic techniques and improvements in instrumentation, especially with newer CCD camera systems. We show that for appropriately selected field stars observed with a network of telescopes or at a high duty cycle site, it will be possible to detect p-mode oscillations from the ground. An alternative to a network of telescopes for asteroseismology would be to develop a dedicated observatory for this purpose at a high duty cycle site, i.e., the South Pole. We estimate the scintillation, the main noise source in asteroseismology, at the pole by modeling the index of refraction structure parameter from meterological data. The model results show that at the Pole the variance of the relative intensity fluctuations--i.e., the scintillation--should be a factor of 5 smaller than at at Mauna Kea. Taking into account the improvements possible with target selection and instrumentation, the South Pole would be an excellent site for asteroseismological work on Sun-like stars.

Stellar photometry software

We describe here the Stellar Photometry Software (SPS) that we have developed at Boston University and the University of Hawaii. SPS combines in a single program procedures for locating stars, computing a mean stellar point-spread function (PSF), and performing aperture and/or multiple PSF-fitting photometry, along with related bookkeeping functions. The software can be run either interactively or in batch mode on computers using the UNIX operating system. The performance of SPS is compared to that of the photometry programs DoPHOT and IRAF/DAOPHOT using both real and simulated CCD observations. A direct comparison of the instrumental magnitudes shows that all three programs produce comparable results.

Characterization of the Praesepe Star Cluster by Photometry and Proper Motions with 2MASS, PPMXL, and Pan-STARRS

Membership identification is the first step in determining the properties of a star cluster. Low-mass members in particular could be used to trace the dynamical history, such as mass segregation, stellar evaporation, or tidal stripping, of a star cluster in its Galactic environment. We identified member candidates of the intermediate-age Praesepe cluster (M44) with stellar masses ~0.11-2.4 M ☉, using Panoramic Survey Telescope And Rapid Response System and Two Micron All Sky Survey photometry, and PPMXL proper motions. Within a sky area of 3° radius, 1040 candidates are identified, of which 96 are new inclusions. Using the same set of selection criteria on field stars, an estimated false positive rate of 16% was determined, suggesting that 872 of the candidates are true members. This most complete and reliable membership list allows us to favor the BT-Settl model over other stellar models. The cluster shows a distinct binary track above the main sequence, with a binary frequency of 20%-40%, and a high occurrence rate of similar mass pairs. The mass function is consistent with that of the disk population but shows a deficit of members below 0.3 solar masses. A clear mass segregation is evidenced, with the lowest-mass members in our sample being evaporated from this disintegrating cluster.

Photometry of giant-branch stars in the M31 globular cluster G1

The first deep two-color (V and I) CCD photometry of individual stars in a M31 globular cluster is presented. The color-magnitude diagram for the stars in cluster G1 shows the brightest two magnitudes of a well-defined giant branch. The position of the giant branch in color indicates that G1 has a metallicity Fe/H abundance ratio of about -0.7, consistent with estimates from spectroscopy of its integrated light. The giant branch of G1 falls roughly in the middle of the range occupied by the halo field stars in M31. Thus, both the photometry and integrated-light spectroscopy show that G1 appears to be near the mean metallicity of the M31 halo population. 40 references.

Building Reliable Data Pipelines for Managing Community Data Using Scientific Workflows

The growing amount of scientific data from sensors and field observations is posing a challenge to “data valets” responsible for managing them in data repositories. These repositories built on commodity clusters need to reliably ingest data continuously and ensure its availability to a wide user community. Workflows provide several benefits to modeling data-intensive science applications and many of these benefits can help manage the data ingest pipelines too. But using workflows is not panacea in itself and data valets need to consider several issues when designing workflows that behave reliably on fault prone hardware while retaining the consistency of the scientific data. In this paper, we propose workflow designs for reliable data ingest in a distributed environment and identify workflow framework features to support resilience. We illustrate these using the data pipeline for the Pan-STARRS repository, one of the largest digital surveys that accumulates 100TB of data annually to support 300 astronomers.