Application of Tracking and Data Relay Satellite (TDRS) Differenced One-Way Doppler (DOWD) Tracking Data for Orbit Determination and Station Acquisition Support of User Spacecraft Without TDRS Compatible Transponders

Many spacecraft are launched today with only an omni-directional (omni) antenna and do not have an onboard Tracking and Data Relay Satellite (TDRS) transponder that is capable of coherently returning a carrier signal through TDRS. Therefore, other means of tracking need to be explored and used to adequately acquire the spacecraft. Differenced One-Way Doppler (DOWD) tracking data are very useful in eliminating the problems associated with the instability of the onboard oscillators when using strictly one-way Doppler data. This paper investigates the TDRS DOWD tracking data received by the Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF) during the launch and early orbit phases for the the Interplanetary Physics Laboratory (WIND) and the National Oceanographic and Atmospheric Administration (NOAA)-J missions. In particular FDF personnel performed an investigation of the data residuals and made an assessment of the acquisition capabilities of DOWD-based solutions. Comparisons of DOWD solutions with existing data types were performed and analyzed in this study. The evaluation also includes atmospheric editing of the DOWD data and a study of the feasibility of solving for Doppler biases in an attempt to minimize error. Furthermore, by comparing the results from WIND and NOAA-J, an attempt is made to show the limitations involved in using DOWD data for the two different mission profiles. The techniques discussed in this paper benefit the launches of spacecraft that do not have TDRS transponders on board, particularly those launched into a low Earth orbit. The use of DOWD data is a valuable asset to missions which do not have a stable local oscillator to enable high-quality solutions from the one-way/return-link Doppler tracking data

The structural properties and star formation history of Leo T from deep LBT photometry

We present deep, wide-field g and r photometry of the transition type dwarf galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The data confirm the presence of both very young (5 Gyr) stars. We study the structural properties of the old and young stellar populations by preferentially selecting either population based on their color and magnitude. The young population is significantly more concentrated than the old population, with half-light radii of 104+-8 and 148+-16 pc respectively, and their centers are slightly offset. Approximately 10% of the total stellar mass is estimated to be represented by the young stellar population. Comparison of the color-magnitude diagram (CMD) with theoretical isochrones as well as numerical CMD-fitting suggest that star formation began over 10 Gyr ago and continued in recent times until at least a few hundred Myr ago. The CMD-fitting results are indicative of two distinct star formation bursts, with a quiescent period around 3 Gyr ago, albeit at low significance. The results are consistent with no metallicity evolution and [Fe/H] ~ -1.5 over the entire age of the system. Finally, the data show little if any sign of tidal distortion of Leo T.Comment: 8 pages, 9 figures, some small textual changes, accepted for publication in the Astrophysical Journa

Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

We present early observations of the afterglow of the Gamma-Ray Burst (GRB) 030329 and the spectroscopic discovery of its associated supernova SN 2003dh. We obtained spectra of the afterglow of GRB 030329 each night from March 30.12 (0.6 days after the burst) to April 8.13 (UT) (9.6 days after the burst). The spectra cover a wavelength range of 350 nm to 850 nm. The early spectra consist of a power-law continuum (F_nu ~ nu^{-0.9}) with narrow emission lines originating from HII regions in the host galaxy, indicating a low redshift of z=0.1687. However, our spectra taken after 2003 Apr. 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find the spectrum of the supernova is remarkably similar to the type Ic `hypernova' SN 1998bw. While the presence of supernovae have been inferred from the light curves and colors of GRB afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.Comment: published by ApJ Letters; additional material avilable at http://cfa-www.harvard.edu/cfa/oir/Research/GRB

Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and supernova contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of a supernova. The early afterglow light curve also shows deviations from the typical power-law decay. A supernova spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the supernova explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.Comment: 57 pages, 13 figures, accepted by ApJ, revised per referee's comments, includes full photometry table. Data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB030329 or through WWW at http://cfa-www.harvard.edu/cfa/oir/Research/GRB

Chemical evolution of the Small Magellanic Cloud based on planetary nebulae

We investigate the chemical evolution of the Small Magellanic Cloud (SMC) based on abundance data of planetary nebulae (PNe). The main goal is to investigate the time evolution of the oxygen abundance in this galaxy by deriving an age-metallicity relation. Such a relation is of fundamental importance as an observational constraint of chemical evolution models of the SMC. We have used high quality PNe data in order to derive the properties of the progenitor stars, so that the stellar ages could be estimated. We collected a large number of measured spectral fluxes for each nebula, and derived accurate physical parameters and nebular abundances. New spectral data for a sample of SMC PNe obtained between 1999 and 2002 are also presented. These data are used together with data available in the literature to improve the accuracy of the fluxes for each spectral line. We obtained accurate chemical abundances for PNe in the Small Magellanic Cloud, which can be useful as tools in the study of the chemical evolution of this galaxy and of Local Group galaxies. We present the resulting oxygen versus age diagram and a similar relation involving the [Fe/H] metallicity based on a correlation with stellar data. We discuss the implications of the derived age-metallicity relation for the SMC formation, in particular by suggesting a star formation burst in the last 2-3 Gyr.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

The α1D-adrenergic receptor is expressed intracellularly and coupled to increases in intracellular calcium and reactive oxygen species in human aortic smooth muscle cells

Background: The cellular localization of the α1D-adrenergic receptor (α1D-AR) is controversial. Studies in heterologous cell systems have shown that this receptor is expressed in intracellular compartments. Other studies show that dimerization with other ARs promotes the cell surface expression of the α1D-AR. To assess the cellular localization in vascular smooth muscle cells, we developed an adenoviral vector for the efficient expression of a GFP labeled α1D-AR. We also measured cellular localization with immunocytochemistry. Intracellular calcium levels, measurement of reactive oxygen species and contraction of the rat aorta were used as measures of functional activity. Results: The adenovirally expressed α1D-AR was expressed in intracellular compartments in human aortic smooth muscle cells. The intracellular localization of the α1D-AR was also demonstrated with immunocytochemistry using an α1D-AR specific antibody. RT-PCR analysis detected mRNA transcripts corresponding to the α1A-α1B- and α1D-ARs in these aortic smooth muscle cells. Therefore, the presence of the other α1-ARs, and the potential for dimerization with these receptors, does not alter the intracellular expression of the α1D-AR. Despite the predominant intracellular localization in vascular smooth muscle cells, the α1D-AR remained signaling competent and mediated the phenylephrine-induced increases in intracellular calcium. The α1D-AR also was coupled to the generation of reactive oxygen species in smooth muscle cells. There is evidence from heterologous systems that the α1D-AR heterodimerizes with the β2-AR and that desensitization of the β2-AR results in α1D-AR desensitization. In the rat aorta, desensitization of the β2-AR had no effect on contractile responses mediated by the α1D-AR. Conclusion: Our results suggest that the dimerization of the α1D-AR with other ARs does not alter the cellular expression or functional response characteristics of the α1D-AR

The α\u3csub\u3e1D\u3c/sub\u3e-Adrenergic Receptor Is Expressed Intracellularly and Coupled to Increases in Intracellular Calcium and Reactive Oxygen Species in Human Aortic Smooth Muscle Cells

Background: The cellular localization of the α1D-adrenergic receptor (α1D-AR) is controversial. Studies in heterologous cell systems have shown that this receptor is expressed in intracellular compartments. Other studies show that dimerization with other ARs promotes the cell surface expression of the α1D-AR. To assess the cellular localization in vascular smooth muscle cells, we developed an adenoviral vector for the efficient expression of a GFP labeled α1D-AR. We also measured cellular localization with immunocytochemistry. Intracellular calcium levels, measurement of reactive oxygen species and contraction of the rat aorta were used as measures of functional activity. Results: The adenovirally expressed α1D-AR was expressed in intracellular compartments in human aortic smooth muscle cells. The intracellular localization of the α1D-AR was also demonstrated with immunocytochemistry using an α1D-AR specific antibody. RT-PCR analysis detected mRNA transcripts corresponding to the α1A-α1B- and α1D-ARs in these aortic smooth muscle cells. Therefore, the presence of the other α1-ARs, and the potential for dimerization with these receptors, does not alter the intracellular expression of the α1D-AR. Despite the predominant intracellular localization in vascular smooth muscle cells, the α1D-AR remained signaling competent and mediated the phenylephrine-induced increases in intracellular calcium. The α1D-AR also was coupled to the generation of reactive oxygen species in smooth muscle cells. There is evidence from heterologous systems that the α1D-AR heterodimerizes with the β2-AR and that desensitization of the β2-AR results in α1D-AR desensitization. In the rat aorta, desensitization of the β2-AR had no effect on contractile responses mediated by the α1D-AR. Conclusion: Our results suggest that the dimerization of the α1D-AR with other ARs does not alter the cellular expression or functional response characteristics of the α1D-AR

Old Stellar Populations of the Small Magellanic Cloud

We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field in the outer SMC. For NGC 121, we measure a true distance modulus of (m-M)0 = 18.96 +/- 0.04 (distance of 61.9 +/- 1.1 kpc), age of 10.6 +/- 0.5 Gyr, metallicity of [Fe/H] = -1.03 +/- 0.06, and initial mass of 4.1 +/- 0.4 x 10^5 Msun, assuming a Salpeter IMF with lower cutoff at 0.1 Msun. In the outer SMC field, we find evidence of stars covering a wide range of ages -- from 2 Gyr old to at least 9-12 Gyr old. We have measured the distance, extinction, and star formation history (past star formation rates and enrichment history) using a CMD fitting algorithm. The distance modulus of the SMC is measured to be (m-M)0 = 18.88 +/- 0.08, corresponding to a distance of 59.7 +/- 2.2 kpc. The overall star formation rate appears to have been relatively constant over this period, although there may be small gaps in the star forming activity too small to be resolved. The lack of current star-forming activity is a selection effect, as the field was intentionally chosen to avoid recent activity. The mean metallicity of this field has increased from an average of [Fe/H] = -1.3 +/- 0.3 for stars older than 8 Gyr to [Fe/H] = -0.7 +/- 0.2 in the past 3 Gyr.Comment: 29 pages, 14 figures accepted for publication in Ap

The Importance of Correlations and Fluctuations on the Initial Source Eccentricity in High-Energy Nucleus-Nucleus Collisions

In this paper, we investigate various ways of defining the initial source eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude $v_2$ lead to most measurements being sensitive to the root-mean-square, rather than the mean of the $v_2$ distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as a function of the number of participating nucleons, \Npart,keeping non-negligible contributions up to \ordof{1/\Npart^3}. We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of two over a wide range in centrality.Comment: 18 pages, 10 figures, submitted to PR

A comparison of statistical hadronization models

We investigate the sensitivity of fits of hadron spectra produced in heavy ion collisions to the choice of statistical hadronization model. We start by giving an overview of statistical model ambiguities, and what they tell us about freeze-out dynamics. We then use Montecarlo generated data to determine sensitivity to model choice. We fit the statistical hadronization models under consideration to RHIC data, and find that a comparison $\chi^2$ fits can shed light on some presently contentious questions.Comment: Proceedings for SQM2003 [7th Int. Conf. on Strangeness in Quark Matter (Atlantic Beach, NC, USA, Mar 12-17, 2003)], to be published in Journal of Physics G (Typos corrected, reference added