Edward Schwieterman | University of Washington (original) (raw)

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Papers by Edward Schwieterman

Astrophysical Journal, 2011

We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that... more We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of X1-X2 orbit transfer, and our potential model results in a ring radius of ~200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, ~2x10^7 Msun and ~0.1 Msun/yr. Star formation in our simulations takes place mostly in the outermost X2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.

Astronomical Journal, 2011

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves ... more We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.

We conducted an intensive observational campaign of Comet 10P/Tempel 2 during its 1999/2000 appar... more We conducted an intensive observational campaign of Comet 10P/Tempel 2 during its 1999/2000 apparition, obtaining 31 nights of imaging with Lowell telescopes over an 11-month interval. Emphasis early in the apparition was given to obtaining nucleus lightcurve measurements while in later months the primary goal was to study coma morphology. Based on data obtained at the 1988 apparition, several researchers showed that Tempel 2 exhibits little cometary activity until shortly prior to perihelion, and that the rotational lightcurve of the nucleus has a large amplitude consistent with a highly elongated nucleus. An overall period of 8.932 hr was determined by Sekanina (1991); however, based on lightcurve data obtained in late 1994, Mueller and Ferrin (1996) obtained 5 possible periods, each different from the 1988 solution and from which they inferred a possible small spin-up or spin-down of the nucleus. Since our early 1999 observations would be taken within the same inter-perihelion interval as the 1994, we would expect no significant torquing due to activity near perihelion, and thus the same period to be present as in 1994. Our observations were planned to discriminate between Mueller and Ferrin's 5 viable solutions, and our preliminary rotation period of 8.937 hr indeed eliminates 4 of their answers, leaving only their solution of 8.939 hr. With two perihelion passages having occured between the 1988 and the 1994 and 1999 data sets, these results suggest that the nucleus rotational period is lengthening by only about 10 seconds per apparition. Our data also exhibit periodic variability of the coma brightness, and an offset in the position angle of the CN fan with respect to the dust. Additional analysis of the coma morphology is ongoing and we will present these results along with a more refined period solution. This research is supported by NASA's Planetary Astronomy Program.

A computer model, called the Exoplanetary Pixelization Transit Model (EPTM), is developed to calc... more A computer model, called the Exoplanetary Pixelization Transit Model (EPTM), is developed to calculate exoplanetary transit light curves and determine exoplanet properties from an observed transit light curve. To establish and test the accuracy of the model, an observation of XO-2 was conducted on 2008 Mar 17 where time-series photometry of the transit of XO-2b was collected. Based on the EPTM, XO-2 hosts a planet, XO-2b, with a planetary radius of R = 1.043 RJ, in a near circular orbit with semimajor axis a = 0.0360 AU and inclination angle i = 89.67. The EPTM also determined the length of the transit and the approximate start and end time of the ingress and egress. Here we describe how the EPTM works: (1) a theoretical light curve is calculated for an initial set of planetary parameters, RP , a, and i; (2) an observed light curve is used to calculate χ2 for that theoretical curve; (3) the planetary parameters are varied in a grid about their initial values to produce a multidimensional array of χ2 values; and (4) the minimum valley in this χ2 array is used to select most probable values and confidence intervals of the planetary parameters. We conclude with future prospects for studying light curve anomalies in exoplanetary transits.

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves ... more We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.

Using Lowell telescopes, primarily the 1.1-m Hall Telescope, we conducted an in-depth observing c... more Using Lowell telescopes, primarily the 1.1-m Hall Telescope, we conducted an in-depth observing campaign of Comet 10P/Tempel 2 during its 1999/2000 apparition and have begun a follow up observing campaign for the 2010 apparition. Thirty-one nights of broadband and narrowband images were obtained for the 1999/2000 apparition over an 11-month interval. Our earlier investigation of broadband R photometry collected early in the 1999/2000 apparition yielded a precise rotation period and confirmed a slight nucleus spin-down (Knight et al. 2010, submitted to AJ). Using narrowband and broadband images collected late in the 1999/2000 apparition to investigate coma morphology, we find a single CN fan and a single dust jet. Relatively benign image enhancements such as azimuthal-subtraction were used to aid in the quantitative determination of the position angles of these radial features. There is an offset between the position angles of the CN fan and the dust jet that is consistent within the uncertainties; during the interval of October 1999 through January 2000 the measured offset between the CN and dust features ranges from 10 to 20 degrees. We are examining the possible cause of this position angle offset. No change in the position angles of the CN fan or dust jet were seen associated with rotational phase, suggesting that both features are very close to the comet's pole. Our preliminary pole solution is in general agreement with Sekanina's pole solution for 1925-1967 (1991; AJ 102, 350-358). Our initial observations from May-July of 2010 (see poster by Knight et al.) also show a single CN fan and dust jet with a larger offset in position angle, possibly due to the change in viewing geometry. Additionally, we see evidence of a dust tail in the anti-solar direction. This project is supported by the NASA Planetary Astronomy Program.

Thirty-one nights of broadband R and narrowband photometry were obtained of 10P/Tempel during its... more Thirty-one nights of broadband R and narrowband photometry were obtained of 10P/Tempel during its 1999/2000 apparition using Lowell Observatory 1.1 and 1.8-m telescopes. Early emphasis was placed on obtaining rotational lightcurves, while narrowband measurements later in the apparition were intended to study coma morphology. From our broadband measurements we determine a double-peaked rotation period of 8.938 hrs with an uncertainty of ±0.002 hours. Mueller and Ferrin (1996) suggested a possible change in Tempel 2's rotation period from the 1988 to the 1994 apparitions, comparing five possible rotation periods from data obtained in October and December of 1994 to Sekanina's (1991) period of 8.932 hours determined for the 1988 apparition. We can conclusively rule out four of Mueller and Ferrin's five periods, leaving their period of 8.939, which is within the uncertainty of our period. It is important to note that Mueller and Ferrin's data were obtained post-perihelion during the 1994 apparition, and our 1999 data were obtained pre-perihelion. (If one presumes any change in period would be caused by gas jet-induced torques, it is reasonable to assume the period remains relatively unchanged between perihelion passages.) Two perihelion passages occurred between the 1988 and 1994 and 1999 data sets, suggesting a spin-down of Tempel 2's rotation rate of about 11 seconds per apparition. We present these results and others. This research was supported by NSF grant AST-0453611 and by the NASA Planetary Astronomy Program.

Astronomy & Astrophysics, 2009

We present times series photometry on VY Aquarii and V2491 Cygni. We produced a lightcurve for VY... more We present times series photometry on VY Aquarii and V2491 Cygni. We produced a lightcurve for VY Aquarii during its superoutburst and calculated a superhump period of 92.81 minutes. The decline of the superoutburst was also examined in VY Aquarii. The new classical nova V2491 Cygni was examined. Fourier analysis revealed no orbital period. The V2491 Cygni data was used to compare Florida Tech Observatory's FLI IMG-1042 CCD with SARA Observatory's Apogee U42 CCD system. This project was funded by a partnership between the National Science Foundation (NSFAST-0552798), Research Experiences for Undergraduates (REU),and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs. Observations were conducted in collaboration with the Center for Backyard Astrophysics (CBA)

Combustion and Flame, 2009

We present preliminary results from a total of 212.1 hours of data from multi-site observations o... more We present preliminary results from a total of 212.1 hours of data from multi-site observations of GW Lib. Our results reveal a signal near the 2.1-hr period previously detected by Woudt & Warner in quiescence, but of slightly shorter period, and also a modulation at 4-hr. Both the 2 and 4-hr modulations appear to vary in period and/or phase. The 4-hr period may be the fundamental period and the 2-hr a harmonic. Fourier analysis also shows a transient 20-min modulation that is anti-correlated in amplitude with the 2-hr periodicity. Using a smaller data set, we investigate higher frequency pulsations and compare to those found by previous authors before outburst. This project was funded by a partnership between the National Science Foundation (NSF AST-0552798), Research Experiences for Undergraduates (REU), and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs. Observations were made in collaboration with the Center for Backyard Astrophysics (CBA).

Astrophysical Journal, 2011

We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that... more We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of X1-X2 orbit transfer, and our potential model results in a ring radius of ~200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, ~2x10^7 Msun and ~0.1 Msun/yr. Star formation in our simulations takes place mostly in the outermost X2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.

Astronomical Journal, 2011

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves ... more We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.

We conducted an intensive observational campaign of Comet 10P/Tempel 2 during its 1999/2000 appar... more We conducted an intensive observational campaign of Comet 10P/Tempel 2 during its 1999/2000 apparition, obtaining 31 nights of imaging with Lowell telescopes over an 11-month interval. Emphasis early in the apparition was given to obtaining nucleus lightcurve measurements while in later months the primary goal was to study coma morphology. Based on data obtained at the 1988 apparition, several researchers showed that Tempel 2 exhibits little cometary activity until shortly prior to perihelion, and that the rotational lightcurve of the nucleus has a large amplitude consistent with a highly elongated nucleus. An overall period of 8.932 hr was determined by Sekanina (1991); however, based on lightcurve data obtained in late 1994, Mueller and Ferrin (1996) obtained 5 possible periods, each different from the 1988 solution and from which they inferred a possible small spin-up or spin-down of the nucleus. Since our early 1999 observations would be taken within the same inter-perihelion interval as the 1994, we would expect no significant torquing due to activity near perihelion, and thus the same period to be present as in 1994. Our observations were planned to discriminate between Mueller and Ferrin's 5 viable solutions, and our preliminary rotation period of 8.937 hr indeed eliminates 4 of their answers, leaving only their solution of 8.939 hr. With two perihelion passages having occured between the 1988 and the 1994 and 1999 data sets, these results suggest that the nucleus rotational period is lengthening by only about 10 seconds per apparition. Our data also exhibit periodic variability of the coma brightness, and an offset in the position angle of the CN fan with respect to the dust. Additional analysis of the coma morphology is ongoing and we will present these results along with a more refined period solution. This research is supported by NASA's Planetary Astronomy Program.

A computer model, called the Exoplanetary Pixelization Transit Model (EPTM), is developed to calc... more A computer model, called the Exoplanetary Pixelization Transit Model (EPTM), is developed to calculate exoplanetary transit light curves and determine exoplanet properties from an observed transit light curve. To establish and test the accuracy of the model, an observation of XO-2 was conducted on 2008 Mar 17 where time-series photometry of the transit of XO-2b was collected. Based on the EPTM, XO-2 hosts a planet, XO-2b, with a planetary radius of R = 1.043 RJ, in a near circular orbit with semimajor axis a = 0.0360 AU and inclination angle i = 89.67. The EPTM also determined the length of the transit and the approximate start and end time of the ingress and egress. Here we describe how the EPTM works: (1) a theoretical light curve is calculated for an initial set of planetary parameters, RP , a, and i; (2) an observed light curve is used to calculate χ2 for that theoretical curve; (3) the planetary parameters are varied in a grid about their initial values to produce a multidimensional array of χ2 values; and (4) the minimum valley in this χ2 array is used to select most probable values and confidence intervals of the planetary parameters. We conclude with future prospects for studying light curve anomalies in exoplanetary transits.

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves ... more We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.

Using Lowell telescopes, primarily the 1.1-m Hall Telescope, we conducted an in-depth observing c... more Using Lowell telescopes, primarily the 1.1-m Hall Telescope, we conducted an in-depth observing campaign of Comet 10P/Tempel 2 during its 1999/2000 apparition and have begun a follow up observing campaign for the 2010 apparition. Thirty-one nights of broadband and narrowband images were obtained for the 1999/2000 apparition over an 11-month interval. Our earlier investigation of broadband R photometry collected early in the 1999/2000 apparition yielded a precise rotation period and confirmed a slight nucleus spin-down (Knight et al. 2010, submitted to AJ). Using narrowband and broadband images collected late in the 1999/2000 apparition to investigate coma morphology, we find a single CN fan and a single dust jet. Relatively benign image enhancements such as azimuthal-subtraction were used to aid in the quantitative determination of the position angles of these radial features. There is an offset between the position angles of the CN fan and the dust jet that is consistent within the uncertainties; during the interval of October 1999 through January 2000 the measured offset between the CN and dust features ranges from 10 to 20 degrees. We are examining the possible cause of this position angle offset. No change in the position angles of the CN fan or dust jet were seen associated with rotational phase, suggesting that both features are very close to the comet's pole. Our preliminary pole solution is in general agreement with Sekanina's pole solution for 1925-1967 (1991; AJ 102, 350-358). Our initial observations from May-July of 2010 (see poster by Knight et al.) also show a single CN fan and dust jet with a larger offset in position angle, possibly due to the change in viewing geometry. Additionally, we see evidence of a dust tail in the anti-solar direction. This project is supported by the NASA Planetary Astronomy Program.

Thirty-one nights of broadband R and narrowband photometry were obtained of 10P/Tempel during its... more Thirty-one nights of broadband R and narrowband photometry were obtained of 10P/Tempel during its 1999/2000 apparition using Lowell Observatory 1.1 and 1.8-m telescopes. Early emphasis was placed on obtaining rotational lightcurves, while narrowband measurements later in the apparition were intended to study coma morphology. From our broadband measurements we determine a double-peaked rotation period of 8.938 hrs with an uncertainty of ±0.002 hours. Mueller and Ferrin (1996) suggested a possible change in Tempel 2's rotation period from the 1988 to the 1994 apparitions, comparing five possible rotation periods from data obtained in October and December of 1994 to Sekanina's (1991) period of 8.932 hours determined for the 1988 apparition. We can conclusively rule out four of Mueller and Ferrin's five periods, leaving their period of 8.939, which is within the uncertainty of our period. It is important to note that Mueller and Ferrin's data were obtained post-perihelion during the 1994 apparition, and our 1999 data were obtained pre-perihelion. (If one presumes any change in period would be caused by gas jet-induced torques, it is reasonable to assume the period remains relatively unchanged between perihelion passages.) Two perihelion passages occurred between the 1988 and 1994 and 1999 data sets, suggesting a spin-down of Tempel 2's rotation rate of about 11 seconds per apparition. We present these results and others. This research was supported by NSF grant AST-0453611 and by the NASA Planetary Astronomy Program.

Astronomy & Astrophysics, 2009

We present times series photometry on VY Aquarii and V2491 Cygni. We produced a lightcurve for VY... more We present times series photometry on VY Aquarii and V2491 Cygni. We produced a lightcurve for VY Aquarii during its superoutburst and calculated a superhump period of 92.81 minutes. The decline of the superoutburst was also examined in VY Aquarii. The new classical nova V2491 Cygni was examined. Fourier analysis revealed no orbital period. The V2491 Cygni data was used to compare Florida Tech Observatory's FLI IMG-1042 CCD with SARA Observatory's Apogee U42 CCD system. This project was funded by a partnership between the National Science Foundation (NSFAST-0552798), Research Experiences for Undergraduates (REU),and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs. Observations were conducted in collaboration with the Center for Backyard Astrophysics (CBA)

Combustion and Flame, 2009

We present preliminary results from a total of 212.1 hours of data from multi-site observations o... more We present preliminary results from a total of 212.1 hours of data from multi-site observations of GW Lib. Our results reveal a signal near the 2.1-hr period previously detected by Woudt & Warner in quiescence, but of slightly shorter period, and also a modulation at 4-hr. Both the 2 and 4-hr modulations appear to vary in period and/or phase. The 4-hr period may be the fundamental period and the 2-hr a harmonic. Fourier analysis also shows a transient 20-min modulation that is anti-correlated in amplitude with the 2-hr periodicity. Using a smaller data set, we investigate higher frequency pulsations and compare to those found by previous authors before outburst. This project was funded by a partnership between the National Science Foundation (NSF AST-0552798), Research Experiences for Undergraduates (REU), and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs. Observations were made in collaboration with the Center for Backyard Astrophysics (CBA).