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Papers by Christopher Stubbs
The Astronomical Journal, 2003
We report improved parameters for approximately 60 beat Cepheids found in 22 MACHO Project survey... more We report improved parameters for approximately 60 beat Cepheids found in 22 MACHO Project survey fields. These parameters incorporate an improved photometric calibration and data taken over an interval of 1000 days. The parameters reported include period, period ratio, mode identification, Fourier amplitudes and ratios, mean magnitude and color, and position.
We are developing an astronomical imaging system which employs a thermoelectrically cooled focal ... more We are developing an astronomical imaging system which employs a thermoelectrically cooled focal plane consisting of two 'edge-buttable' Loral 2048 X 2048 pixel CCDs. To allow strip scanning, the columns of the CCDs are mutually aligned on a custom Kovar mount. The clocking and bias voltage levels for each CCD are independently adjustable, but both CCDs are operated synchronously. Each
Further to CBET 2214, we report the discovery of an additional spectroscopically-confirmed supern... more Further to CBET 2214, we report the discovery of an additional spectroscopically-confirmed supernova in the Pan-STARRS-1 Medium Deep Survey. PS1-1000252 was discovered 12-13 days before peak on May 10.3 UT (r=22) at 10:45:09.35s +58:33:16.5 (J2000).
International Astronomical Union Circular, Oct 1, 2001
IAUC 7731 available at Central Bureau for Astronomical Telegrams.
Fundamental Physics Research in Space, 2009
The potential of the Sloan Digital Sky Survey for wide-field variability studies is illustrated u... more The potential of the Sloan Digital Sky Survey for wide-field variability studies is illustrated using multi-epoch observations for 3,000,000 point sources observed in 700 deg2 of sky, with time spans ranging from 3 hours to 3 years. These repeated observations of the same sources demonstrate that SDSS delivers ˜0.02 mag photometry with well behaved and understood errors. We show that
Astro2010 the Astronomy and Astrophysics Decadal Survey, Mar 19, 2009
The core of scientific research is turning new ideas into reality. From the school science fair t... more The core of scientific research is turning new ideas into reality. From the school science fair to the search for the secrets of dark energy, high-quality research consists of scientific investigation constrained within the scope of a well-defined project. Large or small, generously funded or just scraping by,scientific projects use time, money, and information to turn ideas into plans, plans into action, and action into results. While we, as a community, do much to educate students in the techniques of research, we do not systematically train students in the nature and organization of scientific projects or in the techniques of project management. We propose a two-pronged attack to address this issue in the next decade. First, to generate a broad base of future scientists who have a basic familiarity with the ideas of projects, we propose that the community develop standards for the content of a project design and management course in astronomy and astrophysics. Second, to train future scientists to assume leadership roles in new investigations in astronomy and astrophysics, we propose that the community develop standards for graduate programs in the area of research project leadership.
Drug Development and Industrial Pharmacy, Feb 1, 2007
Metronidazole is a synthetic antibacterial and antiprotozoan agent. Crystallization occurs in aqu... more Metronidazole is a synthetic antibacterial and antiprotozoan agent. Crystallization occurs in aqueous metronidazole benzoate suspensions caused by an anhydrate to monohydrate conversion. This study aimed to develop an aqueous metronidazole benzoate suspension that does not exhibit this hydration and the accompanying crystal growth. Four suspending agent systems were evaluated. Xanthan gum and Avicel RC-591 (a combination of microcrystalline cellulose and carboxymethylcellulose sodium) were found to be the suspending agents that resulted in optimal formulation properties. Monohydrate formation did not occur in product containing Avicel RC-591, indicating that suspending agents may exert a positive effect on metronidazole benzoate suspension stability.
Hst Proposal, Jun 29, 2005
We are requesting 32 HST orbits to help ascertain the nature of the population that gives rise to... more We are requesting 32 HST orbits to help ascertain the nature of the population that gives rise to the observed set of microlensing events towards the LMC. The SuperMACHO project is an ongoing ground-based survey on the CTIO 4m that has demonstrated the ability to detect LMC microlensing events in real-time via frame subtraction. The improvement in angular resolution and photometric accuracy available from HST will allow us to 1} confirm that the detected flux excursions arise from LMC source stars rather than extended objects {such as for background supernovae or AGN}, and 2} obtain reliable baseline flux measurements for the objects in their unlensed state. The latter measurement is important to resolve degeneracies between the event timescale and baseline flux, which will yield a tighter constraint on the microlensing optical depth.
Noao Proposal, Aug 1, 2005
Searches for the transient brightening of LMC stars due to the gravitational lensing by foregroun... more Searches for the transient brightening of LMC stars due to the gravitational lensing by foreground MACHOs have produced a peculiar result: while the event rate indicates that MACHOs comprise at most ~20% of the dark matter halo, it also far exceeds that expected from known stellar populations. The possible explanations range from the presence of previously undetected tidally stripped LMC material to halo dark matter in the form of compact stellar-mass objects. The SuperMACHO program aims to determine the nature of the lenses by collecting 10× more events than previous searches. However, critical complementary evidence must come from study of the LMC stellar populations themselves. In 2004B, the NOAO TAC awarded 6 half-nights on the CTIO 4-m and 7 nights of 1.0-m time to cover the SuperMACHO fields in B and I. Because the 2004B observing season was plagued by poor seeing, telescope problems, and the unavailability of the expected 4K imager on the CTIO 1.0-m, we are proposing for an additional 2 half- nights of CTIO 4-m time and 7 nights of CTIO 1.0-m time to complete this project. These observations will allow us to (1) reveal whether a significant fraction of events prefer a particular LMC stellar population, and (2) measure the structure of the inner LMC Bar and disk, which may help to reveal tidal debris.
Bulletin of the American Astronomical Society, 2010
Though spectrophotometric standard stars enable or support thousands of astrophysical observation... more Though spectrophotometric standard stars enable or support thousands of astrophysical observations: 1. Fundamental calibration of stars to international standards has not been done since 1975 2. The astronomical community's fundamental standard star, Vega, is unique in that it has a debris disk and is rotating pole-on at near breakup velocity making it anything but a single-temperature, uniform surface brightness source 3. NIST has created spectrophotometric standard sources and detectors that provide sub-1% relative uncertainties allowing throughput calibration from 400nm - 1100nm 4. We have built an objective spectrometer to make standardized observations and a "clear air” lidar capable of providing sub-1% extinction measurements to correct for atmospheric extinction, the most significant systematic error in standardization. These new capabilities for directly measuring and correcting for atmospheric transmission and calibrating telescope throughput enable creation of a new generation of fundamentally calibrated standard stars. The astronomical community will certainly benefit from a new network of fundamental spectrophotometric standard stars calibrated to NIST irradiance standards. We describe the techniques and technologies required to compare optical stellar spectra to NIST calibrated detectors, and the atmospheric measurements required to correct accurately for atmospheric extinction. We discuss observations of candidate standards with V ≤ 5.5 selected from an input catalog of approximately 500 northern hemisphere stars. This project is supported by NIST Grant 60NANB9D9121 and AFRL Grant FA9451-08-C-0267.
Physical Review D Particles and Fields, May 18, 2009
Theories that attempt to explain the observed cosmic acceleration by modifying general relativity... more Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small scales to match experiments. We demonstrate that if such screening occurs via the chameleon mechanism, such as in f(R) theory, it is possible to have order unity violation of the equivalence principle, despite the absence of explicit violation in the microscopic action. Namely, extended objects such as galaxies or constituents thereof do not all fall at the same rate. The chameleon mechanism can screen the scalar charge for large objects but not for small ones (large/small is defined by the depth of the gravitational potential and is controlled by the scalar coupling). This leads to order one fluctuations in the ratio of the inertial mass to gravitational mass. We provide derivations in both Einstein and Jordan frames. In Jordan frame, it is no longer true that all objects move on geodesics; only unscreened ones, such as test particles, do. In contrast, if the scalar screening occurs via strong coupling, such as in the Dvali-Gabadadze-Porrati braneworld model, equivalence principle violation occurs at a much reduced level. We propose several observational tests of the chameleon mechanism: 1. small galaxies should accelerate faster than large galaxies, even in environments where dynamical friction is negligible; 2. voids defined by small galaxies would appear larger compared to standard expectations; 3. stars and diffuse gas in small galaxies should have different velocities, even if they are on the same orbits; 4. lensing and dynamical mass estimates should agree for large galaxies but disagree for small ones. We discuss possible pitfalls in some of these tests. The cleanest is the third one where the mass estimate from HI rotational velocity could exceed that from stars by 30% or more. To avoid blanket screening of all objects, the most promising place to look is in voids.
Proceedings of the International Astronomical Union
The Astronomical Journal, 2003
We report improved parameters for approximately 60 beat Cepheids found in 22 MACHO Project survey... more We report improved parameters for approximately 60 beat Cepheids found in 22 MACHO Project survey fields. These parameters incorporate an improved photometric calibration and data taken over an interval of 1000 days. The parameters reported include period, period ratio, mode identification, Fourier amplitudes and ratios, mean magnitude and color, and position.
We are developing an astronomical imaging system which employs a thermoelectrically cooled focal ... more We are developing an astronomical imaging system which employs a thermoelectrically cooled focal plane consisting of two 'edge-buttable' Loral 2048 X 2048 pixel CCDs. To allow strip scanning, the columns of the CCDs are mutually aligned on a custom Kovar mount. The clocking and bias voltage levels for each CCD are independently adjustable, but both CCDs are operated synchronously. Each
Further to CBET 2214, we report the discovery of an additional spectroscopically-confirmed supern... more Further to CBET 2214, we report the discovery of an additional spectroscopically-confirmed supernova in the Pan-STARRS-1 Medium Deep Survey. PS1-1000252 was discovered 12-13 days before peak on May 10.3 UT (r=22) at 10:45:09.35s +58:33:16.5 (J2000).
International Astronomical Union Circular, Oct 1, 2001
IAUC 7731 available at Central Bureau for Astronomical Telegrams.
Fundamental Physics Research in Space, 2009
The potential of the Sloan Digital Sky Survey for wide-field variability studies is illustrated u... more The potential of the Sloan Digital Sky Survey for wide-field variability studies is illustrated using multi-epoch observations for 3,000,000 point sources observed in 700 deg2 of sky, with time spans ranging from 3 hours to 3 years. These repeated observations of the same sources demonstrate that SDSS delivers ˜0.02 mag photometry with well behaved and understood errors. We show that
Astro2010 the Astronomy and Astrophysics Decadal Survey, Mar 19, 2009
The core of scientific research is turning new ideas into reality. From the school science fair t... more The core of scientific research is turning new ideas into reality. From the school science fair to the search for the secrets of dark energy, high-quality research consists of scientific investigation constrained within the scope of a well-defined project. Large or small, generously funded or just scraping by,scientific projects use time, money, and information to turn ideas into plans, plans into action, and action into results. While we, as a community, do much to educate students in the techniques of research, we do not systematically train students in the nature and organization of scientific projects or in the techniques of project management. We propose a two-pronged attack to address this issue in the next decade. First, to generate a broad base of future scientists who have a basic familiarity with the ideas of projects, we propose that the community develop standards for the content of a project design and management course in astronomy and astrophysics. Second, to train future scientists to assume leadership roles in new investigations in astronomy and astrophysics, we propose that the community develop standards for graduate programs in the area of research project leadership.
Drug Development and Industrial Pharmacy, Feb 1, 2007
Metronidazole is a synthetic antibacterial and antiprotozoan agent. Crystallization occurs in aqu... more Metronidazole is a synthetic antibacterial and antiprotozoan agent. Crystallization occurs in aqueous metronidazole benzoate suspensions caused by an anhydrate to monohydrate conversion. This study aimed to develop an aqueous metronidazole benzoate suspension that does not exhibit this hydration and the accompanying crystal growth. Four suspending agent systems were evaluated. Xanthan gum and Avicel RC-591 (a combination of microcrystalline cellulose and carboxymethylcellulose sodium) were found to be the suspending agents that resulted in optimal formulation properties. Monohydrate formation did not occur in product containing Avicel RC-591, indicating that suspending agents may exert a positive effect on metronidazole benzoate suspension stability.
Hst Proposal, Jun 29, 2005
We are requesting 32 HST orbits to help ascertain the nature of the population that gives rise to... more We are requesting 32 HST orbits to help ascertain the nature of the population that gives rise to the observed set of microlensing events towards the LMC. The SuperMACHO project is an ongoing ground-based survey on the CTIO 4m that has demonstrated the ability to detect LMC microlensing events in real-time via frame subtraction. The improvement in angular resolution and photometric accuracy available from HST will allow us to 1} confirm that the detected flux excursions arise from LMC source stars rather than extended objects {such as for background supernovae or AGN}, and 2} obtain reliable baseline flux measurements for the objects in their unlensed state. The latter measurement is important to resolve degeneracies between the event timescale and baseline flux, which will yield a tighter constraint on the microlensing optical depth.
Noao Proposal, Aug 1, 2005
Searches for the transient brightening of LMC stars due to the gravitational lensing by foregroun... more Searches for the transient brightening of LMC stars due to the gravitational lensing by foreground MACHOs have produced a peculiar result: while the event rate indicates that MACHOs comprise at most ~20% of the dark matter halo, it also far exceeds that expected from known stellar populations. The possible explanations range from the presence of previously undetected tidally stripped LMC material to halo dark matter in the form of compact stellar-mass objects. The SuperMACHO program aims to determine the nature of the lenses by collecting 10× more events than previous searches. However, critical complementary evidence must come from study of the LMC stellar populations themselves. In 2004B, the NOAO TAC awarded 6 half-nights on the CTIO 4-m and 7 nights of 1.0-m time to cover the SuperMACHO fields in B and I. Because the 2004B observing season was plagued by poor seeing, telescope problems, and the unavailability of the expected 4K imager on the CTIO 1.0-m, we are proposing for an additional 2 half- nights of CTIO 4-m time and 7 nights of CTIO 1.0-m time to complete this project. These observations will allow us to (1) reveal whether a significant fraction of events prefer a particular LMC stellar population, and (2) measure the structure of the inner LMC Bar and disk, which may help to reveal tidal debris.
Bulletin of the American Astronomical Society, 2010
Though spectrophotometric standard stars enable or support thousands of astrophysical observation... more Though spectrophotometric standard stars enable or support thousands of astrophysical observations: 1. Fundamental calibration of stars to international standards has not been done since 1975 2. The astronomical community's fundamental standard star, Vega, is unique in that it has a debris disk and is rotating pole-on at near breakup velocity making it anything but a single-temperature, uniform surface brightness source 3. NIST has created spectrophotometric standard sources and detectors that provide sub-1% relative uncertainties allowing throughput calibration from 400nm - 1100nm 4. We have built an objective spectrometer to make standardized observations and a "clear air” lidar capable of providing sub-1% extinction measurements to correct for atmospheric extinction, the most significant systematic error in standardization. These new capabilities for directly measuring and correcting for atmospheric transmission and calibrating telescope throughput enable creation of a new generation of fundamentally calibrated standard stars. The astronomical community will certainly benefit from a new network of fundamental spectrophotometric standard stars calibrated to NIST irradiance standards. We describe the techniques and technologies required to compare optical stellar spectra to NIST calibrated detectors, and the atmospheric measurements required to correct accurately for atmospheric extinction. We discuss observations of candidate standards with V ≤ 5.5 selected from an input catalog of approximately 500 northern hemisphere stars. This project is supported by NIST Grant 60NANB9D9121 and AFRL Grant FA9451-08-C-0267.
Physical Review D Particles and Fields, May 18, 2009
Theories that attempt to explain the observed cosmic acceleration by modifying general relativity... more Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small scales to match experiments. We demonstrate that if such screening occurs via the chameleon mechanism, such as in f(R) theory, it is possible to have order unity violation of the equivalence principle, despite the absence of explicit violation in the microscopic action. Namely, extended objects such as galaxies or constituents thereof do not all fall at the same rate. The chameleon mechanism can screen the scalar charge for large objects but not for small ones (large/small is defined by the depth of the gravitational potential and is controlled by the scalar coupling). This leads to order one fluctuations in the ratio of the inertial mass to gravitational mass. We provide derivations in both Einstein and Jordan frames. In Jordan frame, it is no longer true that all objects move on geodesics; only unscreened ones, such as test particles, do. In contrast, if the scalar screening occurs via strong coupling, such as in the Dvali-Gabadadze-Porrati braneworld model, equivalence principle violation occurs at a much reduced level. We propose several observational tests of the chameleon mechanism: 1. small galaxies should accelerate faster than large galaxies, even in environments where dynamical friction is negligible; 2. voids defined by small galaxies would appear larger compared to standard expectations; 3. stars and diffuse gas in small galaxies should have different velocities, even if they are on the same orbits; 4. lensing and dynamical mass estimates should agree for large galaxies but disagree for small ones. We discuss possible pitfalls in some of these tests. The cleanest is the third one where the mass estimate from HI rotational velocity could exceed that from stars by 30% or more. To avoid blanket screening of all objects, the most promising place to look is in voids.
Proceedings of the International Astronomical Union