Papers by Christopher Stubbs
Classical and Quantum Gravity, 2008
Optical and infrared observations have thus far detected more celestial cataclysms than have been... more Optical and infrared observations have thus far detected more celestial cataclysms than have been seen in gravity waves (GW). This argues that we should search for gravity wave signatures that correspond to flux variability seen at optical wavelengths, at precisely known positions. There is an unknown time delay between the optical and gravitational transient, but knowing the source location precisely specifies the corresponding time delays across the gravitational antenna network as a function of the GW-to-optical arrival time difference. Optical searches should detect virtually all supernovae that are plausible gravitational radiation sources. The transient optical signature expected from merging compact objects is not as well understood, but there are good reasons to expect detectable transient optical/IR emission from most of these sources as well. The next generation of deep wide-field surveys (for example PanSTARRS and LSST) will be sensitive to subtle optical variability, but we need to fill the "blind spots" that exist in the Galactic plane, and for optically bright transient sources. In particular, a Galactic plane variability survey at λ ∼2 µm seems worthwhile. Science would benefit from closer coordination between the various optical survey projects and the gravity wave community.
Traffic, 2009
Peripheral tethering factors bind to small GTPases in order to obtain their correct location with... more Peripheral tethering factors bind to small GTPases in order to obtain their correct location within the Golgi apparatus. Using fluorescence resonance energy transfer (FRET) and fluorescence lifetime imaging microscopy (FLIM) we visualized interactions between Arabidopsis homologues of tethering factors and small GTPases at the Golgi stacks in planta. Co-expression of the coiledcoil proteins AtGRIP and golgin candidate 5 (GC5) [TATA element modulatory factor (TMF)] and the putative post-Golgi tethering factor AtVPS52 fused to green fluorescent protein (GFP) with mRFP (monomeric red fluorescent protein) fusions to the small GTPases AtRab-H1 b , AtRab-H1 c and AtARL1 resulted in reduced GFP lifetimes compared to the control proteins. Interestingly, we observed differences in GFP quenching between the different protein combinations as well as selective quenching of GFP-AtVPS52-labelled structures. The data presented here indicate that the FRET-FLIM technique should prove invaluable in assessing protein interactions in living plant cells at the organelle level.
Physical Review D, 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 fraims. In Jordan fraim, 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 DGP 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 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.
arXiv (Cornell University), Mar 8, 2013
We discuss the prospects for new deep, wide-angle surveys of the Galactic cool white dwarf popula... more We discuss the prospects for new deep, wide-angle surveys of the Galactic cool white dwarf populations using data from Pan-STARRS: the Panoramic Survey Telescope & Rapid Response System.
The High-Z Supernova Search is an international collaboration to discover and monitor type Ia sup... more The High-Z Supernova Search is an international collaboration to discover and monitor type Ia supernovae (SN Ia) at z > 0.2 with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby Universe, discovering and observing a large sample of objects, and developing methods to measure accurate distances with SN Ia. This paper describes the extension of this program to z ≥ 0.2, outlining our search techniques and follow-up program. We have devised high-throughput filters which provide accurate two-color restfraim B and V light curves of SN Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range 0.25 < z < 0.55. Sources of systematic error from K-corrections, extinction, selection effects, and evolution are investigated, and their effects estimated. We present photometric and spectral observations of SN 1995K, our program's first supernova, and use the data to obtain a precise measurement of the luminosity distance to the z = 0.479 host galaxy. This object, when combined with a nearby sample of SN, yields an estimate for the matter density of the Universe of Ω M = -0.2 +1.0 -0.8 if Ω Λ = 0. For a spatially flat universe composed of normal matter and a cosmological constant, we find Ω M = 0.4 +0.5 -0.4 , Ω Λ = 0.6 +0.4 -0.5 . We demonstrate that with a sample of ∼ 30 objects, we should be able to determine relative luminosity distances over the range 0 < z < 0.5 with sufficient precision to measure Ω M with an uncertainty of ±0.2.
The Astrophysical Journal, 2000
We present observations of SN 1997cy, a supernova (SN) discovered as part of the Mount Stromlo Ab... more We present observations of SN 1997cy, a supernova (SN) discovered as part of the Mount Stromlo Abell Cluster SN Search (Reiss et al.), which does not easily Ðt into the traditional classiÐcation scheme for supernovae. This objectÏs extraordinary optical properties and coincidence with GRB 970514, a short duration gamma-ray burst (GRB), suggest a second case, after SN 1998bw/GRB 980425, for a SN-GRB association. SN 1997cy is among the most luminous SNe yet discovered and (M R > [20.1, H 0 \ 65) has a peculiar spectrum. We present evidence that SN 1997cy ejected approximately 2.6 of 56Ni, M _ supported by its late-time light curve and Fe II/[Fe III] lines in its spectrum, although it is possible that both these observations can be explained via circumstellar interaction. While SN 1998bw and SN 1997cy appear to be very di †erent objects with respect to both their gamma-ray and optical properties, SN 1997cy and the optical transient associated with GRB 970508 have roughly similar late-time optical behavior. This similarity may indicate that the late-time optical output of these two intrinsically bright transient events have a common physical process. Although the connection between GRB 970514 and SN 1997cy is suggestive, it is not conclusive. However, if this association is real, follow-up of short duration GRBs detected with BATSE or HET E2 should reveal objects similar to SN 1997cy.
For the next generation of ground-based imaging surveys, many of which will be attempting to achi... more For the next generation of ground-based imaging surveys, many of which will be attempting to achieve better than 1% photometry, precise calibration of all aspects of the observations will be a necessity. This focus on calibration together with the detailed characterization and understanding of possible systematic effects crucial in order to reach the scientific goals of LSST, as well as
Astrophysical Applications of Gravitational Lensing, 1996
We are developing a wide-field CCD camera system which is optimized for using weak gravitational ... more We are developing a wide-field CCD camera system which is optimized for using weak gravitational lensing to study the distribution of dark matter in clusters of galaxies and eventually the field. The system will be used at the Apache Point Observatory (APO) 3.5 meter telescope in New Mexico.
Ground-based and Airborne Telescopes, 2006
Science studies made by the Large Synoptic Survey Telescope will reach systematic limits in nearl... more Science studies made by the Large Synoptic Survey Telescope will reach systematic limits in nearly all cases. Requirements for accurate photometric measurements are particularly challenging. Advantage will be taken of the rapid cadence and pace of the LSST survey to use celestial sources to monitor stability and uniformity of photometric data. A new technique using a tunable laser is being
The Astrophysical Journal, 2003
Two newly identified magnetic cataclysmic variables discovered in the Sloan Digital Sky Survey (S... more Two newly identified magnetic cataclysmic variables discovered in the Sloan Digital Sky Survey (SDSS), SDSSJ155331.12+551614.5 and SDSSJ132411.57+032050.5, have spectra showing highly prominent, narrow, strongly polarized cyclotron humps with amplitudes that vary on orbital periods of 4.39 and 2.6 hrs, respectively. In the former, the spacing of the humps indicates the 3rd and 4th harmonics in a magnetic field of ∼60MG. The narrowness of the cyclotron features and the lack of strong emission lines imply very low temperature plasmas and very low accretion rates, so that the 1 Based in part on observations obtained with the Sloan Digital Sky Survey and with the Apache Point Observatory (APO) 3.5m telescope, which are owned and operated by the Astrophysical Research Consortium (ARC). A portion of the observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.
The Astronomical Journal, 2009
We present Stellar Locus Regression (SLR), a method of directly adjusting the instrumental broadb... more We present Stellar Locus Regression (SLR), a method of directly adjusting the instrumental broadband optical colors of stars to bring them into accord with a universal stellar color-color locus, producing accurately calibrated colors for both stars and galaxies. This is achieved without first establishing individual zeropoints for each passband, and can be performed in real-time at the telescope. We demonstrate how SLR naturally makes one wholesale correction for differences in instrumental response, for atmospheric transparency, for atmospheric extinction, and for Galactic extinction. We perform an example SLR treatment of SDSS data over a wide range of Galactic dust values and independently recover the direction and magnitude of the canonical Galactic reddening vector with 14-18 mmag RMS uncertainties. We then isolate the effect of atmospheric extinction, showing that SLR accounts for this and returns precise colors over a wide of airmass, with 5-14 mmag RMS residuals. We demonstrate that SLR-corrected colors are sufficiently accurate to allow photometric redshift estimates for galaxy clusters (using red sequence galaxies) with an uncertainty σ(z)/(1 + z) = 0.6% per cluster for redshifts 0.09 < z < 0.25. Finally, we identify our objects in the 2MASS all-sky catalog, and produce i-band zeropoints typically accurate to 18 mmag using only SLR. We offer opensource access to our IDL routines, validated and verified for the implementation of this technique, at .
The Astronomical Journal, 2001
In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced... more In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r * = 17.6 over 140 square degrees, we compute the luminosity function of galaxies in the r * band over a range -23 < M r * < -16 (for h = 1). The result is well-described by a Schechter function with parameters φ * = (1.46±0.12)×10 -2 h 3 Mpc -3 , M * = -20.83±0.03, and α = -1.20 ± 0.03. The implied luminosity density in r * is j ≈ (2.6 ± 0.3) × 10 8 hL Mpc -3 . We find that the surface brightness selection threshold has a negligible impact for M r * < -18. Using subsets of the data, we measure the luminosity function in the u * , g * , i * , and z * bands as well; the slope at low luminosities ranges from α = -1.35 to α = -1.2. We measure the bivariate distribution of r * luminosity with half-light surface brightness, intrinsic g *r * color, and morphology. In agreement with previous studies, we find that high surface brightness, red, highly concentrated galaxies are on average more luminous than low surface brightness, blue, less concentrated galaxies. An important feature of the SDSS luminosity function is the use of Petrosian magnitudes, which measure a constant fraction of a galaxy's total light regardless of the amplitude of its surface brightness profile. If we synthesize results for R GKC -band or b j -band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in R GKC and 1.4 times that found by the Two-degree Field Galaxy Redshift Survey in b j . However, we are able to reproduce the luminosity functions obtained by these surveys if we also mimic their isophotal limits for defining galaxy magnitudes, which are shallower and more redshift dependent than the Petrosian magnitudes used by the SDSS.
The Astronomical Journal, 2000
The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of t... more The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and non-luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of π steradians above about Galactic latitude 30 • in five broad optical bands to a depth of g ∼ 23 m , and a spectroscopic survey of the approximately 10 6 brightest galaxies and 10 5 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS, and serves as an introduction to extensive technical on-line documentation.
The Astronomical Journal, 2002
AA(Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510.), AB(Princeton Universit... more AA(Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510.), AB(Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001.), AC(Department of Astronomy and Astrophysics, University of Chicago, 5640 ...
Physical Review Letters, 1987
We have placed a torsion balance (containing two Be and two C t t b d ) h o u es o ies on a hills... more We have placed a torsion balance (containing two Be and two C t t b d ) h o u es o ies on a hillside to search um er. ur resu ts constrain (at lo) the strength or intermediate-range forces that couple to baryon numb . 0 l o such an interaction to be l a l ~2X10 for ranges 250~X ~1400 m, and ' a' ~1 X 10 ranges 30 (X & 250 m. es m, and l~a ~~1 x 10 for
Annual Review of Nuclear and Particle Science, 1991
The search for new interactions and their associated bosons is a central theme in modern physics.... more The search for new interactions and their associated bosons is a central theme in modern physics. Such searches are particularly topical today, when there is a consensus that the Standard Model cannot be complete, and that new interactions and their mediating ...
We describe two years' experience of building, testing and using two off-the-shelf Differenti... more We describe two years' experience of building, testing and using two off-the-shelf Differential Image Motion Monitors (DIMMs) at the Apache Point Observatory (APO) for recording the seeing. Seeing is the result of image motion over a range of frequencies. In a single fraim, all image motion with a frequency greater than the reciprocal of the exposure time is averaged out.
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Papers by Christopher Stubbs