The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight

The limiting magnitude of the HST data set used by Cochran et al. (1995) to detect small objects in the Kuiper belt is reevaluated, and the methods used are described in detail. It is shown, by implanting artificial objects in the original HST images, and re-reducing the images using our original algorithm, that the limiting magnitude of our images (as defined by the 50% detectability limit) is $V=28.4$. This value is statistically the same as the value found in the original analysis. We find that $\sim50$ of the moving Kuiper belt objects with $V=27.9$ are detected when trailing losses are included. In the same data in which these faint objects are detected, we find that the number of false detections brighter than $V=28.8$ is less than one per WFPC2 image. We show that, primarily due to a zero-point calibration error, but partly due to inadequacies in modeling the HST'S data noise characteristics and Cochran et al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects in the HST dataset by over a factor of 2, and their conclusions are therefore invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe

Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2

The first detected interstellar object 'Oumuamua that passed within 0.25au of the Sun on 2017 September 9 was presumably ejected from a stellar system. We use its newly determined non-Keplerian trajectory together with the reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past close encounters. Such an "encounter" could reveal the home system from which 'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90% confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249, 3.8Myr ago. Two more stars have encounter distances and velocities intermediate to these. The encounter parameters are similar across six different non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by scattering from a giant planet in one of the systems is plausible, but requires a rather unlikely configuration to achieve the high velocities found. A binary star system is more likely to produce the observed velocities. None of the four home candidates have published exoplanets or are known to be binaries. Given that the 7 million stars in Gaia DR2 with 6D phase space information is just a small fraction of all stars for which we can eventually reconstruct orbits, it is a priori unlikely that our current search would find 'Oumuamua's home star system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown dwarfs every Myr, the plausibility of a home system depends also on an appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa

Database Engineering Processes with DB-MAIN

Software engineering needs more and more to be supported by CASE tools. Since databases are at the heart of information systems, they deserve a particular attention. More and more CASE tools allow method engineers to implement their own methodology and they allow users to record all their actions, with their rationales, in order to improve the quality of the design and the quality of the documentation of the design. DBMAIN is such a database oriented tool with a method description and a documentation generation facilities. But it has its particularities like its procedural non-deterministic Method Description Language, its well integrated multilevel histories and its userfriendly methodological engine

Base damage, local sequence context andTP53mutation hotspots: a molecular dynamics study of benzo[a]pyrene induced DNA distortion and mutability

The mutational pattern for the TP53 tumour suppressor gene in lung tumours differs to other cancer types by having a higher frequency of G:C>T:A transversions. The aetiology of this differing mutation pattern is still unknown. Benzo[a]pyrene,diol epoxide (BPDE) is a potent cigarette smoke carcinogen that forms guanine adducts at TP53 CpG mutation hotspot sites including codons 157, 158, 245, 248 and 273. We performed molecular modelling of BPDE-adducted TP53 duplex sequences to determine the degree of local distortion caused by adducts which could influence the ability of nucleotide excision repair. We show that BPDE adducted codon 157 has greater structural distortion than other TP53 G:C>T:A hotspot sites and that sequence context more distal to adjacent bases must influence local distortion. Using TP53 trinucleotide mutation signatures for lung cancer in smokers and non-smokers we further show that codons 157 and 273 have the highest mutation probability in smokers. Combining this information with adduct structural data we predict that G:C>T:A mutations at codon 157 in lung tumours of smokers are predominantly caused by BPDE. Our results provide insight into how different DNA sequence contexts show variability in DNA distortion at mutagen adduct sites that could compromise DNA repair at well characterized cancer related mutation hotspots

Lightcurves of 20--100 kilometer Kuiper Belt Objects using the Hubble Space Telescope

We report high precision photometry of three small and one larger Kuiper Belt Objects (KBOs) obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope (ACS/HST). The three small bodies are the smallest KBOs for which lightcurve measurements are available. 2003 BF91 has a diameter of 20 kilometers (assuming 10% albedo) and a 1.09 magnitude, 9.1-hour lightcurve that is feasibly explained by the rotation of an elongated, coherent body that is supported by material strength and best imagined as an icy outer Solar System analog to asteroid (243) Ida. Two other small KBOs, 2003 BG91 and 2003 BH91 (diameters 31 and 18 km, with albedo 10%), exhibit an unremarkable lightcurve and no detectable photometric variation, respectively. For the larger KBO 2000 FV53 (116 km diameter, assuming 10% albedo) we strongly detect a non-sinusoidal periodic (7.5 hours) brightness variation with a very small amplitude (0.07 mag). This KBO may be nearly spherical, a result that might not be unusual in the Kuiper Belt but would be remarkable among outer Solar System satellites of similar size. We carry out a study of possible physical states and bulk densities under the assumptions of both fluid equilibrium and finite, non-zero internal friction. The densities for the these KBOs are likely to be in the range 1--2 g/cm3, and a plausible solution for 2000 FV53 is a rubble pile of this density that is held slightly out of the minimum-energy shape by internal friction among constituent blocks that are relatively small. Our interpretation of 2000 FV53 as a pulverized but essentially primordial object and 2003 BF91 as a collisional fragment is consistent with models of collisional timescales in the outer Solar System. We compile all published KBO lightcurve data and compare our results to the larger population. [abridged]Comment: AJ, in press. Tables 1-4 will be electronic only in published version but appear here in full. Figures 1,3,5 in colo

Galaxies in Southern Bright Star Fields I. Near-infrared imaging

As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of K_s imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations 60" from candidate guide stars in the magnitude range 9.0 R 12.4. When analyzed as a "discrete deep field" with 131 arcmin^2 area, our dataset gives galaxy number counts that agree with those derived previously over the range 16 K_s 20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.Comment: 10 pages, 7 figures, accepted by A&A; Table 3 is available at http://www.rzg.mpg.de/~ajb/data.html pending upload to CD

Multidisciplinary Control of a Sparse Interferometric Array Satellite Testbed

The MIT Adaptive Reconnaissance Golay-3 Optical Satellite (ARGOS) is a wide-angle Fizeau interferometer spacecraft testbed. Designing a space-based interferometer, which requires such high tolerances on pointing and alignment for its apertures, presents unique multidisciplinary challenges in the areas of structural dynamics, controls and multi-aperture phasing active optics. In meeting these challenges, emphasis is placed on modularity in spacecraft subsystems and optics as a means of allowing expandability and upgradeability. For the interferometer to function properly, unique methods of coherent wave front sensing are developed and used for error detection in control of the Fast Steering Mirrors (FSMs). The space environment is simulated by floating ARGOS on a frictionless air-bearing that allows it to track fast moving satellites such as the International Space Station (ISS), planets or point stars. A System Identification is performed on ARGOS to determine its dynamic properties and to design optimal controllers for the Attitude Control System (ACS). ACS sensors include an electronic compass with a 2-axis tip-tilt sensor, a viewfinder camera with centroiding algorithm, and a 3-axis rate gyroscope. Nonlinear, quaternion-based control is employed using reaction wheels as the spacecraft's actuators