Time Baseline Of Observations Research Articles

Transiting Exoplanet Monitoring Project (TEMP). III. On the Relocation of the Kepler-9 b Transit

AbstractThe Kepler-9 system harbors three known transiting planets. The system holds significant interest for several reasons. First, the outer two planets exhibit a period ratio that is close to a 2:1 orbital commensurability, with attendant dynamical consequences. Second, both planets lie in the planetary mass “desert” that is generally associated with the rapid gas agglomeration phase of the core accretion process. Third, there exist attractive prospects for accurately measuring both the sky-projected stellar spin–orbit angles as well as the mutual orbital inclination between the planets in the system. Following the originalKeplerdetection announcement in 2010, the initially reported orbital ephemerides for Kepler-9 b and c have degraded significantly, due to the limited time base-line of observations on which the discovery of the system rested. Here, we report new ground-based photometric observations and extensive dynamical modeling of the system. These efforts allow us to photometrically recover the transit of Kepler-9 b and thereby greatly improve the predictions for upcoming transit mid-times. Accurate ephemerides of this system are important in order to confidently schedule follow-up observations of this system, for both in-transit Doppler measurements as well as for atmospheric transmission spectra taken during transit.

An O−C (and light travel time) method suitable for application to large photometric databases

The standard method of studying period changes in variable stars is to study the timing residuals or O−C values of light-curve maxima or minima. The advent of photometric surveys for variability, covering large parts of the sky and stretching over years, has made available measurementsofprobablyhundredsofthousandsofvariablestars,observedatrandomphases. Simple methodology is described which can be used to quickly check such measurements of a star for indications of period changes. Effectively, the low-frequency periodogram of a first-order estimate of the O−C function is calculated. In the case of light travel time (LTT) effects, the projected orbital amplitude follows by robust regression of a sinusoid on the O−C. The results can be used as input into a full non-linear least-squares regression directly on the observations. Extensive simulations of LTT configurations are used to explore the sensitivity of results to various parameter values (period of the variable star and signal to noise of measurements; orbital period and amplitude; number and time baseline of observations). The methodology is applied to observations of three previously studied stars.

THE BENEFITS OF VLBI ASTROMETRY TO PULSAR TIMING ARRAY SEARCHES FOR GRAVITATIONAL RADIATION

Precision astrometry is an integral component of successful pulsar timing campaigns. Astrometric parameters are commonly derived by fitting them as parameters of a timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over several-year spans can yield position measurements with sub-milliarcsecond precision. However, timing-based astrometry can become biased if a pulsar displays any red spin noise, which can be compared to the red noise signal produced by the stochastic gravitational wave background. We investigate how noise of different spectral types is absorbed by timing models, leading to significant estimation errors in the astrometric parameters. We find that commonly used techniques for fitting timing models in the presence of red noise (Cholesky whitening) prevent the absorption of noise into the timing model remarkably well if the time baseline of observations exceeds several years, but are inadequate for dealing with shorter pulsar data sets. Independent of timing, pulsar-optimized very long baseline interferometry (VLBI) is capable of providing position estimates precise to the sub-milliarcsecond levels needed for high-precision timing. We compute a necessary transformation between the International Celestial Reference Frame and pulsar timing frames and quantitatively discuss how the transformation will improve in coming years. We find that incorporating VLBI astrometry into the timing models of pulsars for which only a couple of years of timing data exist will lead to more realistic assessments of red spin noise and could enhance the amplitude of gravitational wave signatures in post-fit timing residuals by factors of 20 or more.

Quasar Detection via Variability in a High Galactic Latitude Drift‐Scan Survey

This dissertation studies the intrinsic variability of quasars as a means of quasar detection. The detection of quasars via a parameter that is independent of quasar color allows for comparison with other color-selected samples of quasars, giving a more complete understanding of any possible selection effects in present and future quasar catalogs. Using the 16 CCD QUEST Phase 1 camera on the 1 m Schmidt telescope at the Venezuelan National Astronomical Observatory, 69 drift-scan observations of a high Galactic latitude region along the celestial equator were obtained. These observations, taken over the course of three observing seasons (1999 February–March, 2000 February–March, and 2001 March–April), cover the region between and , centered at a declination of 1 . h h m 10 15 30 Four broadband filters (B, V, and two R filters) were placed over the four rows of four CCDs, allowing the capture of four images of each object passing across the camera field of view. A large region of the sky ( ) was sampled over a range 2 194 deg of timescales (from hourly to biennially) for a duration of 26 months. This time sampling allows a region of the time domain distinct from other large sky surveys to be investigated. Following standard data reduction using a suite of custom software, incomplete ensemble photometry was used to correct for varying weather conditions and to compile a list of candidate objects that are variable at a statistically significant level. A confidence level for every object in each bandpass was calculated. An object was required to be variable at the 85% confidence level or greater in at least the two R filters to remain viable. Candidate lists were compiled from the data using both a 13 and 26 month time baseline. The quasars published in the ninth edition of the catalog of Veron-Cetty & Veron (2000, A Catalogue of Quasars and Active Galactic Nuclei [ESO Sci. Rep. 19; Garching: ESO]) were used to benchmark the variability characteristics of quasars over both timescales. After 13 months, 38% of the Veron-Cetty & Veron quasars within the survey were seen to vary at greater than the 85% confidence level. Utilizing the full 26 month baseline, 61% were variable at greater than the 85% confidence level. As expected, increasing the time baseline increased the percentage of known quasars in the field, which were seen to vary. A subset of the candidates on both timescales were chosen for spectroscopic confirmation. Low-resolution spectroscopy was obtained for these candidates in 2001 April and 2002 February using the Hydra multiobject spectrograph on the WIYN 3.5 m telescope at Kitt Peak National Observatory. Seventeen objects were confirmed as quasars by means of their distinctive broadened emission features during the 2001 April campaign. An additional 15 quasars, 2 of which overlap with the 2001 April spectroscopic campaign because of slight overlaps between two fields in each observing campaign, were discovered during the 2002 February campaign. As of 2003 October, 19 of the 30 discoveries were independently confirmed via a literature search, and 11 remain new discoveries (A. W. Rengstorf et al. 2004, in preparation). It is confirmed that increasing the time baseline of observations increases the completeness (i.e., the percentage of quasars that will be seen to vary) of the survey. While the density of candidate objects on the sky did not necessitate any cuts other than variability with regard to the number of available spectrograph fibers on Hydra, an a posteriori investigation into the broadband colors of the candidate objects reveal that color cuts in B–V and V–R would have increased the efficiency (i.e., the percentage of the candidate list that are quasars) of the spectroscopic confirmation.