arXiv subjects

Kaspar von Braun

Publications and source records attributed to Kaspar von Braun.

At least 91 records · Page 5Linked to original sources

arXiv2009

Constraints on Secondary Eclipse Probabilities of Long-Period Exoplanets from Orbital Elements

Long-period transiting exoplanets provide an opportunity to study the mass-radius relation and internal structure of extrasolar planets. Their studies grant insights into planetary evolution akin to the Solar System planets, which, in contrast to hot Jupiters, are not constantly exposed to the intense radiation of their parent stars. Observations of secondary eclipses allow investigations of exoplanet temperatures and large-scale exo-atmospheric properties. In this short paper, we elaborate on, and calculate, probabilities of secondary eclipses for given orbital parameters, both in the presence and absence of detected primary transits, and tabulate these values for the forty planets with the highest primary transit probabilities.

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arXiv2009

Refining Exoplanet Ephemerides and Transit Observing Strategies

Transiting planet discoveries have yielded a plethora of information regarding the internal structure and atmospheres of extra-solar planets. These discoveries have been restricted to the low-periastron distance regime due to the bias inherent in the geometric transit probability. Monitoring known radial velocity planets at predicted transit times is a proven method of detecting transits, and presents an avenue through which to explore the mass-radius relationship of exoplanets in new regions of period/periastron space. Here we describe transit window calculations for known radial velocity planets, techniques for refining their transit ephemerides, target selection criteria, and observational methods for obtaining maximum coverage of transit windows. These methods are currently being implemented by the Transit Ephemeris Refinement and Monitoring Survey (TERMS).

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arXiv2009

Exoplanetary Transit Constraints Based Upon Secondary Eclipse Observations

Transiting extrasolar planets provide an opportunity to study the mass-radius relation of planets as well as their internal structure. The existence of a secondary eclipse enables further study of the thermal properties of the the planet by observing at infrared wavelengths. The probability of an observable secondary eclipse depends upon the orbital parameters of the planet, particularly eccentricity and argument of periastron. Here we provide analytical expressions for these probabilities, investigate their properties, and calculate their values for the known extrasolar planets. We furthermore quantitatively discuss constraints on existence and observability of primary transits if a secondary eclipse is observed. Finally, we calculate the a-posteriori transit probabilities of the known extrasolar planets, and we present several case studies in which orbital constraints resulting from the presence of a secondary eclipse may be applied in observing campaigns.

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arXiv2009

Observational Window Functions in Planet Transit Surveys

The probability that an existing planetary transit is detectable in one's data is sensitively dependent upon the window function of the observations. We quantitatively characterize and provide visualizations of the dependence of this probability as a function of orbital period upon several observing strategy and astrophysical parameters, such as length of observing run, observing cadence, length of night, transit duration and depth, and the minimum number of sampled transits. The ability to detect a transit is directly related to the intrinsic noise of the observations. In our simulations of observational window functions, we explicitly address non-correlated (gaussian or white) noise and correlated (red) noise and discuss how these two noise components affect transit detectability in fundamentally different manners, especially for long periods and/or small transit depths. We furthermore discuss the consequence of competing effects on transit detectability, elaborate on measures of observing strategies, and examine the projected efficiency of different transit survey scenarios with respect to certain regions of parameter space.

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arXiv2009

Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars

We present interferometric angular sizes for 12 stars with known planetary companions, for comparison with 28 additional main-sequence stars not known to host planets. For all objects we estimate bolometric fluxes and reddenings through spectral energy distribution fits, and in conjunction with the angular sizes, measurements of effective temperature. The angular sizes of these stars are sufficiently small that the fundamental resolution limits of our primary instrument, the Palomar Testbed Interferometer, are investigated at the sub-milliarcsecond level and empirically established based upon known performance limits. We demonstrate that the effective temperature scale as a function of dereddened $(V-K)_0$ color is statistically identical for stars with and without planets. A useful byproduct of this investigation is a direct calibration of the $T_{\rm EFF}$ scale for solar-like stars, as a function of both spectral type and $(V-K)_0$ color, with an precision of $\bar{ΔT}_{\rm {(V-K)}_0} = 138$K over the range $(V-K)_0=0.0-4.0$ and $\bar{ΔT}_{\rm {SpType}} = 105$K for the range F6V -- G5V. Additionally, we provide in an appendix spectral energy distribution fits for the 166 stars with known planets which have sufficient photometry available in the literature for such fits; this derived "{\tt XO-Rad}" database includes homogenous estimates of bolometric flux, reddening, and angular size.

astro-ph.SR↗

arXiv2009

Strong Water Absorption in the Dayside Emission Spectrum of the Planet HD 189733b

Recent observations of the extrasolar planet HD 189733b did not reveal the presence of water in the emission spectrum of the planet. Yet models of such 'Hot Jupiter' planets predict an abundance of atmospheric water vapour. Validating and constraining these models is crucial for understanding the physics and chemistry of planetary atmospheres in extreme environments. Indications of the presence of water in the atmosphere of HD 189733b have recently been found in transmission spectra, where the planet's atmosphere selectively absorbs the light of the parent star, and in broadband photometry. Here we report on the detection of strong water absorption in a high signal-to-noise, mid-infrared emission spectrum of the planet itself. We find both a strong downturn in the flux ratio below 10 microns and discrete spectral features that are characteristic of strong absorption by water vapour. The differences between these and previous observations are significant and admit the possibility that predicted planetary-scale dynamical weather structures might alter the emission spectrum over time. Models that match the observed spectrum and the broadband photometry suggest that heat distribution from the dayside to the night side is weak. Reconciling this with the high night side temperature will require a better understanding of atmospheric circulation or possible additional energy sources.

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arXiv2008

Constraining Orbital Parameters Through Planetary Transit Monitoring

The orbital parameters of extra-solar planets have a significant impact on the probability that the planet will transit the host star. This was recently demonstrated by the transit detection of HD 17156b whose favourable eccentricity and argument of periastron dramatically increased its transit likelihood. We present a study which provides a quantitative analysis of how these two orbital parameters affect the geometric transit probability as a function of period. Further, we apply these results to known radial velocity planets and show that there are unexpectedly high transit probabilities for planets at relatively long periods. For a photometric monitoring campaign which aims to determine if the planet indeed transits, we calculate the expected transiting planet yield and the significance of a potential null result, as well as the subsequent constraints that may be applied to orbital parameters.

astro-ph↗

arXiv2008

Transit Detection of Radial Velocity Planets

The orbital parameters of extra-solar planets have a significant impact on the probability that the planet will transit the host star. This was recently demonstrated by the transit detection of HD 17156b whose favourable eccentricity and argument of periastron dramatically increased its transit likelihood. We present a study which provides a quantitative analysis of how these two orbital parameters effect the geometric transit probability as a function of period. Further, we apply these results to known radial velocity planets and show that there are unexpectedly high transit probabilities for planets at relatively long periods. For a photometric monitoring campaign which aims to determine if the planet indeed transits, we calculate the significance of a null result and the subsequent constraints that may be applied to orbital parameters.

astro-ph↗

arXiv2008

Observational Window Functions in Planet Transit Searches

Window functions describe, as a function of orbital period, the probability that an existing planetary transit is detectable in one's data for a given observing strategy. We show the dependence of this probability upon several strategy and astrophysical parameters, such as length of observing run, observing cadence, length of night, and transit duration. The ability to detect a transit is directly related to the intrinsic noise of the observations. In our simulations of the window function, we explicitly address non-correlated (gaussian or white) noise and correlated (red) noise and discuss how these two different noise components affect window functions in different manners.

astro-ph↗

arXiv2007

Spitzer 24-micron Time-Series Observations of the Eclipsing M-dwarf Binary GU Bootis

We present a set of {\it Spitzer} 24$μ$m MIPS time series observations of the M-dwarf eclipsing binary star GU Boötis. Our data cover three secondary eclipses of the system: two consecutive events and an additional eclipse six weeks later. The study's main purpose is the long wavelength (and thus limb darkening-independent) characterization of GU Boo's light curve, allowing for independent verification of the results of previous optical studies. Our results confirm previously obtained system parameters. We further compare GU Boo's measured 24$μ$m flux density to the value predicted by spectral fitting and find no evidence for circumstellar dust. In addition to GU Boo, we characterize (and show examples of) light curves of other objects in the field of view. Analysis of these light curves serves to characterize the photometric stability and repeatability of {\it Spitzer's} MIPS 24\micron array over short (days) and long (weeks) timescales at flux densities between approximately 300--2,000$μ$Jy. We find that the light curve root mean square about the median level falls into the 1--4% range for flux densities higher than 1mJy. Finally, we comment on the fluctuations of the 24\micron background on short and long timescales.

astro-ph↗

arXiv2007

The Spitzer 24-micron Photometric Light Curve of the Eclipsing M-dwarf Binary GU Bootis

We present a carefully controlled set of Spitzer 24 \micron MIPS time series observations of the low mass eclipsing binary star GU Boötis (GU Boo). Our data cover three secondary eclipses of the system: two consecutive events and an additional eclipse six weeks later. The study's main purpose is the long wavelength characterization of GU Boo's light curve, independent of limb darkening and less sensitive to surface features such as spots. Its analysis allows for independent verification of the results of optical studies of GU Boo. Our mid-infrared results show good agreement with previously obtained system parameters. In addition, the analysis of light curves of other objects in the field of view serves to characterize the photometric stability and repeatability of {\it Spitzer's} MIPS-24 at flux densities between approximately 300--2,000$μ$Jy. We find that the light curve root mean square about the median level falls into the 1--4% range for flux densities higher than 1 mJy.

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arXiv2003

EXPLORE/OC: A Search for Planetary Transits in the Field of the Southern Open Cluster NGC 6208

The EXPLORE Project expanded in 2003 to include a campaign to monitor rich southern open clusters for transits of extrasolar planets (EXPLORE/OC). In May and June 2003, we acquired precise, high-cadence photometry of the second open cluster in our campaign, NGC 6208. Here, we present preliminary results from our I-band survey of over 60000 stars in the field of NGC 6208, around 5000 of which were monitored with photometric precision better than 1%.

astro-ph↗

arXiv2003

EXPLORE/OC: A Search for Planetary Transits in the Field of NGC 2660

We present preliminary photometric results of a monitoring study of the open cluster NGC 2660 as part of the EXPLORE/OC project to find planetary transits in Galactic open clusters. Analyzing a total of 21000 stars (3000 stars with photometry to 1% or better) yielded three light curves with low-amplitude signals like those typically expected for transiting hot Jupiters. Although their eclipses are most likely caused by non-planetary companions, our methods and photometric precision illustrate the potential to detect planetary transits around stars in nearby open clusters.

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arXiv2003

A Search for Eclipsing Binaries in Galactic Globular Clusters

We report on the discovery and analysis of short-period (0.1 days $< P <$ 5 days), photometrically varying binary stars around and below the main-sequence turnoff of the globular clusters (GCs) NGC 3201, M10, & M12. These eclipsing binaries (EBs) may be used to determine directly the distances to GCs and constrain the Population II stellar main-sequence masses. During our search for binaries, we discovered the signature of differential reddening across the cluster fields which was especially strong for NGC 3201 and M10. We correct for this differential reddening by calculating average $E_{V-I}$ values for stars in small subregions of the field with respect to a fiducial region, which significantly improves the appearance of the GC color-magnitude diagrams (CMDs). The reddening zero point to be added to the differential value is determined by isochrone fitting. The results of our differential dereddening are presented in the form of high-resolution extinction maps. Our search for EBs returned 14 variable stars (11 EBs) in the field of NGC 3201, 3 variables (1 EB) in M10, and 2 EBs in M12. Of these variables, only one EB in NGC 3201 (a blue straggler W Ursa Majoris contact system) is a definite GC-member, based on spectroscopic observations. Another W UMa contact EB in M12 is most likely a member of M12, based on its location in the color-magnitude diagram (CMD) and its empirically calculated absolute magnitude. We present the phased lightcurves for all variables, estimate their distances and GC membership, and show their locations in the GC fields and CMDs, as well as the spectra of the NGC 3201 EBs. Finally, we discuss the implications of our results and outline future work.

astro-ph↗

arXiv2002

Photometry Results for the Globular Clusters M10 and M12: Extinction Maps, Color-Magnitude Diagrams, and Variable Star Candidates

We report on photometry results of the equatorial globular clusters (GCs) M10 and M12. These two clusters are part of our sample of GCs which we are probing for the existence of photometrically varying eclipsing binary stars. During the search for binaries in M10 and M12, we discovered the signature of differential reddening across the fields of the clusters. The effect is stronger for M10 than for M12. Using our previously described dereddening technique, we create differential extinction maps for the clusters which dramatically improve the appearance of the color-magnitude diagrams (CMDs). Comparison of our maps with the dust emissivity maps of Schlegel, Finkbeiner, & Davis (SFD) shows good agreement in terms of spatial extinction features. Several methods of adding an E_{V-I} zero point to our differential maps are presented of which isochrone fitting proved to be the most successful. Our E_{V-I} values fall within the range of widely varying literature values. More specifically, our reddening zero point estimate for M12 agrees well with the SFD estimate, whereas the one for M10 falls below the SFD value. Our search for variable stars in the clusters produced a total of five variables: three in M10 and two in M12. The M10 variables include a binary system of the W Ursa Majoris (W UMa) type, a background RR Lyrae star, and an SX Phoenicis pulsator, none of which is physically associated with M10. M12's variables are two W UMa binaries, one of which is most likely a member of the cluster. We present the phased photometry lightcurves for the variable stars, estimate their distances, and show their locations in the fields and the CMDs of the GCs.

astro-ph↗

arXiv2001

Variable Stars in the Field of the Globular Cluster NGC 3201

We report on the discovery and analysis of 14 short-period variable stars in the field of the southern globular cluster NGC 3201, located within roughly two magnitudes on either side of the main-sequence turnoff. 11 of these variable stars are eclipsing binaries, one is an RR Lyrae, and two are thus far unclassified systems. Among the eclipsing binary stars, nine are of the W Ursa Majoris (W UMa) type, one an Algol (EA) system, and one a detached system. Using spectroscopic follow-up observations as well as analysis of the variables' locations in the color-magnitude diagram of the cluster, we find that only one variable star (a W UMa type blue straggler) is actually a member of NGC 3201. We present the phased photometry lightcurves for all the variable star systems as well as their locations in the field-of-view and in the color-magnitude diagram.

astro-ph↗

arXiv2000

An Extinction Map and Color Magnitude Diagram for the Globular Cluster NGC 3201

Differential $E_{V-I}$ variations of up to $\sim 0.2$ mag on a scale of arcminutes across NGC 3201 are presented in the form of an extinction map. This map, created by calculating average $E_{V-I}$ values for stars in small subregions of the field with respect to a fiducial region, greatly improves the appearance of the CMD of the cluster. We describe how we implemented this technique in detail with our data for NGC 3201. A comparison between our map and that of the same region extracted from the COBE/DIRBE reddening maps published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale similarities between the two maps as well as smaller-scale features which show up in our map but not in the SFD map. Several methods of determining an $E_{V-I}$ zeropoint to add to our differential extinction map are presented. Isochrone fitting proved to be the most successful one, but it produces an average $E_{V-I}$ for the cluster which is smaller than previously published values by $\sim 1.5σ$. Finally, our results seem to support the statement by Arce & Goodman (1999) that the SFD maps overestimate the reddening in regions of high extinction.

astro-ph↗

arXiv1999

Observational Mishaps - a Database

We present a World-Wide-Web-accessible database of astronomical images which suffer from a variety of observational problems, ranging from common occurences, such as dust grains on filters and/or the dewar window, to more exotic phenomena, such as loss of primary mirror support due to the deflation of the support airbags. Apart from its educational usefulness, the purpose of this database is to assist astronomers in diagnosing and treating errant images at the telescope, thus saving valuable telescope time. Every observational mishap contained in this on-line catalog is presented in the form of a GIF image, a brief explanation of the problem, and, when possible, a suggestion for improving the image quality.

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