Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.winer.org/Downloads/KELT-Early-Results-arxiv.pdf Дата изменения: Fri Dec 6 18:13:42 2013 Дата индексирования: Thu Feb 27 22:27:10 2014 Кодировка: Поисковые слова: п п п п п п п п п п п п п п

**FULL TITLE** ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION** **NAMES OF EDITORS**

Early Results from the KELT Transit Survey
Joshua Pepp er, Richard Pogge, D. L. DePoy, J. L. Marshall, Kris Stanek

arXiv:astro-ph/0611947v2 6 Dec 2006

Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH, 43210-1173 Amelia Stutz Department of Astronomy, Univeristy of Arizona, 933 N Cherry Ave, Tucson AZ 85721-0065 Mark Trueblood, Pat Trueblood Winer Observatory, P. O. Box 797, Sonoita, AZ 85637-0797
The Kilodegree Extremely Little Telescope (KELT) pro ject is a Abstract. small-aperture transit survey of bright stars. The pro ject has completed commissioning runs searching for transits in the Hyades and Praesepe, and is well into a multi-year survey of a large portion of the Northern Hemisphere. Here we describe the setup of the telescope and discuss the early data.

There is great scientific p otential in the discovery of transiting planets with bright host stars. Follow-up observation of such systems can determine prop erties of the planets that are not measurable in non-transiting systems, or in transiting systems where the host stars are too faint. The Kilodegree Extremely Little Telescop e (KELT) pro ject is a wide field, small-ap erture survey for such transits, based on a theoretical optimization of all-sky transit searches (Pepp er, Gould, & DePoy 2003). It is similar to the other small-telescop e transit surveys with wide fields (Alonso et al. 2004; McCullough et al. 2006; Bakos et al. 2004; Cameron et al. 2006), but it surveys a larger area of sky than the other surveys. KELT is designed to target stars with magnitudes 8 < V < 10; a range fainter than the stars observed in radial-velocity surveys but brighter than those targeted by most existing transit surveys. KELT consists of a single automated telescop e located at the remote telescop e hosting site Winer Observatory in Sonoita, AZ. The primary KELT mission is a survey of a strip of sky 26 degrees wide at = +32 , broken into 13 equally-spaced fields. The telescop e b egan op erations in Octob er 2004, and sp ent two commissioning runs observing the op en clusters Praesep e and the Hyades. We then b egan observing the 13 survey fields, which together cover ab out 25% of the Northern sky. We have b een gathering data for the past two years, with gaps due to the need to shut down during the summer monsoons, and also due to p eriodic equipment problems. The telescop e is currently op erating well, and returning data regularly. In this proceeding, we briefly describ e the telescop e instrumentation, the survey area and observing strategy, and we discuss the telescop e p erformance and show sample lightcurves.

1


2 1.

Pepp er Instrumentation

KELT employs an Ap ogee AP16E thermoelectrically cooled CCD camera. This camera uses the Kodak KAF-16801E front-side illuminated CCD with 4096 в 4096 9µm pixels (36.88 в 36.88 mm detector area). We use two different lenses with KELT. For the wide-angle survey mode, we use a Mamiya 645 80 mm f/1.9 medium-format manual-focus lens with a 42 mm ap erture. This lens provides a roughly 23 pix-1 image scale and a 26 в 26 field of view, with vignetting at the corners, so the effective clear field of view is circular. Figure 1 shows a sample image of a survey field. We selected the field with galaxy M31 to give p ersp ective on the size of our fields. To provide a narrow-angle campaign mode used for the Hyades and Praesep e observations, we use a Mamiya 645 200 mm f/2.8 APO manual-focus telephoto lens with a 71 mm ap erture. This provides a roughly 9.5 pix-1 image scale and effective 10 8в10 8 field of view. . . To reject the mostly-blue background sky without greatly diminishing the sensitivity to stars (which are mostly redder than the night sky), we use a Kodak Wratten #8 red-pass filter with a 50% transmission p oint at 490 nm (the filter looks yellow to the eye). The filter is mounted in front of the KELT lens during op erations. The optical assembly (camera+lens+filter) is mounted on a Paramount ME Rob otic Telescop e Mount manufactured by Software Bisque. The Paramount is a research-grade German Equatorial Mount designed sp ecifically for rob otic op eration with integrated telescop e and camera control. The CCD camera and mount are controlled by a PC computer located at the observing site that runs Windows XP Pro and the Bisque Observatory Software Suite from Software Bisque.

2.

Survey Area and Strategy

The main targets for KELT are a series of fields, all at = +32 , the latitude of Winer Observatory. The fields are spaced equally in Right Ascension, and we tile b etween two fields at any given time, observing each once b efore slewing to the next field, yielding a cadence on a single field of ab out six minutes, with an exp osure time of 2.5 minutes and 40 seconds for readout and slewing. Over the course of a year, we take ab out the same numb er of images from each field. Since b eginning op erations, we have taken over 40,000 images of our 13 survey fields. We are still building the software pip eline for the data and gathering images from certain fields. By spring 2007, we exp ect to b egin searching our data for transits. Each survey field is ab out 5002 degrees, and together they fill ab out 25% of the Northern sky. This amount of coverage and the magnitude range of our target stars set KELT apart from similar wide-angle surveys. This setup allows KELT to search for the most scientifically interesting transits over the largest part of the sky. Based on estimates from Pepp er, Gould, & DePoy (2003), we exp ect to find 4 transiting planets in these fields.


Transit Search 3. Performance

3

The critical threshold for sensitivity to transits is generally taken to b e an RMS of less than 1%, which corresp onds to the transit by a Jupiter-sized planet of a solar-typ e star. In order to achieve this level of precision, we employ image subtraction using the ISIS package (Alard 2000). Difference imaging is often difficult to implement in general, and is esp ecially prone to complications with very large fields of view. After overcoming various problems, we were able to successfully implement ISIS. Among transit surveys, KELT has the largest field of view for which image subtraction has b een successfully employed. Figure 2 shows the RMS for one of our survey fields from one night of observing. There are over 6000 stars in the field showing sub-1% variation, which would make it p ossible to detect transits in their lightcurves. A more robust measure of transit sensitivity would require computing RMS over the entire course of observations of the field, but would also require the application of a detrending algorithm, such as SYSREM (Tamuz, Mazeh, & Zucker 2005), that would remove nightly atmospheric and airmass variations. We are still testing detrending algorithms with our data, and thus do not yet have a complete analysis for our long-term RMS sensitivity. However, the quality of the singlenight lightcurves demonstrate the p otential of the data. A full description of the p erformance of the telescop e will app ear in an up coming pap er, which will also provide a detailed discussion of the telescop e instrumentation and control and data handling procedures (Pepp er et al. 2006).

4.

Example Lightcurves

Along with the survey data taken to date, we have b een analyzing the commissioning data on Praesep e, which consists of over 3,000 observations taken on 34 nights over the course of 74 days, using the 200 mm lens with the 10 8в10 8 . . fields of view. We have found a large numb er of variable stars, of which we show three examples in Figure 3. We have also b egun searching the Praesep e data for transits. We are still sorting through the data, but we have found twotransit-like curves, shown in Figure 4. These signals are probably not planetary transits, based on their depths and p eriods, but they demonstrate our ability to detect transits with the KELT data. We will b e publishing an up coming pap er describing the analysis of the Praesep e data for variable stars and transits (Pepp er et al. 2007).

Acknowledgments. Thanks to Scott Gaudi for helpful comments. Thanks also to the Local Organizing Committee of this Workshop, Cristina Afonso, David Weldrake, and Maria Janssen-Bennynck. This work was supp orted by the National Aeronautics and Space Administration under Grant No. NNG04GO70G issued through the Origins of Solar Systems program.


4

Pepp er

KELT Survey Field 12
M31

Figure 1.: Image of one 26 в 26 survey field from the KELT camera. The

extended ob ject at the upp er right is M31.

References Alard, C. 2000, A&A, 144, 363 Alonso, R., et al. 2004, ApJ, 613, L153 Bakos, G., et al. 2004, PASP, 116, 266 Cameron, A. C., et al. 2006, to appear in MNRAS, astro-ph/0609688 McCullough, P. R., et al. 2006, ApJ, 648, 1228 Pepper, J., Gould, A., & DePoy, D. L., 2003, Acta Astron, 53, 213 Pepper, J., et al. 2006, in preparation


Transit Search

5

Figure 2.: RMS magnitude scatter of a time-series of magnitude measurements

of one of the survey fields. This plot shows the RMS for 33 images of 73,000 stars over one night of observing, with no detrending applied.
Pepper, J., et al. 2007, in preparation Tamuz, O., Mazeh, T., & Zucker, S. 2005, MNRAS, 356, 1466


6

Pepp er

Figure 3.: Examples of newly discovered variable stars in Praesep e. Each light

curve contains over 3000 p oints.

Figure 4.: Transit-like light curves from KELT observations of Praesep e. These

ob jects are probably not planets, but demonstrate the ability of KELT to detect transits.