Search For TransNeptunian Objects Using COROT Asteroseismology Lightcurves

  • Slides: 1
Download presentation
Search For Trans-Neptunian Objects Using COROT Asteroseismology Lightcurves Chih-Yuan Liu(1, 2, 3), Alain Doressoundiram(1),

Search For Trans-Neptunian Objects Using COROT Asteroseismology Lightcurves Chih-Yuan Liu(1, 2, 3), Alain Doressoundiram(1), Françoise Roques(1), Hsiang-Kuang Chang(2, 3), Michel Auvergne(1) Observatoire de Paris, LESIA, 92195 Meudon cedex, France (2) Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan (3) Institute of Astronomy, National Tsing Hua University, Hsinchu, 30013, Taiwan Abstract Data Processing Trans-Neptunian Objects (TNOs) are the witnesses of the early Solar System and can provide astronomers much valuable knowledge about their formation and dynamical evolution. The current understanding of their properties, however, such as the total mass, orbital parameters and the size distribution, is still far from complete. Here we will present a study of re-examination of COROT asteroseismology lightcurves for the search of TNOs. COROT (COnvection ROtation and planetary Transits) was launched on December 2006. Its two major goals are to search for extrasolar planets and to perform asteroseismology by measuring solar-like oscillations in stars. For our purpose, we will only use asteroseismology data which has the integration time of 1 second. The total observation time avaliable in this work is about 82032. 9 star-hours. We will analyze these fast photometry lightcurves data to search for serendipitous occultations by passing TNOs. Occultation method is a powerful tool to detect small Solar System bodies through their diffraction phenomenon (see Roques et al, 2000, Icarus, 147, 530). The method of occultation will allow to reveal the existence of TNOs which have sizes about several kilometers. Discussion & Future Works Discussion TABLE 2: COROT ASTEROSEISMOLOGY N 1 DATA EMPLOYED Segment run code date begin date end STAR HOURS 1 IRa 01 01/31/2007 11: 06: 34 04/02/2007 07: 12: 15 12455. 77 2 SRc 01 04/11/2007 15: 07: 52 05/09/2007 07: 13: 21 5799. 25 3 LRc 01 05/11/2007 13: 10: 19 10/14/2007 23: 59 33460. 73 4 LRa 01 10/18/2007 08: 57: 24 03/03/2008 09: 49: 35 28665. 71 5 SRa 01 03/05/2008 22: 34: 26 03/31/2008 07: 43: 58 5422. 20 6 SRa 02 10/08/2008 22: 44: 36 11/12/2008 08: 29 7450. 72 7 LRa 02 11/13/2008 22: 49: 46 03/11/2009 10: 31: 38 25137. 60 8 LRc 03 04/01/2009 20: 49: 11 07/02/2009 03: 58 9813. 25 9 LRa 03 10/01/2009 20: 57: 34 03/01/2010 08: 37: 24 16203. 11 TOTAL STAR HOURS • In our COROT data search, there are 519869933 1 -sec bins, and the random probability for -6. 5σ is about 3 x 10 -11. We probably should see a few bins below 5σ. Since there is no detection, it may mean that the fluctuation in our data is not only random noise but also some other things so that the variation estimated from the data itself is larger than the random fluctuation. • A way to derive constraints on the Kuiper Belt from this zero-detection without Figure 1 a Figure 1 b hypothesis on the size distribution, is to consider two parameters, the scanned sky area Sc and the size of detectable objects, rd. The observation gives an upper limit of the density of objects larger than the detectable object (rd) on the scanned sky area (Sc deg 2). The Figure-4 gives the size distribution of objects in which is plotted the last estimates of Schlichting from HST data, some upperlimits from other surveys, and our 11 possible detections thus eliminates any power-law size distribution steeper, setting a stringent constrain to the number density of TNOs. 144, 408. 34 COROT Asteroseismology N 1 Data Introduction Currently we have 165 COROT asteroseismology N 1 lightcurves in this work. Based on the run codes of the observations, we divide these lightcurves into 9 segments, each segment has 10 to 15 lightcurves. The corresponding run codes and accumulated observing time for these 9 segments are shown in Table 2. Objective Properties of 70 AN 1 Lightcurves The direct observation for TNOs is only possible for larger objects with diameters above several tens of kilometers. Small TNOs could only be found when they obscure background stars. Since occultations for these invisible objects are not predictable, the blind search for occultations in lightcurves of monitored stars may be possibly useful. We will apply this method to COROT asteroseismology data for the detection of small TNOs. COnvection, ROtation & planetary Transits COROT has a polar inertial circular orbit (90 -degree inclination) at an altitude of 896 kilometers. The apogee and perigee are respectively 911 and 888 kilometers. The orbital period is 6184 seconds. Twice a year, when the Sun gets closer to the orbit plane and is about to blind the telescope, the spacecraft performs a reversal attitude maneuver, dividing the year into two 6 -month periods of observation (by convention, summer and winter). There are four observing runs (alternately 20 and 150 days) for a year. During the northern summer it will observe in an area around Serpens Cauda and during the winter it will observe in Monoceros. The first four run codes of COROT and their observing area are listed below: the “cause of the rejection” (OVER) is included in the binary table of the lightcurve. The value of OVER indicates the status of the measurement. For our data reduction, we choose the bins with the value of OVER equals zero only. ‘OVER = 0’ means that data within this 1 -sec bin-size is not affected by crossing SAA, energetic particle impacts, glitches or other status changing of the satellite. • After screening, the observing time of the longest and shortest lightcurves are 131. 5 days and 411 seconds respectively. Search algorithm The algorithm we used here is very similar with the method applied to the search of TNO occultation in X-rays: we derive the deviation distributions for all COROT AN 1 lightcurves, set the search criteria and look for the dips. The steps of our search algorithm are described below: Table 3 Figure 2 bin size = 1 sec • Estimate the deviation: For each bin of a lightcurve, we apply a 60 -sec running • IRa 01: in the constellation of Monoceros • SRc 01: in the constellation of Serpens Cauda • LRc 01: in the constellation of Aquila • LRa 01: in the constellation of Monoceros (LR stands for long run, SR for short run, IR for initial run and the small letters a and c for galactic anti-centre or galactic-centre direction). In this work, we will use COROT asteroseismology (level-1) data from 4 observing runs made between 31 January 2007 and 12 November 2008 to search for serendipitous occultations. In each field of view there will be one main target star for the asteroseismology as well as up to nine other targets. Detail information for long observing run and short observing run is shown in Table 1 a & Table 1 b. TABLE 1 a • For our data sets, there are 79 stars monitored by COROT. • Vmag of those 79 stars: 4. 77 ~ 9. 48. • S/N ~ 360 for a V=7. 36 star. • The integration time for COROT AN 1 lightcurves is 1 sec. The information about TABLE 1 b window on it and calculate the statistic values of the intensity of star. We then reinterpret the intensity in the unit of standard deviations instead of the electron numbers in order to plot the deviation distribution. Figure-1 a is the screened lightcurve of the star HD 49933 observed in COROT LRa 01 run. Figure-1 b is replotted with the intensity in the unit of σ. • Set criteria: We perform a linear fitting for the negative part of the Standard- Figure 4 Score (SS) distribution from number of bins 1000 to 3. The bins with SS smaller than threshold T(n) will be the outliers (see Figure-3). T(n) value depends on the window size: between -6. 2 and -9. 3. • Examine the reality of dips: Not every dip we found will be due to an An example of the deviation distributions of the COROT 519859933 data bins. Figure 3 astronomical occultation. For example, if the dip could be found at the same epoch in other lightcurves, it will be an artificial event due to occurring in the terrestrial environment (airplane, satellite, seeing effects etc. ) Preliminary Results COROT ASTEROSEISMOLOGY OBSERVATION PROPERTIES Credit to http: : //smsc. cnes. fr/COROT/sismologie. htm This selection method is applied to Standard-Score distributions with 2 n values from 20 to 180. ➡This research leads to 20 outliers. To validate the reality of these events, we examine the raw data with the assistance from COROT team members: ➡ 7 outliers are excluded because they correspond to de-focusing processes or cross-talk interactions between seismology and exoplanetary CCDs. ➡The others 13 outliers are identified as Possible Occultation Events, the so-called POEs (Figure 4). ➡All the outliers detected with 2 n values larger than 180 are artifacts. See Table 3 for the properties of the 20 outliers. References 1. Zhang et al. The TAOS Project: Results From Seven Years of Survey Data. eprint ar. Xiv (2013) vol. 1301 pp. 6182 Chang et al. Search for serendipitous trans-Neptunian object occultation in X-rays. Monthly Notices of the Royal Astronomical Society (2013) vol. 429 pp. 1626 Schlichting et al. Measuring the Abundance of Sub-kilometer-sized Kuiper Belt Objects Using Stellar Occultations. The Astrophysical Journal (2012) vol. 761 pp. 150 Ofek and Nakar. Detectability of Oort Cloud Objects Using Kepler. The Astrophysical Journal Letters (2010) vol. 711 pp. L 7 Roques et al. Exploration of the Kuiper Belt by High-Precision Photometric Stellar Occultations: First Results. The Astronomical Journal (2006) vol. 132 pp. 819