Diffracto-Astrometry with Hubble. Optics images

Transcription

1 IV Reunión Internacional de ASTRONOMÍA DINÁMICA en LATINOAMÉRICA (ADeLA) El Colegio Nacional, México febrero 2008 Diffracto-Astrometry with Hubble Space Telescope and Adaptive Optics images Leonardo J. Sánchez Christine Allen Arcadio Poveda Alex Ruelas Angel García, Erick Juárez, Javier Olivares, Lucero Zúñiga

2 Diffracto-Astrometry: What is it? To measure what? Diffracto: We use the diffraction pattern characteristics of the Hubble Space Telescope public images as well as images obtained with Adaptive Optics techniques. Astrometry: We measure relative (and possibly absolute) positions in time. We continue the study of the kinematical properties of Trapezium-like stellar systems, in particular we study the relative separation and the kinematics of the main components in the Orion Trapezium. 2

3 1974, Allen, Poveda & Worley first issue of the RevMex! The Kinematics of Trapezium Systems RevMexAA, Vol I, p101,

4 2004, Allen, Poveda &Hd Hdz-Alcántara Internal Motions of Trapezium Systems RevMexAA(SC), Vol 21, p195,

5 Search of HST images of the Orion Trapezium The Orion Trapezium is a region widely observed by the HST. The HST archive contains public observations obtained with the WFPC/WFPC2 over a 16-year period to We utilise the Multimission Archive at STScI (MAST) accesible on the internet at edu/ On most of the images the Trapezium image falls on one of the WF CCDs (CCD 2 3 4) d ti th PC CCD (CCD 1) (CCDs 2, 3,or 4),and sometimes on the PC CCD (CCD 1). In the archive there are approximately ~500 Trapezium images taken with the WFPC2. The images are in FITS format and each complete frame has asizeof10mb. 5

6 Example: Orion Trapezium image on the PC PC (CCD 1) Field 36 x /pix 100 s Filter 502N March 21st,

7 Example: Orion Trapezium on the WF WF (CCD 3) Field 80 x /pix 80 s Filter 439W April 10th,

8 Some characteristics of the images 1 Important problem: CCDs saturation and bleeding The HST PSF is not a perfect Airy pattern: dispersed light, residual aberrations, etc. Saturation and bleeding + Diffraction pattern of the spider that supports the secondary mirror + Ghosts 8

9 Some characteristics of the images 2 Pixelized image (undersampling) + bias overscan at the CCDs edges + cosmic rays + concentric rings pattern +... Cosmic Rays Bias overscan Concentric rings pattern 9

10 Some characteristics of the images 3 Modulation of the spider pattern Dispersed light Concentric rings pattern 10

11 Example: Orion Trapezium on the WF WF (CCD 3) Field 80 x /pix 80 s Filter 439W April 10th,

12 Diagram of the Orion Trapezium 12

13 Orion Trapezium: Orientation, scale and magnitudes Separation(t) of AE? 13

14 Diffracto-Astrometry and its Techniques 1 Detailed Methodology and Analysis Techniques used to measure the relative position between components A and E of the Orion Trapezium: We select images from the Multimission Archive (MAST) at STScI. Choose images of the Orion Trapezium following criteria dictatedd by date, filter, exposure time and CCD (PC or WF). 14

15 Diffracto-Astrometry and its Techniques 2 Select images in which the Trapezium appears centred with respect to the CCD so we avoid to a maximum extent geometrical distortion. Finding the relative positions of the photocentre by using one or both of the following techniques: a) Location of the centre by prolonging the traces of the spider and/or fitting concentric circles to the diffraction rings. 15

16 16

17 Diffracto-Astrometry and its Techniques 3 b) Location of the stars emission maxima by fitting a 2D Gaussian or Lorentzian function, masking the saturated pixels, in order to find the photocentre position with a subpixel precision. Measure vector AE (and its variation in time for different epoch images) with ihits associated uncertainty. 17

18 HST PC F673N 100s d_ae = 4.51 arcsec PA =

19 Separation as a function of time of components A and E (data compiled by Allen, Poveda & Hdz-Alcántara 2004) Data since 1830 till

20 Our measurements : HST data Slope: 35 mas / 10 years It is equivalent to pc Note the accuracy! With this technique the uncertainties are smaller than those obtained with other techniques such as speckle interferometry 20

21 Diffracto Astrometry with images obtained using Adaptive Optics 1 K-band image of the Orion Trapezium, taken with the Adaptive Optics system MCAO-MAD at the VLT UT3. April 4th, 2007 E N Bouy, H., Kolb, E., Marchetti, E.L., et al. Astron. & Astroph. 477, 681,

22 Diffracto Astrometry with images obtained using Adaptive Optics 2 We performed measurements on the MCAO-VLT K image using astrometric calibration and also with the spider traces fitting technique hi The measurements were consistent and resulted in a separation between A and E components of ~4.51 arcseconds 22

23 Conclusions We develope astrometric techniques to exploit all kinds of HST and AO images in particular those that are saturated and bled. These techniques make use of some characteristics of the stellar diffraction pattern (spider and concentric rings). g) We use these techniques in measuring the relative separation -over a 16- year period- of components AE of the Orion Trapezium. We obtain an average separation that is consistent with previous determinations i and we confirm the tendency which h idi indicates that components A and E are separating at a rate of 6.7 km/s ± 1.0 km/s. We are going to use these techniques to measure the time variation of the relative separations of the other components of the Orion Trapezium. We plan to apply these techniques to the study of kinematical properties of other trapezia. 23

24 24