Astrometry in crowded fields (one possible approach) LSST Project - - PowerPoint PPT Presentation

LSST Project & Community Workshop SS blending session

• J. Camargo, M. Banda, L. da Costa, G. Vila Verde, R. Ogando, C.

Adean, R.V. Martins, M. Assafin and the LIneA IT team – Observatório Nacional/MCTIC and LIneA – – INCT do e-Universo –

Astrometry in crowded fields (one possible approach)

Astrometry in crowded fields (one possible approach)

Motivation

• Galactic plane in the background
• Larger number of occultation events but

astrometry (and not only it) is obviously difficult. Astrometric codes plus Difference Image Analysis is one possible solution

Test case: (10199) Chariklo

SOAR/SOI on 2015-07-20T01:37:17 DIA2 – Many thanks to Wojtek Pych Moving object http://users.camk.edu.pl/pych/DIAPL/

Steps

• Astrometry on the dense fields (PRAIA, Assafin et al. 2011
• Gaia FUN-SSO workshop proceedings).
• Template image →

create it from images that are sufficiently separated in time.

• Astrometry on the subtracted images.
• Replace the (x,y) coordinates of the moving object in the

crowded image by that from the respective subtracted image.

Results

• Before:

Target could not even be disentangled from field star close by.

• After:

Δαcosδ = -3 mas Δδ = 12 mas

(dispersion below 10 mas)

Offsets with respect to an accurate ephemeris

The ephemeris Mas-level accuracy!

Comments

• Definitely, a way to deal with crowded fields: lower rejection of

images, higher precision for target's position.

• Relies, among others, on the necessarily good alignment

between images.

• Deblending reference stars – ongoing.
• Template images could perhaps be taken when the moving

body is no longer (or is not still) in the desired field.

• Possible to build a pipeline.