Orbital motion of substellar companions Christian Ginski, Ralph Neuhäuser, Markus Mugrauer, Tobias Schmidt AIU Jena „Brown Dwarfs come of Age“ 22th May 2013 Background Image Credit: ESO/L. Calcada

C. Ginski 2013 May 22th Motivation

Detection Methods

Jupiter Saturn Neptune Uranus

Detection Methods old young

Detection Methods – Direct Imaging i.Multiple images in different observing epochs can be taken to confirm that the companion candidate is co-moving with the primary star. ii.Photometry and spectra can be taken to confirm that the object is low- mass and of a similar age as the primary star. Confirmation of Companion Candidates: Problems: i.Observation campaigns target young associations in which all members exhibit similar proper motion ii.Association members exhibit similar age Detection of orbital motion would solve these problems, i.e. would finally confirm companionship + study of orbit parameters might give insight to planet and brown dwarf formation + determination of the orbit allows dynamic calculation of the total system mass

Observing Epochs and Astrometric Measurements C. Ginski 2013 May 22th

Observations – HD N E Caha 3.5m – ALFA: Ω-CASS H-Band VLT – NaCo N E NB 2.17 Gemini North – Hokupa‘a/QUIRC Potter et al H-Band Dupuy & Liu 2011: ± M ʘ

Observations – GSC VLT – NaCo N E Ks-Band Neuhäuser et al NTT – SHARPI N E 2 arcsec

Observations Very Large Telescope, Chile Calar Alto Observatory, Spain

Archive Data – HD Gemini – Hokupa‘a/QuIRC N E H-Band HST – ACS N E F850 LP Subaru – IRCS N E H-Band Gemini – NIRI N E CH4 (short)

Astrometric Calibration VLT – NaCo Ks-Band N E HIP Cluster 47 TucBinaries Measurement of relative positions of cluster members or binary Comparison with absolute reference frame (HST, Hip…) Proper motion correction Computation of detector pixel scale and orientation

Astrometric Results – HD VLT – NaCo N E NB 2.17

Astrometric Results – HD N E

2.2 ± 3.7 mas/yr

Astrometric Results – HD ± 0.07 deg/yr

Astrometric Results – GSC ± 0.9 mas/yr

Astrometric Results – GSC08047

Orbit Fitting C. Ginski 2013 May 22th

Least-Squares Monte-Carlo Method Implemented in Python SciPy (E. Jones, T. Oliphant, P. Peterson et al. 2001) - open-source software for mathematics, science, and engineering NumPy (D. Ascher et al. 1999) - fundamental package for scientific computing with Python Matplotlib (J. Hunter et al. 2007) - python 2D plotting library which produces publication quality figures Input measurements and constraints for orbital elements First guess from uniform distribution Levenberg- Marquardt optimization Repeat x 1,000,000

Results - HD Hill stability criterion as given in Donnison et al. 2010

Results - HD130948

Results - GSC08047

Conclusions C. Ginski 2013 May 22th

Conclusions Common proper motion could be confirmed for both presented companions orbital motion was detected but no orbit curvature yet the detected orbit motion is consistent with low mass objects on wide orbits high eccentricities would fit scatter scenarios

Further Work Mugrauer, Röll, Ginski et al Small orbit curvature was detected in the case of the PZ Tel system and the orbit could be constrained well with the LSMC method. The system was not discussed here because the study is led by Dr. Markus Mugrauer. P = 110 yr

Thanks for your attention !

Additional Information

LSMC vs MCMC

Absolute Orbits CT Cha by Schmidt et al GQ Lup by Neuhäuser et al HD by Metchev et al. 2006