orbital motion of substellar companions christian ginski, ralph neuhäuser, markus mugrauer, tobias...

Orbital motion of substellar companions

Christian Ginski, Ralph Neuhäuser, Markus Mugrauer, Tobias SchmidtAIU Jena

„Brown Dwarfs come of Age“22th May 2013

Background Image Credit: ESO/L. Calcada

C. Ginski 2013 May 22th

Motivation

Detection Methods

Detection Methods

Detection Methods

Detection Methods

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 – HD130948

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. 2002

H-Band

Dupuy & Liu 2011: 0.1095 ± 0.0022 Mʘ

Observations – GSC 08047

VLT – NaCo

N

E

Ks-Band

Neuhäuser et al. 2003NTT – SHARPI

N

E2 arcsec

Observations

Very Large Telescope, Chile Calar Alto Observatory, Spain

Archive Data – HD130948

Gemini – Hokupa‘a/QuIRC

N

E

H-BandHST – ACS

N

E

F850 LPSubaru – IRCS

N

E

H-BandGemini – NIRI

N

E

CH4 (short)

Astrometric Calibration

VLT – NaCo Ks-Band

N

E

HIP 73357

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 – HD130948

VLT – NaCo

N

E

NB 2.17

Astrometric Results – HD130948

N

E

Astrometric Results – HD130948

2.2 ± 3.7 mas/yr

Astrometric Results – HD130948

0.16 ± 0.07 deg/yr

Astrometric Results – GSC08047

6.3 ± 0.9 mas/yr

Astrometric Results – GSC08047

Orbit Fitting

C. Ginski 2013 May 22th

Least-Squares Monte-Carlo MethodImplemented 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 - HD130948

Hill stability criterion as given in Donnison et al. 2010

Results - HD130948

Results - HD130948

Results - HD130948

Results - HD130948

Results - HD130948

Results - GSC08047

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

Astrometric Calibration of future measurements is vital for orbit determination !

Further Work

Mugrauer, Röll, Ginski et al. 2012

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. 2008

GQ Lup by Neuhäuser et al. 2008 HD203030 by Metchev et al. 2006