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