Download VLTI observations of the central parsec of our

VLTI observations of the
central parsec of our Galaxy

AMBER workshop Grenoble March 2007
Jörg-Uwe Pott
I. Physik. Institut
University of Cologne, Germany
Outline of the presentation:
• Introduction to the Galactic Center (GC; central pc)
• Observational results achieved with AMBER
• Outlook for AMBER & PRIMA
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
The center of the Milky Way is the nearest
nucleus of a galaxy:
– harbors closest supermassive BHs (SMBH, 3*106M⊙) at
only 8 kpc distance (1as~40mpc)
– next similar galactic nucleus (Andromeda) is 100x farther
– unique to study SMBH-host interaction
– we have to understand star formation in the immediate
vicinity of a SMBH and investigate the typical radiative
properties to understand spatially unresolved
observations
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Current knowledge of the central stellar cluster:
– lots of hot and massive stars ionizing the local ISM
– indications for favoured massive star formation,
‘top-heavy IMF‘
– solar metallicity, ongoing star formation, Avis25
J&K two color
K-Naco
< GCIRS 7, K=6.5
< Sgr A*
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Current knowledge of the central stellar cluster (II):
Schödel+‘07
– stellar cusp due to the gravitational potential of the
SMBH appears in stellar number counts
– single telescope confusion limit at K~16mag (seeing
limited) and K~17-18mag (AO-limited at 8, class teles.)
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Current knowledge of the central stellar cluster (III):
Pott+’06,‘07
– indications for a central outflow of SgrA*, of unknown
importance for the stellar surroundings
– a lot of warm dust in the MIR, shock-heated material,
ionized gas
– VLTI/MIDI can be used to study dust formation:
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Why to search for binaries at the GC with VLTI?
– help to understand / distinguish stellar properties of the
central cluster and local star formation
– dust formation in windy binary systems
– analyze recently found ‘comoving groups‘ like IRS13E
and IRS16 cluster, which have been suggested to
harbour intermediate mass black holes of 103-4M⊙
• AMBER advantages:
Schödel+‘05
– the closure phase can be more sensitive to binaries than
the visibility measurements (e.g. Weigelt+’07)
– only UT interferometry is sensitive enough for GC
– only OLBI has sufficient angular resolution (currently only
one eclipsing binary is known: IRS 16SW, Ott+‘99)
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Current phase of the project:
NIR
dust emission 
MIR-10m MIDI obs
– facing the real life: start to observe and gain
experience (e.g.: learn how to select frames...)
– AMBER with UTs in LR-mode is the only option due to
sensitivity
– first target: GCIRS7: red M1 supergiant, Teff=3600K,
expected diameter: 0.5mas, if there is NO hot dust!
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• First observational results:
visibility could be
measured and
calibrated at
short baseline (U3-U4),
but still low SNR
Special thanks to S. Kraus, MPIfR
0.8--
Raw visibilities: where is my banana?
best 10%
best 30%
best 10%
best 30%
7
• ThinkGCIRS
positive:
Data might indicate:
HD 153368
– calibrated visibility slightly increase with wavelength
– 0.9Vis0.95 -> target slightly resolved -> 2mas
– extended structure / binary possible
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Feasibility of GC-AMBER observations was
demonstrated
– aggravating circumstances (high airmass, baseline
tracking problems, strong piston error due to LRmode, bright calibrator etc.) avoided the
measurement of CP, longer baseline visibilities and
higher accuracy in Mar06
• Phase referencing on GCIRS7 appears to be
possible
• Extended structure might exist
– > telescope time was awarded to redo this pioneering
study and measure the long baseline visibilities and
the closure phase in LR-mode in May07
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Potential sources for (phase-referenced) AMBER
observations:
Sources around the Galactic Center
Black Hole
Radius (arcsec)
3.5
3
2.5
2
R(1995.4)
1.5
Rmin
1
0.5
0
8
10
12
14
16
18
[data: Ghez+’98,‘05]
– current Klim~9-10mag (Petrov+‘07), UT-vibro limited
K-band Magnitude
– already potential Klim~11 would help
– off-axis phase-referencing with PRIMA/STS and FSU or
FINITO will dramatically increase No. of targets
– even SgrA* NIR-flares (Genzel, Eckart+) are within reach
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
) Intro ) Observations ) Outlook
• Future: PRIMA astrometry at the GC to increase
precision of stellar orbit measurements and prove the
existence non-Keplerian due to GeneralRelativity
[Schödel+’04]
– several orbiting S-Stars
(K=14..15: #5; K=15..17: #12)
within 0.5 arcsec to SgrA*
– stellar multiplicity and background influence of theses stars
have to be known to understand astrometric errors (impact on
spatial filtering)
– >AMBER measurements can help to investigate these errors
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
Thank You for your attention!
Any questions?
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]