RIPL Radio Interferometric Planet Search

1
RIPLRadio Interferometric Planet Search

• Geoffrey Bower
• UC Berkeley

Collaborators Alberto Bolatto (UMD), Eric Ford
(UFL), Paul Kalas, Anna Treaster, Vince Viscomi
(UCB)
2
Galactic Center Radio Transient
LMXB Outburst Jet Calorimeter Ljet Lx
3
MM Wavelength T Tauri Outburst in Orion

• 2nd most luminous stellar radio outburst
• Briefly, brightest object in nebula
• Required long baselines for detection
• Magnetized T Tauri outburst
• Contemporaneous with X-ray outburst
• Many such objects likely to be found by CARMA
  ALMA

BIMA A configuration images (Bower, Plambeck,
Bolatto, Graham, de Pater, McCrady, Baganoff 2004)
4
Orion Nebula Parallaxw/Star GMR-A
D389 pc /- 5 lt0.1 mas/epoch
Sandstrom, Peek, Bower, Bolatto, Plambeck
2007 Astro-ph/0706.2361
5
Implications of Orion Parallax

• Factor of 4 improvement over previous parallax
  measurement
• 480 /- 80 pc (Genzel et al 1981)
• Lower distance reduces stellar luminosities by
  40
• Resolves problem of overluminous massive stars
• Indicates greater age spread of pre-main sequence
  stars ? process of continuous star formation
  rather than single episode

HST Image of Orion Nebula
6
Taurus Cluster Distance
D141.5 2.7 -2.8 pc Loinard et al 2005
7
Planets are Easy to Detect
8
Companion to GJ 752B Detected w/Optical Astrometry
Pravdo Shaklan 2009
9
White et al
10
Gudel 2002
11
Brown Dwarfs are Radio Sources
Berger et al 2001
Hallinan et al 2007
12
Requirements of a Planet Survey

• Low mass, nearby star
• Astrometric displacement 1 mas
• Nonthermal radio emission
• S 1 mJy
• F GHz
• Positional stability lt 0.1 mas
• Stable Image
• Active, but not too active

13
VLA M dwarf Flux Survey

• 174 X-ray selected nearby M dwarfs
• 10 minute VLA observations with 50 microJy rms
• 40 detections of 29 stars
• Rough agreement X-ray-radio correlation
• No distinction between early and late types

Bower, Bolatto, Ford, Kalas 2009, ApJ, in press
14
Stars are Variable
EV Lac Osten et al 2005
15
Pilot Survey

• 7 stars
• 3 epochs
• lt 10 days
• Hipparcos errors 1 mas/y
• Error over 10 days lt 0.1 mas
• Test
• Detectability
• Image stability

8000 km baselines 3 cm wavelength 1 mas
resolution Astrometry beam/SNR
16
VPAS Astrometry
Secondary calibrator
1 degree
Primary calibrator
Secondary calibrator
5 Minute switching time
17
Results from Pilot StudyApparent Motion of GJ
4247
15 mas
23 March 2006
25 March 2006
26 March 2006
Comparison of radio positions (points) with
predictions from Hipparcos astrometry (solid
line) reveal noise-limited rms residuals 0.1
milliarcseconds, approximately 1 stellar
diameter.

Bower, Bolatto, Ford, Kalas 2009, ApJ, in press
18
Pilot Study Results
GJ 4247
GJ 896A
Residuals are sensitivity limited 0.2 mas
GJ 65B
19
VPAS Results
GJ Detections Proper Motion

65B 3/3 Different from Optical
285 2/3 Optical, sensitivity limited
896A 3/3 Optical, sensitivity limited
4247 3/3 Optical, sensitivity limited
412B 0/3 ----------
803 1/2 ----------
1224 0/3 ----------
20
Results from Pilot StudyConstraints on
Companion Masses

• Agreement with optical astrometry sets upper
  limit on acceleration and therefore companion
  masses
• Mp lt 3 10 MJup _at_ 1 AU
• Sensitivity is limited by the short lever arm of
  VLBA observations 10 days
• RIPL will extend this lever arm by factor of 100

Planet Mass (Mjup)
Semi-major Axis (AU)
Bower, Bolatto, Ford, Kalas 2009, ApJ, in press
21
RIPLRadio Interferometric Planet Search

• 30 stars
• 12 epochs/4 years
• VLBA GBT
• 512 Mb/s
• 2 hours on source 2 hours calibration
• 25 microJy rms
• 4 x lower than pilot survey
• 1392 hours total

Key question What is fraction of long-period
planets around low mass stars?
22
RIPL Sample

• 30 Stars
• M1 M8
• V 9.6 15.8 mag
• S_6cm 0.1 6 mJy
• D 2.7 9.5 pc
• 11 are members of known binary or multiple
  systems

23
Simulated RIPL Results
24
RIPL Sensitivity
25
Current Status

• Observing began Oct 2007
• Approximately 4 observations/month
• Expected completion in mid-2011
• 40 complete
• Pipeline processing underway (see poster by Vince
  Viscomi)
• All stars detected
• 60 of stars detected in every epoch

26
Benefits of Astrometric Detection

• Unique method
• Breaks degeneracy of RV searches for mass,
  inclination angle, and ascending node
• Probes low mass, active stars that are difficult
  to study with RV method
• Planet fraction of low mass stars poorly
  determined
• Detects planets that can be studied with extreme
  AO
• Ties radio and optical astrometric reference frame

27
RV Search ResultsFew M dwarf Hosts
28
RV Search ResultsMost Planets are gt10 pc Distant
29
RV Search ResultsWhat is Mplanet/Mstar?
30
Microlensing Search Results What is
Mplanet/Mstar?
31
Microlensing Search ResultsPlanets are Very
Distant
32
Results of Recent RV Searches

• Detection of long-period, eccentric planet around
  M dwarf
• Johnson et al 2007
• Rates suggest that planet mass tracks stellar
  mass

33
Comparative Sensitivity of Searches
34
Future Directions for Radio Astrometry Planets

• Bandwidth upgrade for VLBA
• 512 Mb/s ? 8 Gb/s
• ?4 x sensitivity
• ?Calibrator density increases by 8 x
• ?In-beam calibrators
• ?10 microarcsec accuracy ? Neptune mass planets
• Square Kilometer Array
• 100 x sensitivity
• 3000-5000 km baselines
• 1 microarcsec accuracy ? Earth mass sensitivity

35
Summary

• Radio astrometry is sensitive to sub-Jupiter mass
  planets around M dwarfs
• We can already exclude BD companions to three
  stars based on only three measurements
• RIPL survey will probe low mass, active star
  parameter space