ASTRO Fall Lecture 19

Transcription

1 ASTRO 2233 Fall 2010 Incidence of Earth Like Planets Lecture 19 Tuesday November 2, 2010

2 Searching for References from Cornell sites: hjp://adswww.harvard.edu/ Click on SEARCH Click on ASTRONOMY AND ASTROPHYSICS SEARCH For Science magazine: - > publicaxons - > Science For very recent results: hjp://arxiv.org/archive/astro- ph - > astro- ph.ep - Earth and Planetary Astrophysics (new, recent, current month) Interplanetary medium, planetary physics, planetary astrobiology, extrasolar planets, comets, asteroids, meteorites. Structure and formaxon of the solar system

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4 Occurrence and Mass DistribuXon of Close- in Super Earths, Neptunes, and Jupiters Howard et al, Science, 330, , Oct 29, Modeling of planet formaxon and theories about planet migraxon predicted that there should be a paucity of planets in the ~1 to 30 Earth mass range inside of ~1 AU of the star. Howard et al set out to test this idea by using the HIRES system on the Keck telescope radial velocity accuracy of ~1 m/s by observing 166 G and K type stars masses 0.54 to 1.28 solar masses and B V < 1.4.

5 HIRES Echelle spectrograph on the 10 m Keck telescope ResoluXon: R 85,000 => resoluxon of ~0.1 Angstrom ( um) Iodine absorpxon cell: yes Radial velocity measurement accuracy: 1 m/s since 2004 Stars acxvity can result in false detecxons but can monitor: During Xmes of high solar acxvity, the flux in an extended network of calcium lines (R HK related to the raxo of the brightness in the Calcium II lines to that just away from the lines) brightens significantly in narrow band filters centered on the near- UV Ca II lines use this to determine if star is suitable or Xme in star spot cycle is suitable.

6 Monitoring of the SK index - monitoring the H and K transixns in Ca II, doubly ionized Calcium - can give you the star- spot cycle Xme Star- spot cycle Xme of 1.6 years Metcalfe et al, to be published in Astrophysical Journal LeJers.

7 The UBV filter system. The three curves show the relaxve response as a funcxon of wavelength for the U, B and V filters. For example, we see that the V filter only transmits light of wavelengths between about 4800 and 6800 Angstroms and is most sensixve to light of about 5400 Angstroms. B V < 1.4 (magnitudes) => stars that are not very low temperature i.e. not too red

8 Supernova 1987a in X- ray and opxcal images Planetary nebula

9 Howard et al used 166 G and K type stars in the 0.54 to 1.28 solar mass range i.e. ~F5 to K10 types

10 Orion Nebula

11 Brown Dwarfs

12 ObservaXons and Results Number of stars monitored: stars had high R HK indices indicaxng significant surface acxvity - from correlaxon between the RV measurements and R HK could remove 2 to 4 m/s of RV variability Type: V < 11 magnitudes - i.e. bright stars in the visible (V filter) Mass in range 0.54 to 1.28 solar masses B V < 1.4 Time span: 5 years Concentrated observaxons: 6 to 12 per star over a 12 night span. Number of planets detected for these stars: 33 planets around 22 stars (not necessarily by this group) Number with P < 50 days: 16

13 NASA University of California Eta Earth Survey: What: 235 G, K and M type stars used to characterize the populaxon of planets. What stars: From Hipparcos catalog of nearby stars: V < 11 magnitude i.e. bright stars Distance < 25 pc Luminosity M V > 3.0 absolute magnitudes Low chromospheric/photospheric acxvity No stellar companions i.e. not in a binary system Howard et al selected 166 of this group observable by the Keck telescope and with masses in the range 0.54 to 1.28 solar masses to carry out long term measurements to determine staxsxcs of the presence of planets with orbital periods of less than 50 days

14 Hipparcos Astrometric Satellite ESA mission launched in 1989 Measured posixons of ~100,000 stars to an accuracy of arc seconds => precision measurements of parallaxes - gives distances out to ~500 pc Knowing how far stars are away from Earth crixcal to planet searches. From Hipparcos data

15 The following 7 slides and the material in the 8 th are from Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

16 Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

17 Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

18 Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

19 Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

20 VelociXes have to be corrected for the Earth s moxon about the barycenter of the solar system equivalent to the center- of- mass for a two body system makes periods of a year suspicious Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

21 Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

22 Fit the planet occurrence rates with a power law : df / (d log M E ) = k M E where df / (d log M E ) is the occurrence rate in a log 10 mass interval Can use to extrapolate to lower masses: M = M sin I / M E k = 0.39, error , = , error +0.12, For M sini = 0.5 to 2 M E and P < 50 days, occurrence rate is 23% of stars, error +16%, - 10% For M sin i = 1 to 3 M E, occurrence rate is ~ 14% of stars Measurements in the two largest mass domains => hot Jupiters around ~1.2% of stars Results not fully in agreement with results from HARPS 1 m/s system Howard et al, The Occurrence Rates of Planets, Science, 330, 653, 29 October, 2010

23 MICROLENSING DetecXon of Planets Best current method for getng staxsxcs on the occurrence of Earth sized planets Arthur Eddington in 1919 detected bending of starlight by gravitaxonal field of the Sun as predicted by General RelaXvity. Einstein predicted gravitaxonal lensing effects. Above telegram is from 1922 TahiX expedixon during eclipse showing change in stellar posixons of 1 to 2 arc seconds.

24 Perfect Einstein Ring background galaxy images around a foreground galaxy. Einstein Rings

25 Distant galaxy lensed by a foreground cluster of galaxies. Irregular gravitanonal field of foreground cluster results in a series of arcs.

26 Four high magnificaxon stellar lensing events (MOA project see also MACHO and OGLE projects)

27 From Sumi et al, ApJ, 710, 1641, Discovery of a Neptune sized planet with MOA

28 Abstract: Sumi et al, ApJ, 710, 641, 2010