Transcript Lecture 2 - X-ray and Observational Astronomy Group

DEPARTMENT OF PHYSICS AND ASTRONOMY
3677 Life in the Universe:
Extra-solar planets
Dr. Matt Burleigh
www.star.le.ac.uk/mrb1/lectures.html
Course 3677 Life in Universe 2013/2014 Academic Year
Course Given by Prof. Mark Sims and Dr. Matt Burleigh
Topics: Life in Universe and Extra-Solar Planets
Lecture Dates and Lecturer
Actual
Lecture
Number
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Lecture by
Topic
Locatio
n
Time
Date
Nominal Course
Order 2013/14
M.R. Sims
M. Burleigh
M. Burleigh
M. Burleigh
M. Burleigh
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M. Burleigh
Both
Life in Universe
Extra-Solar Planets
Extra-Solar Planets
Extra-Solar Planets
Extra-Solar Planets
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Extra-Solar Planets
Continuous
Assessment Answers
Revision Lectures
Phys A
KE LT2
Phys A
Phys A
KE LT2
Phys A
Phys A
KE LT2
Phys B
KE LT2
Phys B
KE LT2
Phys B
1300
1300
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R1
R2
M. Burleigh
M.R. Sims
Phys D
Phys B
0900
0900
7/5/14
15/5/14
Please note course is not in nominal order due to availability of Lecturers
Course has been extensively revised from previous years as Prof. Raine is no longer teaching part of
the course, consequently exam format has changed to 4 questions two short (20 marks each), two
long (30 marks each) all compulsory.
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• Lecture 1
–
–
–
–
Definition of a planet
A little history
Pulsar planets
Doppler “wobble” (radial velocity) technique
• Lecture 2
– Transiting planets
– Transit search projects
– Detecting the atmospheres of transiting planets
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• Lecture 3
– Microlensing
– Direct Imaging
– Planets around evolved stars
• Lecture 4
– Statistics: mass and orbital distributions, incidence
of solar systems, etc.
– Hot Jupiters
– Super-Earths
– Planetary formation
– The host stars
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• Lecture 5
– The quest for an Earth-like planet
– Results from the Kepler mission
– Habitable zones
– Biomarkers
– Future telescopes and space missions
Dr. Matt Burleigh
3677: Life in the Universe
Useful numbers
•
•
•
•
RSun = 6.995x108m
Rjup = 6.9961x107m ~ 0.1RSun
Rnep = 2.4622x107m ~ 4Rearth
Rearth = 6.371x106m ~ 0.1Rjup ~ 0.01RSun
•
•
•
•
MSun= 1.989x1030kg
Mjup= 1.898x1027kg ~ 0.001MSun = 317.8Mearth
Mnep= 1.02x1026kg ~ 5x10-5MSun ~ 0.05Mjup = 17.15Mearth
Mearth= 5.97x1024kg = 3x10-6MSun = 3.14x10-3Mjup
• 1AU = 1.496x1011m
• 1 day = 86400s
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• Planets observed at inclinations near 90o will transit their host stars
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• Planets observed at inclinations near 90o will transit their host stars
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• Assuming
– The whole planet passes in front of the star
– And ignoring limb darkening as negligible
• Then the depth of the eclipse is simply the ratio of the planetary and
stellar disk areas:
pR
Df
=
f*
pR
2
p
2
*
æ Rp ö
=ç ÷
è R* ø
2
• Where Δf is the change in the star’s flux (brightness), Rp is the
planet radius and R* the star’s radius
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• RSun = 6.995x108m
Rjup = 6.9961x107m
Rearth = 6.371x106m
(note: Rjup~ 0.1RSun & Rearth ~ 0.1Rjup ~ 0.01RSun)
• Jupiter transit: depth = 0.01 = 1%
• Earth transit: depth = 8.3x10-5 = 0.0083%
(note: best photometry from ground ~0.1%)
• 55 Cancri R* = 1.15RSun
• Planet 55 Cancri e = 8.3Rearth
• Transit depth = 0.004 = 0.4%
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• In practice:
• We measure the change in magnitude Dm, and obtain the stellar
radius from the spectral type
– Hence by converting to flux we can measure the planet’s radius
æ f ö
– Rem.
Dm = m
- m = 2.5 log ç
÷
*
transit
– Thus
*
è ftransit ø
æ f* ö
0.4Dm
=
10
ç
÷
è ftransit ø
• (rem in magnitude system a smaller number means brighter)
Dr. Matt Burleigh
3677: Life in the Universe
Discovery of first transiting planet:
HD209458b
• HD209458b was discovered
originally via the radial velocity
method
– 3.5 day period
• Astronomer Dave
Charbonneau monitored it with
a small telescope called
STARE
– Transit discovered in 1999
Dr. Matt Burleigh
3677: Life in the Universe
Transits
Example: first known transiting planet
HD209458b

–
–
–
Dm = 0.017 mags
So (f* / ftransit) = 1.0158, i.e. Df=1.58%
From the spectral type (G0) R=1.15Rsun
So using Df / f* = (Rp / R*)2 and setting
f*=100%
– Find Rp=0.145Rsun
– Since Rsun=9.73RJ then
– Rp = 1.41RJ
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• HD209458b more:
– From Doppler wobble method know M sin i = 0.62MJ
– Transiting, hence assume i=90o, so M=0.62MJ
– Density = 0.29 g/cm3
• c.f. Saturn 0.69 g/cm3
– HD209458b is a gas giant!
Dr. Matt Burleigh
3677: Life in the Universe
The shape of the transit light
curve
• Ingress and egress affected by stellar limb darkening
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• For an edge-on orbit, transit duration is given by:
æ PR* ö
Dt= ç
÷
è πa ø
• Where P=period, a=semi-major axis of orbit
• Example: HD209458b
–P=3.52475 days = 304538s
–R*=1.15RSun = 1.15x6.955x108m
–a=0.04747AU=7.1x109m
–Δt=10920s=3.03hours
–Note for Earth (a=1AU) Δt=46668s=12.96hours
Dr. Matt Burleigh
3677: Life in the Universe
Transits
• Probability of transit (for random orbit)
Ptransit
R*
=
a
– For Earth (a=1AU), Ptransit=0.5%
– But for close, “hot” Jupiters, Ptransit=10%
– Of course, relative probability of detecting Earths is lower
since would have to observe continuously for up to 1 year
• (See Kepler mission)
Dr. Matt Burleigh
3677: Life in the Universe
Transits: Advantages
• Easy. Can be done with small, cheap telescopes
• Possible to detect low mass planets, including
“Earths”, especially from space (Kepler mission)
Dr. Matt Burleigh
3677: Life in the Universe
Transits: Disadvantages
• Probability of seeing a transit is low
• Need to observe many stars
simultaneously for long periods of time
• Mimics
– Easy to confuse with starspots
– Easy to confuse with grazing binary
star eclipse
– Blended eclipsing binary in a triple
system, or merely in background
• Low mass red dwarfs, brown dwarfs
and gas giants have same radii
– Needs radial velocity measurements for
confirmation, masses
Dr. Matt Burleigh
3677: Life in the Universe
Super WASP
• Wide Angle Search for Planets (by
transit method)
• First “telescope” located in La Palma,
second in South Africa
• “Telescopes” are 8 x 400mm camera
lenses with a high grade CCD
• Operations started May ‘04
• Data stored and processed at
Leicester
• ~100 new planets detected!
• www.superwasp.org
Dr. Matt Burleigh
3677: Life in the Universe
Super WASP
• SuperWASP monitors about 1/4
of the sky from each site
• That means millions of stars,
every night!
Dr. Matt Burleigh
3677: Life in the Universe
www.ngtransits.org
Belfast, DLR Berlin, Geneva,
Leicester, Warwick, Cambridge
Dr. Matt Burleigh
3677: Life in the Universe
WASP planets in green
Dr. Matt Burleigh
3677: Life in the Universe
NGTS Prototype La Palma 2010
Dr. Matt Burleigh
3677: Life in the Universe
Early NGTS v SuperWASP
Dr. Matt Burleigh
3677: Life in the Universe
NGTS sensitivity (planet periods)
Dr. Matt Burleigh
3677: Life in the Universe
NGTS Site: ESO Paranal observatory, Chile
VLT
Astronomers’ hotel /
baddies’ lair in
“Quantum of Solace”
VISTA
Construction 2014
Operations 2014-2019
NGTS
Dr. Matt Burleigh
3677: Life in the Universe
Dr. Matt Burleigh
3677: Life in the Universe
Transmission spectroscopy
•
•
•
•
•
Transiting planets allow us to make measurements of the chemical
composition and physical properties of their atmospheres
Previously we assumed the planet was an opaque disk with a sharp
edge
In reality, it has an atmosphere & the opacity diminishes with height
By observing a transit at a specific wavelength (eg Na, H) can
measure the extra absorption from that element in the planet’s
atmosphere
Very challenging observations: HST, Spitzer, 8m telescopes
Dr. Matt Burleigh
3677: Life in the Universe
Transmission spectroscopy
Dr. Matt Burleigh
3677: Life in the Universe
Secondary eclipses
• In secondary eclipse the planet passes behind
the star
• The drop in combined light is tiny, but
measurable with careful observations
• Gives thermal emission and temperature of “day”
side of planet
Dr. Matt Burleigh
3677: Life in the Universe
Secondary eclipses
• Note that the secondary eclipse
depth increases with wavelength
– Bcse planets are cooler than
stars, their emission is stronger
at longer wavelengths
Dr. Matt Burleigh
3677: Life in the Universe
Carbon rich atmosphere in WASP-12b
Secondary eclipses
Dr. Matt Burleigh
3677: Life in the Universe
Madhusudhan … Wheatley ...
Pollacco & West 2010, Nature
Phase curve & map of HD189733b
• Equisite observations
of the transiting
planet HD189733b at
8 microns with
Spitzer reveal the
changing brightness
of the planet as it
rotates
• The hottest point on
the “day” side is
offset slightly from
the expected position
– Extreme weather?
Dr. Matt Burleigh
3677: Life in the Universe
Transit timing variations
• The transits of a planet in a
Keplarian orbit around its host
star are exactly periodic.
• However, if a third body is
present in the system, the orbits
are not Keplarian, and the time
between consecutive transits
varies
• This offers the possibility of
detecting non-transiting planets
via photometry.
• It is even possible to determine
the maximum mass of the
planets
Dr. Matt Burleigh
3677: Life in the Universe
Transit timing variations
•
The maximum TTV for an inner planet, due to influence of a more
distant second planet, is given by:
æ M 2 ö æ a1 ö
Dt1 » ç
÷ e2 ç ÷ P2
è M * ø è a2 ø
3
•
•
where M2 and P2 are the mass and period of the second planet, M* the
mass of the star, a1 and a2 are the semi-major axis of the planets’
orbits, and e2 is the eccentricity of the 2nd planet’s orbit.
Note that there is no TTV in this instance if the second planet’s orbit is
perfectly circular!
– Q: What is the maximum TTV in the orbit of the inner planet in a system around a
solar type star, where an inner, Jovian mass planet orbits at a 1=0.05AU with a
period of 4 days, and the outer planet has a mass half that of Jupiter (i.e. 0.5x10 3M
Sun) and a period of 100 days for an eccentric orbit with a 2=0.42AU and
e2=0.5?
A: 3.6 seconds
Dr. Matt Burleigh
3677: Life in the Universe