Transcript Day-7

Astronomy 3040
Astrobiology
Spring_2016
Day-7
Homework -1
 Due Monday, Feb. 8
 Chapter 2:
 1, 3, 16
 23, 24, 26
 29, 30, 33
 44
 53, 54, 56
 The appendices will be useful
Project
 http://www.ulalaunch.com/docs/product_sheet/Delt
aIVPayloadPlannersGuide2007.pdf
 This is the Delta-IV payload guide overview. 20MB.
 Planetary quarantine program.
March 5, 2009 21:48:43 CST
Stellar Mass (Sun=1)
THE HABITABLE ZONE BY STELLAR TYPES
• B0
10
• A0
1
• F0
• G0
• K0
• M0
Habitable Zone
Solar System
0.1
10
100
0.001 0.01 0.1
1
Stellar Radii and Planetary Orbital Semi-Major Axis (A.U.)
The Habitable Zone (HZ) in green is defined here (and often) as the
distance from a star where liquid water is expected to exist on the
planets surface
(Kasting, Whitmire, and Reynolds 1993).
5
Kepler Mission
 4 Methods
 Radial velocity shifts of the parent star
 Direct Imaging
 Gravitational Lensing
 Transits
How do you Find Exo-Planets?
Radial Velocity
PROBING THE RIGHT SEARCH SPACE
10000
Orbital Period (years)
100
0.01 0.1
1
10
Solar planets
pulsar planets
Planetary Mass (M)
1000
Extrasolar
Doppler 3m/s
100
10
1
0.1
0.01
0.1
1
10
Semi-major Axis (AU)
100
The first 50 known extrasolar planets are also shown along with the
planets in our solar system.
The limit for planet detection using Doppler spectroscopy is shown.
The range of habitable planets (0.5 to 10 M) in the HZ is shown in green.
9
1st Direct IR Images
1st direct Optical Image
A Transit
USING PHOTOMETRY TO DETECT PLANETS
•
Transits
Planet crosses line of sight between
observer and star and blocks
a small amount of light from the star
Transit of Mercury in 2003
Transit of HD 209458 observed with HST
13
GEOMETRY FOR TRANSIT PROBABILITY

Not all planetary orbits are aligned along our line of sight to a star
D/2
Stellar
Diameter
Orbital radius
d*
1) Range of Pole Positions =
d*
D/2
2d*/D
2
2) Solid angle of d*/D
for all possible pole positions
for any given LOS
3) Geometric Transit Probability = d*/D

Diameter of Sun d* is about 0.01 AU. Diameter of Earth orbit D is 2 AU

Random probability of detecting a Sun-Earth analog is about 0.5%

So one needs to look at thousands of stars IF all have an Earth
14
PHOTOMETRY CAN DETECT EARTH-SIZED PLANETS
•
The relative change in brightness (DL/L) is equal to the relative areas (Aplanet/Astar)
Jupiter:
1% area of the Sun (1/100)
Earth or Venus
0.01% area of the Sun (1/10,000)
•
To measure 0.01% must get above the Earth’s atmosphere
•
This is also needed for getting a high duty cycle

Method is robust but you must be patient:
Require at least 3 transits, preferably 4 with same brightness change,
duration and temporal separation
(the first two establish a possible period, the third confirms it)
15
Kepler PHOTOMETER – Concept (it’s changed)
Focal plane electronics
15 minute integrations
Sunshade
42 CCDs
read every
3 seconds
1.4 m diameter
primary mirror
0.95 m diameter
Schmidt corrector
Focus
mechanisms
105 sq deg FOV
Focal plane assembly:
CCDs, field flattening lenses
fine guidance sensors
Radiator and heat pipe
for cooling focal plane
Graphite cyanate
structure
Bandpass: 420-830 nm ; Exposures: 15 min (1 min asteroseismology mode)
Focal plane and pointing stability are essential.
Only 35-pixel “postage-stamps” are read out. Raw pixel data is sent down.
16
CONTINUOUSLY VIEWABLE HIGH DENSITY STAR FIELD
One region of high star field density far (>55°) from the ecliptic plane where the
galactic plane is continuously viewable is centered at RA=19 h45m Dec=35°.
The 55° ecliptic plane avoidance limit is defined by the sunshade size for a large
aperture wide field of view telescope in space.
17
FOV
On the Sky
Kepler Fields and Images
Each of the 42 CCDs (2048x2048) samples 6 square degrees
Image is de-focussed to FWHM ~6”
EXTENDED SOLAR NEIGHBORHOOD
The stars sampled are similar to the immediate solar neighborhood.
Young stellar clusters, ionized HII regions and the neutral hydrogen,
HI, distribution define the arms of the Galaxy.
The view is from the north galactic pole looking down onto the galactic plane
21
Neighborhood
Search Space
Kepler Filter vs. BVRI
vs. ugriz
Star Formation - Chemistry
Richard Rand, University of New Mexico
Todd Boroson/NOAO/AURA/NSF
Elemental Abundance
Ages and Chemical Composition
 Ages come from main-sequence turnoff.
 Stars are mostly hydrogen and helium.
 Abundance of heavy elements is 0 – 3%.
 Heavy elements are made in massive stars.
 New heavy elements are ejected into space.
 New stars form with some heavy elements.
 Abundance of heavy elements records the history
of star formation.
Chemical Enrichment
Effect of
Metallicity