physics assignment (A0209)

NATS 1745

Assignment 3: Exoplanets

due: MAR 17 2017, 11:30am

weight: 15%

This project entails a study of the process of discovery and properties of exoplanets, planets that orbit around stars other than our Sun. This project has 3 components:

1. A study of how astronomers find exoplanets via the transit method, using real astronomical data.

2. A study of how astronomers find exoplanets via the Doppler Shift or radial velocity method.

3. A short research paper on a particular exoplanetary system

Make sure your assignment is stapled (or in an envelope) with your name and student number on the front.

Part 1: Transit Method

The transit method uses the light curve, which tracks the brightness of a star over time. Any periodic decrease or dip in brightness may be due to a planet transiting, or crossing in front of the star. Light curves for four stars are given on the attached sheets. For each light curve, follow the described method to estimate the planetary period and average distance from the planet to the star.

Also answer the attached general questions on the transit method.

Part 2: Doppler Shift or Radial Velocity Method

The Doppler shift or radial velocity method uses information about the periodic motion of a star due to one or more planets orbiting around the star. This information is gathered using the spectra from a star, collected over a period of time.

Answer the attached questions, and describe this method used to find exoplanets.

Part 3 Essay on an Exoplanetary System

Choose at least one exoplanetary system, and write a short (minimum 4 pages of text; 12-point double spaced) essay that includes the following:

· type/class of star

· a detailed description of the method of detecting the exoplanet

· the structure and layout of the system (i.e. number of planets discovered, distance from star, eccentricity/shape of orbits, masses of planets)

· likelihood that any of the planets are in the habitable zone (need to define habitable zone)

· any unusual facts about or properties of the planet

· references in APA or MLA format (reference all images used; see “What am I Looking for in a Scientific Essay” on moodle)

· proper use of in text citations

Research starting points

· good exoplanet site; many links www.exoplanets.org

· catalogue of exoplanets: http://exoplanet.eu/catalog/

· NASA Finds Closest Earth Twin Yet http://www.space.com/30026-earth-twin-kepler-452b-exoplanet-discovery.html

· HARPS project http://www.eso.org/public/news/eso1134/

· direct imaging of planets

http://www.space.com/31497-exoplanets-direct-imaging-next-big-thing.html

· closest exoplanetary system

http://www.scientificamerican.com/article.cfm?id=alpha-centauri-planet

· news release on exoplanet discovery in habitable zone (Gleise 581g)

http://www.nsf.gov/news/news_videos.jsp?cntn_id=117765&media_id=68454&org=NSF

· microlensing techniques

http://en.wikipedia.org/wiki/Methods_of_detecting_extrasolar_planets#Gravitational_microlensing

· new results:

http://www.skyandtelescope.com/astronomy-news/exoplanets/

· http://www.skyandtelescope.com/astronomy-news/exoplanet-found-around-proxima-centauri-2408201623

· http://www.skyandtelescope.com/astronomy-news/giant-planets-and-wonky-orbits/

Assignment 3: Exoplanets NAME:______________

ST. NUMBER:______________

Part 1: Transit Method

Data for assignment from:

https://dept.astro.lsa.umich.edu/ugactivities/Labs/exoplanets/ExoplanetMain.html

(stars have been re-numbered for assignment below)

Method

From the following 4 light curves, for Stars 1, 2, 3, and 4:

1. Estimate the period (P) in days

2. Convert the period to years

3. Use Kepler’s 3rd Law: P2 = M a3

where P = period in years, M = mass of star in solar masses (Mʘ),

a = average distance from planet to star in Astronomical Units (AU)

Note – if you can’t do the calculation... use the app at

https://dept.astro.lsa.umich.edu/ugactivities/Labs/exoplanets/Transit-2.html

4. The spectral type is given for each star. M can be obtained from Table 1 below.

5. Summarize your answers in Table 2 below.

6. Answer the general questions on the transit technique.

Table 1: Stellar Masses (in units of solar masses, Mʘ)

Sp Type 05 B0 B5 A0 A5 F0 F5 G0 G5 K0 K5 M0 M5

St Mass 40 17 7.0 3.5 2.2 1.8 1.4 1.07 0.93 0.81 0.69 0.48 0.22

Table 2: Summary of Results:

	P (days)	P (years)	M (Mʘ)	a (AU)
Star 1
Star 2
Star 3
Star 4

Star 1: F5 class

Star 2: G0 class

Star 2: B0 class

Star 4: M0 class

General questions on Transit Method

1. Which star has a planet at a similar distance as the Earth is to the Sun? _________

2. Which star has no evidence for a planet? __________

3. On the circle representing the image of a star below, sketch the position of a planet when it

(A) is starting to transit the star,

(B) is in full transit,

(C) has completed transiting the star.

4. The graph below is a composite / co-addition of many transit events, mapped to create an ‘average’ transit. Indicate on the graph the points in the orbit when the planet

(A) is starting to transit the star,

(B) is in full transit,

(C) has completed transiting the star.

5. How could astronomers use the above graph to estimate the diameter of the transiting planet?

Part 2: Doppler Shift or Radial Velocity Method

Sample spectra:

( A B C )

( planet’s orbit star’s orbit Earth )1. Indicate in the diagram below, possible positions of the star and its orbiting planet, which would result in astronomers obtaining spectra A, B and C above. (Motions of both star and planet are counterclockwise in this diagram.

2. How would astronomers use spectra A, B and C to precisely calculate how fast the star was moving?

3. How would the speed the star is moving allow astronomers to be able to deduce information about the orbiting planet? What type of information could the astronomers calculate?

4. Why did the first exoplanets discovered by this method tend to be called ‘hot Jupiters’? (Define a hot Jupiter.)

5. What is a ‘habitable zone’? How would astronomers decide if a planet was in a star’s habitable zone?