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19-20 Exam for Introduction to Astrophysics
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Exam for Introduction to Astrophysics
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PHY104PHY472
Data Provided:
Formula sheet and physical constants
Data Provided:
A formula sheet and table of physical constants is attached to this paper.
DEPARTMENT OF PHYSICS & Autumn Semester 2009-2010
ASTRONOMY
DEPARTMENT OF PHYSICS AND ASTRONOMY
ADVANCED QUANTUM MECHANICS 2 hours
Spring 2021
AnswerIntroduction to Astrophysics
question ONE (Compulsory) and TWO other questions, one each from3 hours
section A and section B.
Instructions:
All questions are
Answer all marked
FOUR out offrom
questions ten.Section
The breakdown
A and ONE on the right-hand
question side
from Section B. of the
paper is meant as a guide to the marks that can be obtained from each part.
Answering the exam questions should take no more than TWO hours, but you will have THREE
hours in a 24-hour window to complete the exam and upload your answers to Crowdmark.
Make sure you retain time stamped photos/scans of your work in case you experience any
problems with uploading files.
Section A is worth 40 marks in total and all questions in section B are worth 30 marks each.
The breakdown on the right-hand side of the paper is meant as a guide to the marks that can
be obtained from each part.
Cross through any work that you do not wish to be examined.
PHY104 TURN OVER
1
PHY472 TURN OVER
, PHY104
SECTION A
1. Two stars (A and B) have the same radius and temperature, but different apparent
magnitudes. Star A has a V-band magnitude of 12.5, while star B has a V-band
magnitude of 15.5. If star A has a parallax of 75 milli-arcsec, calculate the distance to
star B. Could the parallax of star B be observed by the astrometric satellite Gaia? [10]
2. The monochromatic flux of a radio source has a frequency dependence of Fν ∝ ν −3
when measured in frequency units. What is the slope of a graph of log Fλ against log λ?
At which end of the electromagnetic spectrum would you expect to see the most flux?
[10]
3. An unresolved star cluster is composed of 20 identical stars, each with an apparent
V-band magnitude of 19.0. Calculate:
(a) the V-band magnitude of the cluster and the monochromatic V-band flux of each
star. [7]
(b) If the cluster is at a distance of 200 parsecs, what is its absolute V-band magni-
tude? [3]
Note: the star Vega has a monochromatic flux of 3.6 × 10−11 W m−2 nm−1 in the
V-band.
4. A star has a measured parallax of 49 milli-arcseconds and a proper motion of 200 milli-
arcseconds per year. Spectroscopic observations reveal that the 656.28 nm absorption
line of hydrogen has a measured wavelength of 656.40 nm. Calculate its distance (in
pc) and its three dimensional velocity (in km/s) with respect to the Sun. [10]
PHY104 CONTINUED
2
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