Astronomy C

[pikachu4919]

2022 Question Marathon Thread for Astronomy C.

Question Marathons Explained

[melaniaaachen]

Well, let's get this started with something simple and essential then:

1. What is the Solar Cycle?

2. What is the Hubble constant?

[RasmitDevkota]

Well, let's get this started with something simple and essential then:

1. What is the Solar Cycle?

2. What is the Hubble constant?

Click to Show Answer

1. The solar cycle is an 11-year cycle where, between each cycle, the Sun flips its magnetic field, affecting surface features such as sunspots and solar flares as well as the intensity of solar radiation.
2. Hubble's constant is a value that tells us how fast two points in space are moving away from each other as the universe expands based on their distance. The value of the constant is currently estimated to be somewhere around 70 km/s/Mpc, but due to the possibility of acceleration in the expansion in the universe it is not a true constant with respect to time and thus may vary over time.

[RasmitDevkota]

Well, let's get this started with something simple and essential then:

1. What is the Solar Cycle?

2. What is the Hubble constant?

Click to Show Answer

1. The solar cycle is an 11-year cycle where, between each cycle, the Sun flips its magnetic field, affecting surface features such as sunspots and solar flares as well as the intensity of solar radiation.
2. Hubble's constant is a value that tells us how fast two points in space are moving away from each other as the universe expands based on their distance. The value of the constant is currently estimated to be somewhere around 70 km/s/Mpc, but due to the possibility of acceleration in the expansion in the universe it is not a true constant with respect to time and thus may vary over time.

It's been a while so I'll just continue where we left off!

a) What is the practical application of RR Lyrae in astronomy and b) what property of this variable star class makes them useful in this way?

[Jehosaphat]

a)

Click to Show Answer

 RR Lyrae stars can be used as standard candles to measure stellar distances

b)

Click to Show Answer

 All RR Lyrae stars have the same average absolute magnitude (so when observed in clusters, find the average apparent magnitude and then distance can be calculated)

Ok my turn:
1. What is the region of the HR diagram that variable stars generally reside in?

2. What causes the fluctuations in variable star's luminosity?

[Jehosaphat]

a)

Click to Show Answer

 RR Lyrae stars can be used as standard candles to measure stellar distances

b)

Click to Show Answer

 All RR Lyrae stars have the same average absolute magnitude (so when observed in clusters, find the average apparent magnitude and then distance can be calculated)

Ok my turn:
1. What is the region of the HR diagram that variable stars generally reside in?

2. What causes the fluctuations in variable star's luminosity?

Click to Show Answer

1. THE INSTABILITY STRIP!!!
2. Changes in opacity in the star's atmosphere; helium is ionized, so it becomes opaque and light pushes out, increasing the radius. Temperature then decreases, so helium becomes un-ionized (I forgot the proper term for that) and transparent, so the light is no longer pushes out and the star can contract back down, repeating the cycle.

Hello, I'm back with another signature complicated analysis question for you! This time: A chart with COMIC SANS for you to analyze.

Screenshot 2022-03-01 233412.jpg

The scale for the graph above shows log(number of cataclysmic variables). The y-axis of the graph shows the logarithm of the mass accretion rate for the binary system.

1. The most common type of cataclysmic variable seems to have a period in the range of how many hours?
2. Binary system A has a period of four hours. Binary system B has a period of five hours. Based on this chart, which isprobably accreting at a faster rate?
3. In which group on this chart would most known recurrent novae lie? How did you come to your answer?

[Jehosaphat]

Click to Show Answer

a) 1-2 hours
b) Binary System B
c) The upper right group. The mass accretion rates for recurrent novae are higher, so the upper group would make sense.

Here are some of my own:

1. A type 1a supernova occurred at a measured parallax of 0.103 mas, what was its apparent magnitude?
2. At what distance are two stars in a binary system orbiting each other if Star A weighs 1.2 solar masses, Star B weighs 2.3 solar masses, and they complete one revolution once every 46 years?
3. What is the distance to a RR Lyrae type variable star if its apparent magnitude is 9.4 and it's period is 0.89 days?

[RiverWalker88]

Click to Show Answer

[list=1]
[*] 1/(0.103/1000) = 9708.7 pc. 
m+19.3 = -5+5log(9708.7)
m = -4.364
[*] p^2 = a^3/m => a = [46^2/(1.2+2.3)]^(1/3) = 8.46 AU
[*] Since you didn't provide a PL relationship, I'm going to use one I looked up from https://iopscience.iop.org/article/10.1086/591231/pdf and hope it's close enough (I use Z=0.0005 from 2. Models).

M = 0.839-1.295 log(0.89) + 0.211log(0.0005); M = 0.208
m-M = -5+5log d; d = 689.29 pc
[/list]

A Deep Sky Object Question:

1. Identify the DSO in the attached figure.
2. What wavelength band (Radio, Microwave, Infrared, etc.) were the two images taken in?
3. Look at the Hα image. Surrounding the nebula is a shell-like structure that isn't visible in the NII image. Where might this have come from?
4. Why might we be able to see this shell when looking at Hα emission, but not NII emission?

[AstroClarinet]

A Deep Sky Object Question:

1. Identify the DSO in the attached figure.
2. What wavelength band (Radio, Microwave, Infrared, etc.) were the two images taken in?
3. Look at the Hα image. Surrounding the nebula is a shell-like structure that isn't visible in the NII image. Where might this have come from?
4. Why might we be able to see this shell when looking at Hα emission, but not NII emission?

Click to Show Answer

a. IC 4593 
b. Visible light
c. Mass loss during the TP-AGB 
d. Some probably terrible guesses: Only the very outer layers of the star were lost, which are rich in hydrogen but don't have much nitrogen. Or, there is nitrogen in the outer shell but emission lines are not produced since conditions aren't right in the shell to produce forbidden N II lines. 

[RiverWalker88]

A Deep Sky Object Question:

1. Identify the DSO in the attached figure.
2. What wavelength band (Radio, Microwave, Infrared, etc.) were the two images taken in?
3. Look at the Hα image. Surrounding the nebula is a shell-like structure that isn't visible in the NII image. Where might this have come from?
4. Why might we be able to see this shell when looking at Hα emission, but not NII emission?

Click to Show Answer

a. IC 4593 
b. Visible light
c. Mass loss during the TP-AGB 
d. Some probably terrible guesses: Only the very outer layers of the star were lost, which are rich in hydrogen but don't have much nitrogen. Or, there is nitrogen in the outer shell but emission lines are not produced since conditions aren't right in the shell to produce forbidden N II lines. 

Yep, those look right. I had the first thing you answered in mind for (d) but the second one also makes sense.

Your move.