Astronomy C

[PM2017]

Some theoretical stuff:

Refer to the image below.

1. This spectrum primarily shows the (visual/ultraviolet/near infrared) range, and is characteristic of a (Luminous Blue Variable/ZZ Ceti star/Wolf-Rayet star/Type II Cepheid).
2. What element causes the largest emission line on this spectrum?
3. Why does this type of star have such prominent emission lines?

b. The most prominent line is from C III / C IV
c. WR stars are in far stages of evolution, and have their stellar wind has blown away most of its outer nonmetallic elements (H and He). This allows for heavier elements (like carbon) to be more prominent in their spectra. (This information is a large amount of what I know about WR stars, and if you wanted the reason as to why this star has C III/ C IV lines rather than some form of Nitrogen, I'm sorry.)

[Unome]

Correct, your turn (though you didn't explicitly answer #1, your answer includes most of it). Also, from what I know, the subtypes of Wolf-Rayet stars are mostly dependent on mass and age, since that determines which elements are brought to the surface.

[PM2017]

Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)

[raxu]

Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)

We first calculate the combined mass of the star: . Looking at a table, star 1 is a G2 star with mass , so the other has mass . Finally, using the formula, the other has luminosity .

A supernova has peak apparent magnitude 18, and the H-alpha line appears at 670 nm. What is its peak absolute magnitude? Assume Hubble's constant is 72km/s/Mpc.

[Adi1008]

Sorry this is so late.

In a binary system, one of the stars has a surface temperature of 7000K. The semimajor axis is 2.29 AU, and the period is 2 years. Find the luminosity of the other star, assuming both stars are in the main sequence, and that for main sequence stars Luminosity = Mass^3.5.

(EDIT: Both stars are more massive than the sun)

We first calculate the combined mass of the star: . Looking at a table, star 1 is a G2 star with mass , so the other has mass . Finally, using the formula, the other has luminosity .

A supernova has peak apparent magnitude 18, and the H-alpha line appears at 670 nm. What is its peak absolute magnitude? Assume Hubble's constant is 72km/s/Mpc.

Answer (Click to Show Hidden Text)

about -16.7?

[raxu]

Answer (Click to Show Hidden Text)

about -16.7?

Solution (math mode used) (Click to Show Hidden Text)

We first find the velocity. H-alpha line usually appears at [math]\lambda_0=656\text{nm}[/math].

By [math]\frac{\Delta\lambda}{\lambda_0}=\frac{v}{c}[/math], we find that [math]v=6402km/s[/math].

Then, using [math]v=H_0d[/math], we find [math]d=89Mpc[/math].

Plugging into distance modulus [math]M=m-5\log_{10}(\frac{d}{10\text{pc}})[/math], we get [math]M=-16.7[/math].

Can someone check that the doppler shift equation I used was correct? Thanks!

Also, your turn Adi1008!

[Adi1008]

Answer (Click to Show Hidden Text)

about -16.7?

Solution (math mode used) (Click to Show Hidden Text)

We first find the velocity. H-alpha line usually appears at [math]\lambda_0=656\text{nm}[/math].

By [math]\frac{\Delta\lambda}{\lambda_0}=\frac{v}{c}[/math], we find that [math]v=6402km/s[/math].

Then, using [math]v=H_0d[/math], we find [math]d=89Mpc[/math].

Plugging into distance modulus [math]M=m-5\log_{10}(\frac{d}{10\text{pc}})[/math], we get [math]M=-16.7[/math].

Can someone check that the doppler shift equation I used was correct? Thanks!

Also, your turn Adi1008!

I believe the equation that you used for redshift is fine as long as the recession speeds are not relativistic. Once the objects get very far away, things like comoving distance become important, so the equation gets more complex.


A, B, C, and D represent 4 pulsars. Which one's kinetic energy is decreasing the fastest? Assume (somewhat wrongly) that the moment of inertias of each pulsar are all about the same

[jonboyage]

Answer (Click to Show Hidden Text)

Pulsar A is losing energy the fastest because it is slowing down more rapidly than C or D and it has a quicker initial period than B (and energy increases quadratically with angular velocity, so the same linear decrease at a lower period correlates with faster energy loss)

[Adi1008]

Answer (Click to Show Hidden Text)

Pulsar A is losing energy the fastest because it is slowing down more rapidly than C or D and it has a quicker initial period than B (and energy increases quadratically with angular velocity, so the same linear decrease at a lower period correlates with faster energy loss)

Correct, your turn!

[jonboyage]

A few questions about pulsars and magnetars:

a. Briefly explain how we, from Earth, measure magnetic fields of stellar objects. (mention an effect, starts with a "z")

b. We know that pulsars already have very strong magnetic fields, along which beams of radiation emerge. What, during their formations, causes magnetars to have significantly stronger magnetic fields than other pulsars?

c. What causes magnetars to maintain very strong magnetic fields long after their formation?

d. Does this mean that neutron stars are not completely made of neutrons? What are they actually made of? (name at least 3 particles)

e. Is there another particle present in the interiors of neutron stars that starts with an "h"?

f. Ew, what is this new particle that I've never heard of (although it does sound cool) and what are two ways it affects the neutron star in the long run?