Astronomy C

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Astronomy C

Postby Adi1008 » August 4th, 2018, 11:08 pm

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Re: Astronomy C

Postby antoine_ego » September 4th, 2018, 12:17 pm

Chandra's webinars have been posted on its website, here. This year, they included a Stellar Evolution 101, using last year's DSOs as examples. It's definitely a pretty good resource, especially for beginners.
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Re: Astronomy C

Postby Unome » September 6th, 2018, 4:49 am

I can get so many questions out of 47 Tucanae... :)
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Re: Astronomy C

Postby PM2017 » September 6th, 2018, 5:29 pm

This year looks like its going to be the best of my four years of doing Astronomy, in terms of experience, and content. Good luck to everyone!
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Re: Astronomy C

Postby chaoticevil42 » September 10th, 2018, 8:51 am

Hey guys, I've been working on the DSO list this year and I've got a clarification question. DSO vi. on the list is SN2014, but there are 136 CBAT supernovae using that designation. I think the rules intend SN2014J, which was the brightest supernova of the year, but it doesn't specify.

If any of y'all know anything I'd appreciate it a ton
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Re: Astronomy C

Postby Adi1008 » September 10th, 2018, 9:02 am

chaoticevil42 wrote:Hey guys, I've been working on the DSO list this year and I've got a clarification question. DSO vi. on the list is SN2014, but there are 136 CBAT supernovae using that designation. I think the rules intend SN2014J, which was the brightest supernova of the year, but it doesn't specify.

If any of y'all know anything I'd appreciate it a ton

I think it's supposed to be SN 2014J; "SN 2014" is a typo.

(usual disclaimer: this is not an official clarification)
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Re: Astronomy C

Postby MAAAAC » September 10th, 2018, 9:46 am

Anyone found any actually useful Tully-Fisher equations (or other relationships that may be used for galactic computation)? I've been searching around for a few hours and have found a lot of relationships between variables but very few actually have 1. constants from observational correction or 2. input and output units for the variables, both of which are necessary to actually use an equation for a problem on a test. The closest that I've gotten with Tully-Fisher specifically is a set of equations relating absolute magnitude of a spiral galaxy in different bands to rotational velocity with correctional coefficients and constants, but these equations don't give the units of either variable. Though, I haven't spent as much time searching for other equations based on relationships, I have run into the same problem several times. If anyone has any input, advice, or even an equation, that would be great! Thank you!

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Re: Astronomy C

Postby Unome » September 10th, 2018, 2:38 pm

MAAAAC wrote:Anyone found any actually useful Tully-Fisher equations (or other relationships that may be used for galactic computation)? I've been searching around for a few hours and have found a lot of relationships between variables but very few actually have 1. constants from observational correction or 2. input and output units for the variables, both of which are necessary to actually use an equation for a problem on a test. The closest that I've gotten with Tully-Fisher specifically is a set of equations relating absolute magnitude of a spiral galaxy in different bands to rotational velocity with correctional coefficients and constants, but these equations don't give the units of either variable. Though, I haven't spent as much time searching for other equations based on relationships, I have run into the same problem several times. If anyone has any input, advice, or even an equation, that would be great! Thank you!

I thought exactly the same thing when I was writing a test earlier. I haven't found a calibrated formula so far.
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Re: Astronomy C

Postby PM2017 » September 10th, 2018, 2:43 pm

Unome wrote:
MAAAAC wrote:Anyone found any actually useful Tully-Fisher equations (or other relationships that may be used for galactic computation)? I've been searching around for a few hours and have found a lot of relationships between variables but very few actually have 1. constants from observational correction or 2. input and output units for the variables, both of which are necessary to actually use an equation for a problem on a test. The closest that I've gotten with Tully-Fisher specifically is a set of equations relating absolute magnitude of a spiral galaxy in different bands to rotational velocity with correctional coefficients and constants, but these equations don't give the units of either variable. Though, I haven't spent as much time searching for other equations based on relationships, I have run into the same problem several times. If anyone has any input, advice, or even an equation, that would be great! Thank you!

I thought exactly the same thing when I was writing a test earlier. I haven't found a calibrated formula so far.

I have the same issue. The closest things I've found thus far is this: http://astrosun2.astro.cornell.edu/~masters/lisadistances/tf.htm, but it hasn't been super useful.
I haven't had time to do it yet, but I was planning on looking into calibrating it using the milky way, to at least get a rough idea.
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Re: Astronomy C

Postby chaoticevil42 » September 10th, 2018, 4:48 pm

Adi1008 wrote:
chaoticevil42 wrote:Hey guys, I've been working on the DSO list this year and I've got a clarification question. DSO vi. on the list is SN2014, but there are 136 CBAT supernovae using that designation. I think the rules intend SN2014J, which was the brightest supernova of the year, but it doesn't specify.

If any of y'all know anything I'd appreciate it a ton

I think it's supposed to be SN 2014J; "SN 2014" is a typo.

(usual disclaimer: this is not an official clarification)


I'm thinking (and hoping, since I've already done a bunch of work under that assumption) that's probably it. I'll report it when the rules clarifications open up October 1st and we'll see for sure.

Sidebar: The DSOs this year are way cooler than they were last year.
Last edited by chaoticevil42 on September 10th, 2018, 6:23 pm, edited 2 times in total.
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Re: Astronomy C

Postby syo_astro » September 10th, 2018, 6:17 pm

chaoticevil42 wrote:
Adi1008 wrote:
chaoticevil42 wrote:Hey guys, I've been working on the DSO list this year and I've got a clarification question. DSO vi. on the list is SN2014, but there are 136 CBAT supernovae using that designation. I think the rules intend SN2014J, which was the brightest supernova of the year, but it doesn't specify.

If any of y'all know anything I'd appreciate it a ton

I think it's supposed to be SN 2014J; "SN 2014" is a typo.

(usual disclaimer: this is not an official clarification)


I'm thinking (and hoping, since I've already done a bunch of work under that assumption) that's probably it. I'll report it when the rules clarifications open up October 1st and we'll see for sure.

Sidebar: The DSOs this year are way cooler and more recent than they've been the past few years.


Yes, please submit an official clarification. Otherwise, it is not official and technically can't be confirmed as true. Assumptions are bad! [That said, I actually have no clue how a letter went missing...]

Also, to be fair about DSOs...just a few years ago we had exoplanets, which obviously had a ton of recently (like, really, not 100 yrs ago) discovered objects! The "old" DSOs are cool too!
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Re: Astronomy C

Postby Unome » September 10th, 2018, 6:44 pm

syo_astro wrote:
chaoticevil42 wrote:
Adi1008 wrote:I think it's supposed to be SN 2014J; "SN 2014" is a typo.

(usual disclaimer: this is not an official clarification)


I'm thinking (and hoping, since I've already done a bunch of work under that assumption) that's probably it. I'll report it when the rules clarifications open up October 1st and we'll see for sure.

Sidebar: The DSOs this year are way cooler and more recent than they've been the past few years.


Yes, please submit an official clarification. Otherwise, it is not official and technically can't be confirmed as true. Assumptions are bad! [That said, I actually have no clue how a letter went missing...]

Also, to be fair about DSOs...just a few years ago we had exoplanets, which obviously had a ton of recently (like, really, not 100 yrs ago) discovered objects! The "old" DSOs are cool too!

Alternate opinion: Half the DSOs this year are basically identical - there's only so many ways to ask about a starburst galaxy (47 Tucanae is really nice though).
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Re: Astronomy C

Postby chaoticevil42 » September 10th, 2018, 8:03 pm

Unome wrote:
syo_astro wrote:

Also, to be fair about DSOs...just a few years ago we had exoplanets, which obviously had a ton of recently (like, really, not 100 yrs ago) discovered objects! The "old" DSOs are cool too!

Alternate opinion: Half the DSOs this year are basically identical - there's only so many ways to ask about a starburst galaxy (47 Tucanae is really nice though).


There's just something about the DSOs this year that catches my attention more so than the supernova remnants and LBVs and such that we had last year. (Exoplanets were super cool though I forgot about that I was thinking mostly about last year)
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Re: Astronomy C

Postby MAAAAC » September 11th, 2018, 6:42 am

PM2017 wrote:
Unome wrote:
MAAAAC wrote:Anyone found any actually useful Tully-Fisher equations (or other relationships that may be used for galactic computation)? I've been searching around for a few hours and have found a lot of relationships between variables but very few actually have 1. constants from observational correction or 2. input and output units for the variables, both of which are necessary to actually use an equation for a problem on a test. The closest that I've gotten with Tully-Fisher specifically is a set of equations relating absolute magnitude of a spiral galaxy in different bands to rotational velocity with correctional coefficients and constants, but these equations don't give the units of either variable. Though, I haven't spent as much time searching for other equations based on relationships, I have run into the same problem several times. If anyone has any input, advice, or even an equation, that would be great! Thank you!

I thought exactly the same thing when I was writing a test earlier. I haven't found a calibrated formula so far.

I have the same issue. The closest things I've found thus far is this: http://astrosun2.astro.cornell.edu/~masters/lisadistances/tf.htm, but it hasn't been super useful.
I haven't had time to do it yet, but I was planning on looking into calibrating it using the milky way, to at least get a rough idea.


Ok, we're going to do this! So if we assume that those equations on the Cornell site are calibrated correctly for their respective bands (which I think is a pretty safe assumption, considering the credibility of the source and that they purportedly took the equations directly from Tully and Fisher?) then we have corrected equations that need 2 more things to be usable: input and output units and conversions to more useful quantities (ie. absolute magnitude in the B band isn't that useful, but it would be nice if we could have an equation for visual absolute magnitude or luminosity). From what I have seen through speed-reading random google-search results, the WR units ("rotationa rate for the galaxy") is the same thing as the "rotational velocity" (please correct me if I am wrong) which is typically in units of Km/s and can be found by taking half the measure of the difference in velocity between the two peaks of an H I 21 cm line graph. For the output units, well, its just absolute magnitude corrected for a band so it doesn't have "units" so we're all good there. Next is the matter of making the output values useful. I've hardly ever seen any questions ask for absolute magnitude corrected for the B band, etc. so, unless the test writers are super nice, it probably won't be that helpful. A more useful unit would be something like absolute magnitude in the visual band (which is your typical, normal "absolute magnitude") or Luminosity. This part is harder... and I don't know if it is even possible considering what the bands represent and their discrepancies for different types of stars, etc. From what I have read (https://en.wikipedia.org/wiki/Bolometric_correction, https://www.astro.umd.edu/~ssm/ASTR620/mags.html) It is possible to correct a band magnitude to convert it into bolometric magnitude (and thus, back into visual magnitude) for specific types of stars, but this wouldn't work for galaxies (unless you did something like change the bolometric corrections using the percentages of different stars in a galaxy, etc.) Perhaps it is a lost cause, and what we really need is a TF equation for the visual band or something bolometric. It's weird that we haven't been able to find one of these, as, being the most useful, you would think it would be the first equation to be created...

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Re: Astronomy C

Postby PM2017 » September 11th, 2018, 6:37 pm

MAAAAC wrote:
PM2017 wrote:
Unome wrote:I thought exactly the same thing when I was writing a test earlier. I haven't found a calibrated formula so far.

I have the same issue. The closest things I've found thus far is this: http://astrosun2.astro.cornell.edu/~masters/lisadistances/tf.htm, but it hasn't been super useful.
I haven't had time to do it yet, but I was planning on looking into calibrating it using the milky way, to at least get a rough idea.


Ok, we're going to do this! So if we assume that those equations on the Cornell site are calibrated correctly for their respective bands (which I think is a pretty safe assumption, considering the credibility of the source and that they purportedly took the equations directly from Tully and Fisher?) then we have corrected equations that need 2 more things to be usable: input and output units and conversions to more useful quantities (ie. absolute magnitude in the B band isn't that useful, but it would be nice if we could have an equation for visual absolute magnitude or luminosity). From what I have seen through speed-reading random google-search results, the WR units ("rotationa rate for the galaxy") is the same thing as the "rotational velocity" (please correct me if I am wrong) which is typically in units of Km/s and can be found by taking half the measure of the difference in velocity between the two peaks of an H I 21 cm line graph. For the output units, well, its just absolute magnitude corrected for a band so it doesn't have "units" so we're all good there. Next is the matter of making the output values useful. I've hardly ever seen any questions ask for absolute magnitude corrected for the B band, etc. so, unless the test writers are super nice, it probably won't be that helpful. A more useful unit would be something like absolute magnitude in the visual band (which is your typical, normal "absolute magnitude") or Luminosity. This part is harder... and I don't know if it is even possible considering what the bands represent and their discrepancies for different types of stars, etc. From what I have read (https://en.wikipedia.org/wiki/Bolometric_correction, https://www.astro.umd.edu/~ssm/ASTR620/mags.html) It is possible to correct a band magnitude to convert it into bolometric magnitude (and thus, back into visual magnitude) for specific types of stars, but this wouldn't work for galaxies (unless you did something like change the bolometric corrections using the percentages of different stars in a galaxy, etc.) Perhaps it is a lost cause, and what we really need is a TF equation for the visual band or something bolometric. It's weird that we haven't been able to find one of these, as, being the most useful, you would think it would be the first equation to be created...

Actually, radio would be the most useful, since the Tully-Fischer relationship is really useful at distances where the redshift is enormous.
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