Hubble's Cepheid Variable in M31

[johnrt]

I very much enjoyed pt 1 of Jim Al-Khalili's new BBC4 documentary about the beginning and end of the universe. The section on Edwin Hubble and his Cepheid variable inspired me to go back and have a look at my own data and see if my humble 6" RC had managed to pick it up. I had a good stack of luminance subs to look at from last September.

 

After working out exactly where I should be looking I zoomed in, and there she was!

 

Here's a little bit a blurb I wrote for posting up on my website;

This star is what's known as a Cepheid variable. The brightness of these stars varies as helium gas inside them heats and expands and then cools and contracts in a feedback loop. The period of this pulsation is closely linked with the intrinsic brightness, or luminosity, of the star. By observing the period over which the star peaks in brightness and comparing this to the brightness of the star it is possible to calculate the distance to the object.

When Edwin Hubble calculated the distance to this star in 1923 it became the first ever object to be measured to be outside of our own galaxy, The Milky Way, and became known as the star that changed our understanding of the universe.

These images of Hubble's Cepheid Variable were captured during September 2015 using an Altair Astro 6"RC and Atik 460ex in Sequence Generator Pro.

 

Rather pleased with that and a good excuse to dig out some old data on a cloudy day

 

[gorann]

Very cool!

You made me have a look at an M31 image I took in October. It is with a ES 127ED refractor unguided on aNEQ6, only 3 x 4 min exposures with a Canon 60Da (ISO 1600). So, even a 5" scope with a DSLR camera can pick up a star from another galaxy. The image is much more noisy than yours, probably largely because I only took 3 subs.

How did you find it?

[johnrt]

I found the exact co-ordinates off the Hubble Legacy website and added an equatorial grid to the image using the Pixinsight annotate script, it ended up right under a grid line which didn't really help it tracking it down!

[michael.h.f.wilkinson]

Very interesting to see. As a follow-up, are you going to try to get a light curve?

[laudropb]

Very interesting capture and write up.

[johnrt]

13 minutes ago, michael.h.f.wilkinson said:

Very interesting to see. As a follow-up, are you going to try to get a light curve?

I wouldn't know where to begin!

[gorann]

Are there others stars outside the Milky Way that can been seen with a modest telescope? I assume they would be in Andromeda.

[aparker]

 

 

15 minutes ago, michael.h.f.wilkinson said:

Very interesting to see. As a follow-up, are you going to try to get a light curve?

AAVSO did exactly that as part of a Hubble anniversary event a few years back.

[aparker]

It's also the case that a fair number of the "stars" in your image are actually globular clusters orbiting the core of M31.  There's a reference to that somewhere on-line...

[gorann]

16 minutes ago, aparker said:

It's also the case that a fair number of the "stars" in your image are actually globular clusters orbiting the core of M31.  There's a reference to that somewhere on-line...

Yes, that is what I thought until today, that the bright spots in M31 were either something like large globular clusters or Milky Way stars that just happened to be in that direction.

[ollypenrice]

You have to do a version with VAR scribbled on the picture! History requires it!!

Nice work.

Olly

[johnrt]

Hehehehe

[ollypenrice]

7 hours ago, johnrt said:

Hehehehe

Olly

[physicus]

Very nice !   I was a bit disappointed Jim didn't say something like "you can actually see this with your 10 inch from the back garden", but instead took us to that 11 meter Very, Very, Very, Extremely, Large, Telescope - or whatever they call those things on mountains.  Here for interest are Hubble's origin pics with V1 marked in his own hand (snapped when I was at Huntington Library a while back).

 

[Owmuchonomy]

On 22 March 2016 at 15:08, gorann said:

Are there others stars outside the Milky Way that can been seen with a modest telescope? I assume they would be in Andromeda.

There is always the option to chase down supernovae. 

[gorann]

1 hour ago, Owmuchonomy said:

There is always the option to chase down supernovae. 

but those are exploded giant stars.... What about intact giant stars?