APOD: RS Puppis (2019 May 17)

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APOD: RS Puppis (2019 May 17)

Post by APOD Robot » Fri May 17, 2019 4:06 am

Image RS Puppis

Explanation: Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along its surrounding nebula delayed in time, effectively a light echo. Using measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way.

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Re: APOD: RS Puppis (2019 May 17)

Post by Boomer12k » Fri May 17, 2019 8:09 am

Awesome star spikes... great image...

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Re: APOD: RS Puppis (2019 May 17)

Post by orin stepanek » Fri May 17, 2019 10:28 am

A beautiful measuring stick! 8-) :D
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Re: APOD: RS Puppis (2019 May 17)

Post by rstevenson » Fri May 17, 2019 1:16 pm

My kingdom for a spike removing filter.

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Re: APOD: RS Puppis (2019 May 17)

Post by I-Knight » Fri May 17, 2019 4:19 pm

To the right side of the upper Puppis spike, around 2/5 between the top of the photo and Puppis, there appears to be a star in the cloud with a planet in front of it, or is that black dot a photographic anomaly or artifact?

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Re: APOD: RS Puppis (2019 May 17)

Post by geckzilla » Fri May 17, 2019 5:00 pm

I-Knight wrote:
Fri May 17, 2019 4:19 pm
To the right side of the upper Puppis spike, around 2/5 between the top of the photo and Puppis, there appears to be a star in the cloud with a planet in front of it, or is that black dot a photographic anomaly or artifact?
I'm not sure how that was introduced, but it's definitely not real. There are a number of artifacts such as charge bleeds and cosmic rays spread throughout the image.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: RS Puppis (2019 May 17)

Post by RBANDREO » Fri May 17, 2019 6:08 pm

Yes, that's most definitely an artifact, likely introduced during processing. As Geckzilla pointed out, there are a number of artifacts spread all over the image.

Thanks,
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Re: APOD: RS Puppis (2019 May 17)

Post by Rick357 » Fri May 17, 2019 6:16 pm

and with this light echo data, has anyone managed to use the light echo timing to calculate and map a peudo 3D representation of the gas cloud halo? Could make for an interesting project and lead to more info about the density of the cloud and whether it is part of, associated with or just a by chance superposition of the star with the cloud.

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Re: APOD: RS Puppis (2019 May 17)

Post by neufer » Fri May 17, 2019 10:37 pm

Rick357 wrote:
Fri May 17, 2019 6:16 pm

and with this light echo data, has anyone managed to use the light echo timing to calculate and map a peudo 3D representation of the gas cloud halo? Could make for an interesting project and lead to more info about the density of the cloud and whether it is part of, associated with or just a by chance superposition of the star with the cloud.
  • Knot as easy as one might imagine:
https://www.aanda.org/articles/aa/full_ ... 80-08.html

On geometric distance determination to the Cepheid RS Puppis from its light echoes

Astronomy & Astrophysics / Accepted 28 November 2008

by H. E. Bond - W. B. Sparks
Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA


This figure illustrates the propagation of a train of nested light-echo paraboloids into the dust surrounding RS Pup, as viewed from the Earth. Each parabola marks a maximum in the 41.4-day variation of the illuminating star. The x and z scales are in pc. The corresponding angular scale depends on the distance to the star, and is shown at the top of the figure for a nominal distance of 2 kpc. The dashed circle of radius 0.3 pc encloses the brightest parts of the nebula, but fainter portions are seen out to at least twice that radius.

The vertical dashed line marks the location of Knot 5. Knot 5 has a phase lag of 0.5 cycle relative to RS Pup, so it must lie halfway between a pair of parabolas, but we do not know which pair. K08 resolved the ambiguity by assuming the knots to lie in the plane of the sky. Under this assumption, and making an initial guess at the distance to the star, the integer numbers of cycles in the phase lags become known (in the case of Knot 5, it is 4). Then the fractional phase lag for each knot yields a stellar distance, and the final result was taken as the mean of the distances determined from 10 individual features. K08 recognized that the assumption that the knots lie in the plane of the sky would generally not be true for any particular individual knot, but argued that the assumption would be true in the mean, as long as the spatial distribution of the knots is close to isotropic.
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Re: APOD: RS Puppis (2019 May 17)

Post by ta152h0 » Sat May 18, 2019 5:58 pm

like a good beach volley ball game, you guys spiked it! Pass the ice cold one.
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KR Puppies

Post by neufer » Sun May 19, 2019 7:35 pm

Click to play embedded YouTube video.
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Re: APOD: RS Puppis (2019 May 17)

Post by Peter von Schilling » Thu May 23, 2019 4:54 pm

Hi I'm very new to this.
In the image of RS Pup I notice maybe around 1000 or 1500 small bright spots, which I assume are stars.
Most of these do not have any spikes. What I'm trying to find out: are these stars further away than RS Pup with attached Nebula,
or do they lie in front of RS Pup and Nebula? :roll:

If the answer is that they lie "behind" RS Pup, can I draw the conclusion that also in images of other Nebulae,
most of the stars pictured would lie behind the nebula, and thus the nebula must be very thin for these stars
to shine through the nebula in question?

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Re: APOD: RS Puppis (2019 May 17)

Post by geckzilla » Thu May 23, 2019 5:12 pm

Peter von Schilling wrote:
Thu May 23, 2019 4:54 pm
Hi I'm very new to this.
In the image of RS Pup I notice maybe around 1000 or 1500 small bright spots, which I assume are stars.
Most of these do not have any spikes. What I'm trying to find out: are these stars further away than RS Pup with attached Nebula,
or do they lie in front of RS Pup and Nebula? :roll:

If the answer is that they lie "behind" RS Pup, can I draw the conclusion that also in images of other Nebulae,
most of the stars pictured would lie behind the nebula, and thus the nebula must be very thin for these stars
to shine through the nebula in question?
It's not an either-or answer. Some are behind, some are in front. Same goes for the bright stars with spikes. This object lies close to the galactic plane, so the whole thing is relatively nearby or it would be obscured by dust. If some infrared observations were available, you'd be able to see a lot more of the stars that are behind it. This is all visible light, though.
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Re: APOD: RS Puppis (2019 May 17)

Post by Ann » Thu May 23, 2019 5:36 pm

Peter von Schilling wrote:
Thu May 23, 2019 4:54 pm
Hi I'm very new to this.
In the image of RS Pup I notice maybe around 1000 or 1500 small bright spots, which I assume are stars.
Most of these do not have any spikes. What I'm trying to find out: are these stars further away than RS Pup with attached Nebula,
or do they lie in front of RS Pup and Nebula? :roll:

If the answer is that they lie "behind" RS Pup, can I draw the conclusion that also in images of other Nebulae,
most of the stars pictured would lie behind the nebula, and thus the nebula must be very thin for these stars
to shine through the nebula in question?
Stars vary enormously in brightness. RS Puppis itself is very bright.
Wikipedia wrote:

RS Puppis is a supergiant with a spectral classification of G2Ib, although its spectral type varies between F9 and G7 as its temperature changes.
...
The radius varies between 164 R☉ and 208 R☉, although the changes vary somewhat even from one cycle to the next. The temperature varies between a minimum of 4,640 K and 5,850 K, and the bolometric luminosity between 14,200 L☉ and 29,500 L☉.[9]
A star's bolometric magnitude is its total emission of energy across the electromagnetic spectrum. Stars are always brighter in bolometric magnitude than they are at any specific wavelength. But because RS Puppis is a mid-temperature star, its absolute visual magnitude is not so different from its bolometric one. In short, RS Puppis probably produces about 10,000 to 20,000 as much visual light as the Sun does. That's bright.

The point to understand is that most stars are faint, but the intrinsically bright and reasonably nearby stars stand out very brightly in the sky. Stars as bright as RS Puppis are very rare. Surprisingly enough, even our own Sun is unusually bright as stars go. As a rule of thumb, we can say that 99% of the stars that stand out clearly in the night sky are intrinsically brighter than the Sun, but about 90-95% of all the stars in our galaxy are intrinsically fainter than the Sun. The nearest star to the Earth after the Sun, Proxima Centauri, is a tiny red dwarf star that is 18,000 times fainter than the Sun.

So are the stars that are seen in the apparent vicinity of RS Puppis bright background stars, "normal" stars at RS Puppis' distance, or are they faint foreground stars? That is impossible to say by just looking at the photograph. We may note that many of the small stars are reddish, which suggests either that they are intrinsically small and cool and therefore reddish, or else that they are far away and have been reddened by dust, such as the dust-rich nebula that RS Puppis is immersed in.

A very reasonable guess is that RS Puppis is the intrinsically brightest star that can be seen in this APOD. But even that is not certain. To know for sure we must measure the parallax of each star, which is the star's apparent motion back and forth across the sky as the Earth completes one orbit around the Sun. The spacecraft Gaia is doing just that right now, which is to say that it is measuring the parallaxes of and therefore the distances to, I think, a million - or was it a billion? - stars in the Milky Way. But it will take a long time for the Gaia mission to release its catalogue over the million (or billion) stars whose distances they have measured, and I for one can't imagine how I could browse that catalogue and find the stars that interest me.

So to summarize: Yes, those little bright dots are stars, but no, we can't say if they are background stars or foreground stars. The stars are obviously so faint-looking in the sky, probably around magnitude 15 or fainter, that there currently exists no catalogue than has any really useful information on them.

Ann
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Re: APOD: RS Puppis (2019 May 17)

Post by Chris Peterson » Thu May 23, 2019 8:05 pm

Ann wrote:
Thu May 23, 2019 5:36 pm
So to summarize: Yes, those little bright dots are stars, but no, we can't say if they are background stars or foreground stars. The stars are obviously so faint-looking in the sky, probably around magnitude 15 or fainter, that there currently exists no catalogue than has any really useful information on them.
Gaia. A massive collection of stellar information down to mag 20, and at mag 15 that includes color data, distance, possibly proper motion.
Chris

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Re: APOD: RS Puppis (2019 May 17)

Post by Ann » Fri May 24, 2019 3:40 am

Chris Peterson wrote:
Thu May 23, 2019 8:05 pm
Ann wrote:
Thu May 23, 2019 5:36 pm
So to summarize: Yes, those little bright dots are stars, but no, we can't say if they are background stars or foreground stars. The stars are obviously so faint-looking in the sky, probably around magnitude 15 or fainter, that there currently exists no catalogue than has any really useful information on them.
Gaia. A massive collection of stellar information down to mag 20, and at mag 15 that includes color data, distance, possibly proper motion.
Of course. Sorry. But how can I access it and find the stars that Peter von Schilling was asking about?

Ann
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Re: APOD: RS Puppis (2019 May 17)

Post by Chris Peterson » Fri May 24, 2019 5:10 am

Ann wrote:
Fri May 24, 2019 3:40 am
Chris Peterson wrote:
Thu May 23, 2019 8:05 pm
Ann wrote:
Thu May 23, 2019 5:36 pm
So to summarize: Yes, those little bright dots are stars, but no, we can't say if they are background stars or foreground stars. The stars are obviously so faint-looking in the sky, probably around magnitude 15 or fainter, that there currently exists no catalogue than has any really useful information on them.
Gaia. A massive collection of stellar information down to mag 20, and at mag 15 that includes color data, distance, possibly proper motion.
Of course. Sorry. But how can I access it and find the stars that Peter von Schilling was asking about?
Well, you can get data at https://gea.esac.esa.int/archive/ . But the whole process is fairly technical. I wasn't necessarily suggesting you want to do it, just that a rich catalog of dim stars does exist.
Chris

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Re: APOD: RS Puppis (2019 May 17)

Post by Peter von Schilling » Sat May 25, 2019 9:16 am

Ann wrote:
Thu May 23, 2019 5:36 pm
Peter von Schilling wrote:
Thu May 23, 2019 4:54 pm
Hi I'm very new to this.
In the image of RS Pup I notice maybe around 1000 or 1500 small bright spots, which I assume are stars.
Most of these do not have any spikes. What I'm trying to find out: are these stars further away than RS Pup with attached Nebula,
or do they lie in front of RS Pup and Nebula? :roll:

Stars vary enormously in brightness. RS Puppis itself is very bright.
Wikipedia wrote:

RS Puppis is a supergiant with a spectral classification of G2Ib, although its spectral type varies between F9 and G7 as its temperature changes.
...

The point to understand is that most stars are faint, ..... Surprisingly enough, even our own Sun is unusually bright as stars go. As a rule of thumb, we can say that 99% of the stars that stand out clearly in the night sky are intrinsically brighter than the Sun, but about 90-95% of all the stars in our galaxy are intrinsically fainter than the Sun.........
So are the stars that are seen in the apparent vicinity of RS Puppis bright background stars, "normal" stars at RS Puppis' distance, or are they faint foreground stars? That is impossible to say by just looking at the photograph.........
A very reasonable guess is that RS Puppis is the intrinsically brightest star that can be seen in this APOD. But even that is not certain. To know for sure we must measure the parallax of each star, which is the star's apparent motion back and forth across the sky as the Earth completes one orbit around the Sun.........

So to summarize: Yes, those little bright dots are stars, but no, we can't say if they are background stars or foreground stars. The stars are obviously so faint-looking in the sky, probably around magnitude 15 or fainter, that there currently exists no catalogue than has any really useful information on them.

Ann

Thank you very much for the very illuminating answer to my question.

Peter