Author Topic: Aug 2 2012 Star overlapping galaxy?  (Read 11889 times)

Budgieye

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Aug 2 2012 Star overlapping galaxy?
« on: August 02, 2012, 04:29:07 am »
Aug 2 2012  Star overlapping galaxy?


Can you help me identify what the bright "star" is?



Here is an interesting find by AduN

Hi all,
I need some help here.
I checked it with DR8 and it say that the bright object is star, it has no spectrum avaible. Is there any possibilty that this can be QSO? I mean it really look like integral part of galaxy.

http://www.galaxyzoo.org/examine/AHZ5000d6w

[...]
http://cas.sdss.org/dr7/en/tools/quicklook/quickobj.asp?id=588015508738539544
Here is a tidied version of my reply.

Tough one here.

There are no references on NED, so probably not a quasar. The software for SDSS has looked at every bright star, and tried to guess whether or not it is a quasar. It has found 50,000 or 100,000 quasars.
So it is not likely that it is a quasar. But software can be wrong, and NED and SDSS quasars survey is incomplete.

It could be a star in our galaxy overlapping a distant galaxy. There are similar stars nearby. I have selected one, which is marked by the purple triangle:


588015508738539544588015508738539562
The star+galaxy, and the star in our galaxy for comparison.



But why does the entire galaxy look so bright? and usually these overlapping stars are very round.

I think I agree with most of Budgieye's analysis.  Where I differ is that if'n I had to guess I'd lean to an overlapping star "conjunction", as joinpep does.  Because QSO's are high-energy Xray sources, there have been instruments, e.g. ROSAT, that have gone up to map them.  If none of the references say it's a QSO, it virtually certainly isn't.  I expect one of those spectra got more, and one less, of the star.  But this one is really a "you pays your nickel and you takes your chances" ::)  There was a program on PBS/Nova a couple weeks ago that showed the SDSS instrument and the big metal "plug-in" plates it uses for doing spectra, 640 at a time! :o  I think with a very precise instrument one could probably resolve the question--but, hey, that's the way Science is--every answer leads to a retreating horizon of more questions! :P ;D


So, find more information, click on "SkyServer"
http://cas.sdss.org/dr7/en/tools/quicklook/quickobj.asp?id=588015508738539544

From "Quick Look Skyserver"
The SDSS has not measured a spectrum for this object.
See its Explore entry if you think it should have a spectrum.

From SkyServer Object Explorer
click on "All Spectra"     

YES! It seems there has been a spectrum taken. :)

which takes you to 2 spectra

Reminder:
If z=0, it is a star
If z>0, it is a galaxy

http://cas.sdss.org/dr7/en/tools/explore/obj.asp?sid=421313696233422848
z=0.108, and is only 82% sure that it is a galaxy

The spectral break should be at about 4400Å. The break is not clear, but the z value was probably calculated from the emission peaks.
Looks star-forming, with a slightly active nucleus (the little hydrogen alpha peak), but definitely not a quasar.


http://cas.sdss.org/dr7/en/tools/explore/obj.asp?sid=421595184921313280
z=0.000 This one is 100% certain that it is a star. But stars don't usually have emission lines.


Funny that the bright target is off centre. Will that affect the spectrum?
ra                                                  dec
13.78111615,-0.22220857   00:55:07.46,-00:13:19.95 "star" co-ordinates
13.78111615,-0.22220857   00:55:07.46,-00:13:19.95 galaxy co-ordinates
This is the image in dr8.
It may be a star in front of a galaxy. But why is there all that brightness around it?
The co-ordinates for both of the spectra seem to be from the same place, both slightly off centre.




http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663783666581515
SDSS J005507.46-001320.0
The spectrum description is more specific in dr8, saying that it is a star-forming galaxy.

Then c_cld noticed that the co-ordinates of the objects are in the stripe82 area, where galaxies are imaged and stacked forty times to obtain higher resolution.

This field is in the footprint of Stripe82...
so You could get more hints in this stripe as in navigating we could have references to a star (in NED ) in front of 2 galaxies likely merging:

star 8658198546150588443 SDSS J005507.54-001316.6 r_mag  15.15

galaxy 8658188289762656285 SDSS J005507.46-001320.2 r_mag 17.45
with lots of others Id's in successive runs
galaxy 8658198112357843074 SDSS J005507.64-001320.4 r_mag 19.58


8658198546150653961
the nearby comparison star




The better resolution of stripe82 shows that the bright area looks like a galaxy collision. There is one extremely bright area where the sensors are overloaded. Is it an overlapping star in our galaxy, or a galaxy merger?

Literature search
in Galaxy Zoo: nothing on AHZ5000d6w 588015508738539544 1237663783666581515   SDSS J005507.46-001320.0 
It is not possible to find the ObjectID proper colour stripe 82 images

There is nothing much on NED, except for a reference on galaxy clusters.
Google scholar  Your search - SDSS J005507.46-001320.0   SDSS J00550* -001316* - did not match any articles. 

Flags: the SDSS analysis software has these flags
   DEBLEND_NOPEAK BINNED1 INTERP CHILD
PSF_FLUX_INTERP DEBLEND_NOPEAK INTERP_CENTER STATIONARY BAD_MOVING_FIT BINNED1 INTERP COSMIC_RAY MANYPETRO CHILD
TOO_FEW_GOOD_DETECTIONS MOVED BINNED1 NOPETRO NODEBLEND CHILD BLENDED
stripe82 STATIONARY MOVED BINNED1 CHILD

It can't be a cosmic ray hit, because it occurs in multiple images in stripe82

I wonder if anyone is working on it. The fact that the spectrum was done twice makes me wonder if someone has requested it.

Is it really as bright as I think it is? It is magnitude 16-18, but the target may be off-centre. It seems as bright as a quasar, but doesn't have the pink colour that a quasar should have at that distance.
Here is a quasar at similar z for comparison
588015508738539544 in SDSS dr7
z=0.108
587725552265724093 in SDSS dr7
z=0.118
mag 15-16

It is quite distant at z=0.108, when most galaxies are getting small and yellowish. 


So is it just a star overlapping a galaxy?
« Last Edit: August 02, 2012, 04:47:14 am by Budgieye »

NGC3314

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #1 on: August 02, 2012, 01:30:19 pm »
I think it's a foreground star superimposed on a disturbed galaxy (maybe interacting with something else, hidden by the star's image). In the spectra, the one of the star shows absorption lines at z=0 and emission lines matching the galaxy's redshift, while looking closely at the galaxy spectrum shows weak absorption lines at z=0. The two are so close together on the sky that each spectrum is contaminated by light from the other. In fact, the SDSS image suggests that there may be galaxy light coming from behind the star on all sides.

As they say in theaters, "down in front!"

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #2 on: August 02, 2012, 06:58:34 pm »
I think it's a foreground star superimposed on a disturbed galaxy (maybe interacting with something else, hidden by the star's image). In the spectra, the one of the star shows absorption lines at z=0 and emission lines matching the galaxy's redshift, while looking closely at the galaxy spectrum shows weak absorption lines at z=0. The two are so close together on the sky that each spectrum is contaminated by light from the other. In fact, the SDSS image suggests that there may be galaxy light coming from behind the star on all sides.

As they say in theaters, "down in front!"

I know, what you mean and I agree! The image and your post reminded me of an image, which I had posted.
We had discussed about the below image, but actually not about the star on that image, but if the GPair is an overlap or a merger.
If the star had overlapped the small galaxy, it might have looked similiar to the OOTD.

NED and DR7 say overlap, but DR8 says merger:

587731173306073231 


Stripe82 image:

http://www.galaxyzoo.org/examine/AHZ6000frt
http://cas.sdss.org/stripe82/en/tools/explore/obj.asp?id=8647475120884744681

According to DR7 and NED it is an overlap, but according to DR8 it is a merger!!! Strange!  ???
The redshift of the spiral galaxy is identical in DR7, DR8 and NED: z=0.052 http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663543138910469
The elliptical has in DR7 and NED the redshift 0.209, but in DR8 it has redshift 0.052 (same as the spiral).

http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=587731173306073230
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663543138910468

I haven't seen many cases where we identified the DR7 redshift as being false, although here it is.

The data don't really support being categorical about "false" - the spectrum shows features at both redshifts (the emission lines at the lower z are clear, but Na D, Mg features around 5200 A emitted, and the 4000-A break with Ca lines are seen clearly from z=0.209. Even better, there are spectra from the centers of both galaxies to demonstrate this: northern southern (as just linked). The southern one shows contamination from the disk of the overlapping foreground spiral. DR7 and DR8 can clearly differ in which one they pick when two redshifts are matched in the spectrum - both are in the full data table, but only one is presented per object on the Explore screen.
« Last Edit: August 02, 2012, 11:15:02 pm by zutopian »

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #3 on: August 02, 2012, 09:15:13 pm »
Here is an object, which has a spectrum, nonetheless it is unclear, if it is a galaxy or a star, because the specclasses in DR7 and DR8 are different.
Either it is a star overlapping a galaxy (DR7) or a merger (DR8).
The big galaxy has also spectrum.


DR7: Star    : http://skyserver.sdss.org/dr7/en/tools/explore/obj.asp?id=588015508739063842     <click> "All Spectra"
DR8: Galaxy: http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663783667040348
« Last Edit: August 02, 2012, 09:28:05 pm by zutopian »

Budgieye

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #4 on: August 05, 2012, 05:43:16 am »




Thank you all. I understand now.
The two spectra must be taken from slightly different co-ordinates, even though they are apparently taken from the same place.

It's a galaxyIt's a star
spectral break        should be at 4434, but is hard to see with the star interference                break is  at 4000
hydrogen alpha 6560               wavelength reshifted to 7271 star absorbs hydrogen at 6560,
there is an unlabelled emission peak at 7271
oxygengalaxy emits at various wavengthsstar does not emit or absorb wavelengths of oxygen
but star absorbs wavelengths of Mg and Na
« Last Edit: August 05, 2012, 06:50:43 am by Budgieye »

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #5 on: September 28, 2012, 07:02:24 pm »
Quote
Then c_cld noticed that the co-ordinates of the objects are in the stripe82 area, where galaxies are imaged and stacked forty times to obtain higher resolution.

This field is in the footprint of Stripe82...
so You could get more hints in this stripe as in navigating we could have references to a star (in NED ) in front of 2 galaxies likely merging:

star 8658198546150588443 SDSS J005507.54-001316.6 r_mag  15.15

galaxy 8658188289762656285 SDSS J005507.46-001320.2 r_mag 17.45
with lots of others Id's in successive runs
galaxy 8658198112357843074 SDSS J005507.64-001320.4 r_mag 19.58


I found the coloured Stripe82 image, posted before in various threads.: Newbies, Oddballs and Analysis Tips.:
Here it is.:


http://hubble.galaxyzoo.org/examine/AHZ60004yq
8647474691414229199

Budgieye

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #6 on: September 29, 2012, 04:56:02 am »
It looks more like a star, doesn't it.

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #7 on: October 14, 2012, 05:44:39 pm »
Another case, but from the new GZ.:

GZ image                                                                                                                                            SDSS image, note: rotated

It is subject of a discussion in TALK. So this post is an invitation to talk about it in TALK!
http://talk.galaxyzoo.org/objects/AGZ0005z63/discussions/DGZ100683c
« Last Edit: June 27, 2014, 05:49:30 am by zutopian »

JeanTate

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #8 on: October 24, 2012, 04:25:03 pm »
Invitation accepted!  ;D

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #9 on: November 18, 2012, 02:44:53 pm »
« Last Edit: November 18, 2012, 02:48:03 pm by zutopian »

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #10 on: January 28, 2014, 08:11:01 pm »
Warning: this topic has not been posted in for at least 120 days.

Copy from another topic:

587733081347063839 z=0.0078 , SDSS J113323.47+550420.6  SpecObjID = 285923593806675968
in front of
QSO 587733081347063838 z=0.0085 , SDSS J113323.97+550415.8 SpecObjID = 285642003167838208



awesome..


One of the closest QSO in SDSS 1237658802571968533
background of 1237658802571968534


see also Mrk 1310 -- Seyfert 1 Galaxy (QSO spectrum z=0.01948) 1237650760243216505

A new paper on this precise object has been submitted to MNRAS. They suggest that it's in fact a luminous blue variable (LBV) star erupting over decades, followed by a supernova explosion in 2001. http://arxiv.org/pdf/1401.6798v1.pdf

Well, according to the new paper it is unclear, what it really is. There are going to be observations in the future.
« Last Edit: January 29, 2014, 09:35:31 am by zutopian »

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #11 on: April 22, 2014, 01:28:19 pm »
Another case, which was also presented in an "Object of the Day", but for a different reason.: http://www.galaxyzooforum.org/index.php?topic=278416.0

DR8 spectrum says Star, but DR7 spectrum says Galaxy!


DR8: http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663784194801793
DR7: http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=588015509266759785  <Click> All Spectra



« Last Edit: April 22, 2014, 01:35:43 pm by zutopian »

zutopian

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Re: Aug 2 2012 Star overlapping galaxy?
« Reply #12 on: June 27, 2014, 06:03:36 am »
Copy from another topic:


DR7  : http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=587739843769794627
DR10: http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237667910066569343

It looks like a Galaxy-QSO overlap. The Galaxy isn't a photometric object.
Different spectral classes and redshifts in DR7 vs DR10.: DR7 says Galaxy z=0.079, but according to DR10 it is a QSO, which has z=0.414.
I guess, that it is a double-redshift spectrum.

DR10: http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237667910066569343

It looks like a Galaxy-QSO overlap. The Galaxy isn't a photometric object.
Different spectral classes and redshifts in DR7 vs DR10.: DR7 says Galaxy z=0.079, but according to DR10 it is a QSO, which has z=0.414.
I guess, that it is a double-redshift spectrum.

That looks like an outright error to me. All of the identifiable features are consistent with a z = 0.079 galaxy. If there's a QSO spectrum superimposed it must be nearly featureless (BL Lac object perhaps?).

Taking another look at that spectrum, if there's an overlap it's with an early type foreground star. I see possible absorption features at Halpha, Hbeta, and Hdelta (at least).

I could quantify the likely foreground star contribution if I were at home.

Thanks for your comments! You are probably right, that it is just a star.
It can't be a BL Lac object, because there is no radio source. As far as I know, all BL Lac objects are radio sources.