robin_astro

1 hour ago, Lucas Barclay said:

I'm not too sure what you mean about the brightest of the two spectra nearest to the zero order though.. 

 

Have a look at the image in the Star Analyser manual (I wrote it 😀)

https://www.patonhawksley.com/resources

Cheers

Robin

12 minutes ago, robin_astro said:

 

If the calibration is correct, the lack of signal at the blue end is surprising. Normally H beta at 4861 A is near the peak of the curve.

 

This is more like what I would expect to see (in black)  Are you using a mono or colour camera ?

Here's my stab at a wavelength calibration and line identification

blue is your raw spectrum, red are the Hydrogen Balmer H alpha, H beta green are the telluric bands (O2 and H2O) The others are ripples in the camera response.

If the calibration is correct, the lack of signal at the blue end is surprising. Normally H beta at 4863 A is near the peak of the curve. Is your spectrum correctly exposed with no saturated pixels in the spectrum? (Sirius is a very bright target  and will need very short exposure.)

Check also that you have to correct spectrum, The brighter one of the two nearest the zero order

Sirius is also not an ideal target from the UK as it is low so the star image is likely to be large, reducing the sharpness of the spectrum and scintillation will distort the spectrum in short exposures. 

Cheers

Robin

You have a mix of Hydrogen lines from the star, Telluric bands from the atmosphere and ripples from the spectral response from the camera but it is difficult to wavelength calibrate and identify them with any certainty without the zero order star as a reference point. (Is this outside the camera field?) Can you describe your setup  (telescope, camera and the distance of the grating from the sensor) and also post an image of the raw spectrum please ?

Thanks

Robin 

3 hours ago, PeterW said:

How far away is it, what sort of brightening might a merged result in?

The 0.081 redshift puts the galaxy at about a billion light years away. As to what we might see, nobody really knows as we have not witnessed a supermassive black hole merger before.

Cheers

Robin

White Dwarfs sometimes also "eat" their planets.  The elements they were made up of can be found in the spectrum of the star and detected using amateur equipment.

https://britastro.org/observations/observation.php?id=20210831_232116_04a034fbfd0ae832

Cheers

Robin

1 hour ago, Peter Reader said:

how did you measure the transit? 

I got the idea to observe it after watching a video about this being a proposed target for JWST (link on my BAA page). The equipment I used is described on the BAA page. I just took a series of 1 minute exposures and measured the brightness in each one, relative to a non variable star in the same field (a standard technique for measuring variable stars) .The points in the graph are a 3 point moving average to smooth out the noise a bit.  The transit time was from the NASA exoplanet archive website, also linked from the BAA page. This is very different from the usual exoplanet transits where the brightness just drops by a percent or two.  Here it drops by half, but is it also much shorter compared with typical transits which can last for a couple of hours and a rather faint target (white dwarfs are not very luminous because they are so small) The diagram at the top of the graph shows the configuration inferred from the brightness drop but of course we cannot see that from here

42 minutes ago, markse68 said:

what does it mean “Hydrogen alpha emission at velocities up to +-12000km/s ” and what does it infer

Hi Mark,

Most if not all galaxies have a supermassive black hole at their centre and if there is material nearby (dust, gas and even the odd star) it forms a disc and the  material heats up as it spirals in producing emission at the Hydrogen alpha wavelength. (these galaxies are termed as having  "Active Galactic Nuclei"   Quasars and Seyfert Galaxies are examples of these. You can see this effect in this spectrum of M87, the black hole of which was famously imaged a couple of years back.

https://britastro.org/observations/observation.php?id=20190411_213200_531d1ec6d134b3dc

The width of the line (the doppler effect) is a measure of how fast the material near the black hole is orbiting as, if side on, we see the material  both coming towards and away from us. (Jets can also be produced coming out from the poles  which can have very high velocities)  The orbital velocity can be used to estimate the mass of the black hole.

The mass of the black hole is also closely tied to the total mass of the galaxy. In this case the two mass estimates do not agree. There is also some structure in the line ( a combination of different components moving at different velocities. You get a hint of this in my low resolution spectrum but the higher resolution spectra in the paper shows this in more detail)

The authors of the paper interpret this as an indication that there are two black holes in close orbit round each other (There are other examples of this around so we know these exist) 

What is interesting in this case is the orbital period has been dropping rapidly (from a year to month) as energy is lost from the system as gravitational waves, suggesting an imminent merger. Note though this is hot off the press and not yet a peer reviewed paper. A merger has never been observed but if it does happen though, watch this space ! As the authors put it

"Copious electromagnetic signals are expected, from radio to X-ray band, binary inspiral
stage to post merger, and from locations such as black hole corona, (possible) jet, accretion disk,
interstellar medium, etc. Neutrino production is also possibly detectable as a result of binary black
hole coalescence. We would like to call the attention of the astronomical community to perform
extensive multi-messenger, multi-band observation on this transient AGN source. Hopefully this
campaign will be celebrated by many unprecedented discoveries in the years to come."

According to a paper published last week the 17th magnitude Seyfert Galaxy  SDSSJ1430+2303/ (seen here in my spectrograph guider last night)

contains a pair of supermassive black holes who's orbit is rapidly decaying and which are likely to merge in the next 3 years or possibly even sooner in just 100-300 days time. My spectrum (blue, overlaid on the latest spectrum in the paper in grey and corrected for the redshift) shows Hydrogen alpha emission at velocities up to +-12000km/s 

More on my BAA page here

https://britastro.org/observations/observation.php?id=20220207_205606_9d5b2259183a3d41

Cheers

Robin

The paper linked from that page has the dimensions for 611 Mhz and construction details (appendix 4)

http://www.y1pwe.co.uk/RAProgs/MiniPulsarRx.pdf

1 hour ago, Jjmorris90 said:

 

How can I get rid of the dust?

The flat is there to deal with them but if you want to track them down you can work out which surface they are on from the size using eg a calculator like this

https://astronomy.tools/calculators/dust_reflection_calculator

Cheers

Robin

18 hours ago, SteveBz said:

Is this anywhere near the right calibration and response correction (not divided by 29 Ari)?

The wavelength calibration looks about right but something has gone wrong with the response correction. I recorded a Uranus spectrum with the the ALPY 600 a couple of weeks back. It is in the BAA database. This is what the response corrected spectrum looked like 

https://britastro.org/specdb/data_graph.php?obs_id=11449

and this is what it looks like after division by the Pickles G2v spectrum, compared with the measurement from a professional paper

On 18/01/2022 at 14:14, SteveBz said:

My first question is, I don't even know where the H-Beta line is, if there is one

There are no Balmer lines in the reflectance spectrum (Uranus is not hot enough to produce these) There will be Balmer lines from the reflected sunlight but they are not obvious in G2v spectra at low resolution. If you don't know the dispersion of your setup (eg from past measurements of hot stars), you will have to guess the dispersion, either matching the features in the spectrum of 29Ari to the G0v template or you could use the Telluric bands in 29Ari (They are probably too mixed with the broad methane bands to be used in the Uranus spectrum)

Cheers

Robin

On 18/01/2022 at 14:14, SteveBz said:

What to do next?  I'll work on the 29 Ari file in the meantime, but could I not use a standard library spectrum?

Nice Methane bands ! 

You can divide by a library G2v spectrum to produce the reflectance spectrum but would need to response correct the Uranus spectrum first. 

Cheers

Robin

4 hours ago, SteveBz said:

sadly I don't think I can get that low.

It culminates ~19:00UT at ~50 deg altitude from here in the north of England at the moment so should be a few degrees higher for you.

https://airmass.org/chart/obsid:wright/date:2022-01-11/sso:p%3AUranus

The problem could be the moon though at the moment which is very close tonight, only 4 deg away, moving away but getting fuller over the next few nights.

Cheers

Robin

WD 1856b is a Jupiter sized exoplanet in a close orbit around a much smaller white dwarf star, transiting every 1.4 days. (An interesting conundrum is how it managed to avoid being engulfed during  the parent star's red giant phase).  Actually, partially eclipses is perhaps a more apt description as it is a 56% deep grazing event and so is on  the observing list for the JWST to measure the spectrum of the starlight passing through the planet's atmosphere.  Although much deeper than typical exoplanet transits, measuring it did  present some interesting different challenges  due to its faintness (mag 17) and brevity (8 min).  Here is an image of the star in question and my transit measurement. For anyone interested in following up the discovery of this unusual exoplanet and the planned JWST measurements. I have put some more information up on my BAA page

https://britastro.org/observations/observation.php?id=20220106_172719_c34e10f42c4fc746

Cheers

Robin

11 hours ago, SteveBz said:

Does anyone have some nice ideas for spectroscopy in the current season

Have you bagged a Uranus spectrum yet?  Well placed in the early evening, about  the same brightness as 63 And. It should appear pretty much star like in your short focal length Newt so give a sharp spectrum showing nice Methane bands.  G0v star 29 Ari is conveniently nearby too at the moment and similar enough to the G2v solar spectrum so if you take that as well and divide one by the other (no need to correct for response) you should get the reflectance spectrum of Uranus direct without the contamination from the solar spectrum features.

Cheers

Robin

You also need to watch what gain you run with some of these CMOS cameras if you are stacking a lot of short subs. You can generally get away with more shorter subs with CMOS compared with CCD as the read noise is lower but if you look at the specs for this camera the read noise suddenly shoots up to a poor figure at lower gain settings

https://www.firstlightoptics.com/user/products/large/zwo_asi294mc_read_noise.jpg

Robin

A quick search suggests naturally produced atmospheric I2  may impact  ozone levels though eg

https://www.pnas.org/content/114/38/10053

Robin

16 hours ago, saac said:

It must be standard procedure to subtract an atmospheric background reading when processing any stellar spectrograph surely.

Correct. Spectra of so called telluric standard stars are recorded to correct spectra of the target for atmospheric absorption. (Absorption lines from the interstellar medium are also imprinted on spectra) You probably would not want to be observing directly through a cloud of Iodine though. Molecular Iodine has a lot of lines in the visible spectrum, so much so that Iodine cells are used to calibrate high resolution spectrographs. You might have difficulty "seeing the wood for the trees" !

http://spiff.rit.edu/classes/resceu/lectures/radial_vel/iodine_spec.png

Cheers

Robin

The reference given at the foot of the article appears to an unrelated paper. Here is the original paper 

https://www.nature.com/articles/s41467-021-26920-6

19 hours ago, sirenity said:

naked eye quite red and twinkling like a mad thing

Arcturus perhaps ?  Bright, orange  almost directly West (rather than SW for Ophiuchus) after dark currently. Low in the sky so twinkling due to the thickness of atmosphere we are looking through

Cheers

Robin

This spectrum (taken using the C11 and  ALPY600 spectrograph) is of magnitude 15 star IRAS 00500+6713 in Cassiopeia. It is believed to be the result of a merger between two white dwarfs, kept from complete collapse by a powerful magnetic field and may be the stellar remnant of the supernova seen by Chinese astronomers in 1181.  It is a star of extremes with a temperature of 200,000 K and 16,000 km/s winds. More about this star and references on my BAA page here

https://britastro.org/observations/observation.php?id=20210930_153458_144e8bbb0f30f495

Cheers

Robin

Nice capture but note that AT objects are not necessarily supernovae (in fact most probably are not). To be confirmed as a supernova it needs to have spectrum taken. In this case it turns out to be a Cataclysmic Variable (a dwarf nova) in outburst in our own galaxy. You can see the classification on the Transient Name Server (where AT numbers are generated and where, if they do turn out to be supernovae, the name is changed to SN yyyyabc , the point at which it officially becomes a supernova

https://www.wis-tns.org/object/2021yaf

Cheers

Robin

13 hours ago, Merlin66 said:

2. The movements in the solar surface are clearly seen as "wiggles" in all the absorption lines.

The same wiggles are also seen in the Telluric H2O lines from our own atmosphere so cannot be solar in origin.  See the comparison with a high resolution  annotated professional spectrum

Cheers

Robin