Can very small telescope-spectrographs do useful work for AAVSO?

Affiliation

American Association of Variable Star Observers (AAVSO)

Wed, 05/08/2013 - 09:34

I'm new to astronomy but experienced with scientific instruments and keen to learn how to produce and interpret astronomical spectra. Eventually I'd hope to contribute to the AAVSO endeavour. I live in Sydney and am considering taking measurements in the local park and camping on sites near railway stations out of town. My proposed viewing station is an 80mm triplet refractor (ED80T) on an HEQ5 or NEQ6 tripod mount with an Alpy600 spectrograph and reflective slit for a guide. As I understand this would be capable of studying the brighter novae, supernovae and cataclysmic variables. Would a small low resolution system like this be capable of doing useful work for AAVSO activities?

Thanks Peter

Matthew Templeton

Wed, 05/08/2013 - 14:19

Small telescopes

Hello Peter,

It's hard to say how many projects your telescope could be used for, but a small system would likely have best use for bright objects. A detailed answer would require that we know the throughput of your system, and the resolution of the spectrograph. Based on what you wrote, your system would likely be useful for confirmation of bright novae, since even a low-resolution spectrograph can detect the presence the broad hydrogen emission lines of novae. If the telescope is capable of longer, guided exposures, and the resolution of the spectrograph is reasonably low, that would open up more and more targets for you to observe.

I'm reading the page Christian Buil has on the Alpy600 now -- he's able to reach down to 12th magnitude with an hour of exposure time on an 80mm scope, and that makes a system like this quite useful for nova work.

Matthew

TCB168

Affiliation

Variable Stars South (VSS)

Wed, 05/08/2013 - 23:29

Small spectrographs

[quote=PeterOsman]

Thanks Peter

[/quote]

Dear Peter

I have been taking spectra with a LISA for some time now but using a bigger scope than you have. I was using a 200mm scope but now use a C11. The issue is the light collection of the small scope.

I have confirmed nova and 1 supernova which was published in an astronomers telegram so it is possible to do useful work.

The small scope will limit your practical magnitude limit to something like mag 11. I can get down to about mag 14 with the C11 at least for identification purposed with 90mins of exposure. There are not that many nova or SN that are bright but when they do occur you can confirm them.

The other thing that you can do as well is to contribute to the BESS database of BE stars. I have been slowly surveying the dimmer southern stars from about Dec -45 and furrther south. This is just survey work really at the low resolution of a LISA or Alpy but will show hydrogen emission changes from year to year. No one else is doing it so you could help find changes to these interesting stars.

cheers

Terry

PeterOsman

Affiliation

American Association of Variable Star Observers (AAVSO)

Sun, 05/12/2013 - 13:40

Hi Matthew and

Hi Matthew and Terry,

Thank you both for your advice and encouragement. I held off replying until I had absorbed your advice and had attended our club (ASNSW) annual Star Party. Over the last seven months I’ve been studying, planning and putting an equipment list together and came up with the following, still recognising that it may have a fair number of misconceptions

I’ll mostly observe two or three times a week from a park nearby that is completely screened from the Sydney city lights by trees but of course still with sky glow to contend with.

The Alpy spectrograph is a Littrow design with a 23micron fixed slit, 600 lines/mm reflective grating (grism), a resolving power of R=600 @ 650nm and f-number f/5, spectral dispersion 480 A/mm and a spectral range from 3700 A to 7400 A

The telescope options are either a 200mm f/5 Newtonian with its advantages of aperture size and no chromatic aberration; I’m told that apertures greater then 200mm provide no advantage in the city. Alternatively a more transportable and robust refractor with optics that are more stable over time. The latter would be an 80mm to 100mm f/5.5 APO refractor depending on budget and whether I need to buy a doublet APO or triplet to achieve acceptably accurate spectra. I’m asking for advice on the doublet triplet question at present.

The sensor would be an Atik 314L+ CCD camera based on a Sony ICX-285AL chip. It is a Peltier cooled temperature controlled array of 1392x1040 pixels, size 6.45x6.45u, readout noise 4e, full well capacity 17,500 e, 16 bit ADC, and linearity < 0.4% within the anti-blooming gate range.

The tracking unit would use the Alpy reflective slit guiding module with an Orion Star Shoot Autoguider and the tripod/mount is an HEQ6

Measurement time is expected to be four hours exposure each night for one to three nights a week about eight months a year for about six years depending on weather. We’re just entering an el Nino phase and in Sydney; during La Nina it’s much harder to find decent nights for astronomy.

Thanks Peter

MGQ

Affiliation

None

Sun, 05/12/2013 - 14:13

ALPY 600

Hi Peter,

While my APLY 600 has not yet arrived I feel I must correct a couple of things you mentioned. The ALPY 600 is not a Littrow design and uses a transmission grating not a reflective grating. The basic unit without the guiding unit will most likely be very diffeicult to use except in slitless mode. I am trying to develop an inexpensive fiber optic interface for the ALPY which would solve the finding and tracking of a star problem with the basic unit. The alternative is to purchase the guiding unit which then more than doubles the cost.

BTW, I use a Lhires III which is a Littrow design and uses a 2400 l/mm reflective grating.

I will be discussing the ALPY 600 in detail along with much other spectroscopy information in my new book to be published by Springer the summer or early fall.

Jeff