David's Astronomy Pages
Spectroscopy (1)

Computer Control
Computer
Control
  Home
Home
Page
  Image Gallery
Image
Gallery
 

Bullet Introduction New page to record Spectroscopic observations

 

Spectroscopy Links:
- Astronomical Ring for Access to Spectroscopy (ARAS) | Links

- Robin Leadbeater
- Dale Mais  

- Star Analyser - Yahoo User Group

- VSpec - WebSite | Tutorials 

- Processing LHIRES spectra (En)

- Spectroscopy Section of "Amateur Astronomy Association - Germany" (VdS) 

- The Spectrography Bookmark

Bullet Star Analyser 100
Bullet Spectral Lines - examples
Bullet Spectral Lines - examples
Bullet Dispersion, Plate Factor & Distance from grating to CCD
Bullet Theoretical Resolution
Bullet Practical Resolution
Bullet Software Tools
Bullet Workflow
Bullet Star Spectra - Results
Bullet Planetary Nebula Spectra - Results
Bullet Star Spectra - Synthesized Colour
Bullet Spectral response of combined SA100 / ST-7e CCD system
Bullet Spectral Response of UBVRI Photometric filters (Custom Scientific 1.25")
Bullet Spectral Image Exposure Times
 
 
 

Introduction

Astronomical spectroscopy is the study is the spectrum of electromagnetic radiation, including visible , UV and infrared light which radiates from stars and other celestial objects. Spectroscopy can be used to derive many properties of distant stars and galaxies, such as their chemical composition and also their motion, via the Doppler shift.  

A bright hot source (like a star) emits a continuum of radiation which a spectroscope (diffraction grating or prism) can break down into a spectrum. When a light source passes through a tenuous gas consisting of elements, ions (plasma) or molecules, certain discrete wavelengths are removed from the continuum giving rise to dark absorption lines which fingerprint an element (and/or its ionic state) or molecule. The light from a star passing through the outer atmosphere layers of the star give rise to this effect. When a tenuous gas consisting of elements, ions and/or molecules is excited in some manner (collisional, electrically, heat or by light itself), the gas emits certain discrete wavelengths. These are seen as bright lines. Certain gaseous nebula or planetary nebula are good examples of this.

I began experimenting with spectroscopy in April 2008 soon after listening to an inspiring talk by Robin Leadbeater at a joint meeting of BAA VSS & AAVSO in Cambridge, 10-13th April, 2008. The talk was entitled 'Chasing Rainbows - The European amateur spectroscopy scene'. Covering both high-resolution and low-resolution spectroscopy, it included a description of what can be achieved with relatively simple slitless equipment incorporating Paton Hawksley's Star Analyser 100.

The Star Analyser 100 is a 100 lines/mm transmission grating set in a filter cell. It appeared that it could be relatively easily incorporated into my existing imaging set up, though I would have to free up one of the slots in my filter wheel used by one of my existing BRVI filters, and allow be to explore a whole new area of astronomical study.  Deciding that I could forego the use of my I-Band filter I quickly proceeded with the purchase of a Star Analyser 100 direct from the manufacturer and captured my first star spectra on 17th April 2008, just 6 days after hearing Robin's talk [ first spectra images, 2008-04-17].  

I typically work with Spectra dispersion of 33.5 A/pixel (3733 A/mm), and have a calculated practical resolution of between 70 and 110 A.

Back to Top


Star Analyser 100

I began using a Star Analyser 100 in April 2008.

Image  Star Analyser 100

- high quality transmission diffraction grating mounted in a standard 1.25 inch filter cell
- high efficiency 100 lines/mm blazed design
- grating surface protected by anti-reflection coated glass 
- screws into an eyepiece or filter wheel like a normal filter 
- star and spectrum can be recorded in the same image, which aids identification and calibration
- provides low resolution slitless spectroscopy, but for relatively low cost (78 + p&p, Apr 2008)

Manufactured by :
Paton Hawksley Education Ltd 
Product Page :  http://www.patonhawksley.co.uk/staranalyser.html 

Back to Top


Star Spectra - examples

Vega,  blue-white star
 A0 spectra
Image
Image
Image
Image
CCD Spectra Image
3 x 0.5s, 1x1 binning, Dispersion 33.6 A/px
2008-05-07 23:01hUT (#286046-48)
(colour spectra is synthesized from black-white spectra)
     
R Aur, red star with infrared excess 
M6-M8 spectra
Image
Image
Image
Image
CCD Spectra Image
5 x 60s, 1x1 binning, Dispersion 33.6 A/px
2008-04-24 22:05hUT (#284033-35)
(colour spectra is synthesized from black-white spectra)
     
   

Back to Top


Spectral Lines - examples

Spectral Absorption Lines in Vega (Lyra)
O2 and H2O lines are due to absorption in the Earth's atmosphere)
H-epsilon and H-zeta lines are not visible due to decreasing 
sensitivity of CCD chip in violet region and overall low resolution.
Image
Image
CCD Spectra Image (200%)
3 x 0.5s, 1x1 binning,  Original Dispersion 33.6 A/px
2008-05-07 23:01hUT (#286046-48)
     
Spectral Absorption Lines in Deneb (Cygnus)
O2 and H2O lines are due to absorption in the Earth's atmosphere)
Image
Image
CCD Spectra Image (200%)
5 x 5s, 1x1 binning,  Original Dispersion 33.6 A/px
2008-05-03 01:24hUT (#285161-65)
    
Spectral Emission Lines in P Cyg (Cygnus)
Image
Image
CCD Spectra Image (200%)
3 x 10s, 1x1 binning,  Original Dispersion 33.6 A/px
2008-05-08 01:16hUT (#286177-79)
    
Table of Balmer Lines

Transition of n

\infty→2 9→2 8→2 7→2 6→2 5→2 4→2 3→2

Name

H-η H-ζ H-ε H-δ H-γ H-β H-α
  eta zeta epsilon delta gamma beta  alpha
Wavelength (A) 3646 3835 3889 3970 4102 4341 4861 6563
   

Back to Top


Dispersion, Plate Factor & Distance from grating to CCD

Dispersion
Dispersion is a measure of the change in wavelength of the diffracted length along the surface of the CCD.  It is usually measured in angstrom per pixel.  It can be determined by observing a star spectrum that has known features.  For example in the following spectra of Vega, the H-alpha (6563 A) and H beta (4861 A) lines lie at original pixel values of 440 and 389 respectively.  

Dispersion  (image) = (6563 - 4861) / (440 - 389)    = 33.4 A per pixel

Based on several measurements of several pairs of lines in a number of spectral images an average dispersion value of 33.6 A / pixel was obtained.

Dispersion (average) = 33.6 A per pixel

Spectral Lines in Vega (Lyra)
Image
Image
CCD Spectra Image (200%)
3 x 0.5s, 1x1 binning,  Original Dispersion 33.6 A/px
2008-05-07 23:01hUT (#286046-48)

Plate Factor (P)
Plate Factor, P,  is similarly a measure of the change in wavelength of the diffracted length along the surface of the CCD, but is usually measured in angstrom per mm.   It can be determined from the above Dispersion value knowing the physical pixel size.

For my ST-7e camera (KAF-401-E),  the size of the pixels is 9 x 9 mm (0.009 x 0.009 mm)

Average Plate Factor, P = 33.6 / 0.009  = 3733 A / mm

Distance from grating to CCD (d)
It is not possible to accurately measure the distance between the grating and the CCD, however it can be calculated using the grating equation, which for slitless spectrography and first order spectrum reduces to  sin b = m l where b is the deviation angle, m is the number of grooves per millimeter and l is wavelength.

Image

For Star Analyser 100 (100 groves/mm) I find that the H-alpha line (6563 A) typically lies at a distance of 196 pixels from the zero order star image. Thus, 

    x = 1.764mm  (from 196 * 0.009) 
    l =  0.0006563 mm 

    sin b = 100 g/mm * 0.0006563 mm 
    b = 3.7630 deg
    d = x / tan = 1.764 / tan (3.7630)  

    d = 26.82 mm

Back to Top


Dispersion, Plate Factor & Distance from grating to CCD - Star Analyser 200 / ST-10ME

Dispersion
Dispersion is a measure of the change in wavelength of the diffracted length along the surface of the CCD.  It is usually measured in angstrom per pixel.  It can be determined by observing a star spectrum that has known features.  One method uses two emission/absorption lines, whilst another method uses the zero order star position and one emission/absorption line.  

For example in the following spectra of Vega (produced from 2x2 binned image), disperison is found to lie in the range 25.22 and 25.87

Spectral Lines in Vega (Lyra)
Image
Image
CCD Spectra Image (Star Analyser 200)
(Image rotated & cropped)
1 x 0.2s exposure, 2x2 binning, S Filter
2015-04-21 03:43 h UT (#585269-73)
12" LX200R  (at f/10.4) + ST-10XME

1) Taking the H-alpha (6563 A) and H gamma (4341 A) lines lying at original pixel position of 869.0 and 780.9 respectively gives a dispersion of 25.22 A per pixel  [calculated from  (6563 - 4341) / (869.0 - 780.9) ]

2a) Taking the H-alpha (6563 A) line and zero order star position (0 A) lying at original pixel positions of 869.0 and 613.1 respectively gives a dispersion of 25.65 A per pixel [calculated from  (6563 - 0) / (869.0 - 613.1)  ]

2b) Taking the H gamma (4341 A) line and zero order star position (0 A) lying at original pixel positions of 780.9 and 613.1 respectively gives a dispersion of 25.87 A per pixel [calculated from  (4341- 0) / (780.9 - 613.1)  ]

Dispersion seems to be slightly non-linear. 

Based on Zero Order star and several aborptions lines a non-linear calibration table was defined and used to calibrate the Vega image. Average dispersion for non-linear calibration is 25.5 A/px (2x2 binning)

 

Image

 

Image

 

Plate Factor (P)
Plate Factor, P,  is similarly a measure of the change in wavelength of the diffracted length along the surface of the CCD, but is usually measured in angstrom per mm.   It can be determined from the above Dispersion value knowing the physical pixel size.

For my ST-10E  camera (KAF-401-E),  the size of the pixels at 1x1 binning is 6.8 x 6.8 mm (0.0068 x 0.0068 mm)

At 2x2 binning (currently used for spectroscopy work)

Average Plate Factor, P = 25.5 / (0.0068*2)   = 1875 A / mm

At 1x1 binning the plate factor is still 1875 A / mm   (from P = 12.75 / 0.0068)

Distance from grating to CCD (d)
It is not possible to accurately measure the distance between the grating and the CCD, however it can be calculated using the grating equation, which for slitless spectrography and first order spectrum reduces to  sin b = m l where b is the deviation angle, m is the number of grooves per millimeter and l is wavelength.

Image

For Star Analyser 200 (100 grooves/mm) I find that the H-alpha line (6563 A) typically lies at a distance of 256 pixels from the zero order star image (at 2x2 binning). Thus, 

    x = 3.4816mm  (from 256 * 0.0068 x 2) 
    l =  0.0006563 mm 

    sin b = 200 g/mm * 0.0006563 mm 
    b = 7.519 deg
    d = x / tan = 3.4816 / tan (7.519)  

    d = 26.38 mm
    (cf. 26.82mm for Star Analyser 100 with 8" LX200 & ST-7E)

Calculated dispersion of my 12" LX200 system (values calculated using calculator at http://www.patonhawksley.co.uk/calculator/ )

Grating
Distance
Dispersion
 
(A/px)
mm SA100,
1x1 binning
SA100,
2x2 binning
SA200,
1x1 binning
SA200,
2x2 binning
20 34.0 68.0 17.0 34.0
25 27.2 54.4 13.6 27.2
26.4 * 25.8 51.5 12.9 25.8
30 22.7 45.3 11.3 22.7
35 19.4 38.9 9.7 19.4
40 17.0 34.0 8.5 17.0

26.4 mm is largest practical grating distance achieved with ST-10 + CFW10 filter wheel


Theoretical Resolution

A spectrograph's spectral resolution, R, determines the ability of the instrument to distinguish spectral features separated by Dl . The spectral resolution is a dimensionless quantity that is a measure of spectral purity (Dl).

For the case of my Meade LX200 8" (operating at f7.4), Star Analyser 100 and SBIG ST-7e CCD the following quantities are known: 

d = distance from grating to CCD = 26.8 mm 
k = order of spectrum = 1 
m = number of grooves per mm = 100 g/mm 
D = telescope diameter = 203.2 mm 
F = telescope focal length = 1498 mm 
N = F/D = focal ratio = 7.4

Since the entire surface of the grating is not illuminated the theoretical resolution becomes 

R = mLk, 

where L = gratings lit width (portion of grating illuminated by the star’s image from the telescope), or Dd/F

Dl
l/ R

[ Reference: "Resolution Calculation for a Slitless Spectrograph" By Dr. Doug West. 
http://users.erols.com/njastro/faas/articles/west01.htm ]


For my 8" LX200/ST-7E/SA100 setup  L = Dd / F = (203.2mm) x (26.8mm)/1498mm = 3.64 mm

The theoretical resolution, R  is thus given by  

R = (100 g/mm) x (3.64 mm) x (1) = 364

Spectrographs are considered low resolution when they have R<1000. This with an R value of just 364, my system is confirmed as being low resolution. 

My theoretical resolution, at H-alpha line (6563 A) is thus given by 

Dll/ R = 6563 / 364 = 18 A

The actual resolution of the spectrograph (70 - 110 A) turns out to be much lower. 

With Dispersion of 33.6 A/pixel,  it is immediately apparent that the minimal resolution of the system has to be at least 67 A (from 2 x 33.6). Other factors limiting resolution are Chromatic Coma, Field Curvature and FWHM of the star image. 

 

For my 12" LX200 setup  L = Dd / F = (305mm) x (26.38mm)/3048mm = 2.64 mm

The theoretical resolution with SA100, R  is given by  

R = (100 g/mm) x (2.64 mm) x (1) = 264

The theoretical resolution with SA200, R  is given by  

R = (200 g/mm) x (2.64 mm) x (1) = 528

 

Spectrographs are considered low resolution when they have R<1000. With an R value of 528, my system with SA200 is confirmed as still being low resolution, albeit with twice the resolution of the SA100 grating.  

My theoretical resolutions, at H-alpha line (6563 A) is thus given by 

Dll/ R = 6563 / 264 = 25A  (for SA100)

Dll/ R = 6563 / 528 = 12.5 A  (for SA100)

The actual resolution of the spectrograph (70 - 110 A) turns out to be much lower. 

With Dispersion of 25.5 A/pixel (SA200 at 2x2 binning),  it is immediately apparent that the minimal resolution of the system has to be at least 51A (from 2 x 25.5). Other factors limiting resolution are Chromatic Coma, Field Curvature and FWHM of the star image. 

 

Back to Top


Practical Resolution

The actual resolution of a spectrograph turns out to be much lower than the theoretical resolution. Factors limiting resolution are Chromatic Coma, Field Curvature, FWHM of star image and Sampling Theorem (pixel size).  

For my setup FWHM and Pixel Size are the main limiting factors, which limit spectral resolution to a value of 70 A at best with a more typical value of around 110 A.

These values are derived from calculations shown below which are themselves based on equations given in 
"Resolution Calculation for a Slitless Spectrograph" by Dr. Doug West.  [http://users.erols.com/njastro/faas/articles/west01.htm].

1. Chromatic Coma
The practical formula for the effect of chromatic coma on spectural purity is 

Dl =  (3l)/ (16 N2),  where N is focal ratio

For my 8" LX200 / ST7 system operating at f/7.4 the effect of chromatic coma on spectural purity at the H-alpha line (6563 A) is 

Dl =  (3 x 6563 )/ (16 x (7.4)2 )  = 22.5 A

 

For my 12" LX200 / ST-10 system operating at f/10.4 the effect of chromatic coma on spectural purity at the H-alpha line (6563 A) is 

Dl =  (3 x 6563 )/ (16 x (10.4)2 )  = 11.4 A

 

 

2. Field Curvature
This is the effect on spectural purity cause by the aberration due to field curvature, which results from the cylindrical rather than planar nature of the spectrum’s focus. The defocusing effect produced by field curvature significantly reduces the spectrograph’s resolution.

Resolving power is given by

DlDxP = PL ((1/cosb)-1)  

For my 8" LX200 / ST-7 system operating at f/7.4  at l= 6563 A,  b =  3.7630 deg, L = 3.64 mm and  P = 3733 A / mm, the spectral purity

Dl =  PL ((1/cosb)-1)  = (3733 A/mm) x (3.64mm) x ((1/cos3.763) -1) = 29.4 A

 

For my 12" LX200 / ST-10 system operating at f/10.4  at l= 6563 A,  b =7.519  deg, L = 2.64 mm and  P = 1875A / mm, the spectral purity

Dl =  PL ((1/cosb)-1)  = (1875A/mm) x (2.64mm) x ((1/cos7.519) -1) = 42.9 A

 

3. FWHM of Star Image

In a slitless spectrograph the full width at half maximum (FWHM) of the star’s image becomes the effective entrance slit width for the instrument. The larger the slit width the lower the resolution and spectral resolving power.

The spectral resolving power is given by:

Dl =  (FWHM) x (e) x (P) / cos b

For my 8" LX200 + ST-7 + f/7.4 setup at l= 6563 A,  b =  3.7630 deg, P = 3733 A / mm and typical FWHM of 4 arc sec, equivalent to 3.25 pixels at 1x1 binning, Dl becomes

Dl =  (3.25 px) x (0.009 mm)  x (3733) / cos 3.763  = 109 A

The spectral resolving power for other FWHM values is given in the table below.
In practice a FWHM of 2.0 and resolving power of 55 A is the best that can be achieved at my site for short exposures (1-2 secs duration).

FWHM
(arc secs)
Dl

2.0

55 A

2.5

68 A

3.0

82 A

3.5

96 A

4.0

109 A

4.5

123 A
5.0 137 A
5.5 151 A

For my 12" LX200 + ST-10 + f/10.4 + SA200 setup at l= 6563 A,  b =7.519  deg, P = 1875 A / mm, plate scale = 0.884 arc sec/pixel at 2x2 binning and typical FWHM of 4 arc sec, equivalent to 4.5 pixels at 2x2 binning, Dl becomes

Dl =  (4.5px) x (0.0136 mm)  x (1875) / cos 7.519  = 116 A

In practice a FWHM of 2.0 and resolving power of around 58 A is the best that can be achieved at my site for short exposures (1-2 secs duration).

FWHM
(arc secs)
Dl

2.0

58 A

2.5

73 A

3.0

87 A

3.5

102 A

4.0

116 A

4.5

131 A
5.0 145 A
5.5 160 A

 

4. Sampling Theorem

When a continuous signal is sampled, such as a spectra, this process places a lower limit on the spectra purity. Simply put, the sampling theorem states that the highest frequency present in a sampled waveform is one half the sampling rate. The implication of this theorem on the spectrograph is that the smallest value of spectral purity possible is twice the wavelength interval covered by a pixel, or

Dl =  2 e

For my 8" LX200 imaging setup with Star Analyser 100 and 1x1 binning (9 mm, 0.009 mm pixels) and P  = 3733 A / mm, the smallest value of spectral purity is 

Dl =  2 e P = (2) x (0.009 mm) x (3733  A/mm) = 67.2 A

For my 12" LX200 imaging setup with Star Analyser 100 and 2x2 binning (13.6 mm, 0.0136 mm pixels) and P  = 3750 A / mm, the smallest value of spectral purity is 

Dl =  2 e P = (2) x (0.0136 mm) x (3750 A/mm) = 102 A    (51 A for 1x1 binning)

 

For my 12" LX200 imaging setup with Star Analyser 200 and 2x2 binning (13.6 mm, 0.0136 mm pixels) and P  = 1875 A / mm, the smallest value of spectral purity is 

Dl =  2 e P = (2) x (0.0136 mm) x (1875  A/mm) = 51 A

For my 12" LX200 imaging setup with Star Analyser 200 and 1x1 binning (6.8 mm, 0.0068 mm pixels) and P  = 1875 A / mm, the smallest value of spectral purity is 

Dl =  2 e P = (2) x (0.0068 mm) x (1875  A/mm) = 25.5 A

Whilst 1x1 binning theoretically has higher resolution (25.5 A vs 51 A),  seeing limits the resolution to around 58 A at best at my site (for 2 arc sec FWHM)

Back to Top


Software Tools

Image Acquisition

Spectra Manipulation / Analysis

Back to Top


Workflow

Workflows are still being developed. The following section describes the workflow that has evolved after around 5 or 6 imaging sessions.

General Setup (one time operation per imaging setup)

SA100 image, showing zero order star image with principal 
first order image well position within imaging area

Star Offset: from centre:   N  2 mins / W  3 mins 

Image

 

Target Selection (for each star/other object)

Specification of Spectra Images for the star Spica (Alpha Virginis) 

Image

 

Imaging Run

Imaging Run - Example 

Image

  

Exposure Check 

Image

Image Reduction (after each observing session)

Spectral Image Manipulation/Analysis (for each star object) - example P Cyg

Image

Image

    Image

Image

(need colour synthetic of P Cyg here)

Alternative method: Use VSpec utility - Tools/Synthesis - to produce a monochromatic Spectra Tab, followed by use of the "Colorer" (Colour) option.
This produces a spectra tab that can be captured, resized & cropped. A particularly nice feature of the VSpec utility is that moving vertical line cursor along the Spectra profile, moves a corresponding vertical line cursor on the Spectra Tab.

Image

Image

Image

Image

Image

Wavelength Calibration

 

Radiometric Calibration

Back to Top


Star Spectra - Results

A catalogue of star spectra taken using LX200, Star Analyser 100 and SBIG ST-7e :

Star Name
(designation)
Spectra Type
(catalog)

Spectra Lines  ( Star Analyser 100)
 

Image Date/No. & Notes
 
SAO 49491
Cyg
WR
Wolf Rayet
Image 2008-04-18 (#283378-82)
SAO 69402
HD 190918, Cyg
Wolf Rayet Image 2008-04-25 (#284317-19)
P Cyg B1Iapeq Image 2008-05-08 (#286177-79)
  
10 Lac 09 Image 2008-05-08  (#286167-69)
Zeta (13) Oph
HIP 81377
09 Image 2008-05-08  (#286142-44)
Spica
Alpha Vir
B1 Image 2008-05-02 (#285031-35)
Regulus
Alpha Leo
B7 Image 2008-04-17 (#283073-75)
Albireo(B)
Beta2 Cyg
B8 Image 2008-04-18 (#283311-17)
4 Her B9 Image 2008-04-25 (#284120-22)
108 Vir B9 Image 2008-04-25 (#284301-05)
Vega
Alpha Lyr

A0
Image 2008-04-18 (#283304-10)
Vega
Alpha Lyr
A0 Image 2008-04-25 (#284127-31)
Deneb
Alpha Cyg
A2 Image 2008-05-03 (#285161-65)
Castor
Alpha Gem
A2 Image 2008-04-17 (#283070-72)
Procyon
Alpha CMi
F5 Image 2008-04-17 (#283058-60)
Izar
Epsilon Boo
(A0) Image 2008-05-02 (285050-54)
Sadr
Gamma Cyg
F8 Image 2008-05-03 (#285149-53)
Rastaban
Beta Dra
G2 Image 2008-05-18  (#288137-39)
Groombridge 1830,  UMa G8 Image 2008-04-25 (#284161-63)
Pollux
Beta Gem
K0 Image 2008-04-17 (#283064-66)
Arcturus
Alpha Boo
K2 Image 2008-04-24 (#284006-9)
Albireo(A)
Beta1 Cyg
K3  Image 2008-04-18 (#283311-17)
61 Cyg K5 Image 2008-04-18 (#283268-70)
Groombridge 34 
And
 M1 Image 2008-05-08 (#286242-44)
Yed Prior
Delta Oph
 M1 Image 2008-05-08 (#286147-49)
Betelgeuse
Alpha Ori
M2 Image 2008-04-20 (#283506-11)
Lalande 21185
HIP 54035, UMa
M2  Image 2008-04-25 (#284178-80)
V0973 Cyg
HIP 97151
 M3 Image 2008-05-08 (#286212-14)
R Boo M3-M8  Image 2008-04-25 (#284310-12)
R Vir  M3-M8 Image 2008-04-24 (#284089-91)
XY Lyr   M4 Image 2008-05-08  (#286153-55)
RR CrB M5  Image 2008-04-24 (#284052-56)
 R Lyr   M5 Image 2008-05-08  (#286189-91)
R Aur M6-M9 Image 2008-04-24 (#284033-35)
R Leo  M6-M9 Image 2008-04-24 (#284043-45)
U Her M6-M9 Image 2008-04-17 (#283143-45)
  
Y CVn C5  Image 2008-04-24 (#284106-10)
V0460 Cyg C6,4(N1)  Image 2008-05-08 (#286217-19)
Cyg U C7-C9 Image 2008-04-25 (#284286-88)
  

Back to Top


Planetary Nebula Spectra - Results

Star Name
(designation)
Spectra Type
(catalog)

Spectra  (Star Analyser 100)
  

Image details
(1x1 binning)
NGC 2022 Pl. Neb Image 3 x 120s 
2008-12-18 (#335276-78)
NGC 2392 Pl. Neb Image 3 x 45s 
2009-01-09 (#342143-45)
NGC 6572 Pl. Neb Image 3 x 45s 
2008-04-18  (#283245-47)
NGC 6210 Pl. Neb Image 3x60s
2008-05-18  (#286101-03)
NGC 6826 Pl. Neb Image 3 x 60s 
2008-04-18  (#283337-39)
NGC 7026 Pl. Neb Image 3 x 45s 
2008-05-07  (#286182-84)
NGC 7662 Pl. Neb Image 3 x 60s 
2008-04-18  (#283346-48)
M57 Pl. Neb Image 3 x 30s 
2008-04-18  (#283301-03)
   
  
NGC 6572 Pl. Neb Image 2008-04-18 (#283245-47)
NGC 6826 Pl. Neb Image 2008-04-18 (#283337-39)

Back to Top


Star Spectra - Synthesized Colour 

 

Original monochromatic Spectral Displays with synthesized Coloured Spectral Equivalents
The Synthetic Coloured Spectrums where generated by producing a coloured FITS image
using the LRGB technique, in which the original monochromatic image was used for Luminance (L) frame
whilst RGB frames where calculated from the calibrated wavelength profile.
This calculation was performed via a software routine based on the Delphi Pascal 'WaveLengthToRGB' function listed on 
efg's Spectra Lab page at http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm 
The 'original WaveLengthToRGB' function is based on Dan Bruton's work ( www.physics.sfasu.edu/astro/color.html  )

Visible Light
Range
Image
     
     
Star Name
(designation)
Spectra Type
(catalog)

Spectra Lines  ( Star Analyser 100)
Monochromatic &  Approx Colour
 

Image Date/No. & Notes
 
Spica
Alpha Vir
B1 Image 2008-05-02 (#285031-35)
Spica
Alpha Vir
Image
     
Izar
Epsilon Boo
A0
??
Image 2008-05-02 (285050-54)
Izar
Epsilon Boo
Image
     
R Aur M6-M9 Image 2008-04-24 (#284033-35)
 R Aur   Image significant infrared component
     
NGC 6572
Pl. Neb 
Pl. Neb 
Image 2008-04-18 (#283245-47)
 NGC 6572
Pl. Neb 
  Image

Back to Top


Spectral response of combined SA100 / ST-7e CCD system 

Theoretical overall spectral response of the SA 100 operating 
with KAF-401E CCD Chip in SBIG ST-7e camera 
is shown in the graph below 
Image 
Image 
From Kodak KAF-401 E performance specification (June 2000)
(copy at http://www.lancs.ac.uk/depts/spc/resources/observatory/kaf-0401e.pdf )
   

Comparison of Spectra Response of ST-7e Camera, 
with example stars.

Visible Light
Range
Image
CCD Camera
Response
(ST-7e
 )
  Image  Note relatively low 
response at blue 
end of spectrum,
especially violet and UV
Spica
Alpha Vir
B1 Image 2008-05-02 (#285031-35)
Albireo(A)
Beta1 Cyg
K3  Image 2008-04-18 (#283311-17)
R Aur M6-M9 Image 2008-04-24 (#284033-35)
     
Star Name
(designation)
Spectra Type
(catalog)

Spectra Lines  ( Star Analyser 100)
Monochromatic &  Approx Colour
 

Image Date/No. & Notes
 

 

Back to Top


Spectral Response of UBVRI Photometric filters (Custom Scientific 1.25")

Image 
From http://www.sbig.com/products/filters.htm 
   

Comparison of Spectra Response of ST-7e Camera, 
UBVRI filter characteristics and example stars.

CCD Camera
Response
(ST-7e
 )
  Image  Note relatively low 
response at blue 
end of spectrum
Visible Light
Range
Image
UBVRI
Filters
 
  Image 
     
    Example stars 
Spica
Alpha Vir
B1 Image 2008-05-02 (#285031-35)
Spica
Alpha Vir
Image significant blue and 
?ultraviolet component
     
R Aur M6-M9 Image 2008-04-24 (#284033-35)
 R Aur   Image significant infrared 
component
     
Star Name
(designation)
Spectra Type
(catalog)

Spectra Lines  ( Star Analyser 100)
Monochromatic &  Approx Colour
 

Image Date/No. & Notes
 

 

Back to Top


Spectral Image Exposure Times

 

Graph showing Exposure Times for Spectral Images for different star magnitudes
8" LX200 operating at f/7.4, ST-7E, Star Analyser 100
-1 overexposed, +3 significantly underexposed
Image 
   

Back to Top


This Web Page: Spectroscopy
Last Updated : 2015-05-16
Site Owner : David Richards
Home Page : David's Astronomy Web Site