Volume -5, Issue-2, April 2015 Small Aperture Amateur ...rajiv/planexnews/oldarticles/Volume -5,...
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22 Volume -5, Issue-2, April 2015 22 Volume -5, Issue-2, April 2015 Over several thousand years, astronomy continues to be popular subject among amateurs. Day by day, advance- ments in equipment and reduction in cost has enabled amateur astronomer’s work to become increasingly more scientific rather than conducting only imaging. With in- creasing interest and low cost capabilities in imaging/ photometry/spectroscopy, amateurs are doing appreciable work on it with their limited tool capabilities. The work may not be completely on par with that of professionals but it enables amateur astronomers to understand the sub- ject more scientifically. In this paper, we briefly describe some of the small aperture amateur observational capa- bilities and tools. Introduction: There is enough scope to carry out astronomical observa- tions using moderate size telescopes, mainly known as “Refractors”, “Reflectors” and “Cassegrain Catadioptric Telescopes” along with capabilities of CCD imaging and sky tracking facility. A brief description about these tele- scopes and the used facilities are as follows. Refractor Telescope: Refractor telescope consists of convex lenses to collect, focus and magnify light. The distance between the objec- tive (main) lens and the eyepiece lens is fixed so that they share a common focal point (Fig. 1). Reflecting Telescope: Reflecting Telescope uses a single concave mirror as its primary. Light enters the tube traveling to the mirror at the back end. There light bend forward in the tube to a single point, its focal point. This exact system is known as Newtonian Reflector. Schmidt- Cassegrain Catadioptric Telescope: The third type of telescope, which has gained immense popularity over the last years, is the Schmidt Cassegrain telescope (SCT). This type of telescope uses both lenses and mirrors in a compound system as shown in Fig. 3. Sky tracking facilities: The facility includes telescopes that are generally attached with GOTO mounts and are slewed using planetarium software (For eg. Starry Night pro plus SN7/MaximDL + EQMOD in our case). CCD Imaging: The thermoelectric cooled Charge Coupled Device (CCD) cameras are more sensitive to astronomical light signals due to less dark electric current and high electron quantum efficiency (QE). A typical view of CCD sensor is shown in Fig. 4. The quantum efficiency of a typical CCD chip w.r.t opti- cal wavelength is shown in (Fig. 5). Small Aperture Amateur Observational Capabilities/Tools (Imaging/Photometry/Spectroscopy) Figure 1. Refractor Telescope Figure 2. Reflector Telescope Figure 3. Schmidt- Cassegrain Telescope Figure 4. A typical CCD sensor (KAF8300, Kodak) Back to Contents
Transcript of Volume -5, Issue-2, April 2015 Small Aperture Amateur ...rajiv/planexnews/oldarticles/Volume -5,...
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Over several thousand years, astronomy continues to be popular subject among amateurs. Day by day, advance-ments in equipment and reduction in cost has enabled amateur astronomer’s work to become increasingly more scientific rather than conducting only imaging. With in-creasing interest and low cost capabilities in imaging/photometry/spectroscopy, amateurs are doing appreciable work on it with their limited tool capabilities. The work may not be completely on par with that of professionals but it enables amateur astronomers to understand the sub-ject more scientifically. In this paper, we briefly describe some of the small aperture amateur observational capa-bilities and tools.
Introduction:There is enough scope to carry out astronomical observa-tions using moderate size telescopes, mainly known as “Refractors”, “Reflectors” and “Cassegrain Catadioptric Telescopes” along with capabilities of CCD imaging and sky tracking facility. A brief description about these tele-scopes and the used facilities are as follows.
Refractor Telescope:Refractor telescope consists of convex lenses to collect, focus and magnify light. The distance between the objec-tive (main) lens and the eyepiece lens is fixed so that they share a common focal point (Fig. 1).
Reflecting Telescope:Reflecting Telescope uses a single concave mirror as its primary. Light enters the tube traveling to the mirror at the back end. There light bend forward in the tube to a single point, its focal point. This exact system is known as Newtonian Reflector.
Schmidt- Cassegrain Catadioptric Telescope:The third type of telescope, which has gained immense popularity over the last years, is the Schmidt Cassegrain telescope (SCT). This type of telescope uses both lenses and mirrors in a compound system as shown in Fig. 3.
Sky tracking facilities: The facility includes telescopes that are generally attached with GOTO mounts and are slewed using planetarium software (For eg. Starry Night pro plus SN7/MaximDL + EQMOD in our case).
CCD Imaging:The thermoelectric cooled Charge Coupled Device (CCD) cameras are more sensitive to astronomical light signals due to less dark electric current and high electron quantum efficiency (QE). A typical view of CCD sensor is shown in Fig. 4.
The quantum efficiency of a typical CCD chip w.r.t opti-cal wavelength is shown in (Fig. 5).
Small Aperture Amateur Observational Capabilities/Tools
(Imaging/Photometry/Spectroscopy)
Figure 1. Refractor Telescope
Figure 2. Reflector Telescope
Figure 3. Schmidt- Cassegrain Telescope
Figure 4. A typical CCD sensor (KAF8300, Kodak)
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Imaging/ Observations:The image calibration & processing is an integral part of astronomical observation and result estimations. Many of the amateur astronomical communities use popular imag-ing softwares for different purposes, mentioned below.MaximDL: Image calibration/stacking & PhotometryAPT Tool/Backyard (EOS):CCD Camera controlCCDstack2.0: Image calibration/stackingRSpec: SpectroscopyFew CCD images of Comets (year 2013-2015) C2012S1 ISON, C2013R1 Lovejoy, C/2014Q2 Lovejoy, C/2013A1 Siding Spring, C/2014 E2 Jacques, C/2013V5 Oukai-meden along with supernova SN2014J event in galaxy M82 and recent supernova SN2014dt in galaxy M61 are shown in Fig. 6(a-h).
Figure 5: Typical QE curve of KAF8300 CCD ChipMaximDL: Image calibration/stacking & PhotometryAPT Tool/Backyard (EOS): Image capturingCCDstack2.0: Image calibration/stackingRSpec: SpectroscopyAstrometrica: Plate scale DS9: Image scaling/false color
Figure 6a. Comet C2012S1 ISON
Figure 6b. Comet C2013R1 Lovejoy
Figure 6c. C2013A1 Siding Spring
Figure 6d. C2014Q2 Lovejoy
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Spectroscopy and Photometry
Astronomical Spectroscopy:
Spectroscopy is a branch of Physics/Chemistry in which, the emission and absorption property of atoms or mole-cules are examined. It can be done in Optical, Radio and X-Ray regions of the electromagnetic radiation. Mostly, in amateur astronomical spectroscopy the measurements are done in optical region at different wavelengths from 4000 Å to 7000 Å. The electromagnetic radiation (here visible light signal) is dispersed over the CCD sensor using a dis-persive medium (say prism or star analyser gratings) and spectrum is recorded as an image.
The image data is reduced using spectroscopy software like RSpec, Vspec or ISIS to get relative intensity (y axis) and wavelength (x axis) distribution. Low dispersion transmis-sion blazed gratings of 100 lines/mm grooves or 200 lines/mm grooves are popular among amateur astronomers.
These gratings best work with bright stars, but can also be used to examine the spectra of comets and supernovas. The typical spectrum of Star Vega (A0V) is shown along with few spectra of comets and supernovas.
The Hydrogen Balmer lines are clearly seen in spectrum of star Vega (A0V). Likewise many bright stars and their spectral classes can be easily examined.
Figure 6e. C/2013 V5 Oukaimeden
Figure 6f. C2014E2 Jacques
Figure 6g. SN2014J in M82
Figure 6h. SN2014dt in M61
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Not only bright stars, the bright comets are also good tar-get for amateur astronomers to perform spectroscopy. The spectra of comets show emission peaks of diatomic car-bon C2 “swan bands”, carbide C3, cyanide CN & Am-monia NH3 when comet approaches very near to the Sun.
It is challenging to carry out astronomical spectroscopy at higher positive photometric magnitude (for very faint ob-jects), but careful observation does not disappoint as far as results are concerned. The small telescopes are sufficient to record the spectrum of bright supernova transients. The spectrum of supernovas SN2014J and SN2014dt are re-corded though.
It is always challenging to identify the correct emission / absorption lines in spectral analysis, although the absorp-tion at 6000 Å is best known as Silicon-II (Si-II) in Type Ia supernova among astronomical community. The Si-II absorption line at 6000 Å was found blue shifted (Si-II shows rest wavelength at 6355 Å) as after the supernova explosion the relative cooled nova shell moving very fast towards the observer at earth.
Likewise to sound signals where frequency of sound ap-pears higher when source moves towards listener and vice versa, same thing happens with electromagnetic radiations. This phenomenon is well known as “Doppler effect”. The close observation shows that within a month Si-II line was shifted and found at 6114 Å.
The simple calculation shows that supernova shell was ex-panding with velocity of 16800 km/Seconds.
Figure 7. Spectrum of star Vega (A0V). X-axis: Wavelength (Ao);Y-axis: Relative flux.
Figure 8. Carbon Swan bands of comet C2012S1 ISON
Figure 9. Carbon Swan bands of Comet C2014E2 Jacques
Figure 10. Carbon Swan bands of Comet C2014Q2 Lovejoy
Figure 11. Spectra of SN2014J captured during the first 30 days after detection. The Si feature identifies it as a Type Ia
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Expansion Velocity Vc = [(λobs – λrest) x velocity of light in vacuum (km/s)]/ λrest
Expansion Velocity Vc = [(6000 – 6355) x 3^105] / 6355 = 16800 km/s
The similar spectroscopic study is done for SN2014dt in M61 (Fig. 13).
Astronomical Photometry:It is measuring the electromagnetic flux (luminosity or magnitude) of an unknown astronomical object with re-spect to standard source. The Photometric magnitude esti-mation of a typical supernova SN2014dt (Fig. 14).
Conclusion: Advancements in equipments in astronomy have given new wings to amateur astronomers. Imaging coupled with spectroscopic/photometric data helps in understanding and exploring the universe more scientifically. Presence of molecules in comets, type of supernova (estimation of Doppler shifts, radial expansion velocities), its magnitude, size, the variability in luminosities of binary stars (period and mass) etc can easily be estimated with the spectrum / photometric data.
Figure 12. Expansion velocity profile with time (days)
Figure 13. Spectra of SN2014dt. The Si feature identifies it as a Type Ia
Figure 14. Photometric magnitude estimation of SN2014dt
Malhar Raghunath Kendurkar Kota, India
E-mail:[email protected] Contact: +91-(0)-8806080768
A. Chapman Buenos Aires, Argentina
E-mail: [email protected]: +541155657915
M. Bunnell Price, Utah, USA
E-mail: [email protected]: 435-650-8940
Cepheids Astronomy Group
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