Altair and Tarazed in the constellation Aquila the Eagle.

 

The Summer Triangle above the Jodrell Plank Observatory.

"This time of year in the Northern Hemisphere, Altair and the less bright Tarazed are visible to the naked eye on clear transparent nights in Suffolk. Altair is one of the three bright stars which make up the 'Summer Triangle' asterism.  Altair is the alpha star in the constellation Aquila the Eagle. Tarazed a red giant and nearby Altair, is also in Aquila and is designated Gamma Aquilae.

This part of the summer night sky is awash with stars and dark nebulae (clouds of obscuring dust). Barnards 'E' can be seen in Kurt's image just above and to the right of Tarazed.

 

Kurt is very fond of using the spectrometer, designed and manufactured by our resident engineer, Jolene McSquint-Fleming, to create stellar spectral profiles". - Joel Cairo CEO of the Jodrell Plank Observatory.

Comparative Analysis of Low-Resolution Spectral Profiles of Altair and Tarazed

Prepared by: Prof G.P.T Chat, visiting astrophysicist at the Jodrell Plank Observatory

Date: July 5, 2025

This informal report presents a comparative analysis of the low-resolution spectral profiles of two nearby stars: Altair (α Aquilae) and Tarazed (γ Aquilae). Although they lie close together in the sky within the constellation Aquila, these stars differ significantly in spectral type, temperature, and luminosity class, which become evident when analyzing their spectral features.

Stellar Data Overview

Property Altair Tarazed

Spectral Type A7 V K3 II-III

Effective Temp. ~7,600 K ~4,300 K

Luminosity Class Main Sequence (V) Bright Giant (II-III)

Dominant Color White Orange-red

Spectral Profile Differences

1. Continuum Shape

Altair: Displays a blue-white continuum with a strong rise toward the shorter (bluer) wavelengths. This indicates a hotter surface temperature, consistent with its A-type classification.

Tarazed: Shows a redder continuum, peaking more in the longer (redder) wavelengths due to its significantly cooler surface temperature (~4300 K).

Interpretation: The blackbody radiation curves are shifted—Altair peaks in the UV-visible, Tarazed in the visible-red to near-infrared.

2. Balmer Line Strength

Altair: Prominent and broad hydrogen Balmer lines (especially Hα, Hβ, Hγ). This is typical of A-type stars where the hydrogen absorption is at its strongest due to optimal excitation conditions in the photosphere.

Tarazed: Very weak or absent Balmer lines. Cooler atmospheres do not excite hydrogen sufficiently to produce strong Balmer absorption features.

Interpretation: Balmer line strength peaks in mid-A spectral types and decreases sharply toward both hotter and cooler temperatures.

3. Metallic Lines and Molecular Bands

Altair: Metallic lines are present but not as strong, and molecular bands are virtually absent due to the high temperature preventing molecule formation.

Tarazed: Strong absorption lines of neutral metals such as Ca I, Fe I, and especially the Ca II infrared triplet. Also displays TiO molecular bands, common in cooler K and M-type giants.

Interpretation: Lower temperatures in Tarazed allow molecule formation and enhanced low-ionization metallic absorption. Molecular bands serve as clear markers of late-type stars.

4. Line Broadening

Altair: Broader spectral lines, especially in hydrogen and metal lines. This broadening is primarily due to rapid rotation (~250 km/s), which causes Doppler broadening across the stellar disk.

Tarazed: Narrower absorption lines. As a giant star, Tarazed rotates more slowly, and the lower surface gravity leads to less pressure broadening.

Interpretation: Rotation and gravity play key roles in line profile shape; Altair's fast spin contrasts strongly with Tarazed's more "settled" atmosphere.

Conclusion

In low-resolution spectra, Altair exhibits features typical of a hot, fast-rotating, hydrogen-rich main sequence star, dominated by strong Balmer lines and a blue continuum. In contrast, Tarazed, a cool and evolved bright giant, displays a redder spectrum dominated by metal lines and molecular absorption bands with relatively weak hydrogen features.

The differences in spectral profiles reflect underlying physical contrasts in temperature, gravity, chemical composition visibility, and rotational velocity, making these two stars a textbook example of spectral diversity across the HR diagram.