 Overview of Stellar Spectra | Finding Spectra | Plotting and Measuring Spectra | Classifying Spectra | Links

Findings | Tables | Figures | Conclusion

## Classifying Spectra

### Our Procedure

Our project this summer was to apply Morgan's stellar classification system to Sloan Digital Sky Survey (a telescope project here at Fermilab) data. To do this we followed a few basic steps:

2. Measure the absorption lines of Morgan's standards.
3. Find Trends.
4. Measure the absorption lines in Sloan Digital Sky Survey data.
5. Invert trend to classify.

### Our Findings: O Stars

Only one ratio was found to be successfully used in the classification of B stars 4471: 4541. As the spectral type went from O4 to B0, the ratio was measured to constantly increase from 0.28 to 3.35 respectively. Figure 1 is a Figure of subclass vs. the ratio 4471: 4541 for standard O stars. There is one B0 star added to complete the trend.

### Our Findings: B Stars

The one ratio that showed the best trend was 4026: 3935; as the subclass went from B0 to B9, the ratio decreased. The average 4026: 3935 value for a B0 star was 13.85 where as the average ratio was 0.44 for B9 stars. When the MKK standards were compared to SDSS data, the classification of B star subclasses was found to also depend on the ratio 3935: 3920-3925 which increases from 0.2 to 3.9 in B0 and B9 stars respectively. Both ratios to determine B star subclasses are shown in Figure 2.

### Our Findings: A Stars

The ratio 4385: 4481 was found to be a good indicator for the subclasses A0 to A3. This average ratio for A0 stars was measured for the MKK standards to be 0.35 while this average ratio for A3 stars was measured to be 0.82. Another trend measured was from the strength of 4103 amongst the subclasses A3-A9. The strength of 4103 was found to be 15.56 for A3 stars and 10.34 for A9 stars. Figures 3 and 4 represent the trends for the ratio 4385: 4481 and the strength of 4103 respectively.

### Our Findings: F Stars

It was found that the ratio 4030-4034: 4128-4132 can be used to determined the subclasses F0 to F8. The average of several different MKK F0 standards for this ratio was measured to be 0.49 while the average ratio of F2 standards was measured to be 0.58. This ratio worked so well to differentiate from F0 to F2 stars, it was extended to F8 stars and the trend was found to continue; shown in Figure 5. The ratio 4030-4034: 4128-4132 was measured to be 0.95 for F8 stars. In determining luminosity class, the ratio 4077: 4045 showed to have a slight tendency to decrease as luminosity class went from I to V. For F2 stars, the luminosity class I stars were measured to have a 4077: 4045 value of 1.9 while luminosity class V stars were measured to have a value of 0.9 for the same ratio. The values for the ratio 4077: 4045 amongst F2 stars are shown in Figure 6.It was found that the ratio 4030-4034: 4128-4132 can be used to determined the subclasses F0 to F8. The average of several different MKK F0 standards for this ratio was measured to be 0.49 while the average ratio of F2 standards was measured to be 0.58. This ratio worked so well to differentiate from F0 to F2 stars, it was extended to F8 stars and the trend was found to continue; shown in Figure 5. The ratio 4030-4034: 4128-4132 was measured to be 0.95 for F8 stars. In determining luminosity class, the ratio 4077: 4045 showed to have a slight tendency to decrease as luminosity class went from I to V. For F2 stars, the luminosity class I stars were measured to have a 4077: 4045 value of 1.9 while luminosity class V stars were measured to have a value of 0.9 for the same ratio. The values for the ratio 4077: 4045 amongst F2 stars are shown in Figure 6.

### Our Findings: G Stars

To distinguish between G0 stars and G2 stars, the MKK book suggested to look at the ratios 4045: 4103 and 4226: 4342. The ratios found while using the standards for 4045: 4103 were measured to be 0.40 with a standard deviation of 0.05 for G0 stars and 0.55 with a standard deviation of 0.07 for G2 stars while the ratios measured for 4226: 4342 were 0.52 with a standard deviation of 0.03 for G0 stars and 0.66 with a standard deviation of 0.06 for G2 stars; these trends are shown in Figure 7. The ratio 4144: 4103 was shown to have a strong trend within the subclasses G3 to G8. 4144: 4103 was measured on average to be 0.38 for G3 stars and 0.51 for G8 stars, with nearly a linear trend between these subclasses, as shown in Figure 8. SDSS data was compared to the MKK standards from the Dark Sky and Steward Observatories and the results are shown in Table 1 and displayed in Figure 8. It was found that the two above ratios for SDSS GO stars were within 0.4% of the measured ratios for MKK standards. The SDSS G2 stars were on average around 22% lower than the measured standard ratios while the ratio 4144: 4103 for SDSS G5 stars was over 80 % higher on average than the measured MKK standards.

### Our Findings: K Stars

It was found that the ratio 4226: 4325 depicts a common trend amongst subclasses K2 to K5, which was measured to be 2.78 for K2 stars and 4.51 for K5 stars; shown in Figure 9.

### Our Findings: M Stars

The MKK book suggested the strength of the band 4900- 5200 will lead to an accurate classification of M star subclasses. It was measured that for M0 stars the strength of this band was 41.91 and was 61.86 for M4.5 stars, as shown in Figure 10. For different luminosity classes, the ratio 4045: 4077 was found to show a trend. Specifically, for M2 stars, luminosity class III stars had a value of 3.13 for the ratio 4045: 4077 while luminosity class V stars had a value of 1.71. The results for the ratio 4045: 4077 for M0.5, M2, M3.5, and M4.5 luminosity class V stars are shown in Figure 11.