Spectroscopy

 

Part V – The MILES catalogue of spectra

 

Updated 2017 January 14

 

Contents

 

Spectroscopy, Part I – Using the SSON Transmission Grating Spectrograph

 

Spectroscopy, Part II – Generating a profile using Visual Spec

 

Spectroscopy, Part III – Analysing spectra using Visual Spec

 

Spectroscopy, Part IV - Resources

 

 

Introduction

 

The MILES catalogue of spectra is used by amateurs as a standard for low/intermediate resolution spectroscopy (100 - 10Å say). It can best be accessed using a spreadsheet developed by Paolo Berardi and Marco Leonardi which is described here. Links for downloading the spreadsheet and the database are included in the description. You will also find a modified version of these instructions below plus a worked example including;

- spreadsheet input

- calibrating the selected spectrum with Vspec

 

Spreadsheet

Installation

 

Various versions of the spreadsheet may be downloaded - both 32 and 64 bit versions are available (note that 32 and 64 bit are referred to MS Excel, you can have 64 bit OS and 32 bit Excel, in this case you should use the 32 bit version).

 

MS Excel Spreadsheet (all versions, 32 and 64 bit, 3 Mb):
http://quasar.teoth.it/html/varie/MILES_SEARCH_V1.zip

Miles spectral database (34 Mb):
http://quasar.teoth.it/html/varie/MILES_OBS.zip

 

To install;

- Extract MILES_SEARCH_V1.zip in any place with folder structures option enabled. MILES_SEARCH_V1 folder should contain:

Image
- Extract files s0001-s0985 (file extension .test.dat) from MILES_OBS.zip in the empty folder MILES_OBS. Open the spreadsheet (the version you can use).

Note: if you already have installed the old SPEC_VIEW_V2 package (Miles spectra browser), you can download only spreadsheets. Just put them in the main folder along with the other.

It is recommended that;
- macro execution is allowed;
Excel 2010/2013: File->Options->Trust Center-> Trust Center settings->Macro Setting. Choose Disable all macros with notification (macros are disabled but it will ask your permission each time before running a macro) or Enable all macros (low security)
Excel 2003: Tools->Macro->Security, choose Medium Security (macros are disabled but it will ask your permission each time before running a macro) or Low Security
- rows/columns are not deleted
- only cell content in the input green area is modified
 
I
nstructions

 

The objective is to select suitable reference stars from the Miles spectral library for observing sessions. The spreadsheet calculates altitude, azimuth, parallactic angle and air mass for each Miles star. In addition the data are compared with the target star so that the observer can get a list of suitable stars located at a similar altitude above horizon, and therefore similar atmospheric extinction. Miles stars are selected by means of the input criteria – Figure 1

Image

Figure 1. Input criteria. Credit Paolo Berardi and Marco Leonardi

 

The observer just needs to input geographic coordinates, local time (with a current time “NOW” button option) and observed target RA/Dec. The latter can be provided by editing single fields or by means a Simbad formatted string (copy/paste from Simbad webpage). Beside the use of “NOW” button the observer can also plan the observation session by imputing the planned observation time.

When the above listed fields are filled (note UT time is calculated using time zone and DST extracted from PC setting), the observer can read the target altitude, azimuth, parallactic angle and air mass in the output area.

Pressing the "FIND STARS" button produces a list of Miles stars that meet the following requirements – Figure 2
- above the horizons at preset time
- altitude difference respect to the target lower than preset value
- T eff within the preset range values (to exclude the cooler stars, which are not very suitable for response calculation – roughly with T eff > 7000 you can filter A/B/O classes stars – Table 1)

Class

Effective temperature

Conventional color description

Actual apparent color

Main-sequence mass
(solar masses)

Main-sequence radius
(solar radii)

Main-sequence luminosity
(bolometric)

Hydrogen
lines

Fraction of all
main-sequencestars

O

≥ 30,000 K

blue

blue

≥ 16 M

≥ 6.6 R

≥ 30,000 L

Weak

~0.00003%

B

10,000–30,000 K

blue white

deep blue white

2.1–16 M

1.8–6.6 R

25–30,000 L

Medium

0.13%

A

7,500–10,000 K

white

blue white

1.4–2.1 M

1.4–1.8 R

5–25 L

Strong

0.6%

F

6,000–7,500 K

yellow white

white

1.04–1.4M

1.15–1.4R

1.5–5 L

Medium

3%

G

5,200–6,000 K

yellow

yellowish white

0.8–1.04M

0.96–1.15R

0.6–1.5 L

Weak

7.6%

K

3,700–5,200 K

orange

pale yellow orange

0.45–0.8M

0.7–0.96R

0.08–0.6 L

Very weak

12.1%

M

2,400–3,700 K

red

light orange red

0.08–0.45M

≤ 0.7 R

≤ 0.08 L

Very weak

76.45%

Table 1. Harvard spectral classification. Credit Wikipedia


Altitude difference means that if you put, for example, “Limit delta altitude” to 5 degree and target is at 50 degree above horizon, output list will include all Miles stars having altitude in the range 45 - 55 degree.

Image

Figure 2. Miles stars meeting input criteria. Credit Paolo Berardi and Marco Leonardi

 

Output list, Figure 3, includes:
- main data for the stars (columns B to J)
- absolute altitude difference respect to the target (the sort key)
- angular distance from the target
- parallactic angle difference respect to the target
- altitude
- azimuth
- air mass (with Pickering 2002 interpolative formula)

Parallactic angle difference would help to avoid photometric distortions for narrow slit operations while observing far from the zenith. Also angular distance provide a similar information, making it clear if the Miles star is located in a distant area of the sky respect to the target (an important parameter in case of non-uniform sky condition). Finally, for those who use German equatorial mounts, stars with an azimuth value colored in red may require a meridian-flip to observe them (they are located on the opposite east-west side respect to the target).

If the observer wants to see the spectrum of a Miles star in the output list, he/she can select any cell on Miles star row and press "View spectrum" button, Figure 3. If needed, the observer can go back to "Setup" tab to perform other search.

Image

Figure 3.Output plus selected spectrum. Credit Paolo Berardi and Marco Leonardi

 

Prior to exporting the file for analysis with Vspec select ‘Synthetic de-reddening’ OFF to see what the spectrum actually looks like rather than what it would look like without interstellar extinction.

 

Example

 

Spreadsheet

 

The 32 bit xls version, which required macros to be enabled, was used – simply click on Enable Macros when opening the spreadsheet, Figure 4.

 

Figure 4. Excel macro enabling

 

As I do most of my imaging these days with the SSON robotic telescope located in California, USA the input data reflected that location and observable sky at 00:00 UT on 2015 March 15. Target coordinates were those of Alpha Leo, Regulus – Figure 5.

 

Figure 5. Megastar chart of target area.

 

Selecting Find stars resulted in the list shown in Figure 6.

 

Figure 6. Spreadsheet input and resulting output.

 

HD087737, Eta Leo, was chosen from the list as it was a bright A type star likely to exhibit strong Balmer hydrogen lines. Clicking on View spectrum and then ‘Synthetic de-reddening on E(B-V) value’ Off produced the spectrum shown in Figure 7.

 

Figure 7. Spectrum of HD087737

 

The hydrogen/Balmer lines visible in Figures 7 and 9 include those listed in Table 2.

 

Name

H/Ba alpha

H/Ba beta

H/Ba gamma

H/Ba delta

H/Ba epsilon

H/Ba zeta

H/Beta

Wavelength (Å)

6563

4861

4341

4102

3970

3889

3835

Table 2. Hydrogen/Balmer lines

 

Selecting ‘Export DAT’ generates DAT files which are placed in the Export folder.

 

Vspec

 

The spectrum of HD077737, exported from the spreadsheet was opened in Vspec and a multiline calibration carried out – Figure 8.

 

Figure 8. Multiline calibration

 

A ‘flattened’ spectrum with synthesised version above and spectral lines identified is shown in Figure 9.

 

Figure 9. Flattened spectrum with synthesised version above.

 

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