The McMath-Pierce Solar The McMath-Pierce Solar Telescope Stellar Telescope Stellar

SpectrographSpectrograph

ESS 590 Winter 2007 LectureESS 590 Winter 2007 Lecture

Scientific MotivationScientific Motivation

Jovian System – Io Plasma Torus

STIS observations of Io

Scientific SummaryScientific Summary

• Oxygen and sulfur emission near Io– Localized position of spots show dependence

on orientation of Jupiter’s magnetic field– Integrated intensity shows dependence on

density of the Io plasma torus (work in progress)

Slicer

Collimating mirror

Blazed Grating

Camera mirror

Exit Slit

Spectrograph Schematic

R ~ 120,000 (/) at 6300 Å

Slicer detail5.2”

5.2”

Grating basicsGrating basics

http://www.physicsclassroom.com/Class/light/U12L1b.html

Grating basicsGrating basics• m λ = d (sin(θi) + sin(θm))

http://www.madsci.org/posts/archives/May2003/1053350704.Ph.r.html

http://grus.berkeley.edu/~jrg/ins/node3.html

Blazed gratingBlazed grating• Scattering surfaces are tipped at an angle

to make scattering more efficient at a particular angle

Slicer

Collimating mirror

Blazed Grating

Camera mirror

Exit Slit

Spectrograph Schematic

R ~ 120,000 (/) at 6300 Å

• Stellar spectrograph echelle operated at order m = 36 for [OI]

• Get angular dispersion from derivative of diffraction angle wrt wavelenth:

• High m high dispersion

ia

m

d

id

cos

Example spectrum: 2002 Jan 26

Io [OI] line

Io, Telluric and solar lines identifiedIo, Telluric and solar lines identified

Fitting SoftwareFitting Software

3600 Io spectra, >15,000 calibration images

Clear Detection of Io [OI] SignalClear Detection of Io [OI] Signal

Variation in Io’s [OI] brightness not Variation in Io’s [OI] brightness not quite where you would expect in quite where you would expect in

System IIISystem III

Why?Why?• Details of Io’s orbit and torus

Correlate Multiple Correlate Multiple DatasetsDatasets

• STIS (when we had it)• Ground-based torus

images• Ground-based Io [OI]• Jovian aurora

– Jupiter’s mag field

• Spacecraft flyby– Solar wind or jup mag

field

Cool things to do with the Io [OI] Cool things to do with the Io [OI] datasetdataset

• Compare to Io volcanic record• Compare to solar wind activity• Compare to Io flux tube footprint on Jupiter• Complement spacecraft data (a

permanent in situ probe)– Model of Io [OI] emission variation seems to

work well assuming Io does not disturb the torus. All you need is a scaling factor, which does vary on different days

Example Example Comparison: Comparison: 1997 Oct 141997 Oct 14

• Increase in emission is unusually large in UV lines (but we don’t have many observations)

• Increases like this in groundbased data are common

• Torus images were showing a “knot” in about the right place

Observed Asymmetry in torus Observed Asymmetry in torus images, fall 1997images, fall 1997

Io [OI] model shows there should Io [OI] model shows there should be a factor of 2, not 3 in brighteningbe a factor of 2, not 3 in brightening

BUT that is using the old hand-BUT that is using the old hand-reduced datareduced data

• Machine reduction with the same line list gives the same results

BUT that is using the old hand-BUT that is using the old hand-reduced datareduced data

• Machine reduction with expanded line list gives different results

What does it all mean?What does it all mean?