ALMA Solar Ephemeris Generator
User manualfor version 0.6
2016 December 05

Ivica SkokićCzech ALMA Regional Center Node
Astronomical Institute of the Czech Academy of SciencesOndřejov, Czech Republic

Table of Contents
Description............................................................................................................................................2
Usage....................................................................................................................................................2
Select user interface.........................................................................................................................2
GUI interface...................................................................................................................................3
Input FITS file.............................................................................................................................3
Visualization................................................................................................................................4
Image display..............................................................................................................................4
Pointing.......................................................................................................................................5
Text interface...................................................................................................................................5
Pointing.......................................................................................................................................5
Observation......................................................................................................................................6
How it works........................................................................................................................................8
Notes.....................................................................................................................................................9Warnings......................................................................................................................................9
Precision......................................................................................................................................9
Mirror links.................................................................................................................................9
Version history............................................................................................................................9Acknowledgements............................................................................................................................10
References...........................................................................................................................................112

Description
ALMA Solar Ephemeris Generator is a software tool for easy generation of ephemeris filescompatible with ALMA Observing Tool (OT) for user selectable regions on the Sun. It wasdeveloped for easy preparation of solar observations with the Atacama Large Millimetersubmillimeter Array (ALMA). It can be used to create dummy ephemeris files to be included in theALMA solar proposals but mainly it is used just prior the actual solar observations.

Usage
The Principal Investigator (PI) of the solar ALMA project or the Astronomer on Duty (AoD) may
use this tool to prepare the ephemeris file of the solar feature desired to be observed. ALMA Solar
Ephemeris Generator was developed with a focus on easy and intuitive usage. The tool consists ofthe following panels which are ordered sequentially:
Select user interface
Input FITS file (GUI only)
Visualization (GUI only)
Image display (GUI only)––––

Pointing–

Observation–

selection between graphical (GUI) and text user interface
user first selects or uploads a solar FITS fileuser adjusts the parameters for viewing the FITS fileuser navigates around the image (pan and zoom) and selects
the desired feature (click)a table of the coordinates of the selected feature in various
coordinate systems (GUI) or manual specification of target(text)
user enters the desired parameters of the observation andfinally generates the ephemeris

Select user interface

ALMA Solar Ephemeris Generator provides two user interfaces: graphical (GUI) and text. In
graphical mode, a user selects the target simply by clicking on the solar image. In text mode, thehelioprojective Cartesian (HPC) coordinates are entered manually.

GUI interface
Input FITS file

User can select between:• AIA image (local) – last used AIA image, locally saved (if allowed by the server)• one of the available SDO/AIA channels (see table below)• AIA image (for testing)3

AIA channel(Angstroms)

SourceRegion

Characteristictemperature (K)94

Fe XVIII

Flaring regions

6.3×106131

Fe VIII, XX, XXIII

Flaring regions

4×105, 107, 1.6×107

171

Fe IX

Quiet corona, upper transition region

6.3×105

193

Fe XII, XXIV

Corona. hot flare plasma

1.2×106, 2x107

211

Fe XIV

Active region corona

2×106

304

He II

Chromosphere, transition region

50000

335

Fe XVI

Active region corona

2.5×106

1600

C IV + continuumTransition region, upper photosphere105, 5000

1700

continuum

Temperature minimum, photosphere

5000

4500

continuum

Photosphere5000

The user can also upload his own FITS image. This image should conform to the FITS standard, bewithout compression and needs to have solar WCS keywords as defined by Thompson (2006):• DATE-OBS• CRPIXn• CRVALn• CDELTn• CROTA2• CRUNIT• CRLN• CRLT
Without these keywords ALMA Solar Ephemeris Generator will not function properly.

Visualization

Scaling function is used to scale the FITS data values for better visual presentation. Available
functions are:• linear – no scaling, use original FITS data
• sqrt• cube root
• log
• sqrt-log• log-log

4Color selects the colormap: gray, heat, A or B (as in SAOImage DS9). In multi-frame FITS images,frame selects the desired image. Show grid overlays a coordinate grid over the image, Stonyhurst
heliographic, Carrington heliographic or helioprojective Cartesian. Show ALMA 12m beam size
overlays the 12m ALMA antenna FoV in a selected ALMA band.

Image display

The user can use the mouse or touch input to move the image around. Zoom in/out is achieved byclicking the “+” or “-” buttons or with mouse scroll button. Clicking without dragging will selectthe desired feature and a green cross will mark the position. If Show ALMA 12m beam size ischecked then the circle marking the 12m antenna FoV will also appear and if mosaic is selected, ablue box will be visible too.

Pointing

The coordinates of the selected feature are displayed in four coordinate systems: pixel (from FITS),
helioprojective Cartesian, Stonyhurst heliographic and Carrington heliographic. A manual input into5any of the fields is possible and all the other fields will update automatically. It is also possible toselect a feature outside the solar disc. In that case, no heliographic coordinates will be displayed.
Here it is also possible to visualize the required box size and angle for a mosaic observation. Notethat angle is in heliographic frame (0 degrees means solar east-west). To get the sky angle (inequatorial RA-Dec frame) as required by ALMA Observing Tool, user should add solar P angle toangle value:
angle_sky (for OT) = angle_sun + solar_P

Text interface
Pointing

The coordinates of the target in text mode are entered as helioprojective Cartesian coordinates witha reference date. Reference date should be entered in ISO date format YYYY-MM-DDTHH:NN:SS.
For the calculation of ephemerides, several solar parameters at the reference date are needed: Sun
distance from the observer in meters, solar position (P) angle, and heliographic latitude (B0) andlongitude (L0) of the solar center as seen by the observer. If unknown, these quantities can beacquired from JPL Horizons service by clicking “Get from JPL Horizons”. Note that JPL Horizons
returned values are based on ALMA observing site and not the actual observer position which canintroduce a negligible error.

Observation
Here the parameters of the observation are specified. For start and end date use ISO date format
YYYY-MM-DDTHH:NN:SS. Step size is the step between consecutive entries in the ephemeris.
Differential rotation profile specifies which profile will be used for the calculation of the feature
position in time. Several predefined profiles are available:No rotation-Solid rotation (Carrington) Sunspot groups
H-alpha filaments
Coronal bright points-

User specified-

a feature is fixed as if the Sun is not rotating at all. Note that
because of the Earth revolution, the coordinates of the feature
will change.
a solid rotation where the Sun rotates as solid bodyprofile derived from sunspot groups (Sudar et al. 2014)
profile derived from observation of filaments visible in H-alphaimages (Brajša et al. 1991)
profile derived from movements of coronal bright points inSOHO/EIT images (Wöhl et al. 2010)user specified rotation profile in typical formω=A +B sin 2 φ +C sin 4 φ where φ is heliographic latitude andA, B and C are given in degrees per day.

6

If the selected feature is not on the solar disc but off the limb, selection of the rotation profile will
be disabled and the ephemeris calculation will assume that the feature is co-rotating with Earth i.e.
appearing in the same place as viewed from Earth.
Finally, the height of the selected feature can be specified in kilometers. Selecting the desired
profile will automatically fill the height field with a typical value.
After specifying the desired observation parameters, an ephemeris file for the ALMA Observing
Tool can be generated by clicking “Generate ephemeris” button. This file will be displayed in text
box below and can be easily downloaded by clicking “Download table data”. Two more buttons areavailable just for user convenience, “Show original JPL file” will display the JPL Horizons file withsolar center coordinates for ALMA center of the array, while “Show ephemeris table” will generate
a formatted table of ephemeris data.

How it works
ALMA Solar Ephemeris Generator uses JPL Horizons service for high precision solar ephemeris. Itsends a request to JPL Horizons service with parameters specified in Observation and uses thereceived data to calculate offsets from the solar center for the selected feature. Then it transforms
everything into equatorial J2000.0 Ra-Dec frame. Coordinates of the Sun are astrometric J2000
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coordinates from JPL Horizons for the ALMA center of array. Atmospheric refraction is not taken
into account. Physical ephemeris of the Sun (P, B0, L0) used in the calculation are also from JPL
Horizons specified for ALMA center of array.

NotesWarningsThe ephemeris should not be older than 2 days from the reference image because of theunpredictable nature of solar features. If the ephemeris is older than 2 days, the tool with display awarning in the Status window. This can happen in two ways: either the reference image is to old(please select the latest SDO/AIA image or use a newer image) or the observation is scheduled to
far ahead (see the note on the precision for more information).
If the feature is close to the limb, it could happen that it will move behind in the selected time. Theephemeris will then be invalid and a warning will be displayed in the Status window.

Precision
Precision in calculated HPC x,y is ~0.2 arcsec. This is due to the precision of the input solar angles
B0, L0 which are given to 0.01 degrees by JPL Horizons and many almanacs. In the worst casescenario (Earth at perihelion, feature on the disc center) 0.01 deg error in heliographic coordinatescorresponds to 0.17 arcsec in HPC coordinates.
When calculating RA-Dec offsets, solar P angle affects its precision. P is given as 0.0001 in JPL
Horizons, so it adds ~0.002 arcsec for 1000 arcsec from the solar disc. If it is given as 0.01, theerror rises to 0.17 arcsec and the total error is ~0.4 arcsec. For a reference, 12m ALMA antenna has
a beam size of 26 arcsec at 240 GHz (Band 6).
However, features on the Sun are carried by differential rotation, meridional motions and othervelocity fields that are not known. In addition, the features evolve, change appearance. All thissignificantly affects the precision, much more than errors in the angles given above. They
accumulate over time so it is not possible to accurately predict positions of the features in more thanfew days.

Mirror links• http://www.asu.cas.cz/~skokic/alma/CoordTool.html• http://celestialscenes.com/alma/coords/CoordTool.html

Version history
v0.6, 2016 Dec 05+ New text interface for manual input of pointing coordinates
as HPC(x,y) with a reference date.
+ Added mosaic info into output ephemeris.
+ Added solar parameters info to output ephemeris.
* Text areas are now readonly.
* Default step size changed from 20 to 15 minutes.
* Default observation end time changed from 1 day to 2 days afterobservation start date.

8

v0.5, 2016 Nov 28+ Added mosaic observation for illustration purposes only.
+ Added status window for errors/warnings.
+ Hints added on some controls.
+ Support for 64-bit float FITS files.
* More SDO/AIA channels available in the drop-down menu.
* More ALMA channels for beam size visualization.
* Better handling on touch enabled devices.
* Better handling of table data download.
* Minor code refactorings.
! Using mouse scroll to zoom in/out on image also scrolled theentire page.
! Loading local files finally works.
! When seconds were 0 in start time for ephemeris,e.g. 2016-11-23T12:23:00, no ephemeris was generated.
v0.4, 2016 Apr 13+ Off the limb pointing is now possible (differential rotation
is not applied in this case).
+ The last user selected (latest) 193 AIA image is saved locallyand loaded as default.
! Generated ephemeris table: julian day calculation was off by
one month.
v0.3, 2016 Mar 03+ Ephemeris file: info about selected position, image source, etc.,
embedded as comment fields in header.
! Ephemeris file: declination coordinates, leading zero was missing.
! Ephemeris file: comment lines trimmed to 80 chars.
! Ephemeris file: cleaned unnecessary fields in the last line.
! Fixed parsing string keywords with comments in FITS files.
* Changed calculation for the heliographic coords to include height
before differentially rotating.
v0.2, 2015 Dec 13+ Ephemeris file: option to download generated file directly.
+ Display ALMA 12 m dish beam in selected bands.
+ Display coordinate grid (helioprojective and heliographic).
+ Manual input of position (pixel, helioprojective, Stonyhurst, Carrington).
+ User specified rotation profile.
+ Generate table of ephemeris info.
v0.1, 2015 Apr 23+ Initial release (beta).
Legend:+ new feature- removed feature* update/change! corrected bug? known issue

Acknowledgements
1. ALMA, http://www.almaobservatory.org
2. ESO, http://www.eso.org
3. Czech ARC node Ondřejov, http://www.asu.cas.cz/alma
4. AIA synoptic images courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.
5. jsFITS, JavaScript FITS library, https://github.com/slowe/jsFITS
96. JPL Horizons, http://ssd.jpl.nasa.gov/horizons.cgi
7. Joint Science Operations Center (JSOC), http://jsoc.stanford.edu
8. Hvar Observatory, http://oh.geof.unizg.hr
9. Kanzelhöhe Observatory, http://www.kso.ac.at/
Special thanks to the members of the ALMA Solar Development Team for comments, improvement
suggestions and testing.

References
1. Brajša, R.; Vršnak, B.; Ruždjak, V.; Schroll, A.; Pohjolainen, S. (1991) Solar differential
rotation determined by polar crown filaments. SoPh, 133, p. 195-203.(ADS)
2. Sudar, D.; Skokić, I.; Ruždjak, D.; Brajša, R.; Wöhl, H. (2014) Tracing sunspot groups todetermine angular momentum transfer on the Sun. MNRAS, 439-3, p. 2377-2385.(ADS)
3. Thompson, W. T. (2006) Coordinate systems for solar image data. A&A, 449-2, p. 791-803.
(ADS)
4. Wöhl, H.; Brajša, R.; Hanslmeier, A.; Gissot, S. F. (2010) A precise measurement of thesolar differential rotation by tracing small bright coronal structures in SOHO-EIT images.
Results and comparisons for the period 1998-2006. A&A, 520-A29.(ADS)10