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Astronomical Data Analysis Software and Systems VI ASP Conference Series, Vol. 125, 1997 Gareth Hunt and H. E. Payne, eds.

A Graphical Field Extension for sky
Al Conrad W. M Keck Observatory Abstract. At Keck we use the graphical tool sky to plan observations and to control the telescop e. Since 1992, sky has provided all status via alphanumerics and control via buttons. We recently extended sky to provide status via a graphical star field. The user controls the telescop e by clicking on stars and an overlayed view of the instrument detectors. Geometrical op erations, painful to convey in the alphanumeric sky, b ecome trivial using the graphical approach. In this pap er we discuss the advantages of the new display.

1.

Introduction

Acquisition and guide star selection for the Keck telescop e is accomplished via the sky program. Sky presents two distinct panels, the main display for direct control and the graphical field for staging an observation. We develop ed the main display during early 1992 and have since b een using it to control the Keck telescop es. The graphical field is a recent addition motivated by 1. the need for more intuitive p ointing and rotation control, 2. the need for a more general method to find suitable guide stars, and 3. AO requirements. 2. The Graphical Field Display

Typically a sky user b egins by sp ecifying a group of ob jects, either by reading in a predefined ob ject list or by searching an area of the sky. The group of ob jects is displayed as a tabular list in sky's main display and as a star chart in sky's graphical field. The sky user can overlay an instrument view onto the star chart and use the middle mouse button to drag it and rotate it among the ob jects in the field. As the instrument field is dragged with the middle mouse button, its right ascension and declination are displayed next to the cross hair that moves along with it. As the instrument view is rotated with the middle mouse button, its p osition angle on the sky reads out as in the lower left p ortion of the display. These three p osition values, right ascension (RA), declination (Dec), and p osition angle (PA), taken together with the p ointing origin (PO), completely sp ecify an instrument orientation. To p oint the telescop e, the sky user selects a p ointing origin with the mouse and then drags and rotates the instrument 393

© Copyright 1997 Astronomical Society of the Pacific. All rights reserved.


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field until the desired orientation app ears on the display. At this p oint, the RA/Dec/PA/PO quadruple can b e transferred to the main display by clicking on the button lab eled "Transfer setup to main display." The sky user can also interact with the graphical display to measure distances, measure angles, and display a particular ob ject's name, visual magnitude, and color. A right mouse button click anywhere in the field p ositions a red cursor at that p oint. Rough astrometry data is then displayed for that p oint, including 1. offset p olar coordinates in arcseconds and degrees, 2. offset Cartesian coordinates in arcseconds, and 3. absolute Cartesian coordinates in hours and degrees. If the right mouse button is clicked on an ob ject, then the ob ject's name, visual magnitude, and color are also displayed. In this case, the astrometry data listed ab ove are taken from the catalog and are therefore more precise. In summary, the middle mouse button is used to drag the field, the right mouse button is used to interrogate the field, and the left mouse button is reserved for selecting stars, selecting p ointing origins, and button clicks. 3. Pointing Origins

To p oint the telescop e, the sky user sp ecifies two p oints: a sky location and a detector location. After the telescop e has b een p ointed, and an image has b een read out from the instrument, the sp ecified sky location will app ear at the sp ecified detector location in that image. Moreover, any field rotation that takes place during the exp osure will b e centered ab out these two coincident p oints. The sky location and detector location can b e thought of as a pair of p oints which are pinned together by the act of p ointing. The sky program has always provided features, such as catalog search tools, telescop e limit displays, and predefined star lists, that help the user sp ecify a sky location. Until recently, however, sky had no features to help the user sp ecify a detector location. This shortcoming introduced unnecessary confusion into the p ointing process. In the new sky, the detector location name occupies equal real estate with the target name. A detector location name, such as "slit" or "center pixel" serves the same purp ose in the instrument coordinate frame as does a target name, such as "Vega" or "NGC1234," in the sky coordinate frame. That is, it provides a named key for referencing a set of precise coordinates. While a target name references the right ascension and declination of a given ob ject, a detector location name references the (x, y ) coordinates of a given pixel. In the previous section we describ ed how the user can drag a cross hair pinned to the instrument's view to adjust the intended right ascension and declination. The p oint in the instrument view to which the cross hair has b een pinned is called the currently selected detector location, or, equivalently, the currently selected pointing origin (Wallace 1987). The red circles displayed at sp ecific p ositions in the instrument view indicate the predefined detector locations for the instrument. When the sky user clicks on a red circle, the displayed


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instrument view is shifted to align the sp ecified detector location with the cross hair. Note that when the user changes p ointing origins by clicking on a red circle, the instrument view is shifted to align with the cross hair. Because the cross hair does not move, the intended right ascension and declination do not move either. The notion of a telescop e move that does not alter right ascension or declination can b e confusing if the display offers only an alphanumeric representation, but is readily apparent with the graphical view. 4. Catalogs (and Other Sources of Ob jects for sky)

As describ ed in section 2, the ob jects displayed in the graphical field are either read from a predefined star list or extracted from an online catalog. Many of the features available from sky's graphical field would also b e useful with a real time guider display, with images read from DSS (Morrison 1994) or with images read from image archives. Our success in integrating b etter catalogs, in particular the degree to which we can go faint, will strongly influence our decisions ab out the alternate sources listed ab ove. In particular, if we can provide catalog coordinates with reasonable coverage down to 18th visual magnitude, the urgency to integrate DSS images recedes. Processed image data from DSS is now readily obtained via the Internet. With current Internet bandwidth to Hawaii, these images are barely useful for daytime planning. Even with planned improvements for Hawaii's Internet access, DSS images could not b e used for night time decision making unless either a complete set is available on a juke b ox or a subset is available on a conventional disk. Similarly, the turn around time for accessing past Keck images is sufficiently slow that using these images for planning from within the sky graphical field would barely b e useful for daytime planning and could only b e used for night time work if an appropriate subset of images were loaded onto a conventional magnetic disk b efore the night's observing. For b oth DSS and archive images, the level zero method for integrating images into the sky graphical field is straightforward: simply add a button for loading an arbitrary FITS image. The question of what do to with that FITS image is more subtle. There are three choices: 1. read raw pixel data directly into the sky graphical field, 2. use centroiding and background flattening to generate a stylized version of the FITS image, or 3. produce a stylized image as ab ove and, in addition, scale and translate the ob ject locations to match the results of a catalog search from the same area (Mink 1997). 5. Star Lists

While still at their home institutions, visiting observers prepare a list of ob jects for their run at Keck. In past versions of sky, this list contained only the ob ject


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name, right ascension, declination, and equinox, and, optionally, keyword-value pairs for prop er motion or differential tracking rates. In the new version of sky, the user can optionally include 1. rotator p osition angle, 2. detector location name (also known as, p ointing origin name), and 3. the p ositional coordinates of any movable instrument detectors. Past star lists only describ ed sky ob jects, and provided no information sp ecific to the telescop e or the instrument. With the addition of the ab ove information, each line in a predefined star list can now sp ecify all of the information needed to set up the telescop e completely. 6. Conclusion

The graphical field display makes p ointing and rotating more intuitive. The display provides p oint-and-click mechanisms b oth for setting up an observation and for measuring distances and angles. Sky now provides methods for selecting the detector location as well as the sky location; b oth are needed to set up an observation. The b est method for incorp orating non-catalog sources requires further study and is influenced by the availability of faint guide star catalogs. Acknowledgments. We thank Julie Barreto, Tom Bida, Randy Campb ell, John Gathright, Tony Gleckler, Bob Goodrich, Wendy Harrison, Hilton Lewis, William Lupton, Jerry Nelson, Gerry Neugebauer, and Pat Wallace. References Wright, J. 1993, in ASP Conf. Ser., Vol. 52, Astronomical Data Analysis Software and Systems I I, ed. R. J. Hanisch, R. J. V. Brissenden, & J. Barnes (San Francisco: ASP), 495 Christian, C. A., & Olson, E. C. 1993, in ASP Conf. Ser., Vol. 52, Astronomical Data Analysis Software and Systems I I, ed. R. J. Hanisch, R. J. V. Brissenden, & J. Barnes (San Francisco: ASP), 56 Wallace, P. 1987, The p ointing and tracking of the Anglo-Australian 3.9 metre telescop e Mink, D. 1997, this volume, 249 Morrison, J. E. 1995, in ASP Conf. Ser., Vol. 77, Astronomical Data Analysis Software and Systems IV, ed. R. A. Shaw, H. E. Payne, & J. J. E. Hayes (San Francisco: ASP), 179