Revista mexicana de astronomía y astrofísica

 

Intercalibration of the San Pedro Mártir and ctio dimm units

 

J. M. Núñez, J. Bohigas, F. Lazo, D. Hiriart, T. Calvario, O. Escoboza, and F. P. Guillén

 

Instituto de Astronomía Universidad Nacional Autónoma de México, Ensenada, B. C., México

J. M. Núñez, J. Bohigas, F. Lazo, D. Hiriart, T. Calvario, O. Escoboza, and F. P. Guillen: Instituto de Astronomía, Km. 103 Carretera Tijuana–Ensenada, Ensenada, B. C. 22860, México (jnunez, jbb, lazo, hiriart, tomas, fguillen@astrosen.unam.mx; escobozaosiris@yahoo.com.mx).

 

Received 2006 June 30
Accepted 2007 March 28

 

Resumen

Comparamos mediciones simultáneas de seeing obtenidas durante 14 noches con los monitores de movimiento diferencial de imagen (DIMM) usados en el Observatorio Astronómico Nacional en San Pedro Mártir (SPD) y en Cerro Tololo Inter–American Observatory (RoD). Para el conjunto de datos, compuesto de 1581 mediciones cuasi–simultáneas, encontramos que la media y la mediana de las diferencias de seeing RoD–SPD son +0.004±0.138" y +0.010", respectivamente. También descubrimos que la mediana de las diferencias de seeing RoD–SPD es +0.041" cuando el seeing es inferior a 1"; —0.032" cuando está entre 1", y 1.5" y —0.292" cuando es superior a 1.5". Dado que el seeing es usualmente menor que 1", concluimos que las mediciones hechas con unidades tipo SPD deben incrementarse entre 0.01" y 0.04" al ser comparadas con unidades tipo RoD. Esta corrección es mucho menor que la dispersión natural de medidas de seeing que ocurren a lo largo de cualquier noche, y tiene sentido hacerla sólo si las condiciones operativas en ambos sitios son prácticamente las mismas.

 

Abstract

We compare simultaneous seeing measurements produced by the differential image motion monitor (DIMM) units used at the Observatorio Astronómico Nacional at San Pedro Mártir (SPD) and at Cerro Tololo Inter–American Observatory (RoD), for a total of 14 nights. For the data set, made of 1581 nearly–synchronous measurements, we find that the mean and median RoD–SPD seeing differences are +0.004±0.138" and +0.010" respectively. We also find that the median of the RoD–SPD seeing measurements is +0.041" when seeing is less than 1", —0.032" when it is between 1" and 1.5", and —0.292" when it is larger than 1.5". Since seeing is usually smaller than 1", we conclude that measurements obtained with SPD–like units should be increased by 0.01" to 0.04" when comparisons are made with sites using RoD–like units. This correction is much smaller than the natural dispersion of seeing measurements along any night, and it makes sense only when operational conditions in both sites are practically the same.

Key Words: Site testing

 

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Acknowledgement

This work was made possible thanks to the collaboration of the TMT site testing group and the continuous help and advice of those responsible for site testing at CTIO, Edison Bustos in particular. The support of the administrative and technical staff at SPM, in particular Antolin Cordova, is also gratefully acknowledged. Valuable observations made by Mauricio Tapia lead to many improvements in the paper. Above all, the quality of this paper was greatly benefited by many valuable suggestions and poignant criticisms made by an unknown referee. One of us (JB) acknowledges support from Conacyt project 400380–5–G36531–E and DGAPA–Universidad Nacional Autónoma de México project IN–102803.

 

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