A Photometric and Spectroscopic Evaluation of the Site at Tonantzintla Observatory¹

 

H. M. Hernández–Toledo,² L. A. Martínez–Vázquez,² M. A. Moreno–Corral,³ and A. Pani–Cielo⁴

 

² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70–264, 04510 México, D. F. Mexico. (hector@astroscu.unam.mx, lamb@astroscu.unam.mx).

³ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22860 Ensenada, Baja California, Mexico. (mam@astrosen.unam.mx).

⁴ Observatorio Astronómico Nacional, Tonantzintla, 72840, Puebla, Mexico. (apani@astroscu.unam.mx).

 

Received 2009 March 24
Accepted 2009 October 15

 

RESUMEN

Se presenta una evaluación sobre la calidad del cielo en el Observatorio Astronómico Nacional de Tonantzintla mediante la calibración fotométrica de un conjunto de estrellas estándar en M67 en las bandas B, V, R e I del sistema Johnson–Cousins y la observación del cielo a diferentes distancias cenitales con el espectrógrafo Boller & Chivens. El brillo del cielo se estimó (a) a partir de las observaciones CCD al cúmulo M67 y (b) utilizando un método visual en dirección de estrellas de magnitud conocida. Se obtuvo un valor de 18.5 ± 0.6 mag arcsec^–2. La curva de extinción atmosférica promedio presenta un comportamiento intermedio entre la observada para el OAN–San Pedro Mártir y la asociada a actividad volcánica. Los espectros del cielo en el OAN–Tonantzintla permiten identificar líneas asociadas a lámparas de HgI y NaI a baja y alta presión. Nuestros resultados permiten justificar la actualización y compra de nuevo equipamiento para convertir al OAN–Tonantzintla en el Laboratorio para la Enseñanza de la Astronomía Observacional.

 

ABSTRACT

Based on data obtained at the Observatorio Astronómico Nacional, Tonantzintla, an evaluation of the quality of the local sky is presented. The evaluation is carried out through an absolute CCD calibration to a set of standard stars in the field of M67 in the B, V, R and I Johnson–Cousins system and from Boller & Chivens long–slit spectroscopic observations of the local sky at various elevations. The sky brightness is estimated from our CCD frames yielding a mean value of 18.5 ± 0.6 mag arcsec^–2. The mean atmospheric extinction curve behaves midway between the normal extinction and that related to volcanic outbursts. From the long–slit spectra of the sky at OAN–Tonantzintla, HgI and NaI lines of high and low pressure lamps are identified. These results allow us to justify a major upgrading of the observatory, to convert the OAN–Tonantzintla into the Laboratory for Astronomy Education both for UNAM and for other educational institutions in the center–south part of the country.

Key Words: atmospheric effects — site testing — stars: fundamental parameters — stars: imaging — techniques: photometric — techniques: spectroscopic.

 

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ACKNOWLEDGMENTS

H.M.H.T acknowledges support through grants DGAPA PAPIME–PE103406 and Conacyt 42810/A–1. We have made use of NED and LEDA databases throughout. H.M.H.T thanks the night assistant A. Cielo for their help during all the observing runs at the OAN–Tonantzintla 1 m telescope. H.M.H.T thanks Guadalupe Pardo from CECADESU/SEMARNAT for discussions concerning the implementation of a first campaign to estimate the sky surface brightness and luminic contamination around Tonantzintla Observatory. H.M.H.T thanks the municipal presidents of San Rafael Comac, Santa María Tonantzintla and San Francisco Acatepec for the support provided during this campaign. H.M.H.T thanks the students from the Facultad de Ciencias and the graduate astronomy program at IA–Universidad Nacional Autónoma de México that participated in this sky brightness campaign. H.M.H.T thanks the anonymous referee for his/her careful reading and appropriate questioning that greatly improved this manuscript.

 

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NOTE

¹ Based on data obtained at the 1 m telescope of the Observatorio Astronómico Nacional, Tonantzintla, Puebla, México, operated by the Instituto de Astronomía, Universidad Nacional Autónoma de México.