Volume 552, April 2013
|Number of page(s)||16|
|Section||Galactic structure, stellar clusters and populations|
|Published online||04 April 2013|
Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal.
Escuela Politécnica SuperiorUniversity of Alicante,
Received: 16 November 2012
Accepted: 14 February 2013
Context. The open cluster NGC 7419 is known to contain five red supergiants and a very high number of Be stars. However, there are conflicting reports about its age and distance that prevent a useful comparison with other clusters.
Aims. We intend to obtain more accurate parameters for NGC 7419, using techniques different from those of previous authors, so that it may be used as a calibrator for more obscured clusters.
Methods. We obtained Strömgren photometry of the open cluster NGC 7419, as well as classification spectroscopy of ~20 stars in the area. We then applied standard analysis and classification techniques.
Results. We find a distance of 4 ± 0.4 kpc and an age of 14 ± 2 Myr for NGC 7419. The main-sequence turn-off is found at spectral type B1, in excellent agreement. We identify 179 B-type members, implying that there are more than 1200 M⊙ in B stars at present. Extrapolating this to lower masses indicates an initial cluster mass of between 7000 and 10 000 M⊙, depending on the shape of the initial mass function. We find a very high fraction (≈40%) of Be stars around the turn-off, but very few Be stars at lower masses. We also report for the first time a strong variability in the emission characteristics of Be stars. We verified that the parameters of the red supergiant members can be used to obtain accurate cluster parameters.
Conclusions. NGC 7419 is sufficiently massive to serve as a testbed for theoretical predictions and as a template to compare more obscured clusters. The distribution of stars above the main-sequence turn-off is difficult to accommodate with current evolutionary tracks. Though the presence of five red supergiants is marginally consistent with theoretical expectations, the high number of Be stars and very low number of luminous evolved B stars hint at some unknown physical factor that is not considered in current synthesis models.
Key words: open clusters and associations: individual: NGC 7419 / Hertzsprung-Russell and C-M diagrams / stars: early-type / stars: emission-line, Be / supergiants
Partially based on observations collected at the Nordic Optical Telescope and the William Herschel Telescope (La Palma) and at the 1.93-m telescope at Observatoire de Haute Provence (CNRS), France.
Tables 1 and 2 are available in electronic form at http://www.aanda.org
Tables 3, 4 and 7 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A92
© ESO, 2013
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