University of Alicante
Over the past twenty years, the Stellar Astrophysics Group at the University of Alicante has found a number of new open clusters. Following the astronomical tradition, we have named them after the institution were we work. These clusters (with one exception) had never been identified before. This means that they are not easy to find.
The Alicante clusters come in two main groups. Many of them are small stellar groupings found in the neighbourhood of other clusters or inside OB associations. Most of them were found during an exploration of the Outer Galaxy (Negueruela & Marco 2003). They are generally quite small, but surprisingly contain very massive stars (especially, Alicante 1, 2, 3 & 11).
The second main group (Alicante 7 to 10) are clusters of red supergiants in the region of Scutum. This is an area of very high obscuration, owing to the presence of thick dust clouds in the Scutum-Crux Arm. Associated to one of those clouds is the star-forming cluster Alicante 6. Beyond these clouds lies one of the largest areas of recent star formation in the Milky Way. Because of high distance and obscuration, clusters in this area can only be identified by the presence of very bright red supergiants.
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«Stellar tracers of the Cygnus Arm. II. A young open cluster in Camelopardalis OB3» Negueruela & Marco (2008), A&A 492, 441
Not published as such, but described in «A WN4 companion to BD +62°2296 in Cas OB5», Negueruela (2004), A&A 408, 689
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The cluster is very well seen in Gaia DR2 data, but the astrometric solution for the WR is poor. The average parallax is ~0.28 milliarcsec.
Found in 2001, but never published.
Listed in SIMBAD as Stock 17, after Pandey (1986) BASI 14, 20, but the nominal position of Stock 17 lies about 14′ away and likely refers to the group formed by LS I +61º 43, 45 & 46.
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Retrieved as an open cluster in the search of Gaia DR2 data by Cantat-Gaudin et al. (2018). The median parallax is 0.31 milli-arcseconds.
Found in 2001, but never published.
Idenpendently identified by Wilton Dias and published as part of his open cluster database, where it is listed as Dias 1.
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Retrieved as an open cluster in the search of Gaia DR2 data by Cantat-Gaudin et al. (2018). Marginally separate from the nearby (10′ apart) King 16 in the proper motion plane, seems to have a distinctly larger parallax, although DR3 data will be needed to assess if it is unconnected. The median parallax is 0.37 milli-arcseconds.
Characterised and described in «The open cluster Pismis 11 and the very luminous blue supergiant HD 80077: I. Physical parameters of the cluster», Marco & Negueruela (2009), A&A 493, 79.
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Quite well defined in the proper motion plane in Gaia DR 2 data, though affected by significant differential reddening. Mean parallax around 0.35.
«An obscured cluster associated with the H II region RCW173», Marco & Negueruela (2011), A&A 534, A114.
SIMBAD: Cl Alicante 6
But note that the position in SIMBAD is significantly offset, very likely due to a confusion induced by Baut et al. (2016), who somehow seem to imply that the cluster that they had «discovered» was not the same one that we had reported five years earlier.
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Gaia DR 2 data do not separate well the cluster from the field, but strongly suggest the presence of two main clumps (one inside N37 and the other one around the O7 V star C81) with the same proper motions and reddening. The typical parallax is 0.38 milli-arcseconds, and the unreddened older B-type stars that we investigated seem to be at exactly the same distance.
«A massive association around the obscured open cluster RSGC3», Negueruela et al. (2011), A&A 528, A59.
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Gaia DR 2 data are not good enough to identify the cluster. However, unpublished spectra of several candidates clearly indicate that this is a real cluster of red supergiants. This is further confirmed by the work of Origlia et al. (2019), who observed 7 RSG members.
«Another cluster of red supergiants close to RSGC1», Negueruela et al. (2010), A&A 513, A74.
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This was an excellent cluster candidate based on stellar density and photometry, but radial velocities show that the stars are not a physical group (Asa’d et al. 2023, AJ 165, 212).
«A massive association around the obscured open cluster RSGC3», Negueruela et al. (2011), A&A 528, A59.
SIMBAD: Not in SIMBAD
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There are only three RSGs identified in this area. They share properties and radial velocities. With such a small number, it is difficult to know if this is an open cluster or just an overdensity in the surrounding association. The expected accompanying blue population cannot be separated from the field. We will probably need Gaia-nIR to know.
«A third cluster of red supergiants in the vicinity of the massive cluster RSGC3», González-Fernández & Negueruela (2012), A&A 539, A100.
SIMBAD: Cl Alicante 10
Position in SIMBAD somewhat offset from main concentration of RSGs.
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Given the high number of RSGs with similar radial velocities, this candidate can be considered almost certainly a cluster. Together with RSGC3 and Alicante 7, it defines a huge association that contains no less than 50 RSGs (see also Origlia et al. 2019).
«Open clusters in Auriga OB2», Marco & Negueruela (2016), MNRAS 459, 880.
Identified and observed in 2003, the results weren’t published until 2016. In the mean time, it was marked as a cluster candidate by Froebrich et al. (2007), under code name FSR 777.
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Gaia DR2 data confirm that the properties of this population are indistinguishable from those of Stock 8, which is over 20 arcmin away. The parallax for this area, 0.45 milli-arcseconds indicates a rather lower distance than estimated from photometry and spectroscopy, around 2 kpc.
«Open clusters in Auriga OB2», Marco & Negueruela (2016), MNRAS 459, 880.
Identified and observed in 2003, the results weren’t published until 2016. In the mean time, it was marked as a cluster candidate by Kronberger et al. (2006), under the name Kronberger 1.
Note
Gaia DR2 data confirm that the properties of this population are indistinguishable from those of Stock 8, which is over 20 arcmin away. The parallax for this area, 0.45 milli-arcseconds indicates a rather lower distance than estimated from photometry and spectroscopy, around 2 kpc.
«Cluster membership for the long period Cepheid calibrator SV Vul», Negueruela et al. (2020) MNRAS 494, 3028.
SIMBAD: Not yet in SIMBAD
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In spite of its low contrast, Alicante 13 pops up in the recent automated search for clusters in Gaia DR2 data carried out by Castro-Ginard et al. (2020), where it is given as UBC 130. Although it can hardly be seen, it has a few dozen B-type stars and therefore a mass approaching 1000 solar masses.