2010A&A...510A..44M


Query : 2010A&A...510A..44M

2010A&A...510A..44M - Astronomy and Astrophysics, volume 510, A44-44 (2010/2-1)

Not an open cluster after all: the NGC 6863 asterism in Aquila.

MONI BIDIN C., DE LA FUENTE MARCOS R., DE LA FUENTE MARCOS C. and CARRARO G.

Abstract (from CDS):

Shortly after birth, open clusters start dissolving; gradually losing stars into the surrounding star field. The time scale for complete disintegration depends both on their initial membership and location within the Galaxy. Open clusters undergoing the terminal phase of cluster disruption or open cluster remnants (OCRs) are notoriously difficult to identify. From an observational point, a combination of low number statistics and minimal contrast against the general stellar field conspire to turn them into very challenging objects. To make the situation even worst, random samples of field stars often display features that may induce to classify them erroneously as extremely evolved open clusters. In this paper, we provide a detailed study of the stellar content and kinematics of NGC 6863, a compact group of a few stars located in Aquila and described by the Palomar Observatory Sky Survey as a non existent cluster. Nonetheless, this object has been recently classified as OCR. The aim of the present work is to either confirm or disprove its OCR status by a detailed star-by-star analysis. The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC3 catalogue, and high resolution spectroscopy as well as results from extensive N-body calculations. The spectra of the four brightest stars in this field clearly indicate that they are part of different populations. Their radial velocities are statistically very different and their spectroscopic parallaxes are inconsistent with them being part of a single, bound stellar system. Out of the four stars, only two of them have similar metallicity. The color magnitude diagram for the field of NGC 6863 does not show any clear signature typical of actual open clusters. Consistently, spatial scan statistics confirms the absence of any statistically significant, kinematically supported over-density at the purported location of NGC 6863. Our results show that the four brightest stars commonly associated to NGC 6863 form an asterism, a group of non-physically associated stars projected together, leading to the conclusion that NGC 6863 is not a real open cluster.

Abstract Copyright:

Journal keyword(s): open clusters and associations: individual: NGC 6863 - open clusters and associations: individual: NGC 1901 - open clusters and associations: general - Galaxy: evolution

Nomenclature: Tables 2-3: [MDD2010] N (Nos 4, 5, 7, 8).

Simbad objects: 18

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Number of rows : 18
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 C 0147+270 Cl* 01 50 10 +27 06.9     8.2     ~ 14 0
2 NGC 1901 OpC 05 17 58 -68 20.5           ~ 103 0
3 * sig Ori Y*O 05 38 44.7653828520 -02 36 00.283179888 2.54 3.58 3.79 3.87 4.11 O9.5V+B0.2V(n) 801 0
4 NGC 2664 OpC 08 47 11 +12 36.2           ~ 13 0
5 NGC 5385 Cl* 13 52 27 +76 10.5           ~ 6 0
6 C 1440+697 Cl* 14 40.9 +69 34           ~ 27 0
7 NAME Ursa Major Cluster ClG 15 08.8 +67 07           ~ 409 0
8 * rho Oph ** 16 25 35.11766 -23 26 49.8150 4.30 4.85 4.63 4.27 3.96 B2IV+B2V 648 0
9 * 67 Oph s*b 18 00 38.7157893000 +02 55 53.633402904 3.34 3.96 3.93 3.84 3.81 B5Ib 407 0
10 NAME Aql Region reg 18 31.1 -02 10           ~ 391 0
11 HD 185268 * 19 37 09.6183173088 +29 20 01.323130560 5.84 6.34 6.43     B5V 51 0
12 UCAC3 173-234387 * 20 05 06.0719787792 -03 33 29.314637820       15.06 13.26 ~ 1 0
13 UCAC3 173-234391 PM* 20 05 06.7746767232 -03 33 26.634147696       14.87 13.29 ~ 1 0
14 NGC 6863 ? 20 05 07 -03 33.3           ~ 4 1
15 UCAC3 173-234395 * 20 05 07.6647346944 -03 32 59.312553144       14.59 12.93 ~ 1 0
16 UCAC3 173-234400 * 20 05 08.4967284840 -03 33 22.694251428       14.22 12.27 ~ 1 0
17 * 8 Lac B * 22 35 52.0990532376 +39 37 41.339738568 4.61 5.52 5.67 5.88 6.06 B1.Vs 114 0
18 * 1 Cas * 23 06 36.8178557 +59 25 11.135698 3.93 4.771 4.840     B0.5III 245 0

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