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|Photometry of the five marginally studied open clusters Collinder 74, Berkeley 27, Haffner 8, NGC 2509, and VdB-Hagen 4|
Context: The stellar populations in the outer Galactic disk are asubject of wide interest nowadays. To contribute to a better picture ofthis part of the Galaxy, we have studied the nature of five marginallyinvestigated star clusters (Collinder 74, Berkeley 27, Haffner 8, NGC2509, and VdB-Hagen4) by means of accurate CCD photometry in the V and Ipassbands. These clusters are in fact located in the third Galacticquadrant. Aims: We aim to obtain the basic parameters of these objects,which in some cases are still disputed in the literature. In the case ofVdB-Hagen 4 we provide the first estimate of its fundamental parameters,while for Haffner 8 we present the first CCD photometry. Methods: Theanalysis is based on the comparison between field stars decontaminatedcolor magnitude diagrams and stellar models. Particular care is devotedto the the assessment of the data quality and the statistical field stardecontamination. The Padova library of stellar isochrones is adopted inthis study. Results: The analysis we carried out allowed us to solve afew inconsistencies in the literature regarding Haffner 8 and NGC 2509.Collinder 74 is found to be significantly older than reported before.VdB-Hagen 4 is a young open cluster located more than 20 kpc from theGalactic center. Such an extreme distance is compatible with the clusterbelonging to the Norma-Cygnus arm.Photometric data is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/573
|NGC 2401: A Template of Cygnus Arm Young Population over the Third Galactic Quadrant|
Based on a deep CCD (UBV(RI) [C]) photometric survey and Two-MicronAll-Sky-Survey (2MASS) photometry data we derived the main parameters ofthe open cluster NGC 2401. We found this cluster is located at 6.3 +/-0.5 kpc (V_0 - M_V = 14.0+/-0.2) from the Sun and is 25 Myr old. Thatallows us to identify NGC 2401 as a member of the young populationbelonging to the extension of the Norma - Cygnus spiral- arm over theThird Galactic Quadrant. We additionally constructed the clusterluminosity function down to V ≈ 22 and also the cluster initial massfunction for all stars with masses above M ≈ 1-2 M_V in which case wefound a slope x ≈ 1.8+/-0.2. A spectroscopic study of the emissionstar LSS 440 that lies is the cluster area revealed it is a B0Ve star.Its parameters and probable connection with NGC 2401 are also discussed.
|Spiral structure of the third galactic quadrant and the solution to the Canis Major debate|
With the discovery of the Sagittarius dwarf spheroidal, a galaxy caughtin the process of merging with the Milky Way, the hunt for other suchaccretion events has become a very active field of astrophysicalresearch. The identification of a stellar ring-like structure inMonoceros, spanning more than 100°, and the detection of anoverdensity of stars in the direction of the constellation of CanisMajor (CMa), apparently associated to the ring, has led to thewidespread belief that a second galaxy being cannibalized by the MilkyWay had been found. In this scenario, the overdensity would be theremaining core of the disrupted galaxy and the ring would be the tidaldebris left behind. However, unlike the Sagittarius dwarf, which is wellbelow the Galactic plane and whose orbit, and thus tidal tail, is nearlyperpendicular to the plane of the Milky Way, the putative CMa galaxy andring are nearly co-planar with the Galactic disc. This severelycomplicates the interpretation of observations. In this Letter, we showthat our new description of the Milky Way leads to a completelydifferent picture. We argue that the Norma-Cygnus spiral arm defines adistant stellar ring crossing Monoceros and the overdensity is simply aprojection effect of looking along the nearby local arm. Our perspectivesheds new light on a very poorly known region, the third Galacticquadrant, where CMa is located.
|NGC 2401: a template of the young population of the Norma-Cygnus arm in the Third Galactic Quadrant*|
Based on a deep optical CCD [UBV(RI)C] photometric survey andon the Two-Micron All Sky Survey (2MASS) data, we derived the mainparameters of the open cluster NGC 2401. We found that this cluster isplaced at 6.3 +/- 0.5 kpc (VO-MV= 14.0 +/- 0.2)from the Sun and is 25 Myr old, which allows us to identify NGC 2401 asa member of the young population belonging to the innermost side of theextension of the Norma-Cygnus spiral arm in the Third Galactic Quadrant.A spectroscopic study of the emission star LSS 440 that lies in thecluster area revealed that it is a B0Ve star; however, we could notconfirm that it is a cluster member. We also constructed the clusterluminosity function (LF) down to V~ 22 and the cluster initial massfunction (IMF) for all stars with masses above M~ 1-2Msolar.It was found that the slope of the cluster IMF is x~ 1.8 +/- 0.2. Thepresence of a probable pre-main-sequence (PMS) star populationassociated with the cluster is weakly revealed.
|UBVRI CCD photometric studies of open clusters Berkeley 15, Czernik 18 and NGC 2401.|
CCD photometric observations of three open clusters Berkeley 15 (=OCl414), Czernik 18 (=OCl 426) and NGC 2401 (=OCl 588), obtained for thefirst time in UBVRI filters down to V=20 mag, are presented here. Theyare located at distances of 1259, 955 and 3467 parsecs with theirrespective ages estimated as ~5 x 109 years, ~0.8 to 1 x109 years and ~1 x 109 years. While OCl 414 andOCl 426 are in the direction of the Auriga - Perseus constellations, OCl588 is placed in the direction of Ophiuchus constellation in our Galaxy.The clusters studied here are of intermediate and old age category.
|Open clusters in the third galactic quadrant. I. Photometry|
We have performed a photometric survey of open clusters in the thirdGalactic quadrant in order to study the star formation history andspatial structure in the Canis Major-Puppis-Vela region. In this paperwe describe a catalogue of CCD U BV RI photometry of approximately 65000 stars in the fields of 30 open clusters. The data were obtained andreduced using the same telescope, the same reduction procedures, and thesame standard photometric system, which makes this catalogue the largesthomogeneous source of open cluster photometry so far. In subsequentpapers of this series, colour-colour and colour-magnitude diagrams willbe presented which, amongst other uses, will allow the determination ofan homogeneous set of cluster reddenings, distances, and ages that willconstitute the observational basis for our studies of the spatialstructure and star formation history in the third Galactic quadrant.
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