arXiv subjects

Gustavo Baume

Publications and source records attributed to Gustavo Baume.

23 records · Page 2Linked to original sources

arXiv2003

The old open clusters Saurer A, B and C revisited

We report on deep (V $\approx$ 24.0) $VI$ CCD photometry of 3 fields centered in the regions of the old open clusters Saurer A, B and C. In the case of Saurer A, which is considered one of the oldest known open cluster, we also provide a comparison field. From the analysis of the photometry we claim that Saurer A is as old as M 67 ($\approx$ 5 Gyrs), but more metal poor (Z=0.008). Moreover it turns out to be the open cluster with the largest galactocentric distance so far detected. As for Saurer B, it closely resembles NGC 2158, and indeed is of intermediate-age (1.8-2.2 Gyrs) and significantly reddened. In this case we revise both the age and the distance with respect to previous studies, but we are not able to clearly establish the cluster metal abundance. Finally, Saurer C has an age of about 2 Gyrs, but we emphasize that the precise determination of its properties is hampered by the heavy fieldstars contamination.

astro-ph↗

arXiv2003

A study of the two northern open clusters NGC 1582 and NGC 1663

We present CCD $UBV(I)_C$ observations obtained in the field of the previously unstudied northern open clusters NGC 1582 and NGC 1663. For the former, we also provide high-resolution spectra of the brightest stars and complement our data with Two-Micron All-Sky-Survey (2MASS) near-infrared photometry and with astrometric data from the Tycho-2 catalog. From the analysis of all these data, we argue that NGC 1582 is a very poor, quite large and heavily contaminated open cluster. It turns out to have a reddening $E_{B-V} = 0.35 \pm 0.03$, to be situated $1100 \pm 100$ pc from the Sun and to have an age of $300 \pm 100$ Myr. On the other hand, we were not able to unambiguously clarify the nature of NGC 1663. By assuming it is a real cluster and from the analysis of its photometric diagrams, we found a color excess value $E_{B-V} = 0.20$, an intermediate age value ($\sim 2000$ Myr) and a distance of about 700 pc. The distribution of the stars in the region however suggests we are probably facing an open cluster remnant. As an additional result, we obtained aperture photometry of three previously unclassified galaxies placed in the field of NGC 1663 and performed a preliminary morphological classification of them.

astro-ph↗

arXiv2003

NGC 1883: a neglected intermediate-age open cluster located in the outskirts of the Galactic disk

We report on $BVI$ CCD photometry of a field centered in the region of the open cluster NGC 1883 down to V=21. This cluster has never been studied insofar, and we provide for the first time estimates of its fundamental parameters, namely radial extent, age, distance and reddening. We find that the cluster has a radius of about 2.5 arcmin, and shows signatures of dynamical relaxation. NGC 1883 is located in the anti-center direction, and exhibits a reddening in the range E$(B-V)= 0.23-0.35$, depending on the metal abundance. It turns out to be of intermediate-age (1 billion years old), and quite distant for an open cluster. In fact it is located 4.8 kpc from the Sun, and more than 13 kpc from the Galactic center. This results makes NGC 1883 one of the most peripheral old open clusters, with important consequences for the trend of the metallicity with distance in the outer Galactic disk.

astro-ph↗

arXiv2003

Photometric study of the young open cluster NGC 3293

Deep and extensive CCD photometric observations $UBV(RI)_{C}H_α$ were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to $M_{V} \approx +4.5$, revealing that stars with $M_{V} < -2$ are evolving off the main sequence; stars with $-2 < M_{V} < +2$ are located on the main sequence and stars with $M_{V} > +2$ are placed above it. According to our analysis, the cluster distance is $d = 2750 \pm 250 pc$ ($V_{0}-M_{V} = 12.2 \pm 0.2$) and its nuclear age is $8 \pm 1 Myr$. NGC 3293 contains an important fraction of pre--main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to $2.5 \cal M_{\sun}$ and a mean contraction age of $10 Myr$. This last value does not differ too much from the nuclear age estimate. Actually, if we take into account the many factors that may affect the PMS star positions onto the colour--magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Besides, using the $H_α$ data, we detected nineteen stars with signs of having $H_α$ emission in the region of NGC 3293, giving another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope value $x = 1.2 \pm 0.2$, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.

astro-ph↗

arXiv2000

The highly polarized open cluster Trumpler 27

We have carried out multicolor linear polarimetry (UBVRI) of the brightest stars in the area of the open cluster Trumpler 27. Our data show a high level of polarization in the stellar light with a considerable dispersion, from $P = 4%$ to $P = 9.5%$. The polarization vectors of the cluster members appear to be aligned. Foreground polarization was estimated from the data of some non-member objects, for which two different components were resolved: the first one associated with a dust cloud close to the Sun producing $P_{λmax}=1.3%$ and $θ=146$ degrees, and a second component, the main source of polarization for the cluster members, originated in another dust cloud, which polarizes the light in the direction of $θ= 29.5$ degrees. From a detailed analysis, we found that the two components have associated values $E_{B-V} < 0.45 $ for the first one, and $E_{B-V} > 0.75$ for the other. Due the difference in the orientation of both polarization vectors, almost 90 degrees (180 degrees at the Stokes representation), the first cloud ($θ\sim 146$ degrees) depolarize the light strongly polarized by the second one ($θ\sim 29.5$ degrees).

astro-ph↗