Zero-age Main-sequence Fitting Research Articles

The Sejong Open Cluster Survey (SOS). VII. A Photometric Study of the Young Open Cluster IC 1590

Abstract Young open clusters are ideal laboratories to understand the star formation process. We present deep UBVI and Hα photometry for the young open cluster IC 1590 in the center of the H ii region NGC 281. Early-type members are selected from UBV photometric diagrams, and low-mass pre-main-sequence (PMS) members are identified by using Hα photometry. In addition, the published X-ray source list and Gaia astrometric data are also used to isolate probable members. A total of 408 stars are selected as members. The mean reddening obtained from early-type members is 〈E(B − V)〉 = 0.40 ± 0.06 (s.d.). We confirm the abnormal extinction law for the intracluster medium. The distance modulus to the cluster determined from the zero-age main-sequence fitting method is 12.3 ± 0.2 mag (d = 2.88 ± 0.28 kpc), which is consistent with the distance d = 2.70 − 0.20 + 0.24 kpc from the recent Gaia parallaxes. We also estimate the ages and masses of individual members by means of stellar evolutionary models. The mode of the age of PMS stars is about 0.8 Myr. The initial mass function of IC 1590 is derived. It appears to be a steeper shape (Γ = −1.49 ± 0.14) than that of the Salpeter/Kroupa initial mass function for the high-mass regime (m > 1 M ⊙). The signature of mass segregation is detected from the difference in the slopes of the initial mass functions for the inner ( r < 2 .′ 5 ) and outer regions of this cluster. We finally discuss the star formation history in NGC 281.

$$\varvec{U\!BV\!I}$$ CCD photometry of Berkeley 55 open cluster

Fundamental astrophysical parameters have been derived for Berkeley 55 (Be 55) open cluster based on the UBVI charge-coupled device (CCD) photometric data observed using a AZT-22 1.5 m telescope at Maidanak Astronomical Observatory (MAO) in Uzbekistan. The mean reddening is obtained as \(E(B-V)=1.77\pm 0.10\,\mathrm {mag}\) from early-type members. The zero-age main sequence fitting in the \(Q_{V\lambda }\) – \(Q'\) diagrams indicates the distance modulus, \((V_{0}-M_{V})=12.4\pm 0.20\,\mathrm {mag}\,(d=3.02\pm 0.28\,\mathrm {kpc}\)). This photometric distance is consistent with the distances of Gaia EDR3 (\(d = 3.09 \pm 0.16\,\mathrm {kpc}\)) and period–luminosity relation (\(d =\) 2.78 ± 0.32 kpc) of its Cepheid S5 within the uncertainties. This distance also locates the cluster near the Perseus spiral arm. The Geneva isochrone fittings to the Hertzsprung–Russell diagram and observational colour–magnitude diagrams derive turn-off age, 85 ± 13 Myr, by taking care of five red supergiants/bright giants. The possible inconsistencies in the locations of the bright giants with the rotating/non-rotating isochrones may be due to both the age spread of stars in young open clusters and the diversity in rotational velocities.

Sejong Open Cluster Survey (SOS) – III. The young open cluster NGC 1893 in the H ii region W8

We present a UBV I and H alpha photometric study of the young open cluster NGC 1893 in the H II region W8 (IC 410 or Sh 2-236). A total of 65 early-type members are selected from photometric diagrams. A mean reddening of the stars is <E(B-V)> = 0.563 +/- 0.083 mag. The published photometric data in the near- and mid-infrared passbands are used to test the reddening law toward the cluster, and we confirm that the reddening law is normal (R_V = 3.1). Zero-age main sequence fitting gives a distance modulus of V_0 - M_V = 12.7 +/- 0.2 mag, equivalent to 3.5 +/- 0.3 kpc. From H alpha photometry 125 H alpha emission stars and candidates are identified as pre-main sequence (PMS). The lists of young stellar objects and X-ray sources published by previous studies allow us to select a large number of PMS members down to 1 M_sun. Isochrone fitting in the Hertzsprung-Russell diagram gives a turn-off age of 1.5 Myr and the median age of 1.9 Myr from the PMS members with a spread of 5 Myr. We derive the initial mass function (IMF) for stars with mass larger than 1 M_sun. The slope of the IMF (Gamma = -1.3 +/- 0.1) is well consistent with the Salpeter/Kroupa IMF. A total mass of the cluster appears to be in excess of 1,300 M_sun. Finally, we estimate the mass accretion rate of 82 PMS members in the mass range of 0.6 M_sun to 5 M_sun.

A SEARCH FOR OB ASSOCIATIONS NEAR SOUTHERN LONG-PERIOD CEPHEIDS. V. AQ PUPPIS AND V620 PUPPIS

A photometric UBV survey is presented for 610 stars in a region surrounding the Cepheid AQ Puppis and centered southwest of the variable, based upon photoelectric measures for 14 stars and calibrated iris photometry of photographic plates of the field for 596 stars. An analysis of reddening and distance for program stars indicates that the major dust complex in this direction is ~1.8 kpc distant, producing differential extinction described by a ratio of total-to-selective extinction of R=Av/E(B-V)=3.10+-0.20. Zero-age main-sequence fitting for the main group of B-type stars along the line of sight yields a distance of 3.21+-0.19 kpc (Vo-Mv=12.53+-0.13 s.e.). The 29.97d Cepheid AQ Pup, of field reddening E(B-V)=0.47+-0.07 (E(B-V)(B0)=0.51+-0.07), appears to be associated with B-type stars lying within 5' of it as well as with a sparse group of stars, designated Turner 14, centered south of it at J2000.0 = 07:58:37, -29:25:00, with a mean reddening of E(B-V)=0.81+-0.01. AQ Pup has an inferred luminosity as a cluster member of <Mv>=-5.40+-0.25 and an evolutionary age of 3x10^7 yr. Its observed rate of period increase of 300.1+-1.2 s/yr is an order of magnitude larger than what is observed for Cepheids of comparable period in the third crossing of the instability strip, and may be indicative of a high rate of mass loss or a putative fifth crossing. Another sparse cluster, designated Turner 13, surrounds the newly-recognized 2.59d Cepheid V620 Pup, of space reddening E(B-V)=0.64+-0.02 (E(B-V)(B0)=0.68+-0.02), distance 2.88+-0.11 kpc (Vo-Mv=12.30+-0.08 s.e.), evolutionary age 10^8 yr, and an inferred luminosity as a likely cluster member of <Mv>=-2.74+-0.11. V620 Pup is tentatively identified as a first crosser, pending additional observations.

Cepheid distances from the Baade–Wesselink method

AbstractRecent progress on Baade–Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period–luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

Recalibration of the uvbyβ photometry-based distance scale of OB-type stars using the revised Hipparcos parallaxes

AbstractThe absolute visual and infrared magnitudes of moderately evolved OB-type stars are directly calibrated as a function of Stroemgren four-color and Hβ photometric indices using the trigonometric parallaxes from the new reduction of Hipparcos data. The resulting calibrations have an average accuracy of ~ 0.4 mag and, when applied to members of young open clusters, yield distances that are fairly consistent with those determined using the MV–(B − V) zero-age main-sequence fitting procedure.

Probing the anomalous extinction of four young star clusters: the use of colour-excess, main-sequence fitting and fractal analysis

Four young star clusters were studied in order to characterize their anomalous extinction or variable reddening that could be due to a possible contamination by dense clouds or circumstellar effects. The extinction law (Rv) was evaluated by adopting two methods: (i) the use of theoretical expressions based on the colour-excess of stars with known spectral type, and (ii) the analysis of two-colour diagrams, where the slope of observed colours distribution is compared to the normal distribution. An algorithm to reproduce the zero age main sequence (ZAMS) reddened colours was developed in order to derive the average visual extinction (Av) that provides the best fitting of the observational data. The structure of the clouds was evaluated by means of statistical fractal analysis, aiming to compare their geometric structure with the spatial distribution of the cluster members. The cluster NGC 6530 is the only object of our sample showing anomalous extinction. In average, the other clusters are suffering normal extinction, but several of their members, mainly in NGC 2264, seem to have high Rv, probably due to circumstellar effects. The ZAMS fitting provides Av values that are in good agreement with those found in the literature. The fractal analysis shows that NGC 6530 has a centrally concentrated distribution of stars that is different of the sub-structures found in the density distribution of the cloud projected in the Av map, suggesting that the original cloud has been changed with the cluster formation. On the other hand, the fractal dimension and the statistical parameters of Berkeley 86, NGC 2244, and NGC 2264 indicate a good cloud-cluster correlation, when compared to other works based on artificial distribution of points.

Early-type stars in the open cluster NGC 4852

The southern open cluster NGC 4852 was re-observed in the UBVRI passbands to refine its intrinsic fundamental parameters. An extended spectral coverage was also undertaken aimed at obtaining a clear picture of the kind of stars inhabiting the cluster upper main sequence. We detected an unusual number of B-type stars including a new weak-emission Be star that raises to three the number of confirmed emission objects known in the cluster area. Our analysis, however, is conclusive in that none of them belongs to the cluster. With the new data set, we improved the fundamental parameters of NGC 4852: it is little bit farther than formerly assumed; the reddening, which increases smoothly with the distance, is lower than early estimates; and more importantly, it is really a young object of nearly 40–60 Myr, contrary to the age of 200 Myr stated before. By means of spectroscopic parallaxes we secured the star distances, finding a good agreement between spectroscopic and zero-age main-sequence fitting distances, within the errors. The spatial distribution of the stars allows us to infer that NGC 4852 is the final, closer to the Sun, structure of a star-forming region and that a distant group of early-B-type stars, located immediately beyond the cluster, seems to be part of an extended OB association. The three emission stars detected in the region are related to this farther group. Finally, two extremely faint and blue stars were also found in the cluster zone. They have no connection with NGC 4852 but seem to be white-dwarf candidates.

UBVIJHKPhotometric Study of the Open Cluster NGC 2849

We present UBVIJHK photometry of the open cluster NGC 2849. Color-magnitude diagrams (CMDs) of this cluster show a well-defined main sequence and a sparse red giant branch. In spite of a relatively large color excess of E(B - V) = 0.50 ± 0.04, our color-color analysis shows that the interstellar reddening toward this cluster is compatible with the standard extinction model. The cluster also has a broad main sequence indicative of binary sequence rather than differential reddening or field contamination, as suggested elsewhere. From the ultraviolet excess, we estimate the metallicity to be [Fe/H] = -0.24 ± 0.12. A distance modulus of (m - M)0 = 13.93 ± 0.17 is obtained from zero-age main-sequence fitting. A CMD comparison with the Padua theoretical models published by Bertelli and coworkers gives an age of log t = 8.8 ± 0.1.

Trumpler 27 - A heavily reddened young open cluster with blue and red supergiants

view Abstract Citations (34) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Trumpler 27: a heavily reddened young open cluster with blue and red supergiants. Moffat, A. F. J. ; Fitzgerald, M. P. ; Jackson, P. D. Abstract Trumpler 27 is a heavily reddened cluster of earliest spectral type 09. It contains six blue supergiants, one yellow supergiant, and one red supergiant, CD - 33o12241. The yellow super- giant, of type GO Ia, lies at the luminous blue edge of the Cepheid instability strip. Two Wolf-Rayet stars are probable members. Tr 27 is 2.1 + 0.2 kpc from the Sun, on the basis of mean spectroscopic parallaxes of 16 members and Zero-Age Main Sequence fitting. Fifty probable members are identified on the basis of spectra and UBV photoelectric and photographic photometry complete to V 14.8. The visual extinction ranges from 3 to 8 magnitudes and varies systematically across the face of the cluster. This leads to a value of R = = 3.3 + 0.3. There is no tendency for the intrinsically more luminous stars to be more heavily reddened than stars of lower luminosity. Subject headings: clusters: open - stars: early-type - stars: spectral classification - stars: supergiants - stars: Wolf-Rayet Publication: The Astrophysical Journal Pub Date: July 1977 DOI: 10.1086/155338 Bibcode: 1977ApJ...215..106M Keywords: Early Stars; Open Clusters; Stellar Spectrophotometry; Supergiant Stars; Ubv Spectra; Astronomical Photography; Hot Stars; Interstellar Extinction; Main Sequence Stars; Tables (Data); Astrophysics full text sources ADS | data products SIMBAD (88) GCPD (1)