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تسجيل مستخدم جديدNGC 1893: a young open cluster rich in multi-type variable stars
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In this work, we have studied the variable stars in the young open cluster NGC 1893 based on a multi-year photometric survey covering a sky area around the cluster up to $31 times 31$ wide. More than 23,000 images in the $V$ band taken from January 2008 to February 2017 with different telescopes, complemented with 90 images in the $B$ band in 2014 and 2017, were reduced, and light curves were derived in $V$ for 5653 stars. By analyzing these light curves, we detected 147 variable stars (85 of them being new discoveries), including 110 periodic variables, 15 eclipsing binaries and 22 non-periodic variables. Proper motions, radial velocities, color-magnitude and two-color diagrams were used to identify the cluster membership of these variable stars, resulting in 84 members. Periodic variable members were then classified into different variability types, mainly according to their magnitudes and to their periods of variability, as well as to their positions in the Hertzsprung-Russell diagram for the early-type stars. As a result, among main-sequence periodic variable members, we identified five $beta$ Cep candidates, seven slowly pulsating B-type candidates, and thirteen fast-rotating pulsating B-type (FaRPB) candidates (one of which is a confirmed classical Be star). While most of the FaRPB stars display properties similar to the ones discovered in NGC 3766 by Mowlavi et al. (2013), five of them have periods below 0.1~d, contrary to expectations. Additional observations, including spectroscopic, are called for to further characterize these stars. We also find a binary candidate harboring a $delta$-Scuti candidate.
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In this paper we present time series photometry of 104 variable stars in the cluster region NGC 1893. The association of the present variable candidates to the cluster NGC 1893 has been determined by using $(U-B)/(B-V)$ and $(J-H)/(H-K)$ two colour d
iagrams, and $V/(V-I)$ colour magnitude diagram. Forty five stars are found to be main-sequence variables and these could be B-type variable stars associated with the cluster. We classified these objects as $beta$ Cep, slowly pulsating B stars and new class variables as discussed by Mowlavi et al. (2013). These variable candidates show $sim$0.005 to $sim$0.02 mag brightness variations with periods of $<$ 1.0 d. Seventeen new class variables are located in the $H-R$ diagram between the slowly pulsating B stars and $delta$ Scuti variables. Pulsation could be one of the causes for periodic brightness variations in these stars. The X-ray emission of present main-sequence variables associated with the cluster lies in the saturated region of X-ray luminosity versus period diagram and follows the general trend by Pizzolato et al. (2003).
We present results of multi-epoch (fourteen nights during 2007-2010) $V$-band photometry of the cluster NGC 1893 region to identify photometric variable stars in the cluster. The study identified a total of 53 stars showing photometric variability. T
he members associated with the region are identified on the basis of spectral energy distribution, $J-H/H-K$ two colour diagram and $V/V-I$ colour-magnitude diagram. The ages and masses of the majority of pre-main-sequence sources are found to be $lesssim$ 5 Myr and in the range 0.5 $lesssim$ $M/M_{odot}$ $lesssim$ 4, respectively. These pre-main-sequence sources hence could be T Tauri stars. We also determined the physical parameters like disk mass and accretion rate from the spectral energy distribution of these T Tauri stars. The periods of majority of the T Tauri stars range from 0.1 to 20 day. The brightness of Classical T Tauri stars is found to vary with larger amplitude in comparison to Weak line T Tauri stars. It is found that the amplitude decreases with increase in mass, which could be due to the dispersal of disks of massive stars.
We present time series photometry of 57 variable stars in the cluster region NGC 7380. The association of these variable stars to the cluster NGC 7380 has been established on the basis of two colour diagrams and colour-magnitude diagrams. Seventeen s
tars are found to be main-sequence variables, which are mainly B type stars and are classified as slowly pulsating B stars, $beta$ Cep or $delta$ Scuti stars. Some of them may belong to new class variables as discussed by Mowlavi et al. (2013) and Lata et al. (2014). Present sample also contains 14 pre-main-sequence stars, whose ages and masses are found to be mostly $lesssim$ 5 Myr and range 0.60 $lesssim M/M_{odot} lesssim$ 2.30 and hence should be T-Tauri stars. About half of the weak line T-Tauri stars are found to be fast rotators with a period of $lesssim$ 2 days as compared to the classical T-Tauri stars. Some of the variables belong to the field star population.
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.
We present results of a search for variable stars in the intermediate-age open cluster NGC 7044. We found 23 variable stars in the observed field. One star turned out to be of the delta Sct type with two pulsational modes excited. From the position i
n the color-magnitude diagram we conclude that this star is a member of the cluster. Moreover, we found 13 eclipsing systems, of which five are W UMa stars, one is a beta Lyr variable, six are beta Per binaries showing detached configuration, and the last one is another probable beta Per system. Using the period-luminosity-color relation for W UMa stars we established the membership of the contact binaries, finding four of them to be very probable cluster members. We estimated from these four stars an apparent distance modulus (m-M)_V of NGC 7044 to be 14.2 +/- 0.4 mag, which is smaller than previous determinations of this parameter. We were able to derive orbital period for only four beta Per systems. For the remaining ones we observed only two or three eclipses. Finally, nine stars we found to show irregular light changes. Most of them are red stars not belonging to the cluster. For the cluster core we determined a reddening map, which allowed us to construct a dereddened color-magnitude diagram of NGC 7044 with a narrow main-sequence. By fitting a theoretical isochrone to this diagram we derived E(V-I_C) = 0.92 mag, (m-M)_V = 14.45 mag and log(age/yr) = 9.2.
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