Early-type O stars play an excessively significant role in field of astrophysics. they have high effective temperatures (
Many different studies have been dealing with O-type stars for many years, however their origin, properties and evolution are not completely clear and display many theoretical and observational challenges. their mass-loss rates (Ṁ) depend on the metallicity (Z), For example, as well as effective temperatures, surface gravity and wind structure (e.g., clumping) have been constantly discussed in the literature over the last few years (see, e.g. [2], [9], [13], [14]).
For illustrate some of the questions mentioned earlier, and for further highlight into the problem, we have analyzed the spectra of two new early-type galaxy O4V stars(ALS 19618 and BD+50886) with optical medium-resolution. we used model atmosphere codes TLUSTY204 and SYNSPEC49 to achieve their stellar physical parameters [4].
The rest of the paper is arranged as follows. In Sect.2 we describe the optical observation of those two stars from GOSSS servay. In Sect.3 we give a specification for the atmosphere codes and the selected hypotheses. In sect.4. We provide analysis of (ALS19618) and (Bd +50886). In Sect.5 The estimated physical parameters are given with comparisons to theoretical predictions/appreciation and epitomizes the main results found in this study.
Observations used in this work are retrieved from The Galactic O-Star Spectroscopic Survey (GOSSS) the third installment (see [8]) (GOSSS) is a large survey of Galactic O stars in spectroscopic, established on modern homogeneous, signal-to-noise ratio are very high,
Observational data of two new galagtic O4V stars from GOSSS.
Star | RA (hms) | dec (dms) | spectral type Spectral type are taken from Maíz Apellániz, J. et al. 2016 [8] | V | B-V |
---|---|---|---|---|---|
ALS 19618 | 18 : 20 : 34.493 | -16 : 10 : 11.85 | O4 V (n)((fc)) | 11.29 | +1.11 |
BD+50886 | 04 : 03 : 20.736 | +51 : 18 : 52.46 | O4 V ((fc)) | 11.22 | +1.05 |
we used model atmosphere code TLUSTY204 [4] to determine the main stellar parameters of those two stars, TLUSTY code assumes the atmosphere is a plane-parallel layers, contains line-blanketing, NLTE, hydrostatic equilibrium, radiative equilibrium and present line formed only in photosphere layer.
We use to synthesis the spectra the code SYNSPEC 49 [5] which is a general spectrum synthesis program. The input model atmospheres to SYNSPEC could be taken from TLUSTY or from the literature, for instance from the Kurucz grid of models. Then the program solves the radiative transfer equation wavelength by wavelength in a specified wavelength range and with a specified wavelength resolution. In the present calculation To start our analysis, we calculate a small grid of TLUSTY model based on the OSTAR2002 grid [6], with an effective temperature range between 40,000 K and 45,000 K, and surface gravity range between 3.80 and 4.20, Our new model atmosphere grid uses small steps in effective temperature (1000 K) and surface gravity (0.1 dex). We use the helium lines He I
The results of our analysis and stellar modelling of ALS 19618 and BD +50886 are presented here. For each system a brief background is given, also the results of the analysis of their spectra and stellar modelling is discussed. The values of the effective temperature(Teff), surface gravity (log g) and the rotational velocity (vsin i) is determined from the fitting process with the synthetic one. the variation between the best fit model achieved from the fitting process is small, so visual checking that make the final judgment of the reasonable model.
ALS 19618 is located in the young open cluster NGC 6618 which embedded in the omega nebula (M 17), and it’s the reason for the gases of the nebula to radiate because of radiation from these young, hot stars; It is considered one of the brightest and most massive star-forming regions of the galaxy.
No line blanketed stellar model atmosphere have been applied to study this star, in Fig.1 we show our best fit model to the optical spectrum, several spectral regions were displayed which include the diagnostic lines applied to estimate the stellar parameters. The effective temperature would be very well represented. The He I
the most strong lines for hydrogen and helium in the wavelength range(4000 - 5000) show in Fig.1 are: He I
BD+50 886 This object is the main ionizing source of the H II region Sh 2-206 (NGC 1491) and was classified by [12] as O5neb. The GOSSS spectral classification is O4V((fc)) [8] which agree with our calculations.
Also their is no line blanketed stellar model atmosphere have been applied to study this star. In Fig. 2 we display our best fit model atmosphere for the optical spectrum of BD+50 886. The He I and He II lines are well represented by a
In this study we provided a model atmosphere analysis of two new galactic early type O4 main-sequence stars. We established effective temperature (Teff), surface gravities (log g), and rotational velocities (vsin i) for each star using NLTE model. The effective temperatures are 42,900 and 44,000 K. for ALS 19618 and BD+50886 respectively. BD+50886 has The lowest surface gravity 3.95 ± 0.1 and ALS 19618 has the higher surface gravity 4.0 ± 0.1.the fit with the model performed higher rotational velocity for ALS 19618 (
Steller Parameters of the program stars.
Star | spectral type | Teff (kK) | Log (g) | |
---|---|---|---|---|
ALS 19618 | O4 V (n)((fc)) | 42.9 ± 1.0 | 4.00 ± 0.1 | 210 |
BD+50886 | O4 V ((fc)) | 44.0 ± 1.0 | 3.95 ± 0.1 | 150 |