Whiting 1 is a member of the fast-growing group of young globular clusters in the Milky Way halo. Preliminary estimates of its fundamental parameters have been provided using optical photometry and ...low-resolution spectroscopy. In an attempt to strengthen our knowledge of Whiting 1, in this study we employ a complementary approach. Isochrone fitting method was applied on the near-infrared colour–magnitude diagram and yields an age t = 5.7 ± 0.3 Gyr, metallicity z = 0.006 ± 0.001 (Fe/H = −0.5 ± 0.1) and distance modulus (m − M)0 = 17.48 ± 0.10. Our results confirm that Whiting 1 is a young and moderately metal-rich globular cluster. It is one of the youngest from the Sgr dSph. We fitted an Elson, Fall and Freeman (EFF) profile to the near-infrared number counts, and measured cluster core radius r
c = 9.1 arcsec ± 3.9 arcsec. Two probable eclipsing variables in the cluster were found from multi-epoch V-band photometry. Finally, an unknown galaxy cluster was identified on our K versus (J − K) colour–magnitude diagram. It has a redshift z ∼ 1, and it is located at about 1 arcmin from the centre of Whiting 1 at
$\alpha _{\rm J2000} = 02^{\rm h} 02^{\rm m} 56 {.\!\!^{{\mathrm{s}}}6$
, δJ2000 = −03°16′09′
′, contaminating the cluster photometry.
A search for a correlation between the luminosities of the brightest stars and luminosities of their host galaxies was carried out on archival Hubble Space Telescope (HST)
or
(
V
) and
(
I
) images ...of 150 nearby galaxies. The sample contains only galaxies with ongoing star formation and with known distances we derived with the TRGB-method. We correlated the average absolute luminosities of the three brightest blue and the three brightest red stars with the luminosity of a host. We find a linear relation for both the blue and the red stars in irregular and low-mass spiral galaxies. Their scatters are sufficiently small (
) to make these relations useful for distance determination for low-mass galaxies. We found that all 31 dwarf galaxies
in our sample lack bright massive stars
, probably due to the physical conditions that prevent their birth. For galaxies with higher an average luminosity in the range
, there is an asymmetry in the distribution of the number of galaxies relative to the linear dependence, indicating an increase in the fraction of galaxies with bright stars.
We report the results of photometric and spectroscopic monitoring of CI Cam within 24 years since its outburst in 1998. Over this time, we found a system component emitting in the He II 4686 ...Å emission line, on an elliptical orbit with a period of
days and an eccentricity of 0.44–0.49. The variations of the optical brightness are observed with the same period and with an average amplitude of
. The total amplitude of the He II radial velocity variations is about 380 km s
. The equivalent width of the line is variable on a time scale of tens of minutes as well as with the orbital period. Maximum equivalent widths of the He II line are observed when the component passes the descending node of the orbit. The intensity of the He II 4686 Å emission gradually increases with time. Slow radial velocity variations on a scale of decades were detected by means of high resolution spectroscopy in the iron emission lines and a forbidden nitrogen line formed in the circumstellar nebula. The B-type star turned out to be a pulsating variable. During the period between 2005 and 2009, pulsations were multiperiodic with the dominant periods
,
, and
days. However, since 2012 it has pulsated in a single mode with a variable period in the
day range depending on the star’s luminosity. We identify the 2005–2009 pulsations as a resonance of the radial modes, and the residual stable mode as the first overtone. The pulsations are coherent on a scale of several months, and their average amplitudes are
. The pulsation data constrain the spectral type of the main component to B0–B2 III, the distance to the system to 2.5–4.5 kpc, and the absolute visual magnitude
to the range of
to
. The classification of the CI Cam main component as a Be supergiant is completely ruled out due to the observed pulsation periods. CI Cam may be a system at the stage after the first mass exchange and may be attributed to the FS CMa-type group of objects with the Be phenomenon.
We identify the rich carbon star population of the Magellanic-type dwarf irregular galaxy WLM (Wolf-Lundmark-Melotte) and study its photometric properties from deep near-IR observations. The galaxy ...also exhibits a clear presence of oxygen-rich population. We derive a carbon to M-star ratio of C / M = 0.56\pm0.12, relatively high in comparison with many galaxies. The spatial distribution of the AGB stars in WLM hints at the presence of two stellar complexes with a size of a few hundred parsecs. Using the \ion map of WLM and the derived gas-to-dust ratio for this galaxy N (\ion) / E ( B-V) = 60\pm10 10 super(21) at. cm super(-2) mag super(-1) we re-determined the distance modulus of WLM from the IR photometry of four known Cepheids, obtaining ( m-M) sub(0) = 24.84\pm0.14 mag. In addition, we determine the scale length of 0.75\pm0.14 kpc of WLM disk in the J-band.
Optical monitoring of the z= 4.40 quasar Q 2203+292 Ovcharov, E. P.; Nedialkov, P. L.; Valcheva, A. T. ...
Monthly notices of the Royal Astronomical Society,
20/May , Letnik:
386, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report Cousins R-band monitoring of the high-redshift (z= 4.40) radio-quiet quasar Q 2203+292 from 1999 May to 2007 October. The quasar shows maximum peak-to-peak light curve amplitude of ∼0.3 mag ...during the time of our monitoring, and ∼0.9 mag when combined with older literature data. The rms of a fit to the light curve with a constant is 0.08 and 0.2 mag, respectively. The detected changes are at ∼3σ level. The quasar was in a stable state during the recent years and it might have undergone a brightening event in the past. The structure function analysis concluded that the object shows variability properties similar to those of the lower redshift quasars. We set a lower limit to the Q 2203+292 broad-line region mass of 0.3–0.4 M⊙. Narrow-band imaging search for redshifted Lyα from other emission-line objects at the same redshift shows no emission-line objects in the quasar vicinity.
Context. M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 – the first event of this kind observed in M 31 since 1988. Very few similar events have been confirmed as of 2015. ...Most of them are considered to be products of stellar mergers. Aims. Results of an extensive optical monitoring of the transient in the period January–March 2015 are presented. Methods. Eight optical telescopes were used for imaging. Spectra were obtained on the Large Altazimuth Telescope (BTA), the Gran Telecsopio Canarias (GTC) and the Rozhen 2 m telescope. Results. We present a highly accurate 70 d light curve and astrometry with a 0.05′′uncertainty. The colour indices reached a minimum of 2−3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to be 8.7+3.3-2.2 × 105 L⊙ during the optical maximum. Conclusions. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis.
This paper shows a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we used the results of stellar photometry of the Hubble Space ...Telescope images using the DAOPHOT and DOLPHOT packages. The results of such searches are shown on the example of the galaxies DDO68, M94 and NGC1672. In the galaxy DDO68 the LBV star changes its brightness, and in M94 massive stars can be identified by the excess in the H\({\alpha}\) band. For the galaxy NGC1672, we measured the distance for the first time by the TRGB method, which made it possible to determine the luminosities of the brightest stars, likely hypergiants, in the young star formation region. So far we have performed stellar photometry of HST images of 320 northern sky galaxies located at a distance below 12Mpc. This allowed us to identify 53 galaxies with probable hypergiants. Further photometric and spectral observations of these galaxies are planned to search for massive stars.
We identify the rich carbon star population of the Magellanic-type dwarf irregular galaxy WLM (Wolf-Lundmark-Melotte) and study its photometric properties from deep near-IR observations. The galaxy ...also exhibits a clear presence of oxygen-rich population. We derive a carbon to M-star ratio of $C/M$ = 0.56±0.12, relatively high in comparison with many galaxies. The spatial distribution of the AGB stars in WLM hints at the presence of two stellar complexes with a size of a few hundred parsecs. Using the $\ion{H}{i}$ map of WLM and the derived gas-to-dust ratio for this galaxy N($\ion{H}{i}$)/E($B-V$) = 60±10 1021 at. cm-2 mag-1 we re-determined the distance modulus of WLM from the IR photometry of four known Cepheids, obtaining ($m-M$)0 = 24.84±0.14 mag. In addition, we determine the scale length of 0.75±0.14 kpc of WLM disk in the J-band.
Optical monitoring of the z= 4.40 quasar Q 2203+292 Ovcharov, E. P.; Nedialkov, P. L.; Valcheva, A. T. ...
Monthly notices of the Royal Astronomical Society,
05/2008, Letnik:
386, Številka:
2
Journal Article
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