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- ID:
- ivo://CDS.VizieR/J/ApJ/743/118
- Title:
- BVRIJHK photometry of the 2008 OT in NGC 300
- Short Name:
- J/ApJ/743/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 2008 optical transient in NGC 300 is one of a growing class of intermediate-luminosity transients that brighten several orders of magnitude from a previously optically obscured state. The origin of their eruptions is not understood. Our multi-wavelength photometry and spectroscopy from maximum light to more than a year later provide a record of its post-eruption behavior. We describe its changing spectral energy distribution, the evolution of its absorption- and emission-line spectrum, the development of a bipolar outflow, and the rapid transition from a dense wind to an optically thin ionized wind. In addition to strong, narrow hydrogen lines, the F-type absorption-line spectrum of the transient is characterized by strong CAII and [CAII] emission. The very broad wings of the CAII triplet and the asymmetric [CAII] emission lines are due to strong Thomson scattering in the expanding ejecta. Post-maximum, the hydrogen and CaII lines developed double-peaked emission profiles that we attribute to a bipolar outflow. Between approximately 60 and 100 days after maximum, the F-type absorption spectrum, formed in its dense wind, weakened and the wind became transparent to ionizing radiation. We discuss the probable evolutionary state of the transient and similar objects such as SN 2008S and conclude that they were most likely post-red supergiants or post-asymptotic giant branch stars on a blue loop to warmer temperatures when the eruption occurred. These objects are not luminous blue variables.
- ID:
- ivo://CDS.VizieR/J/A+A/415/521
- Title:
- BVRIJK and velocities for MC Cepheids
- Short Name:
- J/A+A/415/521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high precision and well sampled BVRIJK light curves and radial velocity curves for a sample of five (+1) Cepheids in the SMC. In addition we present radial velocity curves for five (+1) Cepheids in the LMC. The low metallicity ([Fe/H]~-0.7) SMC stars have been selected for use in a Baade-Wesselink type analysis to constrain the metallicity effect on the Cepheid Period-Luminosity relation. The stars have periods of around 15 days so they are similar to the Cepheids observed by the Extragalactic Distance Scale Key Project on the Hubble Space Telescope. We show that the stars are representative of the SMC Cepheid population at that period and thus will provide a good sample for the proposed analysis. The actual Baade-Wesselink analysis are presented in Strom et al., 2004, Cat. <J/A+A/415/531>.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/41
- Title:
- BVRI light curve of OGLE LMC-ECL-11893
- Short Name:
- J/ApJ/788/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the serendipitous discovery of a disk-eclipse system OGLE-LMC-ECL-11893. The eclipse occurs with a period of 468 days, a duration of about 15 days, and a deep (up to {Delta}m_I_~1.5), peculiar, and asymmetric profile. A possible origin of such an eclipse profile involves a circumstellar disk. The presence of the disk is confirmed by the H-alpha line profile from the follow-up spectroscopic observations, and the star is identified as Be/Ae type. Unlike the previously known disk-eclipse candidates, the eclipses of OGLE-LMC-ECL-11893 retain the same shape throughout the span of ~17yr (13 orbital periods), indicating no measurable orbital precession of the disk.
- ID:
- ivo://CDS.VizieR/J/AJ/161/193
- Title:
- BVRI light curve of RR Lyrea V* AX UMa
- Short Name:
- J/AJ/161/193
- Date:
- 10 Dec 2021
- Publisher:
- CDS
- Description:
- The pulsation periods of RR-Lyrae stars usually vary with time, and they are often used as probes to study the mechanism behind the variation. After the early discovery that the pulsation period of the RR-Lyrae star AXUMa decreased rapidly, in further research, we made multiband photometric observations of this star using the Sino-Thai 70cm telescope and the 60cm telescope at Yunnan Observatories, and collected its light-curve data from several photometry sky surveys. The O-C diagram confirmed that AX UMa has a rapid period decrease with a rate of -7.752{+/-}0.005days/Myr, which indicates that it is the fastest-period decreasing ab-type RR Lyrae star in the Galactic field. Moreover, the O-C residuals contain additional periodic variations. We suppose that the variation with a long period is probably caused by the light-travel time effect as the star orbits in a binary system. The calculation shows that the lower mass limit of the companion is about 1M{sun}. Combined with the full amplitudes and color indexes, we suggested that the companion is probably a hot subdwarf star. We compared the light curves of AXUMa and those of another binary evolution pulsator, OGLE-BLG-RRLYR-02792, and found that the former shows the characteristics of ab-type RR-Lyrae stars, while the latter is more like an extreme long-period c-type RR-Lyrae star. However, the absence of a bump in the light curves implies that the mass loss has occurred in the outer atmosphere of AXUMa. The special features of AXUMa make it worth more attention and further observations.
- ID:
- ivo://CDS.VizieR/J/A+A/493/1093
- Title:
- BVRI light curves of {eta} Car
- Short Name:
- J/A+A/493/1093
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The periodicity of 5.5 years for some observational events occurring in {eta} Carinae manifests itself across a large wavelength range and has been associated with its binary nature. These events are supposed to occur when the binary components are close to periastron. To detect the previous periastron passage of {eta} Car in 2003, we started an intensive, ground-based, optical, photometric observing campaign. We continued observing the object to monitor its photometric behavior and variability across the entire orbital cycle. Our observation program consisted of daily differential photometry from CCD images, which were acquired using a 0.8m telescope and a standard BVRI filter set at La Plata Observatory. The photometry includes the central object and the surrounding Homunculus nebula. We present up-to-date results of our observing program, including homogeneous photometric data collected between 2003 and 2008. Our observations demonstrated that {eta} Car has continued increasing in brightness at a constant rate since 1998. In 2006, it reached its brightest magnitude (V~4.7) since about 1860s. The object then suddenly reverted its brightening trend, fading to V=5.0 at the beginning of 2007, and has maintained a quite steady state since then. We continue the photometric monitoring of {eta} Car in anticipation of the next "periastron passage", predicted to occur at the beginning of 2009.
- ID:
- ivo://CDS.VizieR/J/MNRAS/433/394
- Title:
- BVRI light curves of KIC 6382916
- Short Name:
- J/MNRAS/433/394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a multisite photometric campaign on the high-amplitude {delta} Scuti star KIC 6382916 in the Kepler field. The star was observed over a 85-d interval at five different sites in North America and Europe during 2011. Kepler photometry and ground-based multicolour light curves of KIC 6382916 are used to investigate the pulsational content and to identify the principal modes. High-dispersion spectroscopy was also obtained in order to derive the stellar parameters and projected rotational velocity. From an analysis of the Kepler time series, three independent frequencies and a few hundred combination frequencies are found. The light curve is dominated by two modes with frequencies f1=4.9107d^-1^ and f2=6.4314d^-1^. The third mode with f3=8.0350d^-1^ has a much lower amplitude. We attempt mode identification by examining the amplitude ratios and phase differences in different wavebands from multicolour photometry and comparing them to calculations for different spherical harmonic degree, l. We find that the theoretical models for f1 and f2 are in a best agreement with the observations and lead to value of l=1 modes, but the mode identification of f3 is uncertain due to its low amplitude. Non-adiabatic pulsation models show that frequencies below 6d^-1^ are stable, which means that the low frequency of f1 cannot be reproduced. This is a further confirmation that current models predict a narrower pulsation frequency range than actually observed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/413/2709
- Title:
- BVRI light curves of KIC Cepheids
- Short Name:
- J/MNRAS/413/2709
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results of initial work done on selected candidate Cepheids to be observed with the Kepler space telescope. Prior to the launch, 40 candidates were selected from previous surveys and data bases. The analysis of the first 322d of Kepler photometry, and recent ground-based follow-up multicolour photometry and spectroscopy allowed us to confirm that one of these stars, V1154 Cyg (KIC 7548061), is indeed a 4.9d Cepheid. Using the phase lag method, we show that this star pulsates in the fundamental mode. New radial velocity data are consistent with previous measurements, suggesting that a long-period binary component is unlikely. No evidence is seen in the ultraprecise, nearly uninterrupted Kepler photometry for non-radial or stochastically excited modes at the micromagnitude level. The other candidates are not Cepheids, but an interesting mix of possible spotted stars, eclipsing systems and flare stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/694/1237
- Title:
- BVRI light curves of NGC 247 Cepheids
- Short Name:
- J/ApJ/694/1237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report VRI CCD observations of nine Cepheids in the South Polar (Sculptor) Group spiral galaxy NGC 0247. Periods of these Cepheids range from 20 to 70 days. Over the past 20 years, the brightest Cepheid in our sample, NGC 0247:[MF09] C1, has decreased its period by 6%, faded by 0.8mag in the V band, and become bluer by 0.23mag in (V-I).
- ID:
- ivo://CDS.VizieR/J/ApJS/142/71
- Title:
- BVRI observations of LMC Cepheids
- Short Name:
- J/ApJS/142/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A homogeneous set of ground-based BVRI observations of ~600 Cepheids is presented to check the Cepheid period-luminosity (PL) zero point for the Large Magellanic Cloud (LMC). The sample of Cepheids is completely self-contained and has been reduced consistently to eliminate photometric differences caused by combining multiple sources of photometry. The Cepheid distances to nearby galaxies obtained by the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale were computed assuming a "standard" PL relation based on a compilation of photoelectric observations of 34 Cepheids and a standard distance modulus to the LMC of 18.50. The final Key Project results substituted a statistically stronger PL relation obtained by the OGLE collaboration. In this paper we compare our data with the OGLE PL relation; the subsample of LMC Cepheids with similar periods to those discovered in the nearby galaxies is fainter at the relevant periods by 0.04+/-0.02mag than the OGLE sample. Substituting in turn this PL relation for that of the OGLE collaboration would raise the Hubble constant by 2%+/-1%, a correction which is not significant. The multicolor data set will also be useful in considering the effects of reddening and chemical composition and deriving an improved Cepheid period-luminosity relation for the LMC.