The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help us to understand the previous evolution of the ...star. To this end, we report the analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA white dwarf star EC 14012−1446 acquired during four observing epochs in three different years, including a coordinated three-site campaign. A total of 19 independent frequencies in the star's light variations together with 148 combination signals up to fifth order could be detected. We are unable to obtain the period spacing of the normal modes and therefore a mass estimate of the star, but we infer a fairly short rotation period of 0.61 ±0.03 d, assuming the rotationally split modes are ℓ= 1. The pulsation modes of the star undergo amplitude and frequency variations, in the sense that modes with higher radial overtone show more pronounced variability and that amplitude changes are always accompanied by frequency variations. Most of the second-order combination frequencies detected have amplitudes that are a function of their parent mode amplitudes, but we found a few cases of possible resonantly excited modes. We point out the complications in the analysis and interpretation of data sets of pulsating white dwarfs that are affected by combination frequencies of the form fA+fB−fC intruding into the frequency range of the independent modes.
Results of first CCD photometry during the recent deep light decline, and high-resolution spectroscopy, are presented for DY Persei. The spectra show variable blueshifted features in the sodium ...D lines. The C i lines are strong whereas neutron-capture elements are not enhanced. The isotopic 13CN(2, 0) lines relative to 12CN are of similar strength with those for the carbon star U Hya. All these confirm the RCB nature of DY Per and the existence of ejected clouds. At least two clouds are revealed at -197.3 and -143.0 km s-1. A star was detected about 0$\farcs$4 to the west and 2$\farcs$5 to the north from DY Per. This anonymous companion, with observed colour indices $(B-V) = 0.68$ and $(V-R) \simeq 1.1$, may be a foreground star.
Montgomery 1 developed a method to probe convection in pulsating white dwarf stars which allows the recovery of the thermal response time of the convection zone by fitting observed nonsinusoidal ...light curves. He applied this method to two objects; the Whole Earth Telescope (WET) observed the pulsating DB white dwarf GD 358 for just this purpose. Given this WET run's success, it is time to extend Montgomery's method to pulsating DA white dwarf (ZZ Ceti) stars. We present observations of two ZZ Ceti stars, WD 1524—0030 and EC 14012—1446, both observed from multiple sites. EC 14012—1446 seems better suited thAN WD1524—0030 for a future WET run because it has more pulsation modes excited and because it pulsation spectrum appears to be more stable in time. We call for participation in this effort to take place in April 2008.
Triggered star formation in OB associations Chen, W. P.; Lee, H. T.; Sanchawala, K.
Proceedings of the International Astronomical Union,
08/2006, Letnik:
2, Številka:
S237
Journal Article
Recenzirano
Odprti dostop
We present causal and positional evidence of triggered star formation in bright-rimmed clouds in OB associations, e.g., Ori OB1, and Lac OB1, by photoionization. The triggering process is seen also ...on a much larger scale in the Orion-Monoceros Complex by the Orion-Eridanus Superbubble. We also show how the positioning of young stellar groups surrounding the H II region associated with Trumpler 16 in Carina Nebula supports the triggering process of star formation by the collect-and-collapse scenario.
Near-Infrared Study of the Carina Nebula Sanchawala, Kaushar; Chen, Wen-Ping; Ojha, Devendra ...
The Astrophysical journal,
10/2007, Letnik:
667, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We have carried out near-infrared (NIR) imaging observations of the Carina Nebula for an area of similar to 400 arcmin super(2) including the clusters Trumpler 14 and Trumpler 16, with 10 sigma ...limits of J similar to 18.5, H similar to 17.5, and K unk similar to 16.5 mag. A total of 544 Class II candidates, 11 Class I candidates, and 40 red (H - K unk > 2) sources have been found. The majority of the Class II candidates are found to be distributed toward the clusters, whereas most of the red NIR sources are concentrated to the southeast of Trumpler 16, along the V-shaped dust lane. We found indications of ongoing star formation near the three MSX sources, G287.51-0.49, G287.47-0.54, and G287.63-0.72, where red NIR sources and X-ray sources are seen. In particular, two hard X-ray sources are identified near G287.47-0.54, one of which does not have an NIR counterpart and may be associated with a Class I/Class 0 object. The color-magnitude diagrams of the clusters suggest very young stellar population (<3 Myr). The K sub(s)-band luminosity function (KLF) of Trumpler 14 shows a sharp peak at the faint end, likely due to the onset of deuterium burning. The KLF of Trumpler 16, in contrast, rises smoothly until it turns over. The slopes of the mass functions derived for the clusters are in agreement with the canonical Salpeter value for the field stars.
We present a multiwavelength study of the central region of the Carina Nebula, including Trumpler 16 and part of Trumpler 14. Our analysis of the Chandra X-Ray Observatory archival data led to the ...identification of 454 X-ray sources. These sources were then cross-identified with optical photometric and spectroscopic information available from the literature and with newly obtained near-infrared (JHK sub(s)) imaging observations. A total of 38 known OB stars are found to be X-ray emitters. All the O stars and early-B stars follow the nominal relation between the X-ray and bolometric luminosities, L sub(x) 6 10 super(-7) L sub(bol). A few mid- to late-B stars are found to be associated with X-ray emission, likely attributable to T Tauri companions. We discovered 16 OB star candidates that suffer a large extinction in the optical wave bands. Some 300 sources have the X-ray and infrared characteristics of late-type pre-main-sequence stars. Our sample represents the most comprehensive census of the young stellar population in the Carina Nebula so far and should be useful for the study of the star formation history of this massive starburst region. We also report the finding of a compact (2' x 4') group of 10 relatively bright X-ray sources, all of which are detected in the near-infrared wavelengths and are highly reddened. The group is spatially coincident with the dark V-shaped dust lane bisecting the Carina Nebula and may be part of an embedded association. The distribution of the young stellar groups surrounding the H II region associated with Trumpler 16 is consistent with the collect-and-collapse scenario of triggered star formation.
We present cross-identification of archived ROSAT X-ray point sources with W UMa variable stars found in the All-Sky Automated Survey. A total of 34 W UMa stars have been found associated with X-ray ...emission. We compute the distances of these W UMa systems and hence their X-ray luminosities. Our data support the 'supersaturation' phenomenon seen in these fast rotators, namely that the faster a W UMa star rotates, the weaker its X-ray luminosity.
PG 0014+067 is one of the most promising pulsating subdwarf B stars for seismic analysis, as it has a rich pulsation spectrum. The richness of its pulsations, however, poses a fundamental challenge ...to understanding the pulsations of these stars, as the mode density is too complex to be explained only with radial and nonradial low-degree (l < 3) p-modes without rotational splittings. One proposed solution, suggested by Brassard et al. in 2001 for the case of PG 0014+067 in particular, assigns some modes with high degree (l= 3). On the other hand, theoretical models of sdB stars suggest that they may retain rapidly rotating cores, and so the high mode density may result from the presence of a few rotationally split triplet (l = 1) and quintuplet (l = 2) modes, along with radial (l = 0) p-modes. To examine alternative theoretical models for these stars, we need better frequency resolution and denser longitude coverage. Therefore, we observed this star with the Whole Earth Telescope for two weeks in 2004 October. In this paper we report the results of Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG 0014+067 do not appear to fit any theoretical model currently available; however, we find a simple empirical relation that is able to match all of the well-determined frequencies in this star.
The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help us to understand the previous evolution of the ...star. To this end, we report the analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA white dwarf star EC 14012-1446 acquired during four observing epochs in three different years, including a coordinated three-site campaign. A total of 19 independent frequencies in the star's light variations together with 148 combination signals up to fifth order could be detected. We are unable to obtain the period spacing of the normal modes and therefore a mass estimate of the star, but we infer a fairly short rotation period of 0.61 plus or minus 0.03d, assuming the rotationally split modes are ell= 1. The pulsation modes of the star undergo amplitude and frequency variations, in the sense that modes with higher radial overtone show more pronounced variability and that amplitude changes are always accompanied by frequency variations. Most of the second-order combination frequencies detected have amplitudes that are a function of their parent mode amplitudes, but we found a few cases of possible resonantly excited modes. We point out the complications in the analysis and interpretation of data sets of pulsating white dwarfs that are affected by combination frequencies of the form fA+fB- fC intruding into the frequency range of the independent modes.
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