Journal articles: 'Blue star'

1

Clark, Patricia, and Linda Dupree. "Catch the Blue Star Fever." Gastroenterology Nursing 30, no. 2 (March 2007): 145. http://dx.doi.org/10.1097/01.sga.0000267958.21501.19.

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Bond, Howard E., Albert D. Grauer, David Burstein, and Ronald O. Marzke. "Hamuy's blue variable star in Orion." Publications of the Astronomical Society of the Pacific 99 (October 1987): 1097. http://dx.doi.org/10.1086/132085.

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Kraft, Robert P. "On the Halo Blue Star Mystery." Publications of the Astronomical Society of the Pacific 101 (December 1989): 1113. http://dx.doi.org/10.1086/132584.

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Mieske, S., and H. Baumgardt. "On the Efficiency of Field Star Capture by Star Clusters." Proceedings of the International Astronomical Union 3, S246 (September 2007): 195–96. http://dx.doi.org/10.1017/s1743921308015603.

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AbstractAn exciting recent finding regarding scaling relations among globular clusters is the so-called ‘blue tilt’: clusters of the blue sub-population follow a trend of redder colour with increasing luminosity. In this contribution we estimate by means of collisional N-body simulations to which extent this trend can be explained by field star capture occurring over a Hubble time. We investigate star clusters with 103 to 106 stars. We find that the ratio between captured field stars and total number of clusters stars is very low (≲ 10−4), even for co-rotation of the star cluster in a cold disk. This holds for star clusters in the mass range of both open clusters and globular clusters. Therefore, field star capture is not a probable mechanism for creating the colour-magnitude trend of metal-poor globular clusters.

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Golev, V. K., G. R. Ivanov, and P. Z. Kunchev. "The brightest blue stars in M33 galaxy as unresolved star groups." Astrophysics and Space Science 135, no. 2 (1987): 301–6. http://dx.doi.org/10.1007/bf00641566.

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Oh, Sree, Keunho Kim, Joon Hyeop Lee, Minjin Kim, Yun-Kyeong Sheen, Jinsu Rhee, Chang H. Ree, et al. "Impact of galaxy mergers on the colours of cluster galaxies." Monthly Notices of the Royal Astronomical Society 488, no. 3 (July 12, 2019): 4169–80. http://dx.doi.org/10.1093/mnras/stz1920.

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ABSTRACT We examine the ultraviolet and optical colours of 906 cluster galaxies from the KASI-Yonsei Deep Imaging Survey of Clusters (KYDISC). The sample has been divided into two categories, morphologically disturbed and undisturbed galaxies, based on the visual signatures related to recent mergers. We find that galaxies with signatures of recent mergers show significantly bluer colours than undisturbed galaxies. Disturbed galaxies populate more on the cluster outskirts, suggesting recent accretion into the cluster environment, which implies that disturbed galaxies can be less influenced by the environmental quenching process and remain blue. However, we still detect bluer colours of disturbed galaxies in all locations (cluster core and outskirts) for the fixed morphology, which is difficult to understand just considering the difference in time since infall into a cluster. Moreover, blue disturbed galaxies show features seemingly related to recent star formation. Therefore, we suspect that mergers make disturbed galaxies keep their blue colour longer than undisturbed galaxies under the effect of the environmental quenching through either merger-induced star formation or central gas concentration which is less vulnerable for gas stripping.

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Sandquist, Eric L. "Blue Stragglers in Low-Luminosity Star Clusters." Astrophysical Journal 635, no. 1 (November 28, 2005): L73—L76. http://dx.doi.org/10.1086/499124.

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Hodge, Paul. "The Blue Star Clusters of M 31." Symposium - International Astronomical Union 126 (1988): 549–50. http://dx.doi.org/10.1017/s0074180900043011.

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Chornay, N., and N. A. Walton. "One star, two star, red star, blue star: an updated planetary nebula central star distance catalogue from Gaia EDR3." Astronomy & Astrophysics 656 (December 2021): A110. http://dx.doi.org/10.1051/0004-6361/202142008.

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Context. Planetary nebulae (PNe) are a brief but important phase of stellar evolution. The study of Galactic PNe has historically been hampered by uncertain distances, but the parallaxes of PN central stars (CSPNe) measured by Gaia are improving the situation. Aims. Gaia’s Early Data Release 3 (EDR3) offers higher astrometric precision and greater completeness compared to previous releases. Taking advantage of these improvements requires that the CSPNe in the catalogue be accurately identified. Methods. We applied our automated technique based on the likelihood ratio method to cross-match known PNe with sources in Gaia EDR3, using an empirically derived position and colour distribution to score candidate matches. Results. We present a catalogue of over 2000 sources in Gaia EDR3 that our method has identified as likely CSPNe or compact nebula detections. We show how the more precise parallaxes of these sources compare to previous PN statistical distances and introduce an approach to combining them to produce tighter distance constraints. We also discuss Gaia’s handling of close companions and bright nebulae. Conclusions. Gaia is unlocking new avenues for the study of PNe. The catalogue presented here will remain valid for the upcoming Gaia Data Release 3 (DR3) and thus provide a valuable resource for years to come.

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Bell, E. F., R. G. Bower, R. S. de Jong, B. J. Rauscher, D. Barnaby, D. A. Harper, M. Herald, and R. F. Loewenstein. "The star formation histories of Low Surface Brightness galaxies." International Astronomical Union Colloquium 171 (1999): 245–52. http://dx.doi.org/10.1017/s0252921100054403.

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AbstractNear-infrared images of a sample of red, blue and giant low surface brightness disk galaxies (LSBGs) were combined with optical data with the aim of constraining their star formation histories. Most LSBGs have strong colour gradients consistent with mean stellar age gradients. We find that LSBGs have a large range of ages and metallicities, spanning those observed in normal disk galaxies. In particular, red and blue LSBGs have very different star formation histories and represent two independent routes to low B band surface brightness. Blue LSBGs are well described by models with low, roughly constant star formation rates, whereas red LSBGs are better described by a ‘faded disk’ scenario.

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11

Lamers, Henny J. G. L. M. "Observations and Interpretation of Luminous Blue Variables." International Astronomical Union Colloquium 155 (1995): 176–91. http://dx.doi.org/10.1017/s0252921100036940.

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AbstractThe different types of variations of LBVs are discussed. The “typical LBV variations” have amplitudes of ΔV ≃ 0.5 to 2.0 magnitudes and irregular time-scales of months to years. This is due to changes in the stellar radius and the effective temperature. Modelling of this variability for one star, S Dor, shows that the radius of the star varies between 100 and 380 R⊙, the effective temperature between 20,000 and 9,000 K, and the luminosity between log L* = 6.10 to 5.9. The variation of the radius is not an apparent variation of the effective radius of the wind due to a variable mass loss rate (which has often been assumed) but it is a true variation of the radius of the star itself. The changes in L* suggest that about 10−3 to 10−2M* takes part in the expansion of the star. The irregular microvariations with amplitudes of about ΔV ≃ 0.2m on timescales of weeks are probably due to non-adiabatic pulsations with mode-interaction. We argue that LBVs are close to their effective Eddington Limit and discuss a qualitative scenario to explain their location in the HR-diagram.

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Bootz, Vitor, Marina Trevisan, Trinh Thuan, Yuri Izotov, Angela Krabbe, and Oli Dors. "Isolated groups of extremely blue dwarf galaxies." Proceedings of the International Astronomical Union 15, S359 (March 2020): 168–69. http://dx.doi.org/10.1017/s1743921320001830.

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AbstractInteractions and mergers between dwarf galaxies are mostly gas-rich and should be marked by an intense star formation activity. But these processes, which are expected to be common at earlier times, are very difficult to observe at low redshifts. To investigate that, we look in the Sloan Digital Sky Survey (SDSS) for compact groups that contain one luminous compact galaxy (LCG) with very high specific star formation rate (sSFR) and at least two other blue galaxies. We found 24 groups that satisfy these criteria, among which 12 groups have SDSS spectroscopic data for at least 2 member galaxies. Here we want to investigate, using the tidal strength estimator Q, how interactions between neighbouring galaxies affect the sSFR and concentration of each LCG. Statistical tests reveal a correlation between Q and their sSFR, indicating that tidal forces between neighbouring galaxies might be inducing bursts of star formation in the LCGs.

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Hatta, Yoshiki, Takashi Sekii, Masao Takata, and Othman Benomar. "Nonstandard Modeling of a Possible Blue Straggler Star, KIC 11145123." Astrophysical Journal 923, no. 2 (December 1, 2021): 244. http://dx.doi.org/10.3847/1538-4357/ac23c9.

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Abstract Nonstandard modeling of KIC 11145123, a possible blue straggler star, has been asteroseismically carried out based on a scheme to compute stellar models with the chemical compositions in their envelopes arbitrarily modified, mimicking the effects of some interactions with other stars through which blue straggler stars are thought to be born. We have constructed a nonstandard model of the star with the following parameters: M = 1.36 M ⊙, Y init = 0.26, Z init = 0.002, and f ovs = 0.027, where f ovs is the extent of overshooting described as an exponentially decaying diffusive process. The modification is down to the depth of r/R ∼ 0.6 and the extent ΔX, which is a difference in surface hydrogen abundance between the envelope-modified and unmodified models, is 0.06. The residuals between the model and the observed frequencies are comparable with those for the previous model computed assuming standard single-star evolution, suggesting that it is possible that the star was born with a relatively ordinary initial helium abundance of ∼0.26 compared with that of the previous models (∼0.30–0.40), then experienced some modification of the chemical compositions and gained helium in the envelope. Detailed analyses of the nonstandard model have implied that the elemental diffusion in the deep radiative region of the star might be much weaker than that assumed in current stellar evolutionary calculations; we need some extra mechanisms inside the star, rendering the star a much more intriguing target to be further investigated.

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Viotti, R., G. B. Baratta, C. Rossi, and A. di Fazio. "AG Carinae and the WR Phenomenon in Luminous Blue Variables." Symposium - International Astronomical Union 143 (1991): 499–504. http://dx.doi.org/10.1017/s0074180900045666.

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AG Car is a Luminous Blue Variable which recently evolved from AIe to Ofpe/WN9 in four years at about constant bolometric luminosity, while in the visual the star faded by two magnitudes. This change is probably associated with variable opacity of an unstable massive expanding envelope of a hot star. We discuss the main spectral features of the star and of its ring nebula, and the spectral variations.

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15

de la Rosa-Millán, Julián, Edith Agama-Acevedo, Antonio R. Jimenez-Aparicio, and Luis A. Bello-Pérez. "Starch characterization of different blue maize varieties." Starch - Stärke 62, no. 11 (September 28, 2010): 549–57. http://dx.doi.org/10.1002/star.201000023.

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16

Davies, Richard I. "Star-forming regions in blue compact dwarf galaxies." Monthly Notices of the Royal Astronomical Society 295, no. 1 (March 1998): 43. http://dx.doi.org/10.1046/j.1365-8711.1998.01205.x.

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Davies, Richard I., Hajime Sugai, and Martin J. Ward. "Star-forming regions in blue compact dwarf galaxies." Monthly Notices of the Royal Astronomical Society 295, no. 1 (March 1998): 43–54. http://dx.doi.org/10.1046/j.1365-8711.1998.29511205.x.

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18

Fahlman, Steven, and Rodrigo Fernández. "Hypermassive Neutron Star Disk Outflows and Blue Kilonovae." Astrophysical Journal 869, no. 1 (December 4, 2018): L3. http://dx.doi.org/10.3847/2041-8213/aaf1ab.

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19

Zitrin, A., N. Brosch, and B. Bilenko. "Star formation properties of isolated blue compact galaxies." Monthly Notices of the Royal Astronomical Society 399, no. 2 (October 21, 2009): 924–33. http://dx.doi.org/10.1111/j.1365-2966.2009.15332.x.

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20

Sokolov, V. V., A. I. Kopylov, V. G. Kurt, and S. V. Zharykov. "Deep Search for Optical Counterparts of Gamma-ray Bursters." International Astronomical Union Colloquium 151 (1995): 389–92. http://dx.doi.org/10.1017/s0252921100035417.

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AbstractPreliminary results are presented of the first (searching) stage of our observational program of the search and study of weak blue star-like objects in the two small γ-ray burst boxes GB 790418 and GB 790613. The basic search purposes are (1) the selection of star-like objects weaker than 23m inside these boxes, (2) the selection of the bluest ones in B — V among these objects. The first result is the fact that there are no blue (with B — V < 0) star-like objects brighter than 24m in both boxes. But in each of these GRB error boxes one blue object with smaller flux was selected for further study to elucidate their nature. In the smallest of the archival GRB error boxes (GB 790613) obtained by three satellite triangulation, the bluest star-like object with V = 24.56(±0.16) and B — V = −0.20(±0.19) is near the center (at the distance < 10") of the GRB box. In the GB 790418 error box, the bluest star-like object with B = 24.40(±0.20), B — V = −0.40(±0.40) is found at ≈50" from the center.

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Aarseth, Sverre, and Rosemary Mardling. "Neutron Star Binaries in Open Clusters." International Astronomical Union Colloquium 160 (1996): 541–42. http://dx.doi.org/10.1017/s0252921100042342.

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We useN-body simulations of open clusters to examine the evolutionary history of binaries containing neutron stars. The model includes consistent treatment of all the relevant processes (Aarseth 1996):•Synthetic stellar evolution–mass and radius as a function of time (Eggleton et al. 1989)•Accurate treatment of close encounters–Perturbations of binaries and stable multiple systems - Exchange reactions (involving triple and binary-binary interactions) - Collisions → blue stragglers•Binary evolution (primordial and dynamically formed)–Tidal interactions (Mardling & Aarseth 1996) - Stable mass transfer - Common envelope evolution - Magnetic braking - Gravitational radiation - Mergers (including blue stragglers)•Mass loss–Stellar winds - Supernovae - Evaporation of stars from the cluster•Neutron star formation–Supernovae with kick velocities of Lyne & Lorimer (1994), Drukier (1996) - Accretion-induced collapse

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Sarkisyan, A., O. Sholukhova, S. Fabrika, D. Bizyaev, A. Valeev, A. Vinokurov, Y. Solovyeva, A. Kostenkov, V. Malanushenko, and P. Nedialkov. "Luminous blue variable candidates in M31." Monthly Notices of the Royal Astronomical Society 497, no. 1 (July 25, 2020): 687–97. http://dx.doi.org/10.1093/mnras/staa1729.

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ABSTRACT We study five luminous blue variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-m telescope at the Apache Point Observatory and on the 6-m telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, He i, Fe ii, and [Fe ii] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in the V band), which allows us to classify it as an LBV. The star J004415.04+420156.2 shows characteristics typical of B[e] supergiants. The star J004411.36+413257.2 is classified as a Fe ii star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We obtain for the first time the NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in J004341.84+411112.0. This allows us to confirm that MN112 is an LBV, which should show its brightness variability in longer time span observations.

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Yang, Yujiao, Chengyuan Li, Richard de Grijs, and Licai Deng. "The Spatial Distributions of Blue Main-sequence Stars in Magellanic Cloud Star Clusters." Astrophysical Journal 912, no. 1 (April 30, 2021): 27. http://dx.doi.org/10.3847/1538-4357/abec4b.

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Hashimoto, Tetsuya, Tomotsugu Goto, Rieko Momose, Chien-Chang Ho, Ryu Makiya, Chia-Ying Chiang, and Seong Jin Kim. "A young galaxy cluster in the old Universe." Monthly Notices of the Royal Astronomical Society 489, no. 2 (August 12, 2019): 2014–29. http://dx.doi.org/10.1093/mnras/stz2182.

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ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.

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Ghaffari, Zohreh, Martin Haas, Marco Chiaberge, Steven P. Willner, Rolf Chini, Hendrik Hildebrandt, Roberto de Propris, and Michael J. West. "Clustering of red and blue galaxies around high-redshift 3C radio sources as seen by the Hubble Space Telescope." Astronomy & Astrophysics 653 (September 2021): A44. http://dx.doi.org/10.1051/0004-6361/202039404.

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To properly understand the evolution of high-redshift galaxy clusters, both passive and star-forming galaxies have to be considered. Here we study the clustering environment of 21 radio galaxies and quasars at 1 < z < 2.5 from the third Cambridge catalog (3C). We use optical and near-infrared Hubble Space Telescope images with a 2′ field-of-view, where the filters encompass the rest-frame 4000 Å break. Passive red and star-forming blue galaxies were separated in the color–magnitude diagram using a redshift-dependent cut derived from galaxy evolution models. We find that about 16 of 21 radio sources inhabit a galaxy overdensity on scales of 250 kpc (30″) projected radius. The sample shows a diversity of red and blue overdensities and also sometimes a deficiency of blue galaxies in the center. The following tentative evolutionary trends are seen: extended proto-clusters with only weak overdensities at z > 1.6, red overdensities at 1.2 < z < 1.6, and red overdensities with an increased deficit of central blue galaxies at z < 1.2. Only a few 3C sources show a blue overdensity tracing active star-formation in the cluster centers; this rarity could indicate that the powerful quasar activity may quench star-formation in the vicinity of most radio sources. The derived number of central luminous red galaxies and the radial density profiles are comparable to those found in local clusters, indicating that some 3C clusters are already mass-rich and compact.

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Wang, Yi-Wen, Helaina D. Ludwig, Harald Scherm, Marc W. van Iersel, and Savithri U. Nambeesan. "Blue Light Does Not Affect Fruit Quality or Disease Development on Ripe Blueberry Fruit During Postharvest Cold Storage." Horticulturae 6, no. 4 (September 30, 2020): 59. http://dx.doi.org/10.3390/horticulturae6040059.

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Blueberry fruit are perishable after harvesting due to fruit softening, water loss and susceptibility to pathogens. Light, especially blue light, increases the accumulation of anthocyanins and reduces postharvest decay in some fruits, but the effect of blue light on postharvest fruit quality attributes in blueberries is unknown. In this study, we evaluated the effect of blue light on fruit quality, anthocyanin accumulation and disease development during postharvest cold storage (2 °C–4 °C) in two experiments with southern highbush blueberry ‘Star’ and rabbiteye blueberry ‘Alapaha’. Overall, diurnal blue light did not affect postharvest fruit quality attributes, such as visual defects, fruit compression, skin puncture, total soluble solid content and titratable acidity, in the two cultivars compared with their respective controls (diurnal white light or continuous darkness). Further, there was no effect of blue light on fruit color and anthocyanin accumulation. Fruit disease incidence in ‘Star’ ranged from 19.0% to 27.3% after 21 days and in ‘Alapaha’ from 44.9% to 56.2% after 24 days in postharvest storage, followed by 4 days at room temperature, but blue light had no consistent effect on postharvest disease incidence for either cultivar. Disease progression following artificial inoculations with Alternaria tenuissima and Colletotrichum acutatum in ‘Star’ was not influenced by light treatment prior to inoculation and during fruit storage. In a separate experiment, we tested the effect of blue light on color development in ‘Farthing’, a southern highbush blueberry cultivar with fruit prone to non-uniform ripening, whereby the stem-end remains green as the rest of the fruit turns blue. Although green stem-end spots turned blue over time, there was no statistically significant effect of the blue light treatment. Overall, these data indicate that blue light does not affect fruit quality attributes or disease development in ripe blueberry fruit during postharvest storage in the conditions investigated here.

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Iijima, T. "Variable High Velocity Jets in the Symbiotic Star CH Cygni." Symposium - International Astronomical Union 188 (1998): 219. http://dx.doi.org/10.1017/s0074180900114834.

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Highly blue or red shifted broad emission components of H I lines have been noticed in some recent spectra of the symbiotic star CH Cyg. Their intensities, profiles, and displacements from the narrow component have changed with time scale of days. For example, a blue-shifted (-1545 km s−1) intense emission component and a red-shifted weak (+757 km s−1) emission were seen on 1994 September 9. One day after, the blue-shift and red-shift became −2076 km s−1 and +1285 km s−1, respectively.

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Sree, N. Rathna, and A. Ray. "Evolution of a 10MΘ Star With LMC Metallicities." International Astronomical Union Colloquium 106 (1989): 238. http://dx.doi.org/10.1017/s0252921100063065.

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Why stars become red giants has been a subject of investigation in many contexts, most recently in the discovery of the progenitor of the Supernova 1987A. Sanduleak 69°202 was found to be a blue supergiant star although it was generally presumed that type II SNe arise from red supergiants. Immediately after SN1987A, it was suggested that the blue spectral nature was due to lower metallicity in the LMC (Z = ZΘ/3 - ZΘ/4) although the existence of many red supergiants in the 30 Doradus region where SN1987A took place and in particular the observation of low-velocity nitrogen-rich gas presumed to be a circumstellar shell indicates that mass loss may also have played a significant role in bringing SK 69°202 from red to blue. We report here work in progress on the evolution of massive stars in the LMC with and without mass loss which can ultimately produce type II SNe.

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Tanabe, H., and K. Mori. "Blue and Red Brightnesses of the Integrated Starlight Obtained by Star-Counts in 24 Regions." Symposium - International Astronomical Union 139 (1990): 103–4. http://dx.doi.org/10.1017/s007418090024045x.

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Star-counts on the Palomar Sky Survey Atlas were made in 1968-87 in order to estimate the background brightness in zodiacal light and airglow observations. Measured diameters of blue and red images of each star were converted to the magnitude with empirical diameter-magnitude relations. The resultant blue and red brightnesses and colors of the integrated starlight are presented for 24 sky regions, including 4 polar (North Celestial, North Ecliptic, North and South Galactic) and 10 ecliptic regions.

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Spetsieri, Z. T., A. Z. Bonanos, M. Yang, M. Kourniotis, and D. Hatzidimitriou. "The HST Key Project galaxies NGC 1326A, NGC 1425, and NGC 4548: New variable stars and massive star population." Astronomy & Astrophysics 629 (August 22, 2019): A3. http://dx.doi.org/10.1051/0004-6361/201936074.

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Studies of the massive star population in galaxies beyond the Local Group are the key to understanding the link between their numbers and modes of star formation in different environments. We present the analysis of the massive star population of the galaxies NGC 1326A, NGC 1425, and NGC 4548 using archival images obtained with the Hubble Space Telescope Wide Field Planetary Camera 2 in the F555W and F814W filters. Through high-precision point spread function fitting photometry for all sources in the three fields, we identified 7640 candidate blue supergiants, 2314 candidate yellow supergiants, and 4270 candidate red supergiants. We provide an estimate of the ratio of blue to red supergiants for each field as a function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics (MESA) at solar metallicity, we defined the luminosity function and estimated the star formation history of each galaxy. We carried out a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range, and the inverse von Neumann ratio. This analysis yielded 243 new variable candidates with absolute magnitudes ranging from MV = −4 to −10 mag. We classified the variable stars based on their absolute magnitude and their position on the color–magnitude diagram using the MESA evolutionary tracks at solar metallicity. Our analysis yielded 8 candidate variable blue supergiants, 12 candidate variable yellow supergiants, 21 candidate variable red supergiants, and 4 candidate periodic variables.

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Thuan, Trinh X. "Blue Compact Dwarf Galaxies: Laboratories for probing the Primordial Universe." Proceedings of the International Astronomical Union 4, S255 (June 2008): 348–60. http://dx.doi.org/10.1017/s1743921308025064.

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AbstractBlue Compact Dwarf (BCD) galaxies are the most metal-deficient star-forming galaxies known in the universe, with metallicities ranging from 1/40 to 1/3 that of the Sun. I review how they constitute excellent nearby laboratories for studying big bang nucleosynthesis and star formation and galaxy evolution processes in a nearly primordial environment.

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Pasquato, M. "ANALYTICAL SOLUTIONS FOR THE DYNAMICAL CLOCK A+ INDICATOR IN A TOY MODEL OF PURE DYNAMICAL FRICTION." Revista Mexicana de Astronomía y Astrofísica 56, no. 1 (April 1, 2020): 3–6. http://dx.doi.org/10.22201/ia.01851101p.2020.56.01.01.

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Blue straggler stars are more massive than the average star in globular clus- ters, as they originate from the merger of two stars. Consequently, they experience dynamical friction, progressively sinking to the cluster center. Recently, several indicators of the degree of dynamical relaxation of a globular cluster have been proposed, based on the observed radial distribution of blue straggler stars. The most successful is the Alessandrini indicator, or A+ for short, which is the integral of the cumulative distribution of the blue straggler stars minus that of a lighter reference population. A+ correlates with the dynamical age of a cluster both in realistic simulations and in observations. Here I calculate the temporal dependence of the A+ indicator analytically in a simplified model of the evolution of the blue straggler star distribution under dynamical friction only.

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Smith, Nathan. "The isolation of luminous blue variables resembles aging B-type supergiants, not the most massive unevolved stars." Monthly Notices of the Royal Astronomical Society 489, no. 3 (August 16, 2019): 4378–88. http://dx.doi.org/10.1093/mnras/stz2277.

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ABSTRACT Luminous blue variables (LBVs) are suprisingly isolated from the massive O-type stars that are their putative progenitors in single-star evolution, implicating LBVs as binary evolution products. Aadland et al. found that LBVs are, however, only marginally more dispersed than a photometrically selected sample of bright blue stars (BBS) in the Large Magellanic Cloud (LMC), leading them to suggest that LBV environments may not exclude a single-star origin. In both comparisons, LBVs have the same median separation, confirming that any incompleteness in the O-star sample does not fabricate LBV isolation. Instead, the relative difference arises because the photometric BBS sample is far more dispersed than known O-type stars. Evidence suggests that the large BBS separation arises because it traces less massive (∼20 M⊙), aging blue supergiants. Although photometric criteria used by A19 aimed to select only the most massive unevolved stars, visual-wavelength colour selection cannot avoid contamination because O and early B stars have almost the same intrinsic colour. Spectral types confirm that the BBS sample contains many B supergiants. Moreover, the observed BBS separation distribution matches that of spectroscopically confirmed early B supergiants, not O-type stars, and matches predictions for a roughly 10 Myr population, not a 3–4 Myr population. A broader implication for ages of stellar populations is that bright blue stars are not a good tracer of the youngest massive O-type stars. Bright blue stars in nearby galaxies (and unresolved blue light in distant galaxies) generally trace evolved blue supergiants akin to SN 1987A’s progenitor.

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McGregor, Peter J. "Infrared observations of circumstellar ejecta around Luminous Blue Variables." International Astronomical Union Colloquium 113 (1989): 165–76. http://dx.doi.org/10.1017/s0252921100004425.

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AbstractRecent infrared spectroscopy and imaging of LBVs lead to the following results. CO overtone emission at 2.3μm has been found in 13 LBVs in the Galaxy and the LMC. This emission is collisionally excited in warm (3000 – 5000 K), dense (NH> 1010cm-3) circumstellar material. Circumstellar disks offer favorable conditions for the formation and excitation of CO molecules and are very likely the location of the observed emission. It is proposed that the LBVs showing 2.3 μm CO overtone emission possess the highest density circumstellar disks.A group of eight LBVs has been identified in the LMC with He I 2.058 μm emission stronger than H I Brγ. This group includes the CO emission star HD 37836. Helium is over-abundant in these stars withN(He)/N(H) ranging from 0.2 to >0.5. Remarkably five of the helium strong stars belong to the small class of Ofpe/WN9 stars and a further two are probably related to this class.Slit scans of the galactic LBV AG Car have resolved the far-infrared emission from this star, clearly showing it to originate from cool dust in the circumstellar ring structure. Thermal equilibrium considerations require large grains in the ring in order to match the measured grain temperature and radial distance. Similar slit scans of the galactic B[e] star HD 87643 fail to resolve the far-infrared emission from this star at the 10″ level.

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Lequeux, J. "Star Formation Bursts in Galaxies." Highlights of Astronomy 7 (1986): 557–62. http://dx.doi.org/10.1017/s1539299600006924.

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AbstractWe review the tracers of star formation in galaxies and show how they demonstrate the presence of bursts of star formation in various astrophysical contexts: large extragalactic HII regions in spiral and irregular galaxies and in blue compact galaxies, nuclei of some galaxies, extended star formation in other galaxies. We show that strong bursts seem to occur mainly in interacting galaxies. A few comments are made about the theory of such phenomena.

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Alves, D. R., A. Basu, K. H. Cook, and D. L. Welch. "The MACHO Project LMC Variable Star Inventory: Classical Cepheids, AGB Variables, and the Nine Million Star Color-Magnitude Diagram." Symposium - International Astronomical Union 190 (1999): 517–22. http://dx.doi.org/10.1017/s0074180900118753.

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We measure the ratio of ~ 5M⊙ blue and red LMC supergiants (representative of classical Cepheids) using the MACHO Project's 9 million star color-magnitude diagram (9M CMD) of the LMC bar. We find b/r = 0.39, which favors the Z=0.008, 5M⊙ theoretical model of Schaerer et al. (1993) over that of Fagatto et al. (1994). Next, we examine the low mass (old) and low metallicity LMC field population (Pop. II). Features in the 9M CMD and properties of LMC field RRab variables are consistent with a mean iron abundance of [Fe/H] ≈ −1.5 dex for this population. Newly discovered post-HB/early-AGB Pop. II variables are identified in order to delineate the instability strip (IS). Good agreement with the theoretical IS of Bono et al. (1997) is found. We then compare the field RRab with newly identified RRab variables in the LMC clusters NGC 1898 and NGC 1835. We find the mean colors of these cluster RRab lie near the red and blue edges of the IS, respectively, which is similar to their respective (overall) red and blue HB morphologies. Since the field RRab lie on the red side of the IS, we infer the LMC field Pop. II is likely to have a red HB morphology.

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Battinelli, Paolo, and Serge Demers. "The Recent Star Formation History of the LMC Southwest Quadrant." Symposium - International Astronomical Union 190 (1999): 464–65. http://dx.doi.org/10.1017/s0074180900118613.

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Recently, Demers & Battinelli (1998) have shown that the young intercloud stellar aggregates are 10 to 25 Myr old, thus younger than the estimated age (200 Myr) of the last close LMC–SMC encounter (see, e.g., Irwin et al. 1996). These stellar aggregates show a distance gradient that confirms the existence of a “link” between the two Magellanic Clouds. Numerous blue stars have been detected by Demers & Irwin (1991) east of the aggregate ICA76 (the closest to the LMC). These blue stars, that extend to the southwestern periphery of the LMC, may be an aftermath of the close LMC–SMC encounter. Our present study is aimed to survey this SW part of the LMC and to determine the origin of these blue stars.

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Pathak, Suraj Kumar, Ravindra Kumar Gupta, Subrata Nath, D. S. Shankar Rao, S. Krishna Prasad, and Ammathnadu S. Achalkumar. "Columnar self-assembly of star-shaped luminescent oxadiazole and thiadiazole derivatives." Journal of Materials Chemistry C 3, no. 12 (2015): 2940–52. http://dx.doi.org/10.1039/c5tc00009b.

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Carraro, G., R. A. Vázquez, and A. Moitinho. "Blue straggler stars in Galactic open clusters and the effect of field star contamination." Astronomy & Astrophysics 482, no. 3 (March 11, 2008): 777–81. http://dx.doi.org/10.1051/0004-6361:20078629.

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Sanna, N., E. Dalessandro, B. Lanzoni, F. R. Ferraro, G. Beccari, and R. T. Rood. "The blue straggler star population in NGC 6229★." Monthly Notices of the Royal Astronomical Society 422, no. 2 (March 6, 2012): 1171–77. http://dx.doi.org/10.1111/j.1365-2966.2012.20690.x.

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Mahajan, Smriti, and Somak Raychaudhury. "Red star-forming and blue passive galaxies in clusters." Monthly Notices of the Royal Astronomical Society 400, no. 2 (December 1, 2009): 687–98. http://dx.doi.org/10.1111/j.1365-2966.2009.15512.x.

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Fadeyev, Yu A. "The Blue Edge of the Helium Star Instability Strip." International Astronomical Union Colloquium 111 (1989): 261. http://dx.doi.org/10.1017/s0252921100011696.

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AbstractHydrodynamic calculations of nonlinear pulsations were done for models of helium stars with mass 1 M⊙, luminosity from 3220 L⊙ to 12820 L⊙ and effective temperature from 6000K to 8000K. The models with L > 8000L⊙ were found to pulsate in the fundamental mode with large amplitude (ΔR/R ~ 1), whereas less luminous models (L < 8000L⊙) revealed small amplitude oscillations (ΔR/R ~ 0.2) in the first overtone. In the luminosity range considered the blue edge of the instability strip corresponds to an effective temperature of 7500K, that is to the upper limit of the effective temperatures of R CrB stars. Application of the period-luminosity relation to the variables R CrB and RY Sgr gives their luminosities to be of 9000L⊙.

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George, Koshy. "Structural analysis of star-forming blue early-type galaxies." Astronomy & Astrophysics 598 (January 27, 2017): A45. http://dx.doi.org/10.1051/0004-6361/201629667.

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Cooper, Michael C., and Jeffrey A. Newman. "Galaxy Environments in DEEP2: The Birth of the Red Sequence." Proceedings of the International Astronomical Union 2, S235 (August 2006): 167–69. http://dx.doi.org/10.1017/s1743921306005874.

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The galaxy population at z ≲ 1 is effectively described as a combination of two distinct types: red, early-type galaxies lacking much star formation and blue, late-type galaxies with active star formation. For the red galaxy population, recent work by Bell et al. (2004) has shown that the number density of ~L* galaxies on the red sequence has risen by a factor of ~2 from z ~ 1 to z ~ 0. A variety of complementary observations suggests that the build-up of galaxies on the red sequence results from 2 distinct evolutionary trends: (1) the quenching of star formation in blue galaxies and their subsequent migration onto the red sequence and (2) the dissipationless or (“dry”) merging of red-sequence galaxies.

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Smartt, Stephen J. "Massive star abundances in the Galaxy and the Magellanic Clouds." Symposium - International Astronomical Union 212 (2003): 22–29. http://dx.doi.org/10.1017/s0074180900211601.

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The use of photospheric abundances in OB-type main-sequence stars and A and B-type supergiants as probes of rotation and evolutionary status is reviewed. The abundances of CNO and boron can be compared quantitatively with stellar evolutionary calculations. In particular the abundance ratios of N/O and N/C can be derived in blue supergiants to determine if they are consistent with the stars having gone through a red supergiant phase and dredge-up of core material to the surface. The results from several different studies are reviewed and compared. For blue supergiant stars in the mass-range 5-80 M⊙ the situation appears consistent — there is no evidence for stars of any mass having undergone blue-loops in the HR diagram. The stellar samples show significant signs of having N enriched atmospheres, and the quantitative values are consistent with stellar evolutionary calculations which invoke turbulent diffusive mixing while massive stars are on the main-sequence. Results on the interesting blue supergiant Sher 25 are presented, and linked to Sk-69°202; the B3Ia progenitor of SN 1987A. A spectacular ejection nebula surrounds Sher 25, much like that which was ejected by Sk–69°202 during its final stages of evolution. Both of these were thought to have been formed during a mass-loss event when the stars were in the red supergiant phase. The CNO abundances derived in Sher 25 suggest the nebula was ejected during the blue supergiant phase, and that rotation can explain the N-enrichment found in the stellar photosphere.

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Papaderos, P. "Photometric Structure and Star Formation in Blue Compact Dwarf Galaxies." Proceedings of the International Astronomical Union 2, S235 (August 2006): 327. http://dx.doi.org/10.1017/s1743921306006922.

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The star-formation history and chemodynamical evolution of Blue Compact Dwarf (BCD) galaxies are central issues in dwarf galaxy research. In spite of being old in their vast majority, BCDs resemble in many aspects unevolved low-mass galaxies in the early universe. They are gas-rich (Hi mass fraction of typically > 30%) and metal-deficient (7.1 $\la$ 12+log(O/H) $\la$ 8.3) extragalactic systems, undergoing intense star-forming (SF) activity within an underlying low-surface brightness (LSB) host galaxy.

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Marquart, T., G. Östlin, N. Bergvall, P. Masegosa, P. Amram, and I. Márquez. "The Kinematics of Extended Hα Emission in Blue Compact Galaxies." Proceedings of the International Astronomical Union 2, S235 (August 2006): 321. http://dx.doi.org/10.1017/s1743921306006867.

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AbstractBlue Compact Galaxies (BCGs) have received interest mainly because they comprise the best available test-beds for studies of low-metallicity star formation (SF) and allow the study of relatively unevolved systems at low redshift. Their ongoing phase of intense star formation is a transient phenomenon and the best candidates for its trigger are interactions and mergers. Studies of the kinematics are important for the understanding of this process.We present spatially resolved kinematics from the Hα line in five BCGs that show an extended region of ionised emission around the central starburst. We find this region to have near-spherical isophotes at large radii and to be dynamically decoupled from a central disturbance. A scenario where the strong triggered star formation in the center ionises the surrounding gas cloud, still following its original motions, can qualitatively explain these common features. The poster, including the figures, can be found at http://kern-2pt/thomasmarquart.net/pspdf/prague-marquart.pdf.

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Colón, Cristóbal, María Isabel de Andrés-García, Lucía Isidoro-García, and Andrés Moya. "Theoretical Stark Broadening Parameters for UV–Blue Spectral Lines of Neutral Vanadium in the Solar and Metal-Poor Star HD 84937 Spectra." Atoms 8, no. 4 (September 28, 2020): 64. http://dx.doi.org/10.3390/atoms8040064.

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Using Griem’s semi-empirical approach, we have calculated the Stark broadening parameters (line widths and shifts) of 35 UV–Blue spectral lines of neutral vanadium (V I). These lines have been detected in the Sun, the metal-poor star HD 84937, and Arcturus, among others. In addition, these parameters are also relevant in industrial and laboratory plasma. The matrix elements required were obtained using the relativistic Hartree–Fock (HFR) method implemented in Cowan’s code.

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Otter, Justin A., Karen L. Masters, Brooke Simmons, and Chris J. Lintott. "Galactic conformity in both star formation and morphological properties." Monthly Notices of the Royal Astronomical Society 492, no. 2 (January 3, 2020): 2722–30. http://dx.doi.org/10.1093/mnras/stz3626.

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ABSTRACT We investigate one-halo galactic conformity (the tendency for satellite galaxies to mirror the properties of their central) in both star formation and morphology using a sample of 8230 galaxies in 1266 groups with photometry and spectroscopy from the Sloan Digital Sky Survey, morphologies from Galaxy Zoo and group memberships as determined by Yang et al. This is the first paper to investigate galactic conformity in both star formation and visual morphology properties separately. We find that the signal of galactic conformity is present at low significance in both star formation and visual morphological properties, however it is stronger in star formation properties. Over the entire halo mass range we find that groups with star-forming (spiral) centrals have, on average, a fraction 0.18 ± 0.08 (0.08 ± 0.06) more star-forming (spiral) satellites than groups with passive (early-type) centrals at a similar halo mass. We also consider conformity in groups with four types of central: passive early-types, star-forming spirals, passive spirals, and star-forming early-types (which are very rarely centrals), finding that the signal of morphological conformity is strongest around passive centrals regardless of morphology; although blue spiral centrals are also more likely than average to have blue spiral satellites. We interpret these observations of the relative size of the conformity signal as supporting a scenario where star formation properties are relatively easily changed, while morphology changes less often/more slowly for galaxies in the group environment.

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Noirot, Gaël, and Marcin Sawicki. "Hα and Continuum Sizes with the HST/WFC3 G141 GRISM: Outside-in Quenching for z = 1.0–1.4 Fast Quenchers." Research Notes of the AAS 6, no. 7 (July 26, 2022): 150. http://dx.doi.org/10.3847/2515-5172/ac83b9.

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Abstract We investigate the evolution of the physical extent of star formation of M ⋆ > 109 M ⊙ rapidly quenching galaxies at z = 1.0–1.4. We measure the galaxy Hα and stellar continuum sizes from their HST/WFC3 G141 grism spectroscopy and connect the galaxy sizes to time on their evolutionary delayed–τ tracks determined in Noirot et al. Most galaxies (10/13) have non-evolving Hα-to-continuum size-ratios consistent with unity within the measurement uncertainties, suggesting an homogeneous decline of star formation in these galaxies despite a rapid shut-down of their star formation. On the other hand, a handful (3/13) show statistically smaller Hα sizes compared to the stellar continuum as they age and approach the blue-cloud/red-sequence transition region. This suggests an outside-in shut-down of the star formation (potentially driven by environmental mechanisms) in these rapidly evolving galaxies as they move from the blue cloud toward the red sequence.

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Journal articles on the topic 'Blue star'

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