EMISSION-LINE OBJECTS NEAR R CRA

Aims. We study the properties of the nuclear molecular gas of the ultra luminous merger Arp 220 and effects of the nuclear source on gas excitation and chemistry. Specifically, our aim is to investigate the spatial location of the luminous HNC 3-2 line emission and address the underlying cause of its unusual brightness. Methods. We present high resolution observations of HNC J=3-2 with the submillimeter array (SMA). Results. We find luminous HNC 3-2 line emission in the western part of Arp 220, centred on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K at $0\hbox{$.\!\!^{\prime\prime}$ }4$ resolution), narrow (60 ${\rm km~s}^$) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment - even when the high gas column density towards the western nucleus is taken into account. We discuss this briefly in the context of an X-ray affected chemistry and radiative excitation. Conclusions. The luminous and possibly amplified HNC emission of the western nucleus of the Arp 220 merger reflects the unusual, and perhaps transient environment of the starburst/AGN activity there. The faint HNC line emission towards Arp 220-east reveals a real difference in physical conditions between the two merger nuclei.

In this paper, we use high-quality rest-UV spectra of three radio galaxies at z ∼ 3 observed with the FORS2 camera on the Very Large Telescope to measure the flux of several emission lines, including relatively faint ones, such as N iv]λ1486, O iii]λ1663, and [Ne iv]λ2424. Additionally, we collect fluxes of faint rest-UV emission lines in 12 z ∼ 3 radio galaxies from the literature. Previously, physical and chemical properties of narrow-line regions (NLRs) in high-z active galactic nuclei (AGNs) have been investigated mostly by using only strong rest-UV emission lines (e.g., N v λ1240, C iv λ1549, He ii λ1640, and C iii]λ1909). Such strong-line diagnostics are based on various assumptions due to the limitation in the number of available emission-line constraints. In this work, both physical and chemical properties of NLR clouds in each object are estimated by fitting detailed photoionization models to the measured emission-line fluxes. We confirm that the metallicity of NLRs in AGNs at z ∼ 3 is solar or supersolar, without assumptions about the gas density and ionization parameter thanks to the constraints from the faint emission lines. This result suggests that high-z radio galaxies are already chemically mature at z ∼ 3.

From a study of the chromospheric lines listed by Pierce (1968, 1973) indications have been found that first-order plasma satellites appear sometimes as a pair of faint chromospheric emission lines in such places where forbidden lines, mainly of metals, should be located. Second-order satellites are indicated sometimes by an asymmetry in the emission wings of stronger lines, either with respect to intensity or with respect to distance from the line centre and, if so, with the remote wing of diffuse shape. Finally diffuse faint lines, appearing in somewhat greater distances from strong chromospheric lines, suggest the appearance sometimes of fourth-order plasma satellites. All the three types of satellites give electron densities of the order of 1012 cm−3. Traces of possible absorption satellites are found also for some of the lines in the solar spectrum. In this connection special attention is drawn to a few faint solar lines located near the wavelengths of corona emission lines.

We uncover the H2 flows in the Corona Australis molecular cloud and in\nparticular identify the flows from the Coronet cluster. Near-infrared H2 v=1--0\nS(1), 2.12micron-line, narrow-band imaging survey of the R CrA cloud core was\ncarried out. We identify the best candidate-driving source for each outflow by\ncomparing the flow properties, available proper motions, and the\nknown/estimated properties of the driving sources. We also adopted the\nthumbrule of outflow power as proportional to source luminosity and inversely\nproportional to the source age to reach a consensus.\n Results: Continuum-subtracted, narrow-band images reveal several new\nMolecular Hydrogen emission-line Objects (MHOs). Together with previously known\nMHOs and Herbig-Haro objects we catalog at least 14 individual flow components\nof which 11 appear to be driven by the RCrA aggregate members. The flows\noriginating in the Coronet cluster have lengths of ~0.1-0.2 pc. Eight out of\nnine submillimeter cores mapped in the Coronet cluster region display embedded\nstars driving an outflow component. Roughly 80% of the youngest objects in the\nCoronet are associated with outflows. The MHO flows to the west of the Coronet\ndisplay lobes moving to the west and vice-versa, resulting in nondetections of\nthe counter lobe in our deep imaging. We speculate that these counterflows may\nbe experiencing a stunting effect in penetrating the dense central core.\n Conclusions:Although this work has reduced the ambiguities for many flows in\nthe Coronet region, one of the brightest H2 feature (MHO2014) and a few fainter\nfeatures in the region remain unassociated with a clear driving source. The\nflows from Coronet, therefore, continue to be interesting targets for future\nstudies.\n

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar spectra in the region of the obscuring clouds of Ophiuchus and Scorpius. Struve, Otto ; Rudkjobing, Mogens Abstract Joy's remarkable discovery of forty stars having strong emission lines in the vicinity of the great obscuring clouds of Taurus has in- spired a study of the faint stars in the region of the dark nebulae in Ophiuchus and Scorpius. With the 8 -inch telescope of the McDonald Observatory the authors have observed the spectra of approximately twenty stars between photographic apparent magnitudes 12 and 15. TABLE 1. EMIS' No. (1948) 8(1948) Mag. 4 I6 2 8 24113 13 9 16 24.5 -24 14 12.5 10 i6 24.7 -24 i6 15 12 i6 24.1 -2434 13.5 13 i6 25.6 -24 20 12.5- -14.0 FAINT STARS OF EARLY TV 3 1623.0 -2428 13 5 1622.9 -23 50 13 16 1623.8 -23 50 13.5 Five of them were found to have strong emission lines and one of the five (number 13 in our list) is a variable star with a range of at least 1.5 mag. These five stars range in spectral type, as estimated from the absorption features, between K2 and M. They are thus similar to the majority of Joy's stars in Taurus, presumably belonging to the main sequence and having in addition a superposed spectrum of strong emission lines which make them stand out among the ordinary dMe and the dKe stars which are occassionally found among ordinary stellar populations. An interesting feature of the stars 9, 12, and 13 is the great strength of the blend of Caii H and HE which seems to be abnormal since it exceeds the sum of the intensities to be expected in the two blended components. It is possible that this excessive strength of the Caii H line m y be explained by inelastic collisions between Caii ions in the ground state and H atoms in the seventh quantum state. The occurence of dwarf stars with strong emission lines in cosmic dust clouds again raises the problem of the origin of their peculiar spectra. A computation based upon Hoyle's expression for the accretion of mass of a star which rests within a nebula leads to the following ratio of the energy released by the infall of particles to the energy of radiation of the star = I0-iN( 3) 31 It may be reasonable to suppose that the number of atoms per cubic centimeter of the dust cloud is is the order of the 101 or I0 and that the tempera- ON LINE STARS Sp. Description K5 Very strong H and Caii and perhaps weak HeI. The absorption lines are systematically weaker than normal. K2 Fairly strong and very broad H, strong and sharp Caii. Caii H very much stronger than CaiI K. K? Very strong H and Caii, moderately strong FeII. Spectral type estimated from the continuous spectrum because the emission lines overlie the absorption features. M Moderate H and Caii, perhaps weak FeiI. Caii H very much stronger than Caii K. Has TiO absorption bands. Very strong H and weak Cail. HE$ ? Caii H is much stronger than H . Continuous spectrum too weak. E ITHOUT EMISSION LINES Ao Fairly sharp absorption of H. A Very weak and shallow absorption lines of H. ture of the thermal motions of these atoms in the vicinity `of the star may be of the order of I0 . In that case it is reasonable to expect fairly strong emission lines in the spectra of those stars which do not have enough radiation pressure to drive away the dust particles. In addition to the five emission line stars, three faint stars of type A were found within the densest regions of the nebula. Their spectra have no emission lines and only number 16 looks abnormal because of the weakness of its hydrogen absorption lines. This may be an underluminous A star or possibly even a white dwarf. The rest of the stars have normal spectra of types K and M. Most of them are probably foreground stars while a few, near the edges of the nebula may be distant objects shining through the thinner portions of the cloud. Table I gives a list of the more interesting objects. Ferkes Observatory, Williams Bay, Wis., and McDonald Observatory, Fort Davis, Tex. Publication: The Astronomical Journal Pub Date: October 1948 DOI: 10.1086/106193 Bibcode: 1948AJ.....54...51S full text sources ADS |

. IntroductionC/2002 VQ94 (LINEAR) is a long period comet that passed its perihelion on February 7, 2006 at a distance of 6.8 au from the sun. Over an extended period of time the comet had an asteroidal appearance without any sign of cometary activity. Such an activity was first detected before its perihelion passage at the end of August 2003, when it was at a distance of 8.9 au from the Sun. Spectroscopic observations were conducted on March 2006 shortly after perihelion passage. These observations lead to the surprising discovery of N2+ emission lines (Korsun et al., 2006). CO+ and N2+ were confidently measured in 2007 during some other observations (Korsun et al., 2008). Two other observing runs were conducted in March 2008 and March 2009. The observations conducted in March 2008, at 8.36 au from the Sun also revealed N2+ emission lines, however no emissions were found in the spectrum obtained at 9.86 au in 2009. A N2+/CO+ ratio was estimated to be 0.06 (Korsun et al, 2014) based on fluorescence efficiencies published by Lutz et al. (1993) for N2+ and Magnani & A’Hearn (1986) for CO+. Because new fluorescence models have now been published for these two species we reanalyze these data to get updated N2+/CO+ ratio for this comet.2. ObservationsObservations were carried out with the 6-m Big Telescope Alt-azimuth (BTA) operated by SAO in March 2008. A focal reducer SCORPIO attached to the prime focus of the BTA telescope was used with the transparent grisms VPHG1200B as disperser in the spectroscopic mode and a long-slit mask with 6.10’x1.0’’ dimensions was projected on the cometary coma. The spectral resolution of the spectra was about 6 Å. Three different spectra of 1200 s of integration time each were obtained on March 13, 2008, with a spectral range of 3600-5400 Å. These three spectra were combined in a first step by median filtering between the frames and in a second step in a 1D spectrum computed by collapsing the 2D median spectrum in the spatial direction where a coma was detected. The solar continuum was subtracted to the 1D spectrum, based on a theoretical solar spectrum convolved with a similar instrument response function and adjusted to the cometary spectrum.3. ModelingWe used the two fluorescence models developed for both N2+ (Rousselot et al., 2022) and CO+ (Rousselot et al., 2024) to model high-resolution spectra obtained on the comet C/2016 R2 (PanSTARRS). This comet having unusual bright emission lines of N2+ and CO+ (Opitom et al., 2019) constituted an ideal target for testing these fluorescence models. After different tests we managed to get a satisfatory fit of the average 1D spectrum published in Korsun et al. (2014) by using N2+/CO+ ratio of 0.08. Such a ratio is a little bit higher than the first estimate published in this article. Fig. 1 presents this fit.Figure 1: Comparison of the spectrum of comet C/2002 VQ94 (blue) observed at 8.36 au with our modeling of N2+ and CO+. The sum of the N2+ and CO+ emission bands appear in red. Some other faint possible emission lines (e.g. CN band near 388 nm) have not been taken into account in this modeling, the brightest bands of interest being not blended by these possible emission bands.4. ConclusionOur reanalysis confirms the order of magnitude of the previously estimated N2+/CO+ ratio, which appear a little bit greater than this initial estimate. It also confirms that C/2002 VQ94 belongs to the very few comets having a significant fraction of N2+ (and consequently N2) in their coma, this species being usually not detected in the cometary coma. Comets identified so far with a similar N2+/CO+ fraction are C/1908 (Morehouse), C/1940 N2 (Cunningham), C/1947 S1 (Brester), C/1956 (Arend-Roland), C/1969 Y1 (Bennett), C/1973 R1 (Kohoutek), C/1986 P1 (Wilson), C/1987 P1 (Bradfield) and C/2016 R1 (PanSTARRS) (see, e.g. Anderson et al., 2023 for more details).The case of the observations reanalyzed in this work is also unique for the record heliocentric distance at which this species, as well as CO+ was identified (8.36 au). Such large heliocentric distance was also a good test for the new CO+ and N2+ models developped for computing cometary fluorescence spectrumReferencesAnderson S. et al., 2023, MNRAS 524, 5182-5195 Korsun P., et al., 2006, A&A 459, 977-980 Korsun P., et al., 2008, Icarus 198, 465-471 Korsun P., et al., 2014, Icarus Icarus 232, 88–96 Lutz B.L., et al., 1993, Ap.J. 407, 402-411 Magnani L., A’Hearn M.F, 1986, Ap.J. 302, 477-487 Opitom C., et al. 2019, A&A, 624, A64 Rousselot P., et al., 2022, A&A 661, id. A131 Rousselot P., et al., 2024, A&A 683, id. A50

Accurate emission line fluxes from planetary nebulae (PNe) provide important constraints on the nature of the final phases of stellar evolution. Large, evolved PNe may trace the latest stages of PN evolution, where material from the AGB wind is returned to the interstellar medium. However, the low surface brightness and spatially extended emission of large PNe have made accurate measurements of line fluxes difficult with traditional long-slit spectroscopic techniques. Furthermore, distinguishing these nebulae from H II regions, supernova remnants, or interstellar gas ionized by a hot, evolved stellar core can be challenging. Here, we report on an ongoing survey of large Galactic PNe ($r > 5^\prime$) with the Wisconsin H-Alpha Mapper (WHAM), a Fabry-Perot spectrograph designed to detect faint diffuse optical emission lines with high sensitivity and spectral resolution. Our sample includes newly revealed $H\alpha$ enhancements from the AAO/UKST and WHAM $H\alpha$ surveys of Parker et al. and Haffner et al. We present accurate emission line fluxes of $H\alpha$, [N II]$\lambda$6583, and [O III]$\lambda$5007, and compare our data to other measurements. We use the emission line ratios and kinematics of the ionized gas to assess, or in some cases reassess, the identification of some nebulae.

A survey for faint emission line objects has been carried out at Canada- France-Hawaii Telescope using multiaperture spectroscopy. The limiting magnitude is V = 23.1 and the survey covers an area of 0.068 square degrees. Above an emission line signal-to-noise threshold of 6, ten very faint emission line galaxies were detected as well as five quasar candidates. The faintest quasar candidates were detected by the presence of a single strong emission line and are likely to be at z~3 although follow-up spectroscopy is required to confirm the redshifts. The survey (which is most sensitive over the redshift range 2.4 < z < 4.7) is well calibrated and uses emission line search procedures designed to yield reliable space densities from the sample of objects obtained.

More than 110 dense condensations of the dark clouds in Lupus, Corona Australis, Norma, Vela, and Scorpius were observed in the 13CO and C18O (J = 1-0) transitions. The condensations of dark clouds with high star formation activity like the Ophiuchus, Taurus, and Cepheus have average C18O and H2 column densities of 1.8 × 1015 and 1.1 × 1022 cm-2. If we take the average size of the condensations to be 0.2 pc, a condensation must have average H2 volumetric densities ≥2 × 104 cm-3 in order to be a good candidate to form stars. The four Lupus filaments have similar radial velocities and velocity dispersions, suggesting that they originated from the same parental cloud. Among these filaments, Lupus 1 is unique in having recent star formation activity, despite the high number of T Tauri stars observed toward the others. Lupus 1 also shows a complex velocity gradient along its main axis. The distribution of radial velocities of the condensations observed toward Scorpius are in good agreement with the hypothesis that they are in a region with expansion velocity smaller than or equal to 18 km s-1. The Corona Australis cloud has velocity gradients ranging from -0.5 km s-1 pc-1 at one extreme to 0.1 km s-1 pc-1 at the other.

We present a near-infrared extinction map of a large region ($\sim$870 deg$^2$) covering the isolated Corona Australis complex of molecular clouds. We reach a 1-$\sigma$ error of 0.02 mag in the K-band extinction with a resolution of 3 arcmin over the entire map. We find that the Corona Australis cloud is about three times as large as revealed by previous CO and dust emission surveys. The cloud consists of a 45 pc long complex of filamentary structure from the well known star forming Western-end (the head, $N \geq10^{23}$ cm$^{-2}$) to the diffuse Eastern-end the tail, ($N \leq10^{21}$ cm$^{-2}$). Remarkably, about two thirds of the complex both in size and mass lie beneath A$_V\sim1$ mag. We find that the PDF of the cloud cannot be described by a single log-normal function. Similar to prior studies, we found a significant excess at high column densities, but a log-normal + power-law tail fit does not work well at low column densities. We show that at low column densities near the peak of the observed PDF, both the amplitude and shape of the PDF are dominated by noise in the extinction measurements making it impractical to derive the intrinsic cloud PDF below A$_K <$ 0.15 mag. Above A$_K \sim 0.15$ mag, essentially the molecular component of the cloud, the PDF appears to be best described by a power-law with index $-3$, but could also described as the tail of a broad and relatively low amplitude, log-normal PDF that peaks at very low column densities.

The Raman spectra of CCl4 and SiCl4 have been examined under low and high dispersion. In both cases a faint line has been observed close to the line corresponding to the total symmetric vibration. This faint line has a frequency shift of 434 cm.-1 in the case of CCl4 and is interpreted as the octave of the fundamental frequency 217·9 cm.-1 The corresponding line in the case of SiCl4 shows a frequency shift of 440·5 cm.-1 and is interpreted as the octave of the fundamental frequency 221 cm.-1 It is pointed out that the appearance of the octave in these cases might probably be due to its proximity to the total-symmetric vibration frequency which is respectively 459 cm.-1 and 423 cm.-1 in the case of CCl4 and SiCl4. An additional faint line with a frequency shift of 145 cm.-1 has been observed in the Raman spectrum of CC14 which is interpreted as a differential tone arising from the fundamental frequencies 459 cm.-1 and 314 cm.-1, the summational of which causes the splitting of the fourth frequency, and the octave of whose summational appears as a faint broad line at 1538 cm.-1 The broadening of the fourth frequency in the case of SiCl4 might be due to a cause similar to that which causes the splitting of the fourth frequency in the case of CCl4. The total symmetric vibration in the case of CCl4 shows a well-defined wing to its red side, sharply separated from the principal line.

We study the question whether some of the dark matter in the Milky Way may be baryonic. Considering a proposal by Pfenniger & Combes that dark matter might be associated with the Galactic disk, we study first the case whether such a model may be consistent at all. To model the mass distribution in the Milky Way we assume that dark matter may be contained in an isothermal sphere but also within the disk. We add bulge, bar, and two stellar disks, thick and thin. The gas is characterized by a molecular component, HI gas (cold and warm neutral medium), a diffuse ionized gas component, and a more extended halo component giving rise to the soft X-ray background, but also observable as faint HI lines. All disk components are assumed to be isothermal. A self-consistent solution of the Poisson-Boltzmann equation for mass distribution and gravitational potential in 3-D is discussed. We find a pronounced flaring for all of the isothermal disk components. The flaring derived from the model is in excellent agreement with observations. Oort limit and the local gravitational potential perpendicular to the plane agree with observations. In general, such a solution is consistent with all known observational constraints. The proposal that a disk-like dark matter component in the Milky Way exists in form of H2 clumpuscules is found to be very appealing. A “conspiracy” between gas and dark matter would be a natural consequence. Cloud-cloud collisions and evaporation of H2 clumpuscules would explain that we can observe an X-ray background and faint HI emission lines despite the fact that the cooling timescale is similar to the free fall timescale. The turbulent motion of the clumpuscules would be important for the stability of the Milky Way. At the same time turbulence would explain the scale height of the gaseous halo. Such a baryonic dark matter disk would be consistent with the expected baryon fraction. Similar, the angular momentum of the Milky Way disk would get easily explainable.

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New emission lines in M dwarfs. Wildt, Rupert Abstract A number of ultraviolet spectra of K and M dwarfs were obtained with the Qf/2 camera, dispersion about 65A/mm at X325o, attached to the spectrograph of the 8 -inch McDonald reflector. The exposure times were chosen as long as feasible, in order to record the ultraviolet at wave lengths less than X35oo. A cursory inspection of the first exposure of the star BD 2002465 (dM4e) revealed 3 emission lines below X33oo, where the continuum of the star had already faded out; their existence was confirmed by a second exposure. Bright lines of HI and CaiI had been noticed in this star by Swings and Struve,1 and recently it has become famous as a flare-star.2 No photoelectric magnitudes were recorded at Lick during the nights the spectrograms were taken at McDonald, 1950 February 5, 8:oI U.T. and February 7, 6:56 U.T. Since Swings and Struve had stressed the similarity of the emission spectra of BD 2002465 and YY Gem, this star too was examined for emissions in the far untraviolet. Only one spectrogram with an exposure time of 6 hours is available. It shows the continuum extending to about 3250, making it more difficult to disentangle faint emission lines. Omitting two doubtful ones, 6 emission lines were recognized in BD 2002465 and 4 of these also appear in YY Gem. However, their character is quite different in these two stars. In BD 2002465 the emission lines stand out 556 1/2 5.56 3/2 13/2,2 4.63 5.53 7/53/2 z4D0 4.62 549 z6D0 5/2 4.60 7/2 ~4175 9/2 i5 1.69 Figure. 1/32/ 1.09 1.66 ~3/29 4 2 1.07 a4D 3/71/3 1.04 0.96 Fell emissions in M dwarfs. lines observed in BD +20e2465, Q lines observed in VY Gem (Castor C). sharply against the background fog, and there is no doubt about their nature as "lines"; an exception is the rather diffuse emission at X3228 where there is some vignetting by the spectrograph. In YY Gem the emissions are quite diffuse. In particular, X3256 looks nearly 2A wide; and X3278 appears unsymmetrical, the continuous background being of different density to the red and ultraviolet of this line, as if the emission line coincided with the edge of an absorption band degraded toward th ultraviolet. It is fair to say that the existence of these emissions in YY Gem could hardly have been established from a single spectrogram if it had not been for for their previous discovery in BD 2002465. All the lines were identified with the strongest members of two low-excitation multiplets in the spectrum of Fell; they are entered in the term diagram shown in the figure, which also contains the appropriate excitation potentials. The same two multiplets of Feii, including their fainter members, appear in emission in a Herculis (M ) and a Scorpii (MI), according to G. Herzberg's observations.1 He proved that Feii emission does not originate in the atmospheres of the early-type companions of these stars, but is characteristic of the giants themselves, which also have bright H and K lines. Herzberg also lists 8 unidentified emissions; one of them, at X329o.I5, may be identical with a doubtful emission at X3290.o in BD 2002465. Both a Herculis and a Scorpii have also bright H and K lines. Thus there is suggested remarkable parallelism in emission characteristics between dwarfs and supergiants of spectral type M. Further investiagtion of this point seems 1n- dicated. This investigation was supported by the Office of Naval Research. I.Pub. A.S.P. 53, 244, 1941. 2.K. C. Gordon and G. E. Kron, Pub. A.S.P. 6i, 210, 1949. 3.Ap. J. 107, 94, 1948. Yale University Observatory, New Haven, Conn. Publication: The Astronomical Journal Pub Date: 1951 DOI: 10.1086/106629 Bibcode: 1951AJ.....56S..51W full text sources ADS | data products SIMBAD (4)

Symbiotic binaries sometimes hide their symbiotic nature for significant periods of time. There is mounting observational evidence that, in symbiotics that are powered solely by the accretion of the red giant’s wind material onto a white dwarf, without any quasi-steady shell burning on the surface of the white dwarf, the characteristic emission lines in the optical spectrum can vanish, leaving the semblance of an isolated red giant spectrum. Here we present compelling evidence that this disappearance of optical emission lines from the spectrum of RT Cru in 2019 was due to a decrease in the accretion rate, which we derived by modeling the X-ray spectrum. This drop in accretion rate leads to a lower flux of ionizing photons and thus to faint or absent photoionization emission lines in the optical spectrum. We observed the white dwarf symbiotic RT Cru with XMM-Newton and Swift in X-rays and UV and collected ground-based optical spectra and photometry obtained over the last 33 yr. This long-term coverage shows that, during most of the year 2019, the accretion rate onto the white dwarf was so low, Ṁ = (3.2 ± 0.06) × 10−11 M⊙ yr−1 (d/2.52 kpc)2, that the historically detected hard X-ray emission almost vanished, the UV flux faded by roughly 5 mag, the U, B, and V flickering amplitude decreased, and the Balmer lines virtually disappeared from 2019 January through March. Long-lasting low-accretion episodes such as the one reported here may hamper the chances of RT Cru experiencing a nova-type outburst despite the high mass of the accreting white dwarf.

We investigated chromospheric activities of pre-main-sequence (PMS) stars. First, we studied the Ca II infrared triplet emission lines with Subaru/HDS and other spectroscopic instruments. Most PMS stars have narrow Ca II lines whose intensities are as large as the maximum of the zero-age main-sequence (ZAMS) stars. The chromosphere of PMS stars is suggested to be filled by the Ca II emitting region. Second, we found many faint chromospheric emission lines such as Mg I and Fe I for more than half of the ZAMS stars. Third, we searched the periodic light variation caused by a starspot for the 26 PMS stars. Their TESS light variations and Ca II emission line strengths show the positive correlation, and are located on the extensions of the superflare stars. In summary, PMS stars have very active chromosphere driven by strong dynamo process due to the fast rotation and the long convection timescale.