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REVIEW 4 major objections 6 minor 63 references

Small cold spots on slowly rotating young stars live less than six months; on fast rotators they follow an exponential coverage distribution set by stochastic magnetic flux.

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2026-07-31 14:17 UTC pith:24QFZRBE

load-bearing objection Solid multi-region HOYS expansion that delivers a usable exponential coverage distribution for fast rotators; the lifetime claim for the slow-rotator deficit is plausible but uncalibrated because the injection tests never varied coherence time. the 4 major comments →

arxiv 2607.24460 v1 pith:24QFZRBE submitted 2026-07-27 astro-ph.SR

A survey for variable young stars with small telescopes - XI. Spot Lifetimes and Coverage Distributions

Dirk Froebrich , Carys Herbert , Aleks Scholz , Benjamin W. Ryan , Siegfried Vanaverbeke , Jochen Eisl\"offel , Cledison Marcos da Silva , Michel Michaud
show 42 more authors
Kathy Griffiths Ari M. Siqueira Thomas Urtly Francisco C. Sold\'an Alfaro George Fleming Gregg L. Ruppel Domenico Licchelli Stephen R.L. Futcher Ivan L. Walton Matthias Kolb Mario Morales Aimar Geoffrey Stone Yenal \"O\u{g}men Simon Francis Dawes Franz-Josef Hambsch Nick J. Quinn Juan-Luis Gonz\'alez-Carballo Franky Dubois Jos\'e Luis Salto Gonz\'alez Adam Popowicz Krzysztof Bernacki Slawomir Bednarz Tim Nelson Tony Vale Tonny Vanmunster Georg Piehler Stephen C. Percy Jordi Berenguer Amatller Jacopo Fallai Amritanshu Vajpayee Faustino Garc\'ia de la Cuesta Rafael Castillo Garc\'ia Dawid Mo\'zdzierski Krzysztof Kotysz Przemys{\l}aw J. Miko{\l}ajczyk Holly Stokes-Geddes Matthew D. Dickers Ivana I. Grozdanova Chiara F. Kawohl Aashini L. Patel James S. Urquhart Tim M. Kinnear
This is my paper
classification astro-ph.SR
keywords young stellar objectsstarspotsstellar rotationspot lifetimesspot coveragedisc brakingmagnetic activityT Tauri stars
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Young stars spin at two distinct rates even at roughly one million years of age. This paper measures multi-band light curves of 144 such stars across many star-forming regions and converts the amplitudes into cold-spot coverages and temperatures. Once detection biases are removed, the coverage distribution for fast rotators (periods under 5.5 days) is exponential: tiny spots are far more common than large ones, exactly as expected if magnetic flux emerges stochastically. Slow rotators, by contrast, almost never show those small spots. The authors argue the missing spots are not absent or too cool; they simply decay faster than the six-month windows used to find periods. The result is direct evidence that the surface magnetic pattern of a young star depends on how fast it is spinning, giving models of early angular-momentum loss a new observational target.

Core claim

After bias correction the intrinsic cold-spot coverage distribution of fast-rotating young stars is exponential, while slow rotators show a clear deficit of small-coverage cold spots that is best explained by lifetimes shorter than roughly 150–200 days.

What carries the argument

Six-month light-curve slices analysed for multi-band peak-to-peak amplitudes, converted to spot coverage and temperature contrast; injection-recovery simulations then correct the observed coverage histogram, revealing the exponential form for fast rotators and the lifetime cut-off for slow rotators.

Load-bearing premise

The absence of small cold spots on slow rotators is caused by lifetimes shorter than the six-month detection window rather than by cooler contrasts, different geometry, or residual selection effects the recovery tests missed.

What would settle it

High-cadence photometry that recovers the same slow-rotator sample on timescales of weeks instead of months and either detects the missing small-coverage spots or still fails to find them.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Models of YSO magnetic activity must produce an exponential coverage distribution once spots live longer than a few months.
  • Supergranule (or equivalent diffusion) scales are predicted to shrink by a factor of several when a star spins up after disc dispersal.
  • Disc braking alone cannot set the observed period bimodality; an additional rotation-dependent magnetic process is required.
  • Warm/hot-spot solutions separate into two populations (small accretion footprints and larger plage-like features) that can now be tested with phase-curve modelling.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If supergranule size really tracks rotation, the same lifetime–coverage relation should appear in older, fully convective M dwarfs once comparable multi-band baselines exist.
  • The exponential coverage law supplies a ready prior for population synthesis of photometric jitter in young exoplanet-host candidates.
  • Short-lived small spots on slow rotators may still modulate X-ray or UV emission on weekly timescales even when optical periods vanish.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

4 major / 6 minor

Summary. The paper presents a homogeneous analysis of HOYS multi-band (V,R,I) photometry across 25 star-forming regions, identifying 144 YSOs with robust periodic signals from 2047 candidate members. The period distribution is bimodal (55% fast, P<5.5 d; 45% slow), with fast rotators predominantly disc-less and slow rotators split between disc-bearing and disc-free, indicating disc braking alone is insufficient. Spot temperatures and coverages are derived from multi-band amplitudes and photometrically calibrated effective temperatures (Eq. 1). The two headline results are: (i) after bias correction via injection-recovery simulations, the intrinsic cold-spot coverage distribution of fast rotators is exponential, consistent with stochastic flux emergence; (ii) slow rotators show a deficit of small cold spots, which the authors attribute to small-spot lifetimes shorter than ~150-200 d, and interpret via turbulent magnetic diffusivity as evidence for rotation-dependent supergranule sizes.

Significance. If the results hold, the paper delivers the largest homogeneous, multi-region census of YSO spot properties to date (144 rotators across 12 fields, a ~2.5x increase over the IC 5070-only analysis), the first empirically bias-corrected intrinsic cold-spot coverage distribution for young stars, and a testable, falsifiable prediction — that small-spot lifetimes depend on rotation — directly checkable with continuous-cadence light curves from TESS or future PLATO data. The injection-recovery quantification of detection bias (Fig. 3) and the explicit robustness tests against Teff systematics and temperature-contrast selection (Sect. 4.2.1) are real methodological strengths that should be credited. The rotation–disc correlation analysis (Table 2, Fig. 4) is a useful, if incremental, confirmation that disc braking alone cannot explain the period bimodality.

major comments (4)
  1. [Sect. 4.2.2 (also Sect. 3.1, Fig. 3)] The 150-200 d lifetime threshold that anchors the paper's headline interpretation is asserted, not measured. The injection-recovery simulations (Sect. 3.1, Fig. 3) injected strictly coherent sinusoids, so they characterize detectability only on the (period, amplitude) plane and are blind by construction to spot evolution. A spot living ~100 d on a P=15 d star produces a phase-unstable signal over ~9-12 cycles that will fail the multi-method, multi-filter clustering cuts of Sect. 2.3 far more readily than the same lifetime on a P=2 d star (~90 cycles). Detection probability is therefore a function of (P, amplitude, lifetime), and the effective lifetime threshold is period-dependent. This is not a cosmetic issue: if small spots have shorter lifetimes everywhere (consistent with the size-lifetime relation the authors themselves cite, Giles et al. 2017), then part of the small-spot deficit a
  2. [Sect. 4.2.3, Fig. 9] The exponential characterization of the intrinsic cold-spot coverage distribution for fast rotators is a central claim, but no fit parameters, parameter uncertainties, or goodness-of-fit statistic are reported, and the rejection of log-normal and power-law forms is stated without any quantitative model comparison (chi-square, KS, AIC, or similar). Please report the exponential scale and its uncertainty, the number of objects (or slices) entering the fit, the binning sensitivity, and a statistical comparison of the three tested functional forms.
  3. [Sect. 2.2, Sect. 4.2] The sample comprises 620 amplitude sets from 144 objects, with 6-month slices generated every 3 months, so adjacent slices share half their data and multiple slices per object trace the same long-lived spot. The coverage distributions (Figs. 7-9) and the p<6e-5 Monte-Carlo significance (Sect. 4.2) appear to treat slices as independent. Please state explicitly how slices vs. objects were counted, and demonstrate (e.g., by re-computing the significance at the object level or with one randomly selected slice per object) that the period-coverage trend and the exponential fit are not inflated by the correlated repeated measurements.
  4. [Sect. 2.4, Eq. (1)] The Teff calibration of Eq. (1) never states the actual RMS of the fit in Kelvin; only that the worst colour combination is 10% higher than the best. Since the entire spot-fitting step hinges on Teff, the numerical RMS (and its dependence on spectral type within the ~200-star NAP calibration sample) should be given. Relatedly, the calibration absorbs the NAP region's mean reddening into the fit, but the target regions span a range of extinctions; while the Herbert et al. (2023) +-400 K robustness argument mitigates this, a sentence quantifying the differential-extinction risk across regions (e.g., comparing fitted Teff for the IC 5070 subsample against the Fang et al. 2020 spectroscopic values, which Fig. 6 implies exists) would strengthen Sect. 2.4.
minor comments (6)
  1. [Fig. 9] The y-axis label reads 'Fraction of Objcts' (typo). The same figure would benefit from stating N and the fit function explicitly in the caption.
  2. [Sect. 3.1 / Sect. 4.2.3] The bias-correction grid spans V-band amplitudes 0.02-0.16 mag. Please state the mapping from (coverage, temperature contrast) to V amplitude assumed when applying the Fig. 3 correction to the coverage distribution, and confirm the grid covers the full observed coverage range (up to ~0.45 in Fig. 8). Also clarify what contrast is assumed in quoting the detection limit as a coverage of 0.05.
  3. [Table 1] Several entries are surprising and warrant a brief explanation: NGC 2264 contributes 285 light curves but only 1 usable slice, and Berkeley 86 contributes 229 light curves and 25 slices with zero periodic detections. A sentence on why these fields yield so few qualifying slices/detections (cadence, crowding, extinction) would help the reader assess cross-region selection effects.
  4. [Sect. 5 (Conclusion)] The claim of the 'first empirical constraint on the intrinsic spot coverage distribution of YSOs' should be tempered or more carefully situated relative to cited prior work on spot coverage evolution (e.g., Morris et al. 2020) and the authors' own IC 5070 analysis (Herbert et al. 2024), of which this is an extension by a factor ~2.5.
  5. [Sect. 4.2.2] The supergranule-size estimates are read off 'their Fig. 1' (Bradshaw & Hartigan 2014). Please describe this procedure explicitly (which curves, what assumed stellar parameters), since the factor-of-five supergranule scaling is a notable secondary claim.
  6. [Sect. 2.4, Eq. (1); Fig. 7] Notation G_G for the absolute G magnitude in Eq. (1) is non-standard; consider M_G. The HS:CS quality-indicator thresholds used to flag degenerate solutions are referenced to Herbert et al. (2024) but never restated; a one-line reminder of the cut values would make Fig. 7 self-contained.

Circularity Check

1 steps flagged

No load-bearing circularity: exponential coverage and lifetime claims are empirical fits/interpretations on a new multi-region sample, not forced by definition or by self-cited uniqueness.

specific steps
  1. self citation load bearing [Sect. 2.3–2.4; comparison in Sect. 4.1]
    "The search for periodic variability has been conducted following our investigations in Froebrich et al. (2021). ... The fitting of spot properties on the YSOs follows the procedure outlined in Herbert et al. (2023). ... In Herbert et al. (2024), the spot properties in IC 5070 were determined using measured Teff values from Fang et al. (2020). Here, we first compare those results with the updated Teff distributions obtained in this work."

    Period search and spot-fitting procedures are taken from overlapping-author HOYS papers. This is methodological self-citation, but it is not load-bearing for the new claims: the exponential coverage form and the slow-rotator lifetime interpretation are not theorems or numerical results imported from those papers; they are fits and inferences on the expanded multi-region sample. Mild only.

full rationale

This is an observational HOYS paper. The central results—an exponential intrinsic cold-spot coverage distribution for fast rotators after injection–recovery bias correction, and a deficit of small cold spots on slow rotators interpreted as shorter lifetimes—are obtained by applying period-search and multi-band spot-fitting pipelines to a new 144-object, multi-region sample. Those pipelines are reused from the authors’ earlier HOYS papers (Froebrich et al. 2021; Herbert et al. 2023, 2024), which is ordinary method continuity, not a self-citation that forces the scientific conclusion. The exponential is a descriptive fit to the bias-corrected histogram (Fig. 9), not a quantity predicted from a parameter fitted to a closely related subset. The lifetime threshold (≳150–200 d) is an interpretive inference from non-detection in 6-month slices after ruling out detection bias, Teff bias, and temperature-contrast alternatives; it is not defined in terms of the claimed result, nor imported via a uniqueness theorem. Weaknesses in that interpretation (coherent-sinusoid injection tests do not directly calibrate lifetime × period sensitivity) are correctness/assumption issues, not circularity. Score 1 only for non-load-bearing methodological self-citation within the HOYS series.

Axiom & Free-Parameter Ledger

5 free parameters · 5 axioms · 0 invented entities

The central claims rest on standard photometric spot modelling, an empirical Teff calibration, a conventional fast/slow period cut, and the inference that non-detection in 6-month slices equals short lifetime. No new physical entities are postulated; free parameters are the usual analysis thresholds and the exponential scale.

free parameters (5)
  • fast/slow period boundary = 5.5 d
    Adopted at 5.5 d for consistency with prior HOYS papers; modest changes do not alter fractions much, but the cut defines the two populations whose spot distributions are contrasted.
  • exponential scale of cold-spot coverage (fast rotators)
    Functional form chosen after log-normal and power-law rejected; the scale is fitted to the bias-corrected histogram (Fig. 9).
  • Teff colour-fit coefficients p_i = lowest-RMS combination C1=K-W2, C2=H-W1
    Six-parameter empirical fit of Teff to absolute G and colours trained on Fang et al. (2020) NAP sample; used for every star lacking spectroscopy.
  • periodogram power / FAP thresholds and slice length = 6 months / power 0.15 / FAP 0.1 %
    Power >0.15 or FAP <0.1 %, ≥50 points per filter, 6-month slices with 3-month oversampling; these define which signals enter the spot sample.
  • K-W2 disc-excess threshold = 0.5 mag
    0.5 mag cut used to classify inner-disc presence; conventional but still a free analysis choice.
axioms (5)
  • domain assumption Two-temperature (photosphere + single spot temperature) model adequately describes the multi-band amplitudes
    Inherited from Herbert et al. (2023, 2024) and used throughout Sect. 2.4 and 4; real spots have temperature gradients and multiple components.
  • ad hoc to paper Non-detection of a periodic signal in a 6-month slice implies spot lifetime ≲150–200 d
    Core interpretive step in Sect. 4.2.2; alternative explanations (contrast, geometry, latitude) are argued against but not directly measured.
  • domain assumption K-W2 > 0.5 mag traces warm inner-disc dust and is a useful proxy for magnetic star–disc coupling
    Standard infrared excess diagnostic (Teixeira et al. 2012); paper notes dust-depleted discs may be missed.
  • domain assumption Injection-recovery with sinusoidal signals of fixed amplitude ratios adequately captures real detection efficiency
    Sect. 3.1; real light curves contain evolving spots, accretion noise and gaps that may differ from pure sinusoids.
  • domain assumption Gaia astrometric membership yields a sample with negligible field-star contamination
    Sect. 2.1; used to justify that the 144 objects are true YSOs.

pith-pipeline@v1.2.0-grok45-kimik3 · 30923 in / 3044 out tokens · 55473 ms · 2026-07-31T14:17:24.533130+00:00 · methodology

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read the original abstract

We present a homogeneous analysis of rotational variability and spot properties in young stellar objects across multiple star-forming regions observed by the Hunting Outbursting Young Stars (HOYS) project. From over 2000 candidate members, we identify 144 YSOs with robust periodic signals and well-constrained multi-band amplitudes. The sample has a median age of $\sim$1~Myr, effective temperatures of 3500--6500~K (masses $\sim$0.6--2~M$_\odot$), and is dominated by Class~2 objects, one third of which exhibit inner disc dust emission. The rotation period distribution is strongly bimodal, with 55 percent fast rotators ($P<5.5$~d) and 45 percent slow rotators. Fast rotators are predominantly inner disc-less, whereas slow rotators include both disc-bearing and disc-free systems, indicating that disc braking alone cannot explain the observed rotational states. We derive spot properties from multi-band amplitudes and find that, after correcting for observational biases, the intrinsic cold-spot coverage distribution of fast rotators is well described by an exponential function. This implies that small spot coverages are intrinsically much more common than large ones, consistent with stochastic magnetic flux emergence governing spot formation. In contrast, slow rotators show a pronounced deficit of small cold spots. After considering observational biases and alternative physical explanations, we conclude that small spots on slowly rotating YSOs have significantly shorter lifetimes. These results provide new evidence that magnetic surface structure and its evolution depend on stellar rotation, placing new empirical constraints on models of magnetic activity and angular momentum evolution in young stars.

Figures

Figures reproduced from arXiv: 2607.24460 by Aashini L. Patel, Adam Popowicz, Aleks Scholz, Amritanshu Vajpayee, Ari M. Siqueira, Benjamin W. Ryan, Carys Herbert, Chiara F. Kawohl, Cledison Marcos da Silva, Dawid Mo\'zdzierski, Dirk Froebrich, Domenico Licchelli, Faustino Garc\'ia de la Cuesta, Francisco C. Sold\'an Alfaro, Franky Dubois, Franz-Josef Hambsch, Geoffrey Stone, George Fleming, Georg Piehler, Gregg L. Ruppel, Holly Stokes-Geddes, Ivana I. Grozdanova, Ivan L. Walton, Jacopo Fallai, James S. Urquhart, Jochen Eisl\"offel, Jordi Berenguer Amatller, Jos\'e Luis Salto Gonz\'alez, Juan-Luis Gonz\'alez-Carballo, Kathy Griffiths, Krzysztof Bernacki, Krzysztof Kotysz, Mario Morales Aimar, Matthew D. Dickers, Matthias Kolb, Michel Michaud, Nick J. Quinn, Przemys{\l}aw J. Miko{\l}ajczyk, Rafael Castillo Garc\'ia, Siegfried Vanaverbeke, Simon Francis Dawes, Slawomir Bednarz, Stephen C. Percy, Stephen R.L. Futcher, Thomas Urtly, Tim M. Kinnear, Tim Nelson, Tonny Vanmunster, Tony Vale, Yenal \"O\u{g}men.

Figure 1
Figure 1. Figure 1: Left: In blue we show the Teff distribution of the YSOs in the NAP region from Fang et al. (2020). In red the distribution of the fitted Teff values for the rotational variables in all HOYS fields is displayed, while in green the subsample of sources in IC 5070 is shown. Right: A Gaia colour vs. absolute Gmag diagram of the rotational variables in our sample. The symbols are colour coded with the fitted Te… view at source ↗
Figure 2
Figure 2. Figure 2: The period distribution of all rotational variables identified in the HOYS target fields is shown as a red histogram. The corresponding CDF is shown as a solid black line. The green histogram and the dashed CDF are the data for the objects in the IC 5070 field. The vertical dotted line separates fast and slow rotators. indicating a slightly higher fraction of fast rotators than in the full sample. For most… view at source ↗
Figure 4
Figure 4. Figure 4: Relationship between the period, 𝐾 − 𝑊2 colour, and 𝛼SED slope for the rotational variables in our sample. The colour code indicates the region the sources are in. Red dots indicate objects not in any of the 4 populous regions. Dotted lines separate fast and slow rotators at 𝑃 = 5.5 d, sources with and without colour excess at 𝐾 − 𝑊2 = 0.5 mag, and Class 1, 2, and 3 objects based on their 𝛼SED value. Top: … view at source ↗
Figure 5
Figure 5. Figure 5: Gaia absolute magnitude vs. colour of the rotational variables. In the left panel the objects are colour coded based on their distribution in the period vs. 𝐾 − 𝑊2 colour plot, and in the right panel according to the star formation region they are in. In all panels the solid black line is a 1 Myr PARSEC isochrone and the dashed black line a 4 Myr isochrone (Bressan et al. 2012). dispersing their inner disc… view at source ↗
Figure 6
Figure 6. Figure 6: Comparison of spot property distributions from Herbert et al. (2024) and this work for IC 5070. Sample 1 is the original sample from Herbert et al. (2024). In sample 2 we used the same amplitudes but our fitted values of Teff. Sample 3 represents this work. Warm spot properties are in the left column, cold spot properties in the right. The top row shows the coverage distribution and the bottom row the star… view at source ↗
Figure 7
Figure 7. Figure 7: Left: Spot temperature difference 𝑇𝑆 −𝑇★ versus spot coverage for the entire sample of rotational variables. Horizontal dotted lines mark 𝑇𝑆 −𝑇★ = 0 K and 𝑇𝑆 − 𝑇★ = 2500 K, which separate the cold, warm and hot spot solutions. The symbols are colour coded according to the HS:CS{𝑉} ratio, our spot property quality indicator. Values close to zero indicate well constrained cold spot properties. Values near on… view at source ↗
Figure 8
Figure 8. Figure 8: Stellar rotation periods vs. the coverage for all cold spots in our sample. A lack of small spots on slow rotators is evident (bounded by the black dotted lines). The typical uncertainties of the spot coverage are 0.02. The period uncertainties are typically smaller than the symbol size. Before doing so, we assess whether additional selection effects or biases could influence the observed distribution. The… view at source ↗
Figure 9
Figure 9. Figure 9: Exponential fit to the coverage distribution of cold spots on fast rotators. The fit has been corrected for the detection efficiency shown in [PITH_FULL_IMAGE:figures/full_fig_p011_9.png] view at source ↗

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Reference graph

Works this paper leans on

63 extracted references · 2 canonical work pages

  1. [1]

    , keywords =

    A survey for variable young stars with small telescopes: First results from HOYS-CAPS. , keywords =. doi:10.1093/mnras/sty1350 , archivePrefix =. 1804.09128 , primaryClass =

    Pith/arXiv arXiv

  2. [2]

    , keywords =

    A survey for variable young stars with small telescopes: II - mapping a protoplanetary disc with stable structures at 0.15 au. , keywords =. doi:10.1093/mnras/staa158 , archivePrefix =. 2001.05570 , primaryClass =

    Pith/arXiv arXiv 2001

  3. [3]

    Properties of 1687 Gaia selected members in 21 nearby clusters

    A survey for variable young stars with small telescopes - VIII. Properties of 1687 Gaia selected members in 21 nearby clusters. , keywords =. doi:10.1093/mnras/stae311 , archivePrefix =. 2401.16883 , primaryClass =

    Pith/arXiv arXiv

  4. [4]

    , keywords =

    The Gaia mission. , keywords =. doi:10.1051/0004-6361/201629272 , archivePrefix =. 1609.04153 , primaryClass =

    Pith/arXiv arXiv

  5. [5]

    Summary of the content and survey properties

    Gaia Data Release 3. Summary of the content and survey properties. , keywords =. doi:10.1051/0004-6361/202243940 , archivePrefix =. 2208.00211 , primaryClass =

    Pith/arXiv arXiv

  6. [6]

    , keywords =

    The Two Micron All Sky Survey (2MASS). , keywords =. doi:10.1086/498708 , adsurl =

    doi:10.1086/498708

  7. [7]

    VizieR Online Data Catalog , keywords =

    VizieR Online Data Catalog: AllWISE Data Release (Cutri+ 2013). VizieR Online Data Catalog , keywords =

    2013

  8. [8]

    , keywords =

    The UKIRT Infrared Deep Sky Survey (UKIDSS). , keywords =. doi:10.1111/j.1365-2966.2007.12040.x , archivePrefix =. astro-ph/0604426 , primaryClass =

    arXiv 2007

  9. [9]

    , keywords =

    The UKIDSS Galactic Plane Survey. , keywords =. doi:10.1111/j.1365-2966.2008.13924.x , archivePrefix =. 0712.0100 , primaryClass =

    arXiv 2008

  10. [10]

    Spot properties on YSOs in IC 5070

    A survey for variable young stars with small telescopes - VII. Spot properties on YSOs in IC 5070. , keywords =. doi:10.1093/mnras/stac3051 , archivePrefix =. 2210.09895 , primaryClass =

    Pith/arXiv arXiv

  11. [11]

    Evolution of spot properties on YSOs in IC 5070

    A survey for variable young stars with small telescopes - IX. Evolution of spot properties on YSOs in IC 5070. , keywords =. doi:10.1093/mnras/stae812 , archivePrefix =. 2403.10595 , primaryClass =

    Pith/arXiv arXiv

  12. [12]

    Rotation periods of YSOs in IC 5070

    A survey for variable young stars with small telescopes - IV. Rotation periods of YSOs in IC 5070. , keywords =. doi:10.1093/mnras/stab2082 , archivePrefix =. 2107.08524 , primaryClass =

    Pith/arXiv arXiv

  13. [13]

    , keywords =

    The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae. , keywords =. doi:10.3847/1538-4357/abba84 , archivePrefix =. 2009.11995 , primaryClass =

    Pith/arXiv arXiv 2009

  14. [14]

    doi:10.5281/zenodo.4406806 , version =

    scipy/scipy: SciPy 1.6.0. doi:10.5281/zenodo.4406806 , version =

    work page doi:10.5281/zenodo.4406806

  15. [15]

    , keywords =

    PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code. , keywords =. doi:10.1111/j.1365-2966.2012.21948.x , archivePrefix =. 1208.4498 , primaryClass =

    arXiv 2012

  16. [16]

    , keywords =

    Rotation-disk connection for very low mass and substellar objects in the Orion Nebula Cluster. , keywords =. doi:10.1051/0004-6361/200913494 , archivePrefix =. 1001.5141 , primaryClass =

    Pith/arXiv arXiv

  17. [17]

    Protostars and Planets V , year = 2007, editor =

    The Rotation of Young Low-Mass Stars and Brown Dwarfs. Protostars and Planets V , year = 2007, editor =

    2007

  18. [18]

    Research in Astronomy and Astrophysics , keywords =

    Variability of Young Stellar Objects in the Perseus Molecular Cloud. Research in Astronomy and Astrophysics , keywords =. doi:10.1088/1674-4527/acd58b , archivePrefix =. 2305.02514 , primaryClass =

    Pith/arXiv arXiv

  19. [19]

    , keywords =

    Spitzer observations of NGC 2264: the nature of the disk population. , keywords =. doi:10.1051/0004-6361/201015326 , archivePrefix =. 1203.3754 , primaryClass =

    Pith/arXiv arXiv

  20. [20]

    , keywords =

    Discovering protostars and their host clusters via WISE. , keywords =. doi:10.1007/s10509-012-1308-y , archivePrefix =. 1211.4032 , primaryClass =

    Pith/arXiv arXiv

  21. [21]

    , keywords =

    On Sunspot and Starspot Lifetimes. , keywords =. doi:10.1088/0004-637X/795/1/79 , archivePrefix =. 1409.4337 , primaryClass =

    Pith/arXiv arXiv

  22. [22]

    Living Reviews in Solar Physics , keywords =

    Starspots: A Key to the Stellar Dynamo. Living Reviews in Solar Physics , keywords =. doi:10.12942/lrsp-2005-8 , adsurl =

    doi:10.12942/lrsp-2005-8 2005

  23. [23]

    Izvestiya Glavnoj Astronomicheskoj Observatorii v Pulkove , keywords =

    On the nature of solar activity. Izvestiya Glavnoj Astronomicheskoj Observatorii v Pulkove , keywords =

  24. [24]

    Ergebnisse und Probleme der Sonnenforschung

  25. [25]

    Making Sense of Sunspot Decay. I. Parabolic Decay Law and Gnevyshev-Waldmeier Relation. , keywords =. doi:10.1023/A:1004988123265 , archivePrefix =. astro-ph/9706029 , primaryClass =

    Pith/arXiv arXiv

  26. [26]

    Protostars and Planets VI , year = 2014, editor =

    Angular Momentum Evolution of Young Low-Mass Stars and Brown Dwarfs: Observations and Theory. Protostars and Planets VI , year = 2014, editor =. doi:10.2458/azu_uapress_9780816531240-ch019 , archivePrefix =. 1309.7851 , primaryClass =

    Pith/arXiv arXiv 2014

  27. [27]

    , keywords =

    CSI 2264: Investigating rotation and its connection with disk accretion in the young open cluster NGC 2264. , keywords =. doi:10.1051/0004-6361/201629537 , archivePrefix =. 1610.08811 , primaryClass =

    Pith/arXiv arXiv

  28. [28]

    , keywords =

    Disk-locking Regulates Stellar Rotation in Young Clusters: Insights from NGC 2264. , keywords =. doi:10.3847/1538-4357/ad98fb , archivePrefix =. 2412.00520 , primaryClass =

    Pith/arXiv arXiv

  29. [29]

    , keywords =

    A Kepler study of starspot lifetimes with respect to light-curve amplitude and spectral type. , keywords =. doi:10.1093/mnras/stx1931 , archivePrefix =. 1707.08583 , primaryClass =

    Pith/arXiv arXiv

  30. [30]

    , keywords =

    Rotational studies in the Orion Nebula Cluster: from solar mass stars to brown dwarfs. , keywords =. doi:10.1051/0004-6361/200811427 , archivePrefix =. 0906.2419 , primaryClass =

    Pith/arXiv arXiv

  31. [31]

    , keywords =

    Stellar rotation and variability in the Orion Nebula Cluster. , keywords =. doi:10.1051/0004-6361:20021362 , adsurl =

    doi:10.1051/0004-6361:20021362

  32. [32]

    , keywords =

    CSI 2264: Simultaneous Optical and Infrared Light Curves of Young Disk-bearing Stars in NGC 2264 with CoRoT and Spitzer Evidence for Multiple Origins of Variability. , keywords =. doi:10.1088/0004-6256/147/4/82 , archivePrefix =. 1401.6582 , primaryClass =

    Pith/arXiv arXiv

  33. [33]

    , keywords =

    Shadowplay in Hubble's variable nebula. , keywords =. doi:10.1093/mnras/239.2.665 , adsurl =

    work page doi:10.1093/mnras/239.2.665

  34. [34]

    Protostars and Planets VII , year = 2023, editor =

    Accretion Variability as a Guide to Stellar Mass Assembly. Protostars and Planets VII , year = 2023, editor =. doi:10.48550/arXiv.2203.11257 , archivePrefix =. 2203.11257 , primaryClass =

    Pith/arXiv arXiv doi:10.48550/arxiv.2203.11257 2023

  35. [35]

    EAS Publications Series , year = 2013, editor =

    Observation of rotation in star forming regions: clouds, cores, disks, and jets. EAS Publications Series , year = 2013, editor =. doi:10.1051/eas/1362002 , archivePrefix =. 1305.0627 , primaryClass =

    arXiv 2013

  36. [36]

    Protostars and Planets V , year = 2007, editor =

    Protostars and Planets V. Protostars and Planets V , year = 2007, editor =

    2007

  37. [37]

    , keywords =

    Disk Accretion onto Magnetic T Tauri Stars. , keywords =. doi:10.1086/185972 , adsurl =

    doi:10.1086/185972

  38. [38]

    , keywords =

    Testing the Disk-locking Paradigm: An Association between U - V Excess and Rotation in NGC 2264. , keywords =. doi:10.1086/507525 , archivePrefix =. astro-ph/0607206 , primaryClass =

    Pith/arXiv arXiv

  39. [39]

    MHD simulations of accretion onto a dipolar magnetosphere. II. Magnetospheric ejections and stellar spin-down. , keywords =. doi:10.1051/0004-6361/201220168 , archivePrefix =. 1211.4844 , primaryClass =

    Pith/arXiv arXiv

  40. [40]

    , keywords =

    Rotational evolution of solar-type protostars during the star-disk interaction phase. , keywords =. doi:10.1051/0004-6361/201935432 , archivePrefix =. 1910.03995 , primaryClass =

    Pith/arXiv arXiv 1910

  41. [41]

    , keywords =

    High-Resolution Spectroscopy in Tr 37: Gas Accretion Evolution in Evolved Dusty Disks. , keywords =. doi:10.1086/508058 , archivePrefix =. astro-ph/0607534 , primaryClass =

    Pith/arXiv arXiv

  42. [42]

    , year = 1919, month = apr, volume =

    The Magnetic Polarity of Sun-Spots. , year = 1919, month = apr, volume =. doi:10.1086/142452 , adsurl =

    doi:10.1086/142452 1919

  43. [43]

    , keywords =

    A Systematic Study of Hale and Anti-Hale Sunspot Physical Parameters. , keywords =. doi:10.3847/1538-4357/aae31a , archivePrefix =. 1809.08980 , primaryClass =

    Pith/arXiv arXiv

  44. [44]

    , keywords =

    Sunspots: An overview. , keywords =. doi:10.1007/s00159-003-0018-4 , adsurl =

    doi:10.1007/s00159-003-0018-4

  45. [45]

    , keywords =

    The Magnetic Fields of Classical T Tauri Stars. , keywords =. doi:10.1086/519017 , archivePrefix =. 0704.2923 , primaryClass =

    Pith/arXiv arXiv

  46. [46]

    , year = 1961, month = mar, volume =

    The Topology of the Sun's Magnetic Field and the 22-Year Cycle. , year = 1961, month = mar, volume =. doi:10.1086/147060 , adsurl =

    doi:10.1086/147060 1961

  47. [47]

    , keywords =

    Hunt for Starspots in HARPS Spectra of G and K Stars. , keywords =. doi:10.3847/1538-3881/ab9365 , archivePrefix =. 2005.06749 , primaryClass =

    Pith/arXiv arXiv 2005

  48. [48]

    Magnetospheric accretion onto the T Tauri star AA Tauri. I. Constraints from multisite spectrophotometric monitoring. , keywords =

  49. [49]

    , keywords =

    Near-Infrared Photometric Variability of Stars toward the Orion A Molecular Cloud. , keywords =. doi:10.1086/321086 , archivePrefix =. astro-ph/0102446 , primaryClass =

    Pith/arXiv arXiv

  50. [50]

    Results of the ROTOR-program. II. The long-term photometric variability of weak-line T Tauri stars. , keywords =. doi:10.1051/0004-6361:20078476 , archivePrefix =. 0801.3543 , primaryClass =

    Pith/arXiv arXiv

  51. [51]

    , keywords =

    A survey for variable young stars with small telescopes: VI - Analysis of the outbursting Be stars NSW 284, gaia 19eyy, and VES 263. , keywords =. doi:10.1093/mnras/stad407 , archivePrefix =. 2302.02696 , primaryClass =

    Pith/arXiv arXiv

  52. [52]

    , keywords =

    A Continuum of Accretion Burst Behavior in Young Stars Observed by K2. , keywords =. doi:10.3847/1538-4357/836/1/41 , archivePrefix =. 1612.05599 , primaryClass =

    Pith/arXiv arXiv

  53. [53]

    , keywords =

    CSI 2264: Characterizing Young Stars in NGC 2264 with Stochastically Varying Light Curves. , keywords =. doi:10.3847/0004-6256/151/3/60 , archivePrefix =. 1601.03326 , primaryClass =

    Pith/arXiv arXiv

  54. [54]

    , keywords =

    Magnetic activity and accretion on FU Tau A: clues from variability. , keywords =. doi:10.1111/j.1365-2966.2011.19781.x , archivePrefix =. 1109.3474 , primaryClass =

    arXiv 2011

  55. [55]

    , keywords =

    Variability in young very low mass stars: two surprises from spectrophotometric monitoring. , keywords =. doi:10.1093/mnras/stw455 , archivePrefix =. 1602.07925 , primaryClass =

    Pith/arXiv arXiv

  56. [56]

    , keywords =

    Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra. , keywords =. doi:10.1088/0004-637X/767/2/112 , archivePrefix =. 1303.0769 , primaryClass =

    Pith/arXiv arXiv

  57. [57]

    , keywords =

    Measuring the density structure of an accretion hot spot. , keywords =. doi:10.1038/s41586-021-03751-5 , archivePrefix =. 2109.00510 , primaryClass =

    Pith/arXiv arXiv

  58. [58]

    Warm spots on the active star V1598 Cyg

    A survey for variable young stars with small telescopes - III. Warm spots on the active star V1598 Cyg. , keywords =. doi:10.1093/mnras/staa2275 , archivePrefix =. 2007.14969 , primaryClass =

    Pith/arXiv arXiv 2007

  59. [59]

    Protostars and Planets VI , archivePrefix = "arXiv", eprint =

    Episodic Accretion in Young Stars. Protostars and Planets VI , archivePrefix = "arXiv", eprint =. doi:10.2458/azu_uapress_9780816531240-ch017 , adsurl =

    doi:10.2458/azu_uapress_9780816531240-ch017

  60. [60]

    , keywords =

    Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem. , keywords =. doi:10.1086/498066 , archivePrefix =. astro-ph/0510060 , primaryClass =

    Pith/arXiv arXiv

  61. [61]

    , keywords =

    A wide survey for circumstellar disks in the Lupus complex. , keywords =. doi:10.1051/0004-6361/201936756 , archivePrefix =. 2007.14102 , primaryClass =

    Pith/arXiv arXiv 2007

  62. [62]

    , keywords =

    Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association. , keywords =. doi:10.1086/509121 , archivePrefix =. astro-ph/0609372 , primaryClass =

    Pith/arXiv arXiv

  63. [63]

    , keywords =

    Stable accretion in young stars: the cases of EX Lupi and TW Hya. , keywords =. doi:10.1093/mnras/stad3029 , archivePrefix =. 2310.02681 , primaryClass =

    Pith/arXiv arXiv